10

CHAPTER II

LITERATURE REVIEW

2.1 INTRODUCTION

Composting is a controlled process for the rapid decomposition of waste in stack

(Biddlestone & Gray 1988). The stack contains a variety of stages of a food chain

which consists of microflora and macrofauna (Table 2.1). However, microflora such

as bacteria, actinomycetes and fungi play an important role in the real composting

process (Day & Shaw 2001).

Table 2.1 Microflora and macrofauna in the composting process

Microflora

Bacteria,ActinomycetesFungi, AlgaeProtozoa

MacrofaunaMites, ant, Termites, millipede, Spider, beetle, earthworm

Source: Biddlestone & Gray 1988

During the process of composting, microorganisms convert organic materials into

carbon dioxide, biomass, heat energy and a final product which resembles humus. The

main component of organic material is carbohydrates (example cellulose), protein,

lipids and lignin. Through the coupling reaction of microorganisms, complex organic

compounds will be decomposed into smaller molecules which can be utilized by

microbial cell (Golueke 1991). The metabolism of microbes results in the increase of

11

temperature in the compost stack because the heat released by metabolism of microbes

is captured faster than that released to the environment (Miller 1991). The increase in

temperature will enhance the degradation process (Biddlestone & Gray 1988).

2.2 THE MICROBIOLOGY OF COMPOSTING

It has long been known that composting is primarily a microbiological process. If one

has the chance to read the work by (Waksman et al.1939), most likely he will get

impressed with the amount of knowledge about the microbiology of the process that

already existed by that time. The understanding that composting is, above all, a

microbiological process is of paramount importance since this is actually the basis for

good process management (Finstein 1980, de Bertoldi et al. 1983, Golueke 1991).

This was one of the strongest basis for the development of the rutgers system of

composting (Finstein 1980), where process rate is controlled by maintenance of an

appropriate process temperature by forced aeration and it has been one of the guiding

principles in most of the composting systems available nowadays. Although small

animals like earthworms or small insects can be found in composting, most of the

organic matter degradation is carried out by microbes. There are three main groups of

microbes involved namely bacteria, fungi and actinomycetes which may be facultative

or strict aerobic (Huang et al. 2000). They may have individual preferential substrates

and environmental conditions for growth. The materials subjected for composting

usually contain an indigenous population of microorganisms derived from the

atmosphere, water or soil (Gray & Bidlestone 1973). Once materials are piled for

composting, feeding of this microbiological population on the substrates lead to the

production of heat and is accumulation in the pile, causing process temperature to rise

(Finsteinet al. 1987a., Rynk et al. 1992). Microbial activity and the resulting heat

generation trigger a change in the environmental conditions and substrate composition

along process time, which in turn causes a succession of mixture of microbial

populations to occur (Waksman et al. 1939, Gray & Bidlestone 1973, Silveira 1999,

Tiquiaet al. 2002, Nakasaki et al. 2005, Klammer et al. 2008, Chroni et al. 2009).

Microbial populations can be subdivided by the temperature ranges of their activity: i)

psychrophiles, preferring temperatures below 20ºC; ii) mesophiles, for a temperature

12

range in between 20ºC and 40ºC; and iii) thermophiles, above 40ºC (Gray &

Bidlestone 1973).

2.3 BIOPROCESS COMPOSTING

Microorganisms require carbon material, macronutrient such as nitrogen, phosphorus

and potassium and other few side elements for their growth. Carbon is the main

energy source for microorganisms while small constituents from carbon will be

inserted into the cell. Some of the energy formed will be used for microbial

metabolism and the rest of it will be released as heat. Nitrogen is an important element

for microorganism because it is a component of protein, nucleic acid, amino acid,

enzymes, and co-enzymes which are needed for development and cell function

(Golueke 1991).

During composting, the carbon source which is dissolved and biodegradable

such as monosaccharide, starch and lipid will be used by microorganism in the early

stage of composting. pH value will decrease because the organic acid formed as a

result of microbial decomposition compound during the process of degradation.

Microorganisms will later start the process of protein degradation, resulting in

ammonia being released and rise in pH value. After the biodegradable source of

carbon is used up, the compound which takes more time for biodegradable such as

cellulose, hemicellulose and lignin will undergo biodegradable and part of it will be

converted into humus (Crawford 1983).

Ammonia formed will undergo different process depending on the condition of

compost mixture. For example, if it is possible to be dissolved (example NH 4+) will be

later immobilized by microorganisms by using ammonium as nitrogen source and

subsequently changing it back to organic nitrogen. At temperature below 40 0C and

also at a suitable ventilation, ammonia is possible to be converted to nitrate (NO3-) by

nitrating bacteria. During nitration, nitrating bacteria will lower down pH caused by

the released oh hydrogen ion. The process can be simplified as follows:

Nitrosomonas bacteria: 2NH4++ 3O2 2NO2

-+ 4H+ + 2H20

13

Nitrobacter bacteria: 2NO2- + O2 2NO3

-

The lack of oxygen will cause the microorganisms to utilize nitrate as oxygen source

which will cause the occurrence of denitration and halts nitration. At a higher

temperature and pH exceeding 7.5, ammonia can be vaporized and released (Sanchez-

Monedero et al. 2001).

Microorganisms have the tendency to utilize organic molecule which is

dissolved in water. If the moist content falls below the critical level, the microbial

activity will decrease and it will be dormant (not active temporarily). On the contrary,

high moisture content will cause the ventilation of compost to be less efficient,

causing leaching of nutrient and the process to be anaerobic (Golueke 1991).

Humidity is also important is the storage of energy in the stack of compost (Schaub &

Leonard 1996).

Composting process can be either more aerobic or more anaerobic. The

decomposition is faster and lesser foul if the process is more aerobic. This condition

results in a process which is more aerobic to be conducive in order to stabilize the

larger scaled waste. Biochemical equation for an aerobic process in shown as below

(Day & Shaw 2001; Polprasert 1989):

Organic material + O2+ aerobic microbes CO2 + NH3 + H20 + Product + Energy

On the other hand, a more anaerobic process is easier and less costly although

the degradation is time consuming and more have more foul. The biochemical

equation for an anaerobic process is shown below (Day & Shaw 2001; Polprasert

1989):

Organic material + anaerobic microbes CO2 + NH3 + H2S + Product + Energy + CH4

Composting is a microbiological process which relies on the increase and decrease of

temperature. Day and Shaw (2001) stated that microorganisms in a compost stack is

divided into three categories, namely cryophilic or psychrophilic (0-250C), mesophylic

(25-45 0C) and thermophylic (>45 0C). Generally, mesophylic and thermophylic

14

microorganisms are prone to domination in stack compost. The temperature profile for

composting is shown as in Figure 2.1. At optimum condition, composting will go

through three phases namely, mesophylic phase, thermophylic phase (happens from

few days to few months) and cooling and maturation phase (can happen for few

months).

Figure 2.1 Profile of Temperature and Microbial Growth in Compost Stack

Source: Polprasert 1989

The period of each phase relies on natural factors or the condition of organic material

which is compost and the effectiveness of the process which is determined by degree

of ventilation and stirring (Golueke 1991). The addition of starting compost can

eliminate long mesophylic phase and hence speeding up the composting process

(Agamuthu et al. 2000). The active composting phase is considered ended when the

mixture temperature is stabilized and reaching atmospheric temperature (Sanchez-

Monedero et al. 2001). The population of microorganisms in the stack also changes

during the composting process as portrayed in Figure 2.2.

15

When composting is not done properly, the breeding and spread of pathogens

can occur. According to Federal Biosolid Technical Regulation, U.S., to reduce the

risk of pathogens, limit system (windrow) is compulsory to have a minimum

temperature of 55 0C at a compost stack for 15 days, whereas the minimum

temperature of 55 0C in the reactor for 3 days (Day & Shaw 2001).

Figure 2.2 The Change in Overall Population of Microorganisms (total of bacteria,

actinomycetes and fungi) during Sludge-saw dust Composting.

Source: Day & Shaw 2001

2.4 SUITABLE MATERIALS FOR COMPOSTING

Any waste material with high organic matter content is a potential replacement used

for centuries to stabilize human and animal wastes. Recently it has been used for

sewage sludge, industrial wastes (e.g. food, pulp & paper), yard and garden wastes.

Municipal solid wastes (up to 70% organic matter by weight), soft prunings, clippings,

leaves, woody prunings (finely shredded), straw based farmyard and horse manure,

pure wool jumpers, paper shredded mixed with grass cuttings are used sparingly.

Kitchen waste includes waste from fruit, peelings, tea bags, egg shells and bedding

16

from vegetarian pets such as rabbits. When selecting materials for your compost,

avoid using coal ash, metal, glass and plastic, nappies, the roots of persistent weeds

like bindweed and couch grass, leaves with persistent disease such as black spot, meat

or fish and cooked food, especially meat as this attracts vermin (home composting).

2.5 COMPOSTING SYSTEM

Composting system can be classified into reactor and non-reactor. There are two types

of non-reactor system namely long rows (windrow): stirred system and air static

system. Long rows refer to stirred system which is usually done manually. In an air

static system, sludge is piled on a perforated pipe. Air will be forced by air

compressor into the perforated pipe so that there is direct contact between sludge and

air in order to activate the microbes (Hassouneh et al. 1999). In a reactor system,

compost will be circled by container (reactor) and the flow of substance will be

directed according to reactor design. The reactor is usually closed even though there

are researches which uses open reactor system (Papadimitriou et al. 1997). For a

vertical reactor, raw materials are inserted from the top of the reactor while air is

supplied from the bottom so that all substances get sufficient air. In general, reactor is

used for organic material without sludge.

In a horizontal reactor, the reactor is placed in a horizontal or slightly inclined

with small gradient so as to ease the flow of substances in a reactor. The direction of

feed and air feed is opposite in order to maximize the contact time. The final compost

is collected near the air nozzle (Hassouneh et al. 1999). Table 2.2 shows the summary

of composting system of commercial scale. A non-reactor system is less costly but

requires a bigger space (Furhacker & Haberl 1995; Haug 1993). Although it is costly

and requires skilled labor, the reactor system has a good control which makes it more

suitable for sludge composting in a larger quantity (Bhamidimarri & Pandey 1996;

Haug 1993). In order to increase process efficiency and to reduce cost, only active

composting is usually carried out on reactor system while maturation process is

carried out on limit system (Furhacker & Haberl 1995; Vourinen & Shaharinen 1997).

17

2.5.1 Rotating Drum Reactor in Composting

Rotating drum reactor has been long used in composting field either by batch or

continuous in a large and small scale. Compared to the batch process, continuous

process has the ability to manage a larger quantity of material and eliminate the

mesophilic phase (Schulze 1962).

Table 2.2 .Commercial-scale composting system

Decomposing system System’s

Category

Information

Rotating row Not a Reactor A long narrow piles is rotated regularly and passively ventilated.

Static and passive stack ventilation

Not a Reactor Free standing piles is turned occasionally or not at all and aerated without the aid of passive ventilation.

Static pile and long row with the help of passive air

Not a Reactor Piles and the long row with the help of passive air like perforated pipe and forced-air plenum.

Aerated piles and bins Not a Reactor Short barrels and free standing piles with forced ventilation and without rotated.

Stack, long row and barrel with turnaround and ventilation

Not a Reactor Long row or free standing piles or short barrel forced air system. Material will be fixed or sometimes rotated.

Stirred horizontal layers Reactor Material will be composed in long layers with a turnaround narrow, usually with forced ventilation and continuous movement.

Aerated containers Reactor Material will be included in various containers with forced ventilation.

Aerated-stirred containers

Reactor The commercial container stirred, aerated by force and material is moved continuously.

Silo or reactor tower Reactor Forced air system that leads to the movement of material vertically from top to bottom.

Rotating drum Reactor Drum is rotated slowly to stir the material permanently or intermittently and move the material through the system.

Source: Rynk & Richard 2001

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Rotating drum reactor differs in size, design and process management. Rotating drum

reactor has common basic technique which is to increase decomposition by mixing up

the materials in the reactor (Rynk & Richard 2011).

Rotating drum reactor (RDB) is a complex multiphase reaction system Figure

2.3 which includes substrate layer, head space gas, and drum wall. In general,

substrate layer covers 10%-40% of bioreactor volume (Hardin et al. 2000). Schulze

(1962) filled up 67% of RDB’s volume during composting of sewage sludge. RDB is

usually rotated to 2-3 rpm although there are values as low as 3 revolutions per day

and there were also revolution values as high as 40-50 reported before. Drum may

contain internal blades in order to increase mixing action caused by rotation (Hardin et

al. 2000).

Figure 2.3 Showing the multiple phase and matter and energy flow in a rotating drum reactor.

Source: Hardin et al. 2000

In a composting process, rotation functions as to expose the materials to fresh air to

increase oxygen and also to release heat and product gases from decomposition.

Forced ventilation is commonly used to supply fresh air and to eliminate gaseous

products. In a few cases, a short drum can obtain sufficient air by exchange of passive

air through the opening at the end. When forced ventilation is carried out, air will be

directed to compost or the opposite side of where the compost is fed to the output.

19

Drum system are needed for composting less homogeneous materials such as

municipal waste. These drums are of diameter 3 m or more and have a length of more

than 50 m. Some drums can be used in parallel. Smaller drum system can be used to

feed a more homogeneous as excrement, dead animals and leftover food. This unit

range is from 1.5 to 3 m in diameter and 3 to 15 m long. Rotating drum reactor has a

shorter retention time of 3 to 5 days. In practice, the drum works on the early stages of

composting. Material removed from the drum is usually cured in the limit, an aerated

pile composting system or second composting system.

Drum starts feed composting quickly and uniformly in a high and controlled

temperature environment. Drum is effective especially to homogenize heterogeneous

mixture such as municipal waste. Lack of ventilation causes the production of an

organic acid and a decrease in pH in the drum. This is why drum is used in early

stages of composting. In few cases, composting time is extended to a few weeks and

this in turns allows aerobic degradation of many acids with the decrease in ventilation

rate. In other cases, compost will reach maturity after 3 to 5 days in the drum. The

materials released from this short retention time may be useful on only certain

applications for example application on soil during winter and autumn. However,

according to compost maturity analysis, the period of several weeks is necessary in

agriculture application (Rynk & Richard 2001).

One of the important features of rotating drum reactor is its ability to produce

granulate products. In industries such as fertilizer, the granulation process is

successfully done in rotating drum reactor (Walker et al. 2003; Hanafi et al. 2000).

Granulate products are important in order to reduce dust and this will minimize the

risk of material loss, inhalation and blast. It also improves the flow, is manageable,

increase density and speeds up the mixing of materials (Iveson et al. 2001).

2.5.1.1 Rotator Composter Design and Description Used in This Study

Rotator composter reactor system as shown in Figure 2.4 consists of 3 main

components. There are rotator drum, air compressor and gas absorber. Rotator drums

functionally facilitated with 3 phase motor. There are 8 inner blades with length of 5

20

cm each in order to enhance the mixing in the reactor. On the other hand, air

compressor functions as to provide air to the reactor, hence the function of gas

absorber is to absorb gas and air resulting from the process inside the reactor.

Absorber used in this reactor is charcoal. The characteristic of each components of the

reactor is as shown in Table 2.3. Mixing of palm oil mill effluents (POME) and empty

fruit bunches (EFB) is inserted through the feeding part.

Figure 2.4 Rotator composter reactor system

Table 2.3 Rotator composter reactor system specifications

Rotator Composter System

Material Stainless steel

Length 3 m

Diameter 0.6 m

Initial active volume 0.4 m3

Maximum rotation 2 rpm (rotation per minute)

To be continued…

21

Air Compressor

Model SWAN DR 115

Ability 122 liter/min

Speed 1450 rpm (rotation per minute)

Cycle 50 Hz

Motor

Model CHENTA, Taiwan

Volt 400 V

Current 9.1 A

Cycle 3.50 Hz

2.5.2 Bin-composting

This type of composting can be done easily even at home provided that there is

enough space to install the composter. The composter can be installed in the garden or

on a balcony. Composter is a simple box, made of wood or plastic that can also be

home-made. It has a lid to prevent rodent and other animals from eating the compost

feedstock and is in contact with soil to enhance biological activity. In general, yard

trimmings, preferably shredded and food waste can be added to the composter.

Nevertheless, a few restrictions on what kind of organic waste should be put in the

composter must be observed. Meat, fish, dairy products and sanitary material (e.g.

diapers) are to be avoided because they are likely to attract vermin. Besides that, the

temperature in the compost heap is usually too low to kill potential pathogens present

in such waste and contamination must be avoided (USEPAEnviro.com 2006).

Composter can be more sophisticated: the composter might have a forced aeration

system or be automatically turned on. It might also have an odor-control system as

well as a leachate collection system. In this study, the composter size is 90 cm high

and its width is 60. The composter has system of natural ventilation at its bottom and

the plastic compost bin is made of dark color so as to absorb as much heat from the

Continued…

22

Sun as seen in Figure 2.5. Through access doors at the bottom, the finished compost

can be moved out. The organic waste was poured from the upper part of the composter

and it involves waste collected from wet market with removed non composting

materials (such as plastics, metal etc.) which has been chopped or shredded into

smaller sizes for faster decomposition and has been well mixed.

Figure 2.5 Bin composter

2.5.2.1 Types of compost bins

There are several types of compost bins available as follows. Description of each bin

is explained in details.

1. Worm Bins

Worm composting is unique because it uses only food scraps and not yard waste. It is

ideal for people with very small yards or with no yard. Plastic storage bins with holes

drilled on the bottom and on the sides are good for starting out. Homemade wood bins

are easy to make. Manufactured bins with layers help in separating worms from

compost work reasonably well and can be kept indoors but they can be expensive

(Compost Bins).

2. Heaps

This is the simplest composting method. However, compost in a heap may take up

more space than a bin. It is not recommended for food scraps as four-legged critters

23

are likely to visit looking for a meal. To keep it from drying out in summer and getting

too wet during the winter, a heap or open pile should be covered (Compost Bins).

3. Hoops

This type of bin is not costly and can be made from lengths of wire fencing or from

wooden pallets. Hoops are enclosed and are tidier than a heap and can be moved and

covered easily. However, they are generally not animal resistant. Hoops are easy to

take apart and reassemble when turning or removing compost (Compost Bins).

4. Tumbler or Spinner

These self-contained barrels, drums or balls rotate for easy mixing and fast

decomposition. They are more costly than other systems. Although most models are

easy to turn, end-over-end models can be nearly impossible to turn and poorly

balanced when they are full. Tumblers and spinners are suitable for small spaces and

are usually animal resistant. Since they must be loaded in batches, you will either have

to store fresh materials or use two tumblers. The materials in one will be decomposing

while the other is being loaded (Compost Bins).

5. Multi Bin System

This is a great system for a household or community space generating a significant

amount of waste. It is efficient, allowing you to have three working piles at different

stages of decomposition. It is easy to turn and harvest. This style bin can be made

animal resistant (Compost Bins).

6. One Bin System

A one-bin system can be square, circular or cone shaped and can be commercial or

homemade. Most commercial bins have lids and good ventilation. They are of animal

resistant. These bins are good for smaller yards where there is a small amount of

material to be composted. Bins aid in moisture and heat retention. Many prefer the

neat appearance of enclosed bins. Although some have small doors near the base,

turning the material and/or removing the compost typically requires lifting the bin up

and over the material and reloading it (Compost Bins).

24

Figure 2.6 Types of compost bins

2.6 OPTIMUM FACTORS FOR THE COMPOSTING PROCESS

Composting process control is very important in order to achieve a short processing

time at a lower cost, consistent results and free from pathogens and odour (de Bertoldi

et al. 1985). The composting of sludge is controlled by few factors such as

temperature, ratio of C to N (C/N), moisture content, free air space, pH, ventilation,

rotation and material adapter like stools, wood dust, flying ash and etc. These factors

rely on each other (Figure 2.7) (Campbell et al. 1990).

Figure 2.7 Schematic of granulation process

Source: Iveson et al. 2001

25

2.6.1 Temperature

Temperature in the composting material is a function of the rate of heat evolution and

heat loss to the environment (Miller 1992; Liang et al. 2003). The temperature in the

compost pile is very important to be controlled because it affects metabolism and

microbial population (Liang et al. 2003; Campbell et al. 1990). Temperatures between

30 and 50 0C increase microbial activity based on the highest oxygen consumption (de

Bertoldi et al. 1983). Temperature below 20 0C and more than 60 0C is proven to

decrease microbial activity (Liang et al. 2003). However, the normal operating

temperature range used are as follows: >55 0C to maximize sanitation, 45-55 0C to

maximize biodegradation rate and 35-45 0C to maximize microbial diversity

(Stentiford 1996). For sludge composting, temperature was found to be responsible for

sludge drying (Buchanan et al. 1999; Walker et al. 1999).

Figure 2.8. Major Factors which affect decomposition in composting

Source: Campbell et al. 1990

26

2.6.2 Ratio of C to N

Sewage sludge with a low C/N ratio causes ammonia to become steam and

temperature to not reach thermophilic temperatures (Qiao & Ho 1997). The high

ammonia emissions can also cause toxicity in microbes and reduce the rate of

biodegradation of cellulose (Shin & Jeong 1996). Available carbon source such as

green waste and sucrose is added to sludge to improve the C/N ratio (Qiao & Ho

1997). When C/N ratio exceeds 35, microorganisms must go through a long life cycle

to oxidize excessive carbon to a suitable C/N ratio for their metabolic process to be

achieved (de Bertoldi et al. 1983). This causes the composting process to become

longer. Additional resources for nitrogen source such as stool or urea will reduce the

composting time and cause the end result to be better as the ground adapter material

(Hackett et al. 1999; Jokela et al. 1997).

At optimum conditions, thermophilic phase in stack is achieved in a shorter

time and dehydration of material will be more effective (Jokela et al. 1997; Walker et

al. 1999). Metcalf and Eddy (1991) mentioned that excellent C/N ratio is of range 25-

35. In a larger scale, C/N ratio of 43 can also be considered since thermophilic

temperature can be achieved within 24 hours and rate of water elimination is high

(Jokela et al. 1997). Sludge composting and solid waste from farm using ventilated

limits with C/N ratio of about 18 was found not to hinder degradation of microbes

(Tiquia & Tam 2001). Table 2.4 shows the early C/N ratio for a few composting

process.

Sludge Suitable Ratio Compostin References

27

materials of C:N

g Time, day

Pulp and Paper Mill Flying ash 70 245 Hackett et al. 1999Pig Farms Waste 18 77 Tiquia& Tam 2000Olive Mill Solid waste

of olive industry27 60 Papadimitriou et al.

1997Sewage Waste 25 50 Pera et al. 1991

Cow Dung Peat moss 16 20 Yu et al. 1991Cow Dung Paper 18 20 Yu et al. 1991

Wood dust 25 18 Liao et al. 1997Pig faeces Peat moss 16 14 Lau et al. 1992

Grape residue Chicken manure 14 25 Ferrer et al. 2001Vinasse (sugar industry) Cotton residue 19 70 Diaz et al. 2002

Gelatin-grenetine industry Urea and wood dust

30 55 Hoyos et al. 2002

Olive Mill Cotton residue 23 182 Paredes et al. 2002Sewage Sugar, clay, and

wood dust13 50 Qiao& Ho 1997

Paper Mill Domesticated poultry waste

64 168 Charest & Beauchamp 2002

Table 2.4 Initial ratio of C/N used in variety composting processes.

Source: Hackett et al. 1999 & Jokela et al. 1997

2.6.3 Moisture Content and Free Air Space

Sludge differs from organic materials because it does not contain fibre and is not

capable of supporting high moisture content. When the free space in compost is filled

with water, sludge will have a weaker structure and acts like a plastic. This will cause

aerobic composting to stop and oxygen transfer will be prohibited. Aerobic

composting will occur when the spaces are filled with air. There are five methods of

lowering down moisture content of sludge which are recycling of materials that have

been composted, the addition of bulking agents such as wood dust, the fixed use of

agitation for compost aeration, addition of dry adapter and lastly, the drying of sludge

before being composted (Buchanan et al. 1999).

Liang et al. (2003) mentioned that moisture content is to be given more

priority for monitoring compared to temperature in order to increase microbial

28

activity. Optimum moisture content will fasten oxygen transfer hence increasing

microbial activity, fastens decomposition and reduces odour (Goldstein 2002; Liang et

al. 2003; Schaub & Leonard 1996; Tiquia et al. 1996). An optimum moisture content

is needed to overcome early cooling problems and also to avoid increase in bulk

density (Goldstein 2002). Liang et al. (2003) mentioned that the minimum moisture

content for sludge-saw dust composting is 50% in order to obtain microorganisms

exceeding 1.0 mg g-1 hour-1. According to Metcalf and Eddy (1991), moisture content

cannot exceed 60% for non-reactor system and 65% for reactor system. Goldstein

(2002) stated that optimum moisture content for composting mixture of sludge and

wood dust in aerated static pile is 55-65%. Table 2.5 shows the initial moisture

content for few composting processes.

Moisture content (MC) and free air space (FAS) affect the air movement and

oxygen transfer in decomposing materials. Free air space is defined as ratio of gas

volume to total volume. Free air space is closely related to other physical

characteristics such as porosity (the ratio of vacant space volume with total volume),

structure and bulk density. Biddlestone and Gray (1988) reported that the minimal

porosity is 30%. Optimal bulk density for sewage sludge composting using reactor

system and non-reactor system are 400-500 kg/m3 and 475-593 kg/m3respectively

(Goldstein 2002; Schulze 1962). Haug (1993) combined free air space (%), porosity

(P, %) and MC (%) through the following equation:

Whereby,

Whereρb is bulk density (g cm-1) and ρp is the particle density (g cm-1). Combining

equation (1) and (2) results in,

Sludge Adapter

Materials

Initial

moisture

content, %

Composting

time, day

Reference

FAS = P (1 - MC100 ) ----- (1)

P = 100 (1 - ρb

ρp ) ----- (2)

29

Pulp and paper mill

Fly ash 53 245 Hackett et al. 1999

Pig Farms Waste 65 77 Tiquia& Tam 2000

Olive Mill Solid waste of olive fruitindustry

51 60 Papadimitriou et al. 1997

Sewage Waste 62 50 Pera et al. 1991

Cow Dung Peat moss 64 20 Yu et al. 1991

Cow Dung Paper 69 20 Yu et al 1991Fish waste Wood dust 60 18 Liao et al. 1997

Sewage Glucose + wood dust + clay

59 50 Qiao& Ho 1997

Pig Faeces Peat moss 66-69 14 Lau et al. 1997

Gelatine-grenetineindustry

Urea and Sawdust 71 55 Hoyos et al. 2002

Rearranging equation (3),

Moisture content (%) can be expressed in terms of FAS (%). Free air space of

compost can be increased by adapter materials such as recyclable compost product

and bulking agents such as saw dust. There are evidences stating that minimum

moisture content for certain materials are related to the percentage of minimum free

air space. Ventilation is difficult to attain in the initial stage of decomposition before

steaming is carried out for drying the mixture and to increase the volume of space.

Addition of adapter materials can speed up the rate of composting process (Buchanan

et al. 1999).

Table 2.5 Initial moisture of various composting process

2.6.4 pH

FAS = 100 (1 - ρb

ρp)( 1 -

MC100 ) ----- (3)

MC = 100 - (FAS

1−ρb

ρp

) ----- (4)

30

pH values are important since they play a huge role in affecting the soil acidity as well

as composting process. An optimal pH value for sludge composting is in between 6 to

9 (Metcalf & Eddy 1991). If the pH is too alkaline, this will result in extreme rise in

temperature which will lead to death of bacteria and volatilization of ammonia. When

pH values are not in this range, bacterial activity will experience retardation and

degeneration will slow down or stop entirely (Schaub & Leonard 1996). Addition of

materials such as cotton waste and fly ash to the sludge will increase its pH value

(Diaz et al. 2002; Hackett et al. 1999). Table 2.6 shows the pH value for few

composting processes.

Table 2.6 Initial pH value for multiple composting process

Sludge Adapter

material

Initial pH

value

Composting

time, days

Reference

Pulp and paper mill

Fly ash 8.9 245 Hackett et al. 1999

Pig Farms Waste 8.6 77 Tiquia& Tam 2000

Olive Mill Solid waste of olive fruitindustry

7.2 60 Papadimitriou et al. 1997

Sewage Waste 7.0 50 Pera et al. 1991

Sewage Glucose + wood dust + clay

7.0 50 Qiao& Ho 1997

Paper Mill chicken droppings

7.5 168 Charest & Beauchamp 2002

2.6.5 Aeration

Aeration is required for metabolic heat production from aerobic microbial. However,

excessive air supply rate will increase cost and cause loss of heat from the compost

pile while too little ventilation will cause anaerobic process (Polprasert 1989). In

addition, aeration is important to remove the main waste product, carbon dioxide and

water (Haug 1993). Table 2.7 shows the rate of aeration in few composting processes.

31

Failure in aeration system can cause a slow decomposition, a process with high

odour, a delay in achieving maximum temperature, a lower maximum temperature and

low rate of water removal (Diaz et al 2002; Ferrer et al. 2001; Haug 1993). According

to Campbell et al. (1990), aeration rate depends on biodegradation properties of

compost mixture. The harder the biodegradation, the lower the rate of optimum air

required. For sludge composting, the proposed value is between 300-700 m3 air/tones

of volatile compounds (VC)/days (Biddlestone & Gray 1988; Schulze 1962). Daily

aeration with rate exceeding 1 000 m3 air/min tones of (VC)/days will cause cooling

effect in composting (Campbell et al. 1990; Lau et al. 1992).

Aeration is carried out either through natural passive air movement or by

forced air. Passive aeration uses absorbing and natural air movement. Forced air

depends on the fan to move the air through composting materials. There is a

possibility of a third mode which is pure oxygen gas being injected into the reactor

(Rynk & Richard 2001).

Natural aeration or passive occur when there is diffusion and natural air

movement. Natural or passive aeration is driven by at least three mechanisms namely

molecular diffusion, wind and thermal convection. Oxygen is absorbed into the

material because there is more oxygen in the outer than in the compost media. On the

other hand, carbon dioxide will diffuse out. However, this process is slow and might

give an impact to the aerated pile. If the compost pile is exposed, oxygen transfer is

carried out by the wind (Haug 1993).

Thermal convection is the main mechanism in most passive aeration

composting system. Heat generated from the composting process raises the

temperature of the gas causes a reduction in the density of the material. Hot gas moves

out of the composting process, creating space and the cold outside air will enter.

Ventilation rate is determined by the temperature difference between the gas in the

ambient air and the air flow resistance of compost media. Thus, the actual air flow in

the compost heap is dependent on the production of heat to drive the heat convection

32

and the existence of the physical structure of the porous media in compost (Rynk et al.

1992).

Forced aeration can be supplied in a positive or negative way. Positive forced

aeration is forcing air into the compost material while negative forced aeration is

sucking the air out of the compost material. Positive forced aeration is good for air

movement while negative aeration is suitable for inhaling the odour (Rynk & Richard

2001).

Forced aeration can be performed continuously or intermittently depending on

the requirements of the process. Continuous aeration can reduce the rate of air flow,

reduce temperature fluctuations and oxygen. However, continuous aeration will cause

the slope of the composting environment, causing extreme drying and cold areas that

remain in the air in (Rynk & Richard 2001). Aeration can also be supplied

intermittently so that the maximum temperature in the process can be achieved for

longer time and final compost will be safer (Lau et al. 1992).

2.6.6 Rotation

Rotation can be conducted using the front loading tractor. Rotation provides

ventilation, reduced particle size, ensuring that the material experiences the highest

temperature, renewing microbial activity, increasing porosity and producing a more

uniform compost heap (Biddlestone & Gray 1991; Diaz et al. 2002; Hackett et al.

1999; Thambirajah & Kuthubutheen 1989). It is also the primary mechanism for

aeration and temperature control systems for composting using bounds (Tiquia et al.

1997).

Heap of pile which is rotated experiences reduction in volume by 55 to 72%

(Larney et al. 2000). The loss is found in mass of C, K and Na (Tiquia et al. 2002).

Maturation process is achieved at a faster rate for composting of faeces by rotation

(Tiquia et al. 1997).

33

The rate of rotation also contributes to the effectiveness of composting. It is

suggested that inversion of 3-4 days in a week is necessary for composting (Tiquia et

al. 1997; Wong et al. 2001). High frequency of rotation leads to electrical

conductivity and low NH4-N content and also a low rate of thermophilic phase

because of heat loss by evaporation and volatilization of ammonia in the stack (Wong

et al. 2001).

The disadvantages of using front loading are that it takes a longer time and

uses a large space (Biddlestone & Gray 1991; Tiquia & Tam 1998). Rotation can also

be carried out in rotating drum. The main function of rotation in composting is that it

exposes materials to fresh air, increases oxygen and dissipates the heat and gas from

the product of composting (Rynk & Richard 2001).

Rotation in the rotating drum can also reduce air pollution (Tiquia & Tam

1998) and ease the mixing process. However, the rate of rotation has to be minimized

because frequent rotation will produce large lumps. In the composting of sludge-

waste, the rotation of rotating drum was carried out for 5 minutes after the materials

were added and also 5 minutes before the materials were removed (Schulze 1962). In

the research by Smars et al. (2001), the rotation was limited to only 10-20 minutes per

day.

2.6.7 Adapting Materials

Adapting materials such as sawdust, paper, fruit waste and etc. greatly influence the

decomposition process for active composting, maturation and storage (Eklind &

Kirchman 2000). There are two types of adapter namely structural adapter and energy

adapter. Structural adapter acts as a bulk weight reduction and increases air space

thereby improving its aeration. Energy adapter increases the amount of biodegradable

organic matter in the compost mixture (Liao et al. 1997). Adapter materials are

necessary in composting because they influence the pH, C/N ratio, humid content and

air supply to aerobic bacteria (Golueke 1991). Therefore, adapter materials are

significant in improving microbial degradation process and also in producing good

quality compost so as to ensure its compatibility as fertilizer and soil adapter (Liao et

34

al. 1997). The release of ammonia from mass of compost has been reduced by

addition of woody material, peat and vermiculate (Bhamidimarri & Pandey 1996; Liao

et al. 1997; Qiao& Ho 1997). Coal fly ash is found to reduce the potential of the metal

reactions (availability) in sewage sludge composting (Wong et al. 1997).

Composting study of vinasse (sludge sugar industry) mixture and grape residue

was performed in the reactor system. Increase in amount of vinasse (0-40% wet

weight) was studied for 43 days. The increase in quantity of vinasse did not affect the

pH value. Evolution of organic materials show higher loss and higher capability of

biodegradation when vinasse mixture having a lesser volume. Loss of Nitrogen

increased when quantity of vinassein in the mixture increased. The optimum rate of

vinasse was found to be in between 10-20% (Diaz et al. 2002). Composting of vinasse

and cotton waste was carried out by adding vinasse (0-80% mass) in the reactor for 23

days. It was found that 20-30% of vinasse is the optimum condition since the final

product was of good quality, higher rate of biodegradation and the minimum loss of N

(Diaz et al. 2003).

Ash was mixed at 0-50% (dry weight) together with sewage sludge and

composted for three months. The emission of carbon dioxide for every amount of ash

was found to be similar except for 50% of ash. However, the emission of carbon

dioxide experienced a reduction as the quantity of ash was increased. This indicated a

decrease in microbial activity. The increment in content of salt and pH was believed to

cause this inhibition. Rise in more than 25% (dry weight) resulted in a decrease in the

growth of thermophilic bacteria and the production of carbon dioxide. Dry ash of

lesser than 25% in amount is compatible for composting of ash-sludge (Fang et al.

1999; Wong et al. 1995; Wong et al. 1997).

Shin and Jeong (1996) have reported studies of food waste composting with

various amounts of paper of 33%, 50% and 67% (wet weight). Mixture which

contained 33% of paper was found to have inhibitory impairment due to excessive

release of ammonia. From this study, it was found that the highest degradation of

cellulose is 61% when the paper content in the mixture is high.

35

One of the commonly used adapter materials in the composting process is

wood waste such as sawdust and bark. Wood waste takes a longer time to be

biodegraded and is usually burned to be disposed. There are numerous studies on

reuse and recycling of sawdust such as making fuel, liquid absorbent, building

additives and etc. Wood waste is less suitable as a soil adapter since its C/N ratio is

high. However, by adding nitrogen source such as sludge, wood waste can be

converted into soil adapter materials (Siddiqui & Alam 1990).

The use of wood waste as an adapter material in the composting process

appears to increase the porosity, ability to hold nutrients, reducing odour and

enhancing its energy when applied at the appropriate amount (Bhamadimarri &

Pandey 1996; Liao et al. 1994; Tiquia & Tam 2000). Wood waste was found to have

the ability to reduce pathogens more effectively compared to other agricultural waste

during composting of sewage sludge (de Sales-Papa 2002). The difference in

composition of different wood tissues from species to species results in the

inconsistent rate of decomposition of wood dust on every different species. Liao et al.

(1997) reported that sawdust from hardwood is more readily biodegradable compared

to sawdust from softwood. Sawdust from hardwood is better in holding nitrogen.

However, it produces a higher concentration of phenol during the process of

composting.

In sewage sludge composting, usage of sawdust is more suitable as a bulking

agent compared to hay and grass (Furhacker & Haberl 1995). Waste wood has the

highest reduction of organic matter, dries the sludge and reduces pathogens compared

to other materials (de Sales-Papa 2002). In swine waste composting, wood waste is

partially decomposed in swine waste providing sufficient empty air space and thus

allowing delivery of oxygen to the microorganisms (Tiquia & Tam 1998).

Bhamadimarri & Pandey 1996 reported that wood dust has the ability to absorb

moisture, providing carbon source, withhold nutrients and providing the appropriate

porosity in the compost pile.

Furhacker and Haberl (1995) reported that volume of wood waste must be

more than 33% in sewage sludge composting using rotating drum. If the density of the

36

sludge and wood waste is estimated to be 700 kg/m3and 100 kg/m3 respectively, then

the minimum amount of wood waste needed is 10%. Liao et al. (1994) have carried

out the composting of fish waste by using 25%, 33% and 50% by weight of sawdust.

The end result had a C/N ratio of less than 20 except for when sawdust of 50% was

used. The pH value of compost with sawdust of 50% is lower than the others because

of low ammonia content.

2.7 COMPOST MATURATION

According to Commision of the European Communities (CEC 1986), compost is the

product of a stable composting process and free from pathogens which is beneficial

for plant growth. It has undergone an early and fast decomposition process and also

the process of humification. Humification is the process of partial conversion of the

original material into humus which is a humic substance and is relatively inert

(Tuomela et al. 2000).

The usage of immature compost will prevent the uptake of nutrients by the

microbial population which will further cause nitrogen deficiency in plants. Other than

contributing to excess of carbon source, the presence of phytotoxicity materials such

as ammonia and organic acid will speed up the decomposition process of immature

compost which in turn will have a negative impact to the soil and plants. Plants

interact with the retarded environment by lowering down metabolic rate, decrease in

root respiration, drop in nutrient absorption and lowers down the synthesis and

transport of gibrelin and cytokinins (Jimenez & Garcia 1989).

According to Jimenez and Garcia (1989), the techniques of observing compost

maturity is divided into five namely, physical tests, microbial activity research,

methods of compost humic fractions, chemical method and biological method. The

physical test includes observation of physical characteristics of compost mixture such

as its temperature, odour and colour. Microbial activity research includes counting of

total microorganisms, respirometric research, biochemistry parameters for microbial

activity and analysis of biodegradable material. On the other hand, method of compost

humic fraction covers chromatography test and photocalorimetric method. Chemical

37

method includes C/N ratio (solid state), pH, cation exchange capacity and the presence

of nitrate and nitrite. Example of biological method is the test of germination of seed

to detect phytotocity.

The maturation process greatly depends on the composting materials and not

on the type of system (reactor or non-reactor) used (de Bertoldi et al. 1983). Faeces-

straw composting in rotary rotating drum requires three months of composting for

compost maturation using the row system (Vourinen & Shaharinen 1997). Furhacker

and Haberl (1995) composted sewage sludge with wood chips for 4 to 5 days and the

maturation process took 6 months. Composting of paper industry sludge with faeces

using row system failed to undergo maturation after 6 months based on C/N ratio and

calometric test (Charest & Beauchamp 2002). Table 2.7 shows the time taken for

composting process in multiple systems.

Table 2.7 Duration of composting process for combination of systems and materials

System Mixture Range of composting time

Usual composting time

Maturation

Static stack LeavesLivestock manure

2-3 years6 months – 2 years

2 years1 year

--

Aerated static pile

Sludge + wood waste

3-5 weeks 4 weeks 1-2 months

Bounds,irregular round

Leaves

Livestock manure

6 months-1 year4-8 months

9 months

6 months

4 months

1-2 months

Bounds with passive ventilation

Livestock manureFish waste + peat

10-12 weeks

8-10 weeks

-

-

1-2 months

1-2 months

Stirred layer Sludge+compound waste orFaeces+wood dust

2-4 weeks 3 weeks 1-2 months

Rotating drum

Sludge and/or solid waste

3-8 days - 2 months

Source: Carr et al. 1995

38

2.8 COMPOST AS SOIL ADAPTER MATERIAL

The addition of direct waste into the soil will cause a change in the ecosystem of the

growing plant. The waste which is not composted and added to the soil causes

microflora to decompose them and produce transition metabolites which will inhibit

the growth. In addition, a tussle between microorganisms and soil nitrogen, a high

carbon to nitrogen ratio and the production of ammonia in the soil will occur (de

Bertoldi et. al 1983). These conditions can be improved by the production of good

compost.

Compost releases nutrients at a slower rate (Keeling et al. 1994; Maeda et al.

2003). Sikora and Enkiri (2000) described the rate of mineralization of sludge

compost to be about 9.3% to 29% of the total nitrogen. Composting has many uses in

the field of agronomic, horticulture and forestry. It can be used for field crops, tree

seedlings, plants in the greenhouse, nursery plants, flowers and herbs grown on the

land. It can also be used to maintain organic matter, structure and fertility of

agricultural land, to support urban landscape, to reclaim abandoned land such as

mining areas, to create a landscape and to close the landfill space (Rynk 1992).

Function of compost in the soil and in the relationship of the land-plant

interaction is different with conventional fertilizer even though compost has nutrients

like N, P, and K. The main purpose is not to enrich the soil compost with this element

but is to supply humus and improve soil structure (de Bertoldi et. al 1983). Humus is

an organic material that is relatively stable. It is very important in maintaining good

soil structure, especially in fine-textured soils. It increases the cation exchange

capacity, resulting in the loss of elements such as potassium, calcium, and magnesium

(Tisdale & Nelson 1975). Application of sludge-waste composting in city has found to

improve soil-water content, water holding capacity, saturated hydraulic conductivity,

compression, aggregation, total porosity and pore size distribution (Aggelides &

Londra 2000; Yadav et al. 2002). Atiyeh et al. (2001) stated the potential of compost

to supress soil-borne plant pathogen. Table 2.8 indicates the various types of compost

quality which is produced from sludge. Compost is easier to be applied to soil, easily

maintained, easily stored and transported as compared to sludge/waste without

39

composted. It is also a soil medium adapter which is not costly (Hackett et al. 1999;

Van Heerden et al. 2002).

Table 2.8 Quality of compost of sludge for soil adapter materials

Type ofsludge

AdapterMaterials

OrganicMaterial%

N, % P, ppm

K, ppm

Note Reference

Gelatin industry

Wood dust 55-58 2.4-4.3

2000-3000

40000-42000

No odour for final compost

Hoyos et al. 2002

Paper industry

Livestock manure

53-58 0.7-0.9

2600-3700

3000-4000

Achieved compost of B Standard

Clarest& Beauchamp 2002

Pulp and paper industry

Fly ash 58-63 Not stated

100-119

870-970

Application for 15m3/ha to improve soil nutrient

Hackett et al. 1999

Sewage Horse droppings

Not stated

1.1-1.2

9600-16000

8200-9400

Addition of compost and peat improves tree growth

Warman & Termeer 1996

Olive industry

Cotton waste/cornstalk

36-88 1.4 - 1.7

Not stated

Not stated

Adapter materials influences compost product

Paredes et al. 2002

Sugar industry

Grape waste/cotton waste

Not stated

1.8-2.7

32 000

17000-20000

Suitable with moderate compost dose application

Madejon et al. 2001

2.8.1 Plant growth and factors affecting it

Growth is interpreted as a progressive development of an organism. Plant growth can

be referred as the development of a specific organ or the whole plant. Growth can be

40

expressed within the definition of dry weight, length, height or diameter. The factors

which affect plant can be divided into two namely genetic and environmental (Tisdale

& Nelson 1975).

Environmental factors which are important in affecting plant growth are

temperature, moisture content, energy radians, atmospheric composition, gas content

in the soil, soil reaction, biotic factors and supply of mineral elements. Temperature

has a direct impact on plant functions such as photosynthesis, respiration, cell wall

permeability, absorption of water and nutrients, transpiration, enzyme activity and

protein coagulation. Water is required for construction of carbohydrates, maintaining

protoplasm hydration and also as a tool for food and mineral elements translocation.

When the temperature or water content is not optimal, then plant growth will decrease.

Plants will generally grow well in low light intensity than in high light intensity.

However, plants vary in their response to light. Air content consisting of sulphur

dioxide, carbon monoxide and hydrofluoric acid can cause toxicity in plants (Tisdale

& Nelson 1973).

Among the mineral elements which are essential in plant growth are nitrogen,

phosphorus and potassium. Nitrogen is an important plant nutrient. It is absorbed by

plants in the form of nitrates although it can also be absorbed in the form of

ammonium ion and urea. When adequate nitrogen is supplied, plant growth occurs

well and are coloured green. However, when the supply of nitrogen is in excess, it can

cause slow plant maturity, causing plant fibers to become softer and more susceptible

to disease and insect attack. Lack of nitrogen causes the plant to be retarded and

yellowish. Initially, the process of plant becoming yellowish will strike the bottom of

the plant, followed by parts of plants. When nitrogen deficiency is more critical, plants

can also die.

Phosphorus is absorbed by plants in the form of ions in the form of

orthophosphate, H2PO4- and dissolved organic phosphate. Phosphorus plays a

significant role in plant root development. It also accelerates the maturation of plants,

increase the quality of product and resistance to disease. Phosphorus deficiency will

also retard the overall growth. Plants absorb potassium in the form of K+. Potassium

41

deficiency is most easily detected by inhibition of leaf characteristics. In addition,

potassium deficiency causes the plant growth to be reduced, reduced resistance to

disease, degradation of roots and reduction in photosynthesis. The other important

features of potassium are that it maintains an appropriate water-plant relationship and

plant metabolism (Tidale & Nelson 1975).

Soil structure greatly influences the development of roots and the shoot of

plants. The higher the bulk density of the soil, the more compact the soil will be,

causing weakened soil structure and smaller air space. High soil bulk density results in

mechanical resistance to root penetration to increase. This condition usually affects

the rate of oxygen absorption into the soil porous space and root respiration is directly

associated with the gas supply is adequate and continuous. Water holding capacity of

compost/soil shows the maximum moisture that can be supported by the dry soil at

standard conditions. The value of water holding capacity is essential to determine the

moisture needed for plant growth. Porous area/porosity is the volume fraction of

soil/compost that is not filled by a solid material. Porous space is important for air and

water movement in the soil (Iswaran 1980).

In addition, the amount of oxygen in the soil is also important for plant growth.

Soil reaction (soil acidity, pH) affect plant growth by influencing the availability of

certain elements needed for plant growth. At acidic pH, the reaction capacity of

phosphate, manganese and molybdenum were found to decrease. When nitrogen in

ammoniacal form is applied on the surface of the soil at a pH above 7, the ammonia

will be lost due to volatilization. In addition, the disease from the soil can also be

caused by neutral-alkaline soil conditions. There are many biotic factors that will limit

plant growth for farming operations and shows the potential threat to reduce the crop,

if not to the destruction of the crops. Imbalance of available nutrients can also increase

the incidence of disease and insect infestation (Tisdale & Nelson 1973).

2.8.2 Effect of various amount of compost on plant growth

Compost affects physical, chemical and biological characteristics of soil by

influencing the permeability, porosity and structure, as well as the redistribution of

42

movement and transport of nutrients. Therefore, the occurrence of some of the

activities and biosynthetic microbial degradation results in improvement of soil

fertility, particularly in terms of the supply of nutrients to plants. Nutrient intake

occurs at rhizosphere (zone encircling the land and influenced by plant roots) and it is

stimulated by microbial metabolites. Microbial metabolites are capable of influencing

or enhancing the influence of the enzymes in plants. Composting improves mineral

nutrition, protein synthesis and carbon assimilation and increases the production of the

entire plant. In addition, the roots will produce more exudates to the soil. Thus,

composting is a new source of energy that stimulates the growth and microbial

processes and subsequently, the metabolism and plant growth (Figure 2.9) (Tomati et

al. 1996).

Soil reactions to the application of compost depends on a number of factors

including the type of compost and composition, level and application method, soil

properties and weather conditions (Abdel-Sabour & Abo El-Seoud 1996). Pinamonti

et al. (1997) reported that ornament plants were found to grow well with a mix of 50%

sewage sludge compost and bark. Hountin et al. (1995) reported that the application of

compost with peat shrimp waste exceeding 240 tonnes/ha also showed no increase in

the development of barley. However, Klock (1997) reported that trees namely

Impatien and Snapdragon can grow fertile in 100% composted sewage sludge

together with farm waste. Applications of droppings on sandy soil can improve crop

production of plantation Brassica parachinensis and Brassica chinensis compared to

sandy soils alone and treatment with synthetic chemical fertilizers (Wong & Wong

1987). Composting of sewage sludge is also found to increase the yield of corn and

grain (Abdel-Sabour & Abo El-Seoud 1996).

43

Figure 2.9 Influence of compost on plant system

Source: Tomati et al. 1996

2.9 GENERATED SOLID WASTE

Total solid waste that is generated in Peninsular Malaysia is increasing from day to

day. The average of solid waste produced can be divided into 45.0 percent food, 24.0

percent plastic, 7.0 percent paper, 6.0 percent steel, 3.0 percent glasses and etc. (Ninth

Malaysia Plan). Generation rate of these solid waste differ depending on types of area,

total population and occupation or business (Agumuthu 2001).

44

2.10 DOMESTIC WASTE

Solid wastes that are produced everyday are result of thrown waste of domestic and

housing sectors. There are specific categories that have been identified in producing

these solid waste including housing waste, commercial waste, construction waste,

environmental waste and etc. These waste produced are mainly from housing wastes

which includes food waste, papers, plastic which are in the forms of solid, semi-solid,

or liquid. Organic materials are easy to decompose, decay at a faster rate and extract

odd odour that can disrupt public peace (Agumuthu 2001).

2.10.1 Housing Waste

Housing waste produced from activities done by individual in every home are also in

forms of solid, semi-solid and liquid. Most of these housing wastes consist of food

waste, papers, boxes, plastic and aluminum which are easily decomposed and decayed

(Agumuthu 2001).

2.10.2 Business Waste

These types of wastes are a result of business activities, management and trading.

These wastes are usually in forms of solid/semi-solid and are easily disposed through

combustion. Examples of business waste are business premises waste and office

utilities such as papers, files, stationeries, plastic and etc. (Agumuthu 2001).

2.10.3 Industrial Waste

Almost half of waste from industrial sectors and factories exist in forms of solid and

liquid. Examples of industrial waste include wood, plastic, scrap metal, sheet metal

and etc. Generally, these industrial wastes are divided into two parts, which are danger

and non-danger wastes. Danger wastes usually contain chemical substances, biology

process waste and also radioactive waste, whereas non-danger waste are of plastics,

steel, fiber, and etc. (Agumuthu 2001).

45

2.10.4 Construction Waste

Constructions waste are mainly produced from constructions of new building,

construction sites, road repairing work, building renovation, demolition of old

building and etc. Most of the wastes are in solid form such as woods, steel, rock,

plaster, concrete and etc. (Agumuthu 2001).

2.10.5 Environmental Waste

Most of the environmental wastes produced are in forms of solid. Examples include

dried leaves, grasses, tree branches, wood and other waste from gardens and landscape

(Agumuthu 2001).

2.11 FACTORS INFLUENCING THE REVENUE OF SOLID WASTE

According to studies by (Laiman et al. 2005) entitled ‘Revenue and Composition of

Solid Waste’ in Mukim Melaka Tengah, Melaka, there are various factors influencing

the increasing revenue of solid waste. Amongst them are mainly housing type that

involves way of living and eating styles in every house namely the high-class, middle-

class, and low-class housing.

Besides that, according to Yusof (2007) in Comparative Research between the

Usage of Soil and Wood Powder on Organically Kitchen Waste Composting System,

among the involving factors that influence the generation of solid waste are

geographically, seasonal, attitude of individual and types of residence.

2.11.1 Geographical Factor

Generally, the geographical factor of an area or country does affect its weather. For

example, Malaysia is a country that is situated on the equator line that is always

experiencing moist and hot weather throughout the year. However, the monsoon wind

that hit this country will cause the raining season on certain times of the year. On top

46

of that, the frequent cooking will increase during these seasons and result in rise of

food waste produced than usual.

2.11.2 Seasonal Factor

Seasonal factor includes the fruits seasons, festive, vacations/school breaks and etc.

Generally, the rate of waste disposal during these seasons will increase and become

the generated factor of solid waste in Malaysia. The solid wastes produced are food

wastes generated in large quantity from food prepared by the house residence and also

from fruit skin waste from the orchards during fruit seasons.

2.11.3 Society Attitude Factor

The attitude of the society and public that underestimates the result of increased solid

waste contributes to the increasing generation of solid waste. Generally, the public are

unaware of their attitude of throwing rubbish which in real fact is affecting the

cleanliness of the environment.

2.11.4 Type of Residence Factor

The quality of the environment can easily be affected by the attitude of residence in

Malaysia. In studies conducted by Laiman et al. (2005), lifestyles and economic

factors can affect the amount of expenses and eating styles whereby it is proven that

the higher the expenses and the bigger the size of a family, the more solid wastes are

generated.

2.12 SOLID WASTE MANAGEMENT

Solid waste management in Malaysia is not systematic and efficient. Generally, the

waste produced will be disposed at the disposal site provided. Five years ago, there

were 230 disposal site set up in this country. However, only 170 disposal sites are

registered to accommodate the rising waste produced. Unfortunately, almost 80% of

47

the disposal sites available now will be closed in a period of two to three years in the

near future.

There are few methods being applied to overcome the increasing amount of

solid waste produced in Malaysia such as recycling, composting system of wet waste,

and the reduction of reusable waste. For recycling process, either all or some parts of

the items are being reused again.

2.12.1 Disposal Sites

Solid waste disposal sites are the easiest and cheapest method used. Generally, the

disposal sites are operated by dumping the wastes into the Earth and then by burying

them. These disposal sites are usually situated in places of abandon quarry, mining

area and loan holes. According to Syarina (2007) the disposal sites are divided into

two types which are sanitary and non-sanitary disposal sites. However, almost all

disposal sites in Malaysia are non-sanitary disposal sites. This method requires the

waste to be trimmed and compressed inside the ground with heavy-machinery. The

surface of the waste are then sealed with soil to prevent bad odor. However, this

method can contaminate the environment through the diffusion of waste in the ground

and then to underground water. On the other hand, sanitary disposal sites are covered

with geotextile fiber to prevent waste diffusion into the underground water. This

diffusion will then be channeled and treated at a diffusion treatment plant.

2.12.2 Incinerator

Incinerator is a type of solid waste disposal that involves waste combustion. This

method will convert the solid waste into heat, gases, vapour, ashes, and chemicals.

However, there are few places in the world that has stopped this method due to its

destructive effect to the environment and also to health. The ashes from the incinerator

contain poisonous materials including lead, mercury and cadmium.

48

2.12.3 Recycle

Recycling is a process of obtaining or ensuring half of the materials of solid waste can

be reused again. The recycled materials include glasses, plastic, paper product and

aluminum can. There are multi types of recycling barrels that can be seen in public

places to tell the public the importance of recycling. According to Yusof (2007), the

success of recycling can reduce the control cost of handling solid waste and

environmental pollutions. Malaysia has targeted the rate of recycling to increase by

22% in the year 2020.

2.12.4 Composting System

Solid waste in organic form such as plants, food waste and paper products can be

recycled using the method of composting system and biological digestion to

decompose the organic matter. This method can be easily done and managed to

produce fertilize compost product that can be used in agriculture. This method of

composting was practiced before the Second World War. However, it is still not used

traditionally in today’s world (Day et al. 1998).

2.13 PALM OIL MILL EFFLUENT SLUDGE (POMES)

The market for palm oil industry is continuously being an attractive topic even though

it is now sold at about one half of its highest price recorded. In Malaysia, palm oil

industry is growing quickly becoming a significant agriculture-based industry. A total

of about 80 million tonnes of palm oil and 57.4 tonnes of palm oil mill effluent

(POME) was generated in the year 2009 (MPOB 2009). Malaysian government is also

supporting the treatment process of palm oil mill effluent (POME) in order to generate

biogas that can be an alternative source of electricity. Moreover, the palm oil industry

provides a source of livelihood to rural families through the government land schemes

and private small holders as well as employment opportunities to agriculture workers

in estates (Ma et al., 1993).

49

The production of palm oil may result in the generation of huge quantities of

highly polluting waste water, also called as palm oil mill effluent (POME). The

properties of POME include thick brownish viscous liquid waste but non-toxic as no

chemicals is added during oil extraction. However, it has an unpleasant odour. POME

is predominantly organic in nature but highly polluting (Ma 2000). Other than that,

POME is a colloidal suspension of 95 – 96 % water, 0.6 – 0.7 % oil and 4 – 5 % total

solids including 2–4% suspended solids originating from mixture of sterilize

condensate, separate sludge and hydrocyclone wastewater (Ahmad et al. 2003).

POME has been identified to be one of the major sources of water pollution due to its

high biochemical oxygen demand (BOD) and chemical oxygen demand (COD)

concentrations. Hence, Malaysian government had enacted the Environmental Quality

Act (EQA) in 1978 and parameter limits were set for the discharge of POME into the

environment. The parameter limits are as shown in Table 2.9.

Due to the mentioned characteristics of POME, a wide range of approaches for

POME treatment have been developed to alleviate the pollution problems caused by

the palm oil industry. The conventional treatment technology of POME employed in

most of the palm oil mill factories in Malaysia which is the ponding system of

biological treatment have been adapted (Chin et al., 1982). However, with the

increasing production in most palm oil mills, the under-sized biological treatment is

unable to cope with the increased volume of POME (Ismail 2005). Therefore, a proper

POME treatment is needed urgently in order to ensure the sustainable economic

growth of palm oil industry without neglecting the precious environment.

Table 2.9. Characteristic of POME and its respective standard discharge limit by the Malaysian Department of Environment.

Parameters Concentration (mg/L) Standard Limit (mg/L)pH 4.7 5-9

Oil and Grease 4000 50

BOD 2500 100

COD 50000 -

Total Solids 40500 -

Suspended Solids 18000 400

50

The global energy demand is growing rapidly and at present time, about 88% of this

demand is met by fossil fuels. Researches have shown that the energy demand will

increase during this century by a factor of two or three (EIA 2006). At the same time,

concentrations of greenhouse gases in the atmosphere is rising rapidly, with CO2

emission derived from fossil fuels being the most significant contributor. Therefore,

environmental pollution due to the use of fossil fuels as well as their gradual depletion

makes it necessary to find alternative energy and chemical sources which are

environmental friendly. For fossil fuel-derived energy, reduced environmental impacts

by providing a clean fuel from renewable feedstock such as energy crops, organic

fractions of municipal solid wastes and agro-industrial wastes is necessary

(Chynoweth et al. 2001). Palm oil mill effluent (POME) from palm oil mill waste

water is one of the obvious wastes in Malaysia. In Malaysia, palm oil is utilized for

the production of biodiesel (palm oil methylester or palm oil diesel) for buses and cars

and is a major expansion of Malaysian diesel production with 5% palm oil is expected

for biodiesel production from the year 2006 (Kalam & Masjuki 2002 ; Reijnders &

Huijbregts 2008).

The production of biogas through anaerobic digestion offers significant

advantages over other forms of bioenergy production. This has been evaluated as one

of the most energy efficient and environmentally beneficial technology for bioenergy

production (Fehrenbach et al., 2008). The proper control of anaerobic digestion of

POME treatment will generate gas and renewable energy. Megat et al., (1989) and

Borja et al., (1996) had investigated the performance of anaerobic digestion of POME,

whereby 62 – 98 % of COD reduction and 34 – 98 % of methane production was

reported depending on feed rate, substrate concentrations and system operation.

2.13.1 Anaerobic Digestion in POME Treatment

Anaerobic treatment is the most suitable method for the treatment of effluents

containing high concentrations of organic carbon (Perez et al., 2001). A wide range of

approaches have been developed for the POME treatment. This is because anaerobic

system offers more potential for POME treatment due its high organic content. On the

other hand, anaerobic treatment does not require high energy for aeration and allows

51

the recovery of energy in the form of methane. The conventional way to treat POME

which is widely used in Malaysia is the ponding system. Ma et al., (1993) reported

that more than 85% of the palm oil mills in Malaysia have adopted ponding system for

POME treatment. However, ponding system requires long retentions time and large

treatment facilities because the system usually consist of de-oiling tank, acidification,

anaerobic and facultative pond with hydraulic retention time (HRT) of 1, 4, 45 and 16

days respectively (Ma & Ong 1985). Another disadvantages by using ponding system

as reported by Chin et al., (1996) are the system could not meet the effluent quality

requirement. For instance, COD and BOD5 in the effluent were about 1725 and 610

mg/L respectively.

Sporadic researches have been performed in order to find approachable

solutions for POME treatment. The main aim of the researchers in POME treatment

nowadays are to shorten the treatment time, lessen the land required and at the same

time to collect the useful biogas produced. Borja et al. (1995) in their research

reported on usage of two stages up flow anaerobic sludge blanket (UASB) system in

POME treatment. They observed that the optimum organic loading rate (OLR) in

order to produce a good methane yield and COD reduction of greater than 90% is 30

g/l.d. COD. In addition, 4.1 g/l.d of acetic acid is produced at OLR of 16.6.g/l.d. COD

at only 0.9 days of hydraulic retention time (HRT).

Furthermore, Zhang et al., (2007) examined the integration of biological

method and membrane technology in treating POME. In their study, 43% organic

matter in POME was converted into biogas and COD reduction efficiency reached

93% in the expended granular sludge blanket (EGSB) system. Najafpour et al., (2005)

demonstrated the use of up flow anaerobic sludge fixed film bioreactor (UASFF) in

treating POME. Their study showed a high COD removal of 89% and 97% at HRT of

1.5 and 3 days respectively. Besides, the highest organic loading rate (OLR) value of

0.346 l.CH4/g. COD removed of methane yield was obtained. The OLR value gradually

increased from 2.63 to 23.15 g COD/l.d in this study.

52

Table 2.10 Literature on POME treatment using variable of anaerobic reactor

System Influent

COD

(mg/L)

COD removal

(COD/mg.L)

HRT

(h or d)

Methane

Production

(%)

Reference

UASB 30600 94 6.5d 63 Borja and Banks (1994)

Anaerobic Pond

30000- 40000

97.8 40d 54.4 Yacob et al., (2006)

AF Digester

25000 80.7 20d 36 Yacob et al., (2005)

UASFF 15000– 35000

97 3d 71.9 Najafpour (2006)

CSTR 20000– 35000

80 18d 62.5 Tong and Jaafar (2005)

SBR 11000– 18650

96 20h NM* Chan et al., (2009)

EGSB 79723 91 2d 70 Zhang et al., (2007)

UASFF 44300 94 1.5d - 2.2d NM Zinatizadeh et al., (2005

Anaerobic Contact Process

25000 93.3 4.7d 63 Ibrahim et al., (1984)

Fluidised Bed

15000 78 0.25d NM Borja and Banks (1995)

On top of that, Zinatizadeh et al., (2005) studied about the kinetic evaluation of

POME digestion in high rate up flow sludge fixed film bioreactor. They reported that

with HRT ranges between 1 and 6 days, the removal efficiency of COD was between

80.6% and 98.6%. The methane production rate was between 0.287 and 0.384 l.CH4/g.

COD removed. Their study also demonstrated the apparent rate constant, K calculated by

simplified Monod model which were in the range of 2.9 – 7.41 l.CH4/g. COD. Other

literatures on POME treatment using anaerobic treatment is simplified as shown in

Table 2.10.

53

2.14 NITROGEN FIXING BACTERIA

Nitrogen is the most limiting nutrient for increasing crop productivity. Nitrogen is a

critical nutrient for virtually all life forms. Input efficiency of nitrogenous fertilizers is

low (Prasad et al. 1990) and in turn contributes substantially to environmental

pollution. Nitrogen which is present in the atmosphere occupies about 79% of the air.

Plants cannot use nitrogen in its gaseous state (Sing 2005). Many industrial important

compounds such as ammonia, nitric acids, organic nitrates and cyanides contain

nitrogen. However its conversion in utilizable form is very less and requires high

amount of energy due to presence of triple bond between two N atoms (Singh 2005).

Nitrogen fixing microbes (bacteria and blue green algae) has a natural power to bring

about the conversion of N2 into NH3 which is further being incorporated into amino

acids and finally into proteins. Nitrogen must be fixed or combined into either

ammonia, NH3 or nitrate, NO3. Specifically, tree legumes (Nitrogen Fixing Trees,

NFTs) are valuable in subtropical and tropical agroforestry. They can be integrated

into the agroforestry system to restore nutrient cycling and self-reliance fertility (Craig

& Wilkinson 1995). There are many species of Nitrogen Fixing Trees (NFTs) that

can provide numerous useful products and functions including food, wind protection,

shade, animal fodder, wood fuel and timber in addition to providing nitrogen to the

system (MacDicken 1994). Biological nitrogen fixation is the process that changes

inert N2 into biologically useful NH3. This process is mediated in nature only by

bacteria. In legumes and a few other plants, the bacteria lives in small growths on the

roots called nodules. Within these nodules nitrogen fixation is done by bacteria and

the NH3 produced is absorbed by the plant. Biological nitrogen fixation can take many

forms in nature, including in blue green algae which is a bacterium, in lichens, and in

free-living soil bacteria (Lindemann 2003). An enzyme called nitrogenase performs

this. Nitrogen fixing microorganisms fix nitrogen in five different modes. Through

biological nitrogen fixation, 180 x 106 tones nitrogen per year is being added to the

soil but this figure is still insufficient to replace completely the use of chemical

fertilizers. Various Nitrogen fixing systems shares this global fixation and the

estimated contribution of each component is shown in Table 2.11.

54

Table 2.11 N-fixing systems share this global fixation and the estimate of contribution

of each component

Nitrogen fixing system Estimated contribution (kg/h/year)Free living 15Cyanobacteria 7- 80Aossciative Bacteria 36Azolla/Anabaena 4.5-450Frankia 2.0-362Rhizobium-legume 24-585

2.14.1 Nitrogen Fixing Bacteria - Frankie

Nitrogen is a critical nutrient for virtually all life forms. We get our nitrogen either

directly or indirectly from plants. While nitrogen makes up about 79% of our

atmosphere, plants cannot use nitrogen in its gaseous state. It first must be fixed or

combined into either ammonia, NH3 or Nitrate, NO3-. The natural nitrogen cycle relies

on nitrogen fixing bacteria like those found in the Frankia family of actinobacteria to

supply the fixed nitrogen. Fixed nitrogen is often the limiting factor for growth, both

in your garden and in the general environment.

About 15% of the world's nitrogen fixed naturally is from symbiotic

relationships between various species of the Frankia family of actinobacteria and their

host plants. The plants that form symbiotic relationships with Frankia are called

actinorhizal plants. Scientists have found over 160 plants that host these

actinomycetes including alders, Russian olive, bayberry, sweet fern, bitterbush and

cliffrose. The Frankia is able to provide most or all of the host plant's nitrogen needs.

These nitrogen fixing bacteria and their host plants are often pioneer species on young

nitrogen deficient and disturbed soils such as moraines, volcanic flows and sand

dunes. They help in creating a reservoir of nitrogen rich soil that the next wave of

plants can benefit from.

Scientists believe that much of the new nitrogen in temperate forests, dry

chaparral, sand dunes, moraines, and mine waste tailings is as a result of the

mutualism of Frankia and host plants. They are the main nitrogen fixing relationships

55

in large parts of the world and will only become more important as we adjust the

climate change.

Figure 2.10.Nitrogen fixing bacteria – Frankie

2.14.2 Nitrogen Fixing Trees for Agroforestry

Nitrogen fixation is a pattern of nutrient cycle which has successfully been used in

perennial agriculture for ages. Legumes, which are nitrogen fixers, are of particular

importance in agriculture. The tree legumes (nitrogen fixing trees, hereafter called

NFTs) are especially valuable in subtropical and tropical agroforestry. They can be

integrated into an agroforestry system to restore nutrient cycling and fertility self-

reliance.

The "pioneer" plants (plants which grow and thrive in harsh, low-fertility

conditions) begin the cycling of nutrients by mining and accumulating available

nutrients. As more nutrients enter the biological system and vegetative cover is

established, conditions for other non-pioneering species become favorable. Pioneers

like nitrogen fixing trees tend to benefit other forms of life by boosting fertility and

moderating harsh conditions.

NFTs are often deep rooted, which allows them to gain access to nutrients in

subsoil layers. Their constant leaf drop nourishes soil life, which in turn can support

more plant life. The extensive root system stabilizes soil, while constantly growing

56

and atrophying, adding organic matter to the soil while creating channels for aeration.

There are many species of NFTs that can also provide numerous useful products and

functions, including food, wind protection, shade, animal fodder, fuel wood, living

fence, and timber, in addition to providing nitrogen to the system.

2.14.3 Nitrogen: From the Air to the Plants

Nitrogen is often referred to as a primary limiting nutrient in plant growth. In another

phrase, when nitrogen is not available plants stop growing. Although lack of nitrogen

is often viewed as a problem, nature has an immense reserve of nitrogen everywhere

plants grow, even in the air. Air consists of approximately 80% nitrogen gas (N 2),

representing about 6400 kg of N above every hectare of land. However, N2 is a stable

gas, normally unavailable to plants. Nitrogen fixation, a process by which certain

plants "fix" or gather atmospheric N2 and make it biologically available, is an

underlying pattern in nature.

2.14.4 How to Use NFTs in a System

In the tropics, most of the available nutrients (over 75%) are not in the soil but in the

organic matter. In subtropical and tropical forests, nutrients are constantly cycling

through the ecosystem. Aside from enhancing overall fertility by accumulating

nitrogen and other nutrients, NFTs establish readily, grow rapidly, and regrow easily

from pruning. They are perfectly suited to jump-start organic matter production on a

site, creating an abundant source of nutrient-rich mulch for other plants. Many fast-

growing NFTs can be cut back regularly over several years for mulch production. The

NFTs may be integrated into a system in many different ways including clump

plantings, alley cropping, contour hedgerows, shelter belts, or single distribution

plantings. As part of a productive system, they can serve many functions:

microclimate for shade-loving crops like coffee or citrus (cut back seasonally to

encourage fruiting); trellis for vine crops like vanilla, pepper, and yam; mulch banks

for home gardens; and living fence and fodder sources around animal fields.

57

2.14.5 Literature Review on Nitrogen Fixing Bacteria in Composting

Pramanik et al (2006) have studied the effect of organic wastes; cow dung, grass,

aquatic weeds and municipal solid waste with lime and microbial moculants on

chemical and biochemical properties of vermicompost. In this research, it shows that

cow dung was the best substrate of vermicompost compared to other organic wastes.

Application of lime and inoculation of microorganisms increases the nutrient content

in vermicompost. Besides, Bacillus Polimyxa, the free-living N-fixer, has increased

the N-content of vermicompost significantly. The results show that the C/N ratio for

cow dung was decreased from 18.95 to 12.46 and it was the least C/N ratio reading.

Other than that, cow dung recorded the maximum increase in nutrient content of 275%

in the vermicompost over its initial reading.

Diazotrophs, the potential use of free-living nitrogen fixing bacteria as a

source of nitrogen nutrition for crops has not been realised in most parts of the world,

largely because of the inability of the organism to multiply effectively in temperature

of agriculture soils (Keeling 1998). The population of Diazotrophic was enhanced

300% over the long term and nitrogen uptake by plants increased by over 100% in the

first 2 months post 15 gl−1 glucose treatment in compose-grown swards while soluble

starch-treated sward growth was inhibited.

In addition, a typical field soil similarly treated with glucose failed to respond

to the treatment. Contrary, a nitrogen immobilizing effect was observed. It was

concluded that significant nitrogen fixation and plant N availability was stimulated by

the glucose treatment of compose but the mechanisms of these processes require more

extensive research.

Low (2008) studied on the isolation and characterization of nitrogen free fixer

bacteria from empty fruit bunches (EFB) of oil palm. In his study, the ability of the

microorganism to fix nitrogen freely was examined by using the N-free mannitol agar

medium. The microorganisms which were able to grow in N-free mannitol agar

medium were considered as free living nitrogen fixing bacteria (Alexander 1977). The

medium used containing carbon source without the supplement of nitrogen. Based on

58

C:N ratio, the microorganisms that were able to fix the nitrogen were able to grow on

the medium. In his study, 16 isolates of free living nitrogen fixing microorganisms

namely actinomycetes and bacteria were isolated from the empty fruit bunches (EFB)

of oil palm. From 16 isolates, 14 isolates were free living nitrogen actinomycetes and

2 isolates were free living nitrogen fixing bacteria. All microorganisms studied were

Gram Positive except 2 of the isolates were Gram Negative. Besides, all the isolates

were tested for biochemical properties using Catalase test, Simmon’s-citrate test, triple

sugar iron (TSI) test and Voges-Proskauer (VP) Test. From the biochemical properties

experiment, 7 of isolates showed positive result for catalase test, 1 isolate showed

positive result for TSI test, 2 isolates showed positive reaction to Simmon’s-citrate

test and all the isolates (16 isolate) showed negative results for VP test. From his

study, 1 isolate which was named as strain B1 was identified as Azotobacter sp. due to

the formation of cyst structure. The free living nitrogen fixing actinomycetes were

recognized as the slow grower microorganisms (Sylvia et al., 1999). Low (2008) in

his study showed that the actinomycetes took an incubation period approximately 10-

12 days in order to grow well. By having the isolates grown on N-free mannitol agar

medium, it was observed that the free living N-fixing bacteria possessed slimy,

glistening and sticky appearance. For free living nitrogen fixing actinomycetes, the

colonies appeared to be white powdery and chalky colonies. In his study, the

actinomycetes colonies were observed to be powdery colonies. Other than that, the

gram staining results from his study shows that free living nitrogen fixing bacteria

could be of Gram Positive and Gram Negative. However, the free living nitrogen

fixing bacteria actinomycetes were mostly Gram Positive with the shape of rod.

Cayuela et al, (2009) have done a study on the impact of different N-rich

animal wastes on the composting of ligro-cellulosic wastes by a range of classical and

novel methods. The compost were analyzed using physic-chemical and biochemical

properties meanwhile two composting mixture was used. Mixture A was a mixture of

cotton carding wastes, wheat straw and meat meal. On the other hand, Mixture B was

a mixture of cotton carding waste, wheat straw, blood meal and horn and hoof meal.

As the result, compost B showed that it contained more problematic organisms and a

wider variety of other bacteria than compost A. This is because of the high variety of

59

N-sources such blood, horn and hoof meals used to make the compost. Bacillus and

Sphingobacterium were found in the sample of compost B after3 days.

Gadori et al. (2003) have done an investigation to examine the performances

of Azospirillum isolates on growth and N uptake of Gailardia pulchella with two

nitrogen levels. This study was aimed to develop N2 fixing inoculants to increase yield

of the G. Pulchella plants using efficient Azospirillum isolates from ornamental plants

with different levels of nitrogen. Seven efficient Azospirillum strains which were

OAD-2, OAD-3, OAD-9, OAD-11, OAD-29, OAD-37 and OAD-57 were isolated

from the ornamental flower plant. As the result, maximum nitrogen uptake showed at

the 120 DAT (days after transplanting) which was 92.0 kg ha-1 when compared to

other stages of plant growth. Azospirillum strains OAD-2/ OAD-3/OAD-9/OAD-11

inoculations also showed increase in nitrogen uptake than that of inoculation with A.

Brasilense BR-11001 and Azospirillum strains AOD-5 at all stages of plant growth.

Highest N uptake was recorded in plant receiving Azospirillum strains OAD-2 + 150

kg N ha-1, which was significantly superior over all other Azospirillum strains

inoculated and not inoculated control plants. Use of Azospirillumas nitrogen fixing

inoculants is well documented in cereals or non-legume plants. In conclusion,

Azospirillum strains OAD-2 and OAD-11 could be potential N-fixing inoculants for

blanket flower G. Pulchella and other ornamental flower crops after screening them

under different field trails.

Kumar et al. (2000) have studied on enriching vermicompost by nitrogen

fixing and phosphate solubilising bacteria. Three N-fixing which have been choosen

to be assessed were Azotobacter chroocooccum strains, Azospirillum lipoferum and

the phosphate solubilizing Pseudomonas striata. As the result, it showed an increasing

value in N and available P contents during the incubation period. Initially, the

vermicompost contained only 1.40(g/100g) of N which was increased to 2.72(g/100g)

on the 60th day after inoculation with A. Chroococcum. For inoculation of other strains

of Azotobacter, N content increased to 2.53 and 2.50(g/100g). Besides, Azospirillium

lipoferum also increased N content up to 2.18(g/100g). However, from the

observation, Azosprillium lipoferum was less efficient than Azotobacter strains. P.

Striata caused a significant effect on the available P content in vermicompost when it

60

was inoculated alone or with 1% Mossoorie Rock Phosphate (MRP). However,

available P content was greater with MRP and P. Striata combination at 60th day

which was 1.97(g/100g) compared to 1.52(g/100g) for P. Striataonly. As a

conclusion, Azotobacter, Azospirillium and Pseudomonas inoculation helped in

increasing the N and P contents of vermicompost, and rock phosphate was solubilized

during composting.

In other study, Beauchamp et al (2005) have studied about the isolation of

free-living dinitrogen –fixing bacteria and their activity in compost containing de-

inking paper sludge. This research founded that two gram-negative N2-fixing isolates

were identified as Pseudomonas. The N2-fixing activities increased at each cycle for 3

and 1-year old composts but decreased after two cycles for the 0.5-year old compost.

Among these isolated bacteria, only four were found to be able to fix atmospheric N2.

After performing the diagnostic test, the N2-fixing bacteria were grown on TSA

(Tryptic Soy Alga). However, the isolates from 0.5-year old compost were unable to

fix atmospheric N2. This study showed that approximately 5% of the population of

DPS composts consisted of free-living N2-fixing bacteria which belong to the

Pseudomonas genus.

Table 2.12. List of studies found in the literature on nitrogen fixers in composting.Treatment system

Phosphate Nitrogen Composting period

N-fixer Reference

Enriching vermin compost by nitrogen fixing & phosphate solubility bacteria.

1.45 2.73 75 days A. Chroococcum

Vivek Kumar et al. 2000

1.40 2.16 A. Lipoferum1.52 1.68 P. Striata1.97 1.68 P. Striata+ 1%

MRP

61

Table 2.13 List of studies found in the literature on nitrogen fixers in composting.

Treatment system

Initial C/N ratio

pH FinalC/N ratio

T C0

CompostingPeriod

N-fixer Reference

Plant & animal wastes composting:Effects of the N sources on process performance

30.1 8.1 11.3 70 92 days Bacillus Maria CuzCayuela et al., 2009

32.7 7.7 10.9

Isolation of free-living dinitrogen-fixing bacteria & their activity in compost containing de-inking paper sludge.

- - 35.6 12-25

30 days Pseudomonas

Chantal J. Beauchamp et al., 2005

- - 37.8

- - 36.2

N-fixing in vermicompost of biodegradable organic wastes under liming and microbial inoculants.

Cow dung 18.95

6.65

12.46

37 85 days Bacillus Polimyxa

P.Pramanik et al., 2006

Grass 21.65

6.95

12.93

Aquatic weeds 19.96

6.80

13.35

MSW 31.84

7.05

21.77

2.15 ENERGY BALANCE in COMPOSTING

Energy balance is an important consideration in composting. The considerations of

energy balance will be discussed below.

2.15.1 Heat balance considerations

62

The solution of coupled heat and mass balance equations in time and in some cases,

spatially has provided the basis for most compost process models. The general form

adopted for heat and mass balance analysis has been as follows:

Accumulation = input − output ± transformation

Heat balance components in composting models have included sensible heating of the

system contents, sensible heat of input and output streams, input air, water vapour and

any supplementary water, exit gases and vapours, conductive/convective losses,

radioactive inputs and losses, latent heat of evaporation of water and biological heat

production. Biological heat production and latent heat of evaporation of water have

been shown to be the most significant terms in the heat balance for full-scale systems

(Bach et al., 1987). Coefficient (U), which incorporates the combined roles of

convection, conduction and radiation at system boundaries, has typically been

employed, although the term conduction is frequently used in this context. Radiation

as a separate term has typically been ignored.

2.15.2 Energy Balance In Composting Models

Accumulation = input − output ± transformation (1)

Sensible heating of reactor contents = (Sensible heat of inlet dry air, sensible and

latent heat of inlet water vapour, sensible heat of supplementary water, radiation) -

(Sensible heat of dry exit gas, sensible heat of exit water vapour,

conductive/convective losses, radiation losses, latent heat of evaporation) ±

Biologically generated heat.

A generalized heat balance model for a representative volume of material in

which axial heat and moisture variations in the direction of airflow are small and

configured for sensible heat accumulation as the dependent variable is presented

below:

d (mcT )dt = GHi - GH0 - UA ( T – Ta ) + Hc

dBVSdt

→(2)

63

Where m is the mass of the composting material (kg), c is the specific heat of the

composting material (kJ/kg.oC), T is the temperature of the composting material (oC), t

is the time (s), G is the mass flow rate of air (kg/s), Hi and Ho are the inlet and exit

gas enthalpies (kJ/kg), BVS is the mass of biodegradable volatile solids (kg), Hc is the

heat of combustion of the substrate (kJ/kg), U is the overall heat transfer coefficient

(kW/m2. oC), A is the reactor surface area (m2), and Ta is the ambient temperature

(oC). Eq. (2) has units of kJ/s (kW).

A number of authors have treated mc in Eq. (2) as a constant term (Lier et al.,)

resulting in expressions of the following form:

mcdTdt

=GH i+d ( BVS)

dtH c−GH o−UA (T−Ta)→(3 )

from which the expression for the rate of temperature change is:

dTdt

=GH i+

d (BVS )dt

H c−GH o−UA (T−T a)

mc→( 4 )

2.16 CO-COMPOSTING OF SOLID WASTE WITH PALM OIL MILL

SLUDGE (POMS)

Co-composting is the controlled aerobic degradation of organics using more than one

materials (sludge and organic solid waste). Sludge has a high moisture and nitrogen

content while biodegradable solid waste is high in organic carbon and has good

bulking properties (i.e. it allows air to flow and circulate). By combining the two, the

benefits of each can be used to optimize the process and the product. For dewatered

Output (sensible heat in exit gases, latent heat of evaporation in water vapour )

Input (sensible heat in air and water vapour)

Output (conductivity , convective , radioactive losses )

64

sludge, a ratio of 1:2 to 1:3 of dewatered sludge to solid waste should be used. Liquid

sludge should be used at a ratio of 1:5 to 1:10 of liquid sludge to solid waste.

There are two types of Co-composting designs: open and in-vessel. In open

composting, the mixed material (sludge and solid waste) is piled into long heaps

called windrows and left to decompose. Windrow piles are turned periodically to

provide oxygen and ensure that all parts of the pile are subjected to the same heat

treatment. Windrow piles should be at least 1m high, and should be insulated with

compost or soil to promote an even distribution of heat inside the pile. Depending on

the climate and available space, the facility may be covered to prevent excess

evaporation and protection from rain.

To adequately treat excreta together with other organic materials in windrows,

Who (1989) recommends active windrow co-composting with other organic materials

for one month at 55-60°C, followed by two to four months curing to stabilize the

compost. This achieves an acceptable level of pathogen killed for targeted health

values. In-vessel composting requires controlled moisture and air supply as well as

mechanical mixing. Therefore, it is not generally appropriate for decentralized

facilities.

In-vessel composting requires controlled moisture and air supply, as well as

mechanical mixing. Therefore, it is not generally appropriate for decentralized

facilities. Although the composting process seems like a simple, passive technology, a

well-working facility requires careful planning and design to avoid failure. A Co-

composting facility is only appropriate when there is an available source of well-

sorted biodegradable solid waste. Mixed solid waste with plastics and garbage must

first be sorted. When done carefully, Co-composting can produce a clean, pleasant,

beneficial product that is safe to touch and work with. It is a good way to reduce the

pathogen load in sludge.

Depending on the climate (rainfall, temperature and wind) the Co-composting

facility can be built to accommodate the conditions. Since moisture plays an important

role in the composting process, covered facilities are especially recommended where

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there is heavy rainfall. The facility should be located close to the sources of organic

waste and feacal sludge (to minimize transport) but to minimize trouble, it should not

be too close to homes and businesses. A well-trained staff is necessary for the

operation and maintenance of the facility.

Adding excreta especially urine to household organics produces compost with

a higher nutrient value (N-P-K) than compost produced only from kitchen and garden

wastes. Co-composting integrates excreta and solid waste management thus

optimizing efficiency.

Although the finished compost can be safely handled, care should be taken

when handling the faecal sludge. Workers should wear protective clothing and

appropriate respiratory equipment if the material is found to be dusty. Robust grinders

for shredding large pieces of solid waste (i.e. small branches and coconut shells) and

pile turners help to optimize the process, reduce manual labour and ensure a more

homogenous end product.

The mixture must be carefully designed so that it has the proper C:N ratio,

moisture and oxygen content. If facilities exist, it would be useful to monitor helminth

egg inactivation as a proxy measure of sterilization. Maintenance staff must carefully

monitor the quality of the input materials, keep track of the inflows, outflows, turning

schedules, and maturing times to ensure a high quality product. Manual turning must

be done periodically with either a front-end loader or by hand. Forced aeration

systems must be carefully controlled and monitored.