LCAPurpose of an LCA - reduce environmental impacts. Cradle to grave approach as it follows the extraction of raw materials to return of wastes to landfill. Eval-uates inputs, outputs and the potential environmental impacts of a product. As-sessment of raw material production, manufacture, distribution, use and dis-posal including all transportation steps.

LCA Methodology: - Goal and Scope: intended application and reason for carrying out study,

intended audience. Definition of system boundaries, functional unit, descrip-tion of data quality, assumptions and limitations, review considerations

- Inventory Analysis: detailed flow diagrams, data collection, calculation of environmental burdens, validation of data.

- Impact Assessment: selection of impact categories, calculating magni-tude of categories, weighting of indicators for their relative importance, data quality analysis

Mid Point Categories: noise, climate change, acidification, eutrophication, land use, depletion of biotic resources, human toxicity, eco-toxicity, global warming.

Biomass Resources

Ligno-cellulosic biomass – most abundant in biomass (33%). Readily available and economical to produce. Uses include solid woods, flibre materials, combus-tion for heating, fuels, chemicals and new materials. Ligno-cellulosic materials and constituents: wood, bagasse, corn stover, straw, switch grass, bamboo, etc. Lignin sits in the middle lamella layer and glues the fibres together.

Hardwood has broad leaves, the seed is a fruit, darker coloured, shorter fibres. Eg. Eucalyptus. Softwood has needle like leaves, the seed is long and cone shaped, light coloured, long fibres. Eg. Pine

There is a significant amount of carbon that is tied up in biomass. Large scale land clearing would decrease carbon stocks and increase CO2 in the atmos-phere. CO2 can also be generated when burned for fuel. Carbon can be se-questered in biomass by growing trees and preserving wood once harvested.

Before using biomass as a feedstock, different factors need to be checked. The density of the material (whether it is green or dry), its moisture content and the annual growth increment need to be observed.

The density of wood will affect calculations of fibre mass and it would differ be-tween the species, growing patterns and breeding processes.

Making supply estimates: wood density, annual growth, fraction of annual growth used (eg, what part of the tree is used and taking in account the residue from sawmilling)

The consumption of energy from petrol is 7 times as much as what can be pro-duced by biofuels currently. However, refineries have the sufficient capacity in order to produce these biofuels. To improve this, higher growth rates are avail-able as currently, trees are only used for timber and paper.

Palm Plantations as BioresourcesThe fruit of the oil palm tree consists of a seed inside a shell, surrounded by a fleshy mesocarp from which the oil is extracted. The kernel oil is a secondary byproduct. Palm oil is advantageous due to its higher annual yield compared to other oils. Energy content is also higher. Short chain fatty acids are of a lower boiling point and are more soluble in wa-ter. Unsaturated acids also have a lower point compared to the saturated ones.

Applications of palm based oleochemicals: soals, detergents, textiles, candles, paints and coatings, printing ink, biofuels, pharmaceuticals, animal feeds, rub-ber, lubricants, etc...

Unit operations involving palm oil mills:I. Loading ramp - weighbridge and unloadingII. Sterilisation - batch autoclave processIII. Stripping - separate fruit from bunchIV. Digestion - fruit is mashed in stream heaterV. Extraction - passed through screw press and vibrating screensVI. Separations of nut from fibre - in a cycloneVII. Nut Cracking - in a centrifugal cracker to remove kernel from shell.

Ist Gen Biodiesel - from seed oils, fruit oils, and waste animal fats. Advantages include the fact that they are a renewable resource, extraction and processing is relatively simple, the fuel properties are close to diesel fuel, no sulphur means no SOx emissions, minimal toxicity and is biodegradable. Easy to blend with any type of petroleum as well. Disadvantages include the lower energy content, higher cloud and pour point (freezes at a higher temperature), so this means that the fuel is incompatible with some hoses or gaskets. Usually higher NOx emissions and is normally used as a blend rather than B100.

Biodiesel Process Overview: produced by chemically reacting vegetable oil with an alcohol in the presence of a catalyst. The product is a mixture of methyl es-ters and glycerol. This process is known as transesterification. There are only five chains of fatty acids that are common in these vegetable oils and animal fats. The relative amounts of these chains determines the physical properties of the fuel.

