biogas from kitchen waste full report

8/17/2019 Biogas From Kitchen Waste Full Report

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Production of Biogas Using Kitchen Waste


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Table of ContentsAcknowledgement ....................................................................................................................................... 5

Abstract ........................................................................................................................................................ 6

Introduction ................................................................................................................................................. 7

Chapter # 1 .................................................................................................................................................. 9

1.1 Energy Mix of Pakistan .............................................................................................................. 9

1.2 Fossil Fuels and Current energy Demands ............................................................................... 9

1.3 Renewable Energy Sources ...................................................................................................... 10

Chapter # 2 ................................................................................................................................................ 12

2.1 Biomass Conversion Process .................................................................................................... 12

2.2 Thermochemical Conversion Processes .................................................................................. 15

2.2.1 Combustion ........................................................................................................................ 15

2.2.2 Gasification ........................................................................................................................ 15

2.2.3 Pyrolysis ............................................................................................................................. 15

2.2.4 Other Processes ................................................................................................................. 15

2.3 Bio-chemical Conversion .......................................................................................................... 15

2.3.1 Fermentation ..................................................................................................................... 16

2.3.2 Anaerobic Digestion .......................................................................................................... 16

Chapter # 3 ................................................................................................................................................ 17

3.1 Anaerobic Digestion .................................................................................................................. 17

3.1.1 Historical facts ................................................................................................................... 17

3.2 Anaerobic Digestion .................................................................................................................. 17

3.2.1 Hydrolysis .......................................................................................................................... 18

3.2.2 Acidification ....................................................................................................................... 18

3.2.3 Methanogenesis ................................................................................................................. 18

3.3 Classification of Anaerobic-Digestion ..................................................................................... 19

3.3.1 Temperature Basis: Mesophilic or Thermophilic .......................................................... 19

3.3.2

Wet or Dry Processes ........................................................................................................ 20

3.3.3 Other Classifications ......................................................................................................... 20

3.4 Parameters Affecting Digestion Process ................................................................................. 20

3.4.1 Temperature ...................................................................................................................... 20

3.4.2 PH ....................................................................................................................................... 20

3.4.3 Mixing ................................................................................................................................ 20


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3.5 Value Addition processes.......................................................................................................... 21

3.5.1 Thermal Pre-treatment ..................................................................................................... 21

3.5.2 Co-Digestion Process ......................................................................................................... 21

3.6 Up Gradation Technologies ...................................................................................................... 22

3.6.1 Carbon Diode Removal .................................................................................................... 22

3.6.2 Hydrogen Sulphide Removal ........................................................................................... 23

3.7 By Product Digestate ................................................................................................................ 23

3.8 Pros and Cons of Anaerobic digestion process ....................................................................... 23

3.9 Family Scale Biogas Digester units .......................................................................................... 24

Chapter 4 ................................................................................................................................................... 26

4.1 Developing Lab Scale Digester Model for Experimentation ....................................................... 26

4.1.1 Inlet Line ............................................................................................................................ 27

4.1.2 Gas Line ............................................................................................................................. 27

4.1.3 Outlet Pipe ......................................................................................................................... 27

4.1.4 Inoculum insertion ............................................................................................................ 27

4.1.5 Food waste preparation .................................................................................................... 27

4.1.6 Loading rate ...................................................................................................................... 27

4.1.7 Results and Findings of Experiment ............................................................................... 27

Chapter 5 ................................................................................................................................................... 28

5.1 Case Study: Biogas from Kitchen Waste of UET ................................................................... 28

Glossary ..................................................................................................................................................... 30

References .................................................................................................................................................. 31


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List of Illustration

Figure 1 Energy Mix of Pakistan ...................................................................................................... 9

Figure 2 Biomass to Biogas conversion routes ............................................................................. 12

Figure 3 Ven Krevlen Diagram ...................................................................................................... 14

Figure 4 Anaerobic Digestion Process Steps ................................................................................. 19

Figure 5 Potential of Kitchen Waste ............................................................................................. 21

Figure 6 Membrane separation technology ................................................................................. 22

Figure 7 Wet Scrubing System ...................................................................................................... 23

Figure 8 Conventional Digester models ........................................................................................ 25

Figure 9 Steps involved in digester construction .......................................................................... 26

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Acknowledgement

All praise to ا ع و ل who provided us with the strength to accomplish this main project. All

respects are for His HOLY PROPHET ملسو هيلع هللا ىلص whose teachings are true source of knowledge &

guidance for whole mankind.

Before anybody else we thank our Parents who have always been a source of moral support,

driving force behind whatever we do.

Work is conducted during technical report on utilization of kitchen waste for Biogas production

under the umbrella of SPACE. Authors are very thankful to SPACE Team for their cooperation

and support without which forum cannot survive.

Submitted By

Team Renewable Energy Forum


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Abstract

Ever growing world population demands energy resources growing with the same pace but in

reality conventional energy resources are depleting with exponential rate and in opposite

direction. To meet the energy demand and supply gap, alternative sources other than

conventional fossils needs to be exploited.

To ensure sustainable development, fossil fuels are being switched with renewable energysources which are gaining importance because of their environment friendly nature and cost

effectiveness. Among these sources popular contenders are Solar, wind, hydro and biomass.

Applicability of these sources strongly depends upon locality and regional conditions, if wind is

applicable for one locality; solar is feasible for other. Biomass is among those names which

provide feasible solution for almost every place.

Currently we have around 4000 MW electricity shortfall which reveal the worse energy crises

being faced by Pakistan. Common Energy sources powering our economy are Oil and Gas.

Major reserves of these conventional fossils are expected to be depleted by 2025. So to tackle

this energy crisis in presence of political and geographical constraints, bio-gas is good option forcountry like Pakistan providing quick solution.

This report will deal with the feasibility analysis of biogas production from organic waste

material especially from kitchen waste.

Kitchen waste containing high content of organic material can be utilized in community level

digester unit to obtain high calorific value biogas (even 4700 kcal) which is otherwise

environmental pollution. After certain cleaning processes gas can be used for either direct

heating or for power generation to fulfill energy demands of community.

Our University provides accommodation to more than 3000 students while total visitors on daily basis are about 7000, so a number cafeterias and canteens are there to serve them foods. These

Kitchens produce a lot of organic waste which can be used for biogas generation which is

otherwise pollution for environment. So this report contain a case study in which this bio mass is

considered for bio gas generation.


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Introduction

Energy is the most vital tool ensuring the prosperous growth of economy of any country. Current

industrialization and globalization demands for more energy ever used by humanity and this

hunger of energy is increasing with exponential rate just like rolling ice balls while conventional

and typical resources are depleting with same pace but in opposite direction. So to make

sustainable development there is no option other than switching from conventional to non-

conventional and renewable energy resources.

Pakistan is among those under developed countries which have abundance of natural resources

but still face the worst energy demand-supply gap. Due to industrial growth and increasing

population energy demands are increasing exponentially, with no progress on supply side

eventually ending up ever growing shortfall. Last fiscal year’s results shows that we used more

than $ 15 Billion on oil import but still unable to fulfill even power sector needs which results in

4000-7000 MW electricity shortfall. Adding salt to injury, statistics shows that by 2025 major oil

and gas reserves are supposed to be depleted such as Mari, Sui etc.

Careful examination of economy reveals that Pakistan is an agrarian economy where 70%

population is directly or indirectly earning bread and butter from agriculture. Millions of cattle

produce huge amount of manure which can be used as source of biogas. On the other hand

Kitchen Waste (KW) and/or Municipal Solid Waste (MSW) contain large amount of volatile

solids so their improper dumping is a serious environment hazard. Only minute amount of this

waste is dumped in a proper way, remaining fraction is left in open fields causing formation of

uncontrolled methane, leachate which simultaneously affect air and water quality. These open

dumping site serve as colonies for mosquitoes as well.

Long term solutions are the actual sustainable solutions but to tackle current crises short term

and relatively low capital demanding solutions can work as quick response force. Kitchen waste

is a name of environmental pollution which can be used as power source if managed properly. It

contains remarkable amount of organic compounds which is treated anaerobically to produce

clean pipeline quality gas.

So first chapter of this report will deal the current energy scenario of Pakistan, where major

energy sources will be discussed briefly. Next chapter will give some insight of available

processes for conversion of organic waste to useful energy form.


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In third chapter anaerobic digestion is studied in detail along with parameters affecting the

process. In last chapter a case study has been presented which gives feasibility report of Kitchen

waste biogas plant for UET canteens.

Biogas can be obtained from kitchen waste by two stage process, firstly long and complex

organic molecules are converted into small and simple alcohol, glycerol and sugar molecules. Asa second step these simple structured molecules are used by another type of bacteria which

produces methane and carbon dioxide. [1] Production rate of methane is very much affected by

ambient conditions and it shows higher efficiencies at high temperature. Biogas resulting from

mix feed (i.e. animal feast and vegetable/crop residue) is greater as compared to animal manure

alone.

Emission of Carbon oxides is playing major role behind global warming so to reduce this

phenomena alternative fuels have to be used. Biogas from kitchen and other organic wastes

provides feasible and cost effective solution.


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Chapter # 1

1.1 Energy Mix of Pakistan

As mentioned earlier energy mix of any country reveals its economic stability and quality of life.

Pakistan is under developing country with 18 billion populations to be feed by utilizing limited

energy resources. Conventional energy sources being exploited in Pakistan are Oil, Gas with

some role played by renewable energy such as hydro power.

1.2 Fossil Fuels and Current energy Demands

Electricity demand of Pakistan is 15000 to 20,000 MW which is subjective matter and fluctuates

with seasonal changes. But overall production is 11,500 which means more than 4000 MW short

fall all the time present causing intensive load shedding some time ranging 16 hour per day.

Interesting fact is that only 55 % of overall population has access to electricity.

Oil contributes some 30% in overall energy mix which major use in transport and power sector.

Last year 15 billion dollar from foreign exchange is used on oil import. As we are dependent on

international oil market so instability and political crises of oil exporting countries have direct

impact on our national economy and have shown adverse impact in second month of 2015 when

loss of billions of rupees was faced due to shortage of Oil.

Figure 1 Energy Mix of Pakistan


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Gas is relatively clean and instant form of energy, sharing 44 % of energy mix. Overall current

requirement is 6.5 Billion SCF of gas but availability is 4 Billion SCF which means shortfall is

2.5 billion SCF. Major reserves of gas in Pakistan are reported to be depleted by 2025, so to

tackle this shortage Pakistan-India-Iran gas pipeline is being considered as a solution.

Coal reserves in Pakistan are some 185 billion ton which is massive amount but this indigenous

coal cannot be used directly for power production because of high sulpher and moisture contents

and low quality. Even coal fired boilers are using imported coal. But reasonable work has been

performed by government to promote use of this coal for electricity generation, bids for eight

coal-fired power plants has been invited. Underground gasification was tried but this option also

proved to be non-compatible with Pakistani coal. So in current scenario coal share in energy mix

not more than 10 %.

Recently LNG is imported from Qatar which is costly as compared to indigenous natural gas butstill it gave hope to power and fertilizer sector.

1.3 Renewable Energy Sources

To cope with the energy crises and global warming fossil fuels are being replaced with

renewable and sustainable energy sources such as solar, tidal, wind, geo, hydro and biomass. As

an example we can quote Brazil which is obtaining its 70% energy needs from concept of green

energy that is biomass.

Pakistan has potential for wind power plants, only in Sind estimated power capacity is 10,000 –

50, 000 MW. But still this potential is not exploited, only in Jhampir 50 MW power plant isinstalled by Fauji Fertilizer Company. In short, wind plants are not contributing actively in

national energy grid.

100,000 MW solar potential we have in Pakistan but due to large capital cost individuals cannot

afford it. On large scale one solar park has been approved by government whose construction is

under way. On small scale solar energy is being used for water heating or some time solar cells

are used for water pumps.

Hydro power is the extraction of energy from moving water by using hydro turbines. Around 34

% of total electricity is being obtained from hydro power i.e. 6555 MW against total potential of

45000 MW. Some mega projects such as Neelam Jhelum project are under construction phase

and can provide promising future.


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A lot of biomass is produced on daily basis in Pakistan which is a rich source of power in

developed countries while in our country due to improper management it is considered to be a

waste causing environmental pollution. Urban areas produce 55,000 tons of solid waste

(containing large portion of kitchen waste) over 1 million tons of animal manure and 225, 000

tons of crop residue is produced daily. Bio chemical and thermochemical processes can be

applied to convert this waste into power and nutrients rich fertilizer, as being discussed in next

section.

Table 1: Capacity of hydro-power stations in PAK


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Chapter # 2

2.1 Biomass Conversion Process

A number of bio-degradation techniques have been developed to gain energy from available

biomasses, but selection of any specific technique will depend upon following listed constraints:

Quality along with quantity of available biomass.

Energy Requirements of end user.

Available on hand capital and economic conditions.

Environmental concerns and state regulations.

So depending upon the type and state of biomass list of processes is available.

Figure 2 Biomass to Biogas conversion routes


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Energy can be obtained by biomass by either utilizing thermochemical route or by using bio-

chemical route. Mechanically forced extraction processes are sometime also used as in case of

bio-diesel extraction form seeds.

Depending upon literature and source some authors has defined two more processes as chemicaland thermal processes. All these processes have their own charm and limitation. Historically

combustion is the most ancient method for conversion of biomass into energy and most simple as

well. Among biochemical processes fermentation also have very old history, being used for

converting fruits into alcoholic products. Study of all these processes is not the major goal of this

report but brief introduction will be provided in upcoming lines.


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Before getting in to discussion of biomass conversion techniques it is important to mention that

amount of energy obtained from different biomasses can be compared in term of their O: C or H:

C ratio and is depicted by Ven Krevlen Diagram. And these ratios are strong function of feed

composition

Historically this diagram was developed for study of petroleum products and their level of

maturity as well as origin by comparing hydrogen, carbon and oxygen level. But this graph is

also used for measuring heating value of biomass. As being depicted by figure, biomass has

reasonable heating values when compared with coal or peat.

Figure 3 Ven Krevlen Diagram


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2.2 Thermochemical Conversion Processes

Biomasses are converted in to applied energy forms by following explained thermochemical

processes,

2.2.1 Combustion

Burning process of biomass in air, producing intense heat some time increasing temperature of

flue up to 8000C is used in diverse applications such as power generation, process heating etc.

Combustion process in not given much appreciation because of low net efficiency (10-40 %) and

harmful nature for fragile environment. But still it is being applied over all on massive scale due

to ease of application.

Moisture is hurdle in burning hence feed having moisture >50% is not combust rather used for

biodegradation processes. In such constraints CO-combustion of organics with coal can be usedas well.

2.2.2 Gasification

Biomass conversion into combustible mixer of gases by high T partial oxidation is Gasification.

Low heating value (some 5 MJ/N m3) product is directly applied to fuel engines [2]. Chemical

Production by using Synthesis gas as feedstock is also alternative option.

Integrated process of energy production by gasification calls for application of turbines whichrun on syngas with net efficiency of 50%.

2.2.3 Pyrolysis

Pyrolysis applies high T (500) heating in absence of air to produce mix of solid, gas and liquid

fuels.[3] by utilizing process of flash pyrolysis high content of bio-oil (efficiency about 79.9%)

can be obtained, that can be used as a feedstock for refineries.[4] Up gradation processes are

essential requirement to reduce oxygen and alkali contents.

2.2.4 Other Processes

Other choices are hydro thermal up gradation and liquefaction processes producing partial

oxygenated fuels by processing biomass in wet environment at high pressure, main products areliquid fuels. HTU is considered to be costly than pyrolysis.

2.3 Bio-chemical Conversion

Under umbrella of Bio-chemical processes only two main techniques are available being

explained briefly in upcoming lines:


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2.3.1 Fermentation

Fermentation is biochemical conversion mostly resulting in formation of ethanol; abundantly

used feed stock is sugar cane residues (pronounced as bagasse) sometime also consuming starch

crops like maize. By action of enzymes sugars are produced form these feed stock, remaining’s

of fermentation processes can be used as animal feed or for further gasification process.Conversion of lignocellulose biomass is difficult due to complex and long chain molecules and

hence can’t be used as feed until acidic enzymatic hydrolysis is applied which is premature

process not so well developed.

2.3.2 Anaerobic Digestion

Organic Material is directly converted into biogas which is mostly methane and carbon diode

with minute amount of other gases. This conversion is in fact due to bacteriological action

resulting in gas having lower heating value of feed material. Biogas production is well

developed, well proven technology utilizing high moisture content raw material (about 90%moisture). By further up gradation natural gas quality product can be obtained by removing CO2.


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Chapter # 3

3.1 Anaerobic Digestion

3.1.1 Historical facts

Anaerobic digestion process is not newly developed idea, rather its roots have been found in late

nineteen century when first digester was developed in Bombay, India. Since than a number of

plants have constructed throughout the Asian Countries. In decade of 1970 China and India

implemented policy of small scale digester unit (6-7 m size) funded by government, mostly units

were constructed in rural areas to provide power for home lightening and waster irrigation

system.

More than 20 million plants are operating in China, and every year 1 million new small size plants are added in this figure. National policy on Biogas is supposed to be activating after which

green revolution is to be expected, by 2020 small and medium size plants will reach the figure of

40 million. From centuries, European countries are using this process to convert their waste into

bio fertilizer and biogas.

A number of Policies has been made by Pakistani government as well. But since 1970 not more

than 20,000 household level units has been installed. And these units only consider animal

manure, so these plants must be upgrade so that they can handle to MSW and other kitchen waste

as well as animal wastes.

Now a day, certain working bodies are taking interest in these green energy process such as

AEDB (i.e. Alternative energy Development Board) and many other. But need is to enforce their

policies and provide special funds and loans on root level so that these documentary statements

could be translated into ground realities.

3.2 Anaerobic Digestion

As being revealed by name it is biological decaying process occurring in the absence of air

producing biogas and high nutritious bio fertilizer. In three stages overall degradation of bio-

degradable waste takes place by methanation bacteria. As a first step complex molecular

structures are hydrolyzed into simple molecules such as alcohol and sugar.

This transformation shows a net decrease in PH due to acid formation and hence rate of this step

can be checked by measuring the falling rate of PH, which again rises by the end of second

degradation phase. At last methanation bacteria produce methane and Carbon oxide.


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3.2.1 Hydrolysis

Long chains of proteins, carbohydrates and lipids are decomposed by bacteria into smaller

molecule, such as poly saccharides are converted into monosaccharide and proteins results information of amino acids.

So monomers and oligomers are produced by consumption of polymers, Hydrolytic enzymes

converts biopolymers into simple soluble compounds

3.2.2 Acidification

3.2.2.1 Acidogenesis

As a second step of digestion this involves production of acetic acid, hydrogen and

carbon dioxide along with volatile fatty acid as well as alcohol by the action of

acidogenic bacteria. Small amount of energy is needed as a input because bacteria alone

is unable to perform this decomposition. Bounded oxygen and atmospheric oxygen (if

present any) is consumed here and as a result anaerobic conditions are produced which is

the requirement of third step.3.2.2.2 Acetogenesis

Certain products of Acidogenesis cannot be used by methanogenic bacteria for methane

formation so acetogenesis bacteria oxidize those compounds into hydrogen and acetates.

Acetogenesis and Methanogenesis usually run in parallel.

3.2.3 Methanogenesis

This is step where anaerobic bacteria converts low molecular weight compound into carbon

dioxide and methane. These bacteria are very sensitive to ambient conditions and slight changes

in T and P can results in dramatic change in amount of methane.


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This is the most important step as well as slowest in whole process. Slight aeration, Digester

overloading, change in PH can stop methane formation.

3.3 Classification of Anaerobic-Digestion

3.3.1 Temperature Basis: Mesophilic or Thermophilic

Mesophilic process requires 25-45 OC range of temperature while in case of Thermophilic

process temperature range is 50-65 0C. Both processes are practical and currently being used and

have their own pros and corns. In Mesophilic process ambient temperature range mean low

energy requirement but at the expense of less gas production per unit feed and slow process ofDecomposition.

Thermophilic process offer high rate of digestion and its efficiency in term of gas per unit feed is

also high as it kills more pathogens which are hazardous for process. As it applies circulation of

hot water to maintain the temperature of digester so it requires large capital investment and also

operating capital is high. In case of Mesophilic process also offer risk of ammonia inhibition.

Figure 4 Anaerobic Digestion Process Steps


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3.3.2 Wet or Dry Processes

Main difference between the two processes is of moisture content and condition of feed. Dry

process takes feed usually as it is in dry solid form while in wet processing it is converted intoslurry form which is pumped to digester. Wet AD is used in case of farm plants while MSW is

treated under dry conditions.

3.3.3 Other Classifications

AD can also be classified on the basis of loading rate or by number of digestion units:

Continuous or Batch process Single or multiple digester units

3.4

Parameters Affecting Digestion Process

Microbial activity has direct relation with amount of gas produced so all those parameters which

adversely affect the performance of microbes should be kept under eye. Some important factors

are being discussed briefly:

3.4.1 Temperature

Usual digestion take place under mesophilic conditions (20-54oC) or thermophilic conditions

(50-65 0C), both differing in temperature range only. Higher temperature destroys hazardous

pathogens and speeds up the process and hence reducing the retention time. But temperatureshould be maintained at constant level to gain a steady flow of gas.

3.4.2 PH

PH requirement for two main steps Acidogenesis and Methanogenesis is different. In

Acidogenesis step acids such as lactic, acetic and formic acids are produced causing reduction in

PH, if PH is already acidic performance of this step would be slow. Methanogenesis step can’t

proceed effectively under PH of 6.4 or less, ideal range is 6.6 to 7 for this step. That’s why to

control the PH some time buffer solutions or alkalis are applied.

3.4.3 Mixing

As in all other reactive cases mixing increases the surface area and hence more probability for

bacteria to perform its decaying action. Mixing also prevents development of temperature


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pockets and gradients zones resulting in even digestion. But excessive mixing causes hurdles in

bacterial action so slow mixing is used if needed.

But usual recommendation is to thoroughly mix the feed before entering the container, once

entered no more mixing is needed.

3.5 Value Addition processes

3.5.1 Thermal Pre-treatment

Gas production can be enhanced enormously by thermally pre-treating the Kitchen waste.

Because of increased dissolution capacity, it also destroy Pathogens; Harmful organism. Odor

problems are also minimized up to certain extent.

3.5.2 Co-Digestion Process

Animal manure is considered to be good feed stock for anaerobic digestion and same statement

for Kitchen waste. But application of both in mix form has shown synergistic effects and

methane yield is 34 % more as compared to produced when KW was used alone. Some Major

Advantages are:

Per m3 volume of digester more biogas is generated and hence process is financially

beneficial.

Nutrients and hence value of digestate is increased as organic fertilizer.

Figure 5 Potential of Kitchen Waste


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Total feed rate is increased, so it can be used for continuous process and can compete

other gas providing sources.

3.6

Up Gradation Technologies

Bio gas produced from kitchen waste can be used as such but by certain treatment process we

can upgrade this gas to compete with pipe line quality gas.

3.6.1 Carbon Diode Removal

Biogas contain significant amount of Carbon Dioxide which is combustion product and hence

contribute nothing toward calorific value. So to increase quality and heating value we can

remove this CO2 by any of following commercial processes:

Membrane Separation

Wet Scrubbing

Molecular Sieve

Ethylene Glycol Solvent

Membranes Separation is newly developed technique but it is proved to be effective for gas

purification. It can molecular level holes/pores from which selective molecules are allowed to

diffuse, resulting product is free from acidic gases.

Ethylene Glycol is a well-developed solvent for removal of acidic gases from natural gas and

can be used for biogas as well. It is beneficial because it remove simultaneously carbon oxide

along with sulpher oxide. But because of chemical nature, its regeneration is costly.

Figure 6 Membrane separation technology


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Wet scrubbing is also good option in which water can be

used as a solvent which absorb acidic gases by providing

counter current contact with gas. As process is totally

physical so solvent can be regenerated easily for re-use but

it is recommended to use water from sewage treatment

plant which is waste water and abundantly available, so no

need for reuse.

3.6.2 Hydrogen Sulphide Removal

Hydrogen Sulphide is acidic gas which is causes the problems of corrosion, so its removal is necessary. Common techniques for H2S removal are

water scrubbing and sodium hydroxide scrubbing. Activated carbon can also provide reasonable

separation.

3.7 By Product Digestate

By digestion process bounded nutrients are mineralized and hence readily available to plants.

Carbon to nitrogen ratio in digestate is lower as compared to untreated slurry so it is rich source

of nitrogen, in fact replaces synthetic fertilizers. Due to its liquid nature and flow properties it is

easily mixed with water and penetrates readily in soil.

Avoid too much agitation or stirring before applying to ground in order to save nitrogen contents

which can leak in the form of nitrates and ammonia.

3.8 Pros and Cons of Anaerobic digestion process

Pros

Anaerobic digestion plays an important role in reduction of greenhouse gasses. Well-

managed digester produce methane for use but it does not evolve hazardous gases to

environment so reducing net emission of greenhouse gases. It provides a source of energy

without increasing carbon that participates in climate change.

The most important advantage of anaerobic digestion is that feedstock needed for this is

renewable source. Energy generated by this process can release the fossil fuels demand. It

also decrease synthetic fuel used for fertilizer production by giving digestate.

Figure 7 Wet Scrubing System


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It reduces the chances of soil water and soil pollution as compared to disposal of

untreated slurries.

It damages all weed seeds and reduce the need of herbicides.

Fusing treatment of different organic waste.

Pollution control

Cons

Anaerobic digestion has significant capital and operational costs. This can be minimized

by using its other products.

Pathogenic contents of waste can impose serious risk to human health but it can be

reduced by following SOPs during handling.

Risk of explosion and fire.

With respect to economy of scale units are not so much economical as they should be, so

intensive work is required by field expert to make it more economical.

Presence of Heavy metals and ammonia contents have shown serious impacts on humans,so ammonia and other ammonia compound should be managed properly whether as a

constituent of gas or as a part of digestion slurry.

Needs large start-up time.

The vicinity of sulphur nourishes prompts the generation of carcinogenic gas hydrogen

sulphide amid assimilation. This H2S will then structure a part of the created biogas. As

Hydrogen Sulphide is amazingly destructive and its vicinity obliges the buy of more

strong and along these lines cost generators.

3.9 Family Scale Biogas Digester units

Asian countries like China, India Nepal etc. have installed millions of simple household digester

unit which accept kitchen waste as feed and resultant gas is used foe home lighting and heat

generation purposes. These models are simple in construction, robust and usually have no

instrumentation and run on mesophilic conditions as ambient temperature is mostly 20-400C.Material of Construction is local metal which is easy to maintain, HRT ( retention time) is

slightly longer than commercial scale units.

Chinese model digester is common in which underground vessel of volume 6-8 m3 is used. They

operate in batch process where feed is charged once a day along with discharge of effluents. No

mechanical stirring is applied, and 2 to 3 times per year it is totally cleaned and then one fifth ofvolume is filled with inoculum before start up.

Indian type digester are also in practice which is similar as Chinese units but difference is in its

vertical shape where effluents are collected in bottom and floating dome serve as gas holder.


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Above shown digester are most common although other models such as horizontal, hybrid etc. are also

good options. Type of digester and prevailing conditions are effect the product composition and quality,

in our case product of interest is biogas. Typical composition of biogas obtained and their energy contents

are being listed in following table.

Composition of biogas

Figure 8 Conventional Digester models


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Chapter 4

4.1 Developing Lab Scale Digester Model for Experimentation

For studying properties of resultant biogas Lab scale unit can be designed by using 20 liter watercane acting as Digester. Three holes are drilled in digester one for feed inlet, second as a

digestate outlet and third for gas removal. From Digester gas can be moved to a storage vessel, in

our case it is a tube.

For constructing model on lab scale, two options for storage vessel are available. In first

case gas can be stored in a tube and as a second option gas can be stored in a water bath

Figure 9 Steps involved in digester construction


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with calibration. Second storage option have advantage that it can also measure amount of

gas but more costly.

4.1.1 Inlet Line

Pipe with 1.5 inch diameter can be used as inlet for feed, connection should be made by joint andunion and it should ensure that hole is air tight. Otherwise aerobic bacteria will suppress activity

of anaerobic bacteria resulting in no or very minute gas formation.

4.1.2 Gas Line

On the top of digester gas line is connected through which gas move toward gas collector. Gas

collector could be a tube or some gas holder dipped in water. Through Water dipped holder we

can also measure amount of gas produced by finding displaced water.

4.1.3 Outlet Pipe

At the height of 10 cm outlet pipe is connected to the digester which takes digestate material out,

again point of air leakage should be kept in mind.

4.1.4 Inoculum insertion

Inoculum is used to start microbial activity, after started process is continuous. Inoculum is

mixture of water and cow dung or digestate taken from already running unit. Usually it is

prepared by mixing 1:1 one day old cow dung and water.

4.1.5 Food waste preparation

Kitchen waste material was collected and prepared for loading by in the form of homogeneous

mixture or paste form. For making paste take fresh waste and convert it into small pieces and add

equal amount of water, this slurry usually contain cooked rice, vegetable peels etc.

4.1.6 Loading rate

Loading should be in such a way that neither digester should be over load nor it should be empty.

Overloading means accumulation of acid causing hurdle in methane formation and if unit is

underfed, amount of resultant gas will be small. Steady state plant is loaded on daily basis but it

can also operate in batch form.

4.1.7 Results and Findings of Experiment

This experimental rig can be used to find amount of gas produced from different form of wastes

and other effect of other parameters such as temperature can be found. Once gas is formed its

heating value can be measured as well. In our experiment gas was produced but due to air

leakages in the unit aerobic bacteria started its action so we were unable to collect reasonable

amount. So must take measures to avoid theses leakages which can destroy whole experiment.


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Chapter 5

5.1 Case Study: Biogas from Kitchen Waste of UET

In UET Lahore we have 15 Hostels with a large colony containing more than 200 houses and a

dozens of canteens and fruit shops producing huge amount of organic waste have disposal issues.

This waste can be utilized in biogas production.

This amount of waste consists of seasonal fruit peels, chicken waste, vegetable waste, pieces of

breads etc. which can be biodegraded easily.

For the sake of simplicity, in above shown table only main café and canteens have been quoted,

although hostels and staff houses are also producing healthy amount of kitchen waste.

So,

Daily organic Waste = 223 Kg

Annual waste = 81 tons

One ton waste produces gas = 157 m3

Annually produced biogas = 81 * 157 = 12,779 m3

So only from waste of main cafeterias and canteen annual production of biogas is more than12,000 m3. Also effectively reducing load on dumping site.

Table 2: Organic waste of UET


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Conclusion & Recommendations

Anaerobic digestion is the process through which one can consume waste and energy is obtained

in the form of clean gas containing methane content up to 65%. During this digestion process by

product in the form of organic fertilizer is also earned. So we must say anaerobic digestion not

only promise prosperous future in term of energy but also consumes waste so load on landfills

and dumping site reduces up to 30 %.

This process not only takes kitchen waste but also applicable to MSW, farm Waste and crop

residuals. So this digester is applicable in farms as well. In light of all above discussion

following lines are being recommended.

As biogas is being produced from nowhere other than waste material so raw material

cost nothing more than collection cost. Even this cost could be cut down by installing

small size (Chinese model) on spot digester.

Government should provide short term loans to farmers (such as being provided with the

name of yellow cap scheme) as well as subsidies so that village level energy

requirements could be fulfill on spot without increasing load on national grid.

Pakistan should participate actively in international green energy forum, by this we can

learn from experience of developed countries and can get exposure as well.

Data and facts with respect to local biomasses such as their composition, calorific

values, ideal digestion conditions etc. are needed to be found. So for intensive researchHEC focus on this field as well.

Media should play its effective role by launching awareness campaigns, in which locals

should be guided about benefits of household digesters.

Policies on national scale should be formed in which installation of community level

digester for treating waste of same community should be made compulsory.

This waste to energy process is not the only solution of energy crises which will fulfill energy

demands in nights, but is sustainable process which will reduce demand and supply gap for sure.

The only need is to take interest and take sincere initiative!


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Glossary

Aerobic Treatment

Degradation process of Organic compounds in the presence of Oxygen.

Anaerobic Digestion

Processing of organic compound in the absence of Oxygen to produce compost and biogas.

Biodegradable Material

Compound that can be converted to simple molecular structures (CO2, H2O etc.) easily by using

microorganisms and bacteriological actions.

Digestate

Sludge or slurry left after anaerobic digestion when biogas is separated, still contain large

amount of nutrients and used as fertilizer.

Mesophilic

Microbial action which process in moderate temperature range (20 to 45oC).

Methanogenesis

Last step of Anaerobic Digestion where acetic acid plus hydrogen is converted into biogas

Thermophilic

Microbial degradation process taking place at relatively high temperature (50 to 65oC).

Volatile Solids or VS

Amount of organic matter present usually measures in percentage of total solid.


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References

1. Ravi P. Agrahari, G. Tiwari N., 2013.The Production of Biogas Using Kitchen Waste

2. McKendry, P., 2001. Energy production from biomass (part 2): conversiontechnologies(LRZ,1993; Nat-ural Resources Institute,1996)

3. McKendry, P.,2000. Energy production from biomass (part 1): conversion technologies

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5. McKendry, P.,2001. Energy production from biomass (part 2): conversion technologies

6. Ravi P. Agrahari, G. Tiwari N., 2013.

The Production of Biogas Using Kitchen Waste

7. Rongping Li., Shulin C., 2009. Anaerobic Codigestion of Kitchen Waste with Cattle

Manure for Biogas Production

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McKendry, P.,2001. Energy production from biomass (part 1): conversion technologies9. Voegeli, Y., Zurbrüg C,. 2008, Decentralised Anaerobic Digestion of Kitchen And

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anaerobic digestion of fruit and vegetable wastes. Process Biochemistry. 2005; 40:989 –

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biogas from kitchen waste full report

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