Biodiesel Process Description: Pretreatment of the feedstock, removal of dirt or water using centrifuges or oil dryers. The oil is heated in pre-heating tanks. Methanol and sulphuric acid are added to start the esterification. The mixture of oil and biodiesel is dried and neutralised. The methanol and NaOH is dis-solved in the alcohol and added to the oil. The total amount of catalyst de-pends on the level of fatty acids.

The temperature is raised to 65C under 3bar to prevent the loss of methanol vapour and facilitate rapid transesterification. The mixture of biodiesel and glycerol is purged from the reactor. Separation is done using centrifuges or set-tling tanks. The biodiesel is transferred to a washing station where it is passed through a centrifuge or filter press to remove dissolved contaminants like soap or glyc-erol. Then passed through a filtration unit to purify the biodiesel.

Feedstock purity: Free fatty acid (FFA) requires more catalyst resulting in a higher salt and soap formation. Higher water content creates soap and higher phosphorous increases the difficulty in separating the biodiesel from the glyc-erol.

1st Generation Fuels: corn, rapeseed oil, sugar cane, palm oil, wheat. Advan-tages: familiar feedstocks, well established production, scalable processed, compatibility with fossil fuels, commercial production and use in several coun-tries. Disadvantages: competition with food crops, high cost feedstocks lead to high production costs, modest reduction in fossil fuel use and greenhouse gas emis-sions, production of by products exceeds demand.

Second generation fuels: from energy crops such as poplar, switchgrass, wil-low, food wastes, manure, straw, waste wood. Advantages: similar process to the petrol/chemical/bio industry, no competition issues with food, reduction in the amount of waste that needs to be treated/disposed of. Disadvantages: unfamiliar feedstock and the available is fluctuating/uncertain. High capital and energy costs, competition for land and water, only a fraction of waste can be used.

Third generation fuels: microalgae. Advantages: high oil content, can be culti-vated in a range of systems, a wide spectrum of processing routes and biofu-els. Disadvantages: not commercially available yet, high initial costs, high water content, could require large areas, could impact on marine life if exploited from oceans.

Some sustainability issues: - Environmental: global warming potential, land availability, biodiversity. - Economic: feedstock costs, investment costs, biofuel price, local income

generation.- Social: human health, labour rights, land ownerships, impact on food se-

curity, community development and the impact on indigenous people.

Ethanol as fuel: less energy compared to petrol but a higher octane level.

Second Gen Biochemical: uses cellulase (that produce bacteria) and it is capa-ble of breaking down cellulose. Cellulose is difficult to breakdown and therefore the fermentation process is quite slow.

Second Gen Thermochemical: uses any ligno-cellulosic as feedstock Heat is supplied by circulating hot synthetic olivine sand. Gasification occurs and pro-

duces syngas, tars, solid char. The solid char is burned to regenerate sand. The syngas can be used to produce alcohols and electricity.

PLA Lifecycle: atmospheric CO2, corn production, dextrose production, lactic acid production, lactide production and polymerisation, packaging manufac-ture, comsumption, landfillPP Lifecycle: natural gas extraction, natural gas liquids, ethylene and propylene production, pp polymerisation, packaging manufacture, consumption, landfill

Recycling for white paper: deinking is the main process, based on mineral flota-tion. Measure of recycled paper quality is the brightness, visible ink specs and stickies. Recycling for brown paper: generally poor quality, simpler process.

Dual Separation process: separation of fibres from contaminants, removal of said contaminants using screens, washing, etc.

Recycling unit operations:1.Hydrapulper: adding water to the dry fibres. Mechanical action with sus-pension separation. The fibres separate from each other and contaminants (plastics, inks, toner) are removed. The force applied by the rotor must be enough to defibre the paper but not break down the contaminants as they will be much harder to remove. 2.Screens: coarse and fine screens to remove different sized flakes. 3.Cleaners - the pulp is fed tangentially. Separation is based on density and shape of the flakes. 4.Flotation Cells: main purpose is to remove ink.

Flotation Mechanism:The air bubble approaches the particle and there is contact. The particle slides over the surface of the liquid film separating the bubble from the particle. The film ruptures which brings the particle and the bubble in contact. The particle, bubble and fluid form a quick three phase contact. The bubble stabilises and the particle can only be removed by severe turbulence.

Sodium Hydroxide - adjusts the pH level to alkaline which hydrolyses the ink resins. The fibres are able to absorb water which causes swelling and cracks the ink off the fibres. Hydrogen Peroxide - used to decolourise wood or paper pulp. Chelating agents - form soluble complaxes with metal ions in order to avoid the hydrogen peroxide breaking down eg. Sodium Silicate

Surfactants - form chain molecules with the hydrophobic or hydrophilic parts. Dispersants cover particles with the hydrophilic layer. This helps when separat-ing inks from the fibres. Collectors anionic molecules are added to aid flotation. Displectors are a combination of dispersant and collector. They adhere to air bubbles and prevent the redeposition of hydrogen peroxide.

Chemical Pulping: liberation of fibres from ligno-cellulosic wood and non-wood materials. The process can be mechanical by grounding the wood into fibres

using grindstones or disk refiners. The process could also be chemical by de-grading the dissolving the lignin.

Kraft Process: chemicals react with the lignin and the hemicellulose. The wash-ing process removes the chemicals and all the dissolved wood content. The or-ganics are burnt for energy and the chemical are recovered. The wood chips have to be the right size in order for the liquor to penetrate and have a com-plete cooking process. Thinner chips will be cooked too much.Wood density is important. Increase in the amount of wood packed into the di-gester means increased production. The wood density could vary depending on different tree species and the age of the tree, thicker cell walls. Juvenile wood has shorter and narrower fibres, thinner cell walls, lower density, lower cellulose content. White Liquor - usually consists of NaOH, Na2S, Na2CO3, Na2SO4.

The cooking chemicals are dissolved in water. There are two transport mecha-nisms that could occur: I. Capillary penetration: the liquor penetrates the chip through pores. It is

effective over long distances in grain direction but ineffective across the grain.

II. Diffusion: of ions through the liquid present in the chip. Most effective in water saturated wood, only effective over short distances and effective across the grain.

Batch Digester: filled with chips and cooking liquor. The digester is sealed and the heating begins. There is venting of air and non-condensable gases to pre-vent pressure build up in the vessel. Continuous Digester: tube shaped reactor in which the chips move through continuously. There are different zones in the reactor - charging, impregnation, heating, cooking.

Chip Packing methods: the most common method is to load the chips along with the liquor. The liquor helps to lubricate the chips and improve packing. Re-duces loading time of the digester. Steam packing can also be done to increase the packing density. The chips enter in a tangential motion which results in a flat bed of chips rather than a conical profile.

Heating: is done externally by an external heat exchanger. This gives a uniform form of heating and liquor distribution. Heating can also be done internally through steam applied through the bottom of the digester. Convection allows the heat to pass from the top and bottom (due to temperature difference). The disadvantages of this method is that the steam dilutes the liquor and the non-uniform temperature causes non-uniform cooking which reduces the quality of the fibres.

Washer: the chips are cooled rapidly and fresh washing liquor. The chemicals are removed through a diffusion controlled process.

Batch vs Continuos; the batch process is more flexible with regards to grade changes and fibre sources. Less maintenance issues and the production is flexi-ble. The continuous process has lower energy costs and is easier to control. The whole system is relatively compact and has a steady state flow rate.

Recovery of Liquor: - White liquor - fresh pulping liquor for the kraft process - Black liquor - waste liquor from the kraft process. Contains most of the

organic inorganic components and a high concentration of dissolved organics. - Green liquor - partially recovered kraft liquor

Recovery Cycle: burns the black liquor in a recovery boiler. Filter out the smelt and separate calcium and carbonate. Regenerate original chemicals.

Papermaking: 1. Forming: jet of fibre suspension (usually 5kg of solids per 1000kg of sus-

pension). Consists of gravity dewatering. The fibres deposit themselves on a continuously moving filter mat. This mat drains the water. The mats need to be cleaned using high pressure showers for continuous mats and washing with acid for batch processing. This process requires the right amount of draining (not too much or the sheet will start to seal) and the right amount of agitation to keep the fibres dispersed.

2. Pressing: the sheet is still very weak and wet (around 20%). Mechanical pressure is used to remove the remaining water.

3. Drying4. Additional

Wastewater Treatment

Wastewater sources:← Industrial wastewater: high concentration of pollutants, small volume and

more toxic components← Municipal wastewater: low concentration of pollutants, large volume and

less toxic chemicals← Agricultural runoff: fertilisers and pesticides← Storm water and urban runoff: oil, heavy metals, low concentration of

pollutants

Physical Characteristics of waste water consist of solids (suspended or dis-solved), odour, colour, temperature, turbidity

Chemical Characteristics of waste water consist of organic material, nutrients, chlorides, micro pollutants, metals and acidity

Organic Matters:← Total Organic Carbon (TOC): the total amount of carbon that is

bound to an organic compound. The organics are oxidized by heating to a high temperature and measuring the production of carbon diox-ide. ← Biological Oxygen Demand (BOD): the oxygen demand of polluted

water caused by microorganism under aerobic conditions. The BOD is normally measured for 5 days, units mgO2/L← Chemical Oxygen Demand (COD): the oxygen demand caused by

oxidising polluted water by chemical oxidants such as potassium permanganate or dichromate)

The biodegradability of wastewater is calculated by BOD/COD. If the value is >0.3, the water is biodegradable and if it is <0.2, it is non-biodegradable.

Biological Characteristics of waste water consist of bacteria, parasitic worms, viruses, algae and protozoa.

Impact of wastewater: Public health: pathogenic microorganisms can lead to dangerous dis-

eases to humans and animals. The wastewater contains toxic substances such as pesticides and heavy metals. The odour can affect the public as well.

The environment and ecosystem: toxic pollutants can destroy aquatic systems. Eutrophication can occur (increase in nutrient concentration in the water body that leads to algal blooms). Pollutants can change the colour of the ecosystem.

Treatment options of Industrial wastewater:← Discharge to a centralised wastewater treatment plant of a municipal

wastewater treatment plantBenefits: the company can concentrate on its core business, reduce the

footprint of the plant and may reduce capital and optional costs. Preconditions required: nearby wastewater treatment plant. Quality of

the wastewater needs to meet certain requirements. Untreated wastewater could lead to workers being exposed to toxic substances. Expensive sludge treatment options may be required. Corrosion may occur due to sub-stances in the wastewater. Toxic substances could be led out into the envi-ronment. All of these problems can be controlled by pretreatment, waste minimisation, recycling and or re-use.

2. Discharge to natural water bodiesThere is a need to meet local and national discharging standards. The

key target pollutants are the COD, BOD and TOC, N, P and heavy metals. A highly efficient treatment process with comprises of several chemical and bio-logical units is required.

3. RecyclingCould be used for cooling water, process water and other things such as

car washing, grass watering, etc. The target pollutants are salts, pathogens and micro pollutants. An advanced treatment process must be used.

Factors for selection of wastewater treatment processes← Characteristics of the wastewater← Discharge or reuse standards← Cost← Future plans

Pretreatment of industrial wastewater is required to:← To prevent the introduction of pollutants into the next process that will

interfere with their operation and pass through the treatment works← To improve opportunities to recycle and reclaim waste waters and rele-

vant sludge.

Primary Treatment consists of screening, sedimentation, flotation, oil separa-tion, equalisation and neutralisation.

Screening: Racks are used to prevent logs, stumps, heavy debris from entering the treatment process. Coarse screens are then used to remove large solids and debris. Fine screens and micro screens are used to remove small solids and reduce the amount of suspended solids.

Equalisation: to minimise or control fluctuations in wastewater characteristics. Similar to a CSTR.

Neutralisation: Mixing acidic and alkaline waste streams. For example, acid wastes are neutralised through limestone beds.

A pump station is usually required as wastewater typically flows through the treatment process by gravity and will eventually reach a substantial depth. Types of pumps include a centrifuge and a screw pump.

Sedimentation: to remove smaller suspended solids. The mechanism utilises gravity (the density of the targeted suspended solid must be higher than the density of water). One or more steps of sedimentation may be needed in a treatment sequence. Eg. grit sedimentation (inorganic sand), primary (organic solids) and secondary sedimentation (activated sludge).

Types of Settling: ← Type I (Discrete settling): each particle settles independently. eg. grit

chamber← Type II (Flocculent settling): particles flocculate as they settle. eg. pri-

mary sedimentation← Type III (Zone or hindered settling): particles interfere with each other

forming a lattice which settles. This happens are a high solid concentra-tion. eg. secondary sedimentation

← Type IV (Compression settling): the weight of the particles cause further settling. Eg. Sludge thickening.

Design of the grit chamber: is done to protect the mechanical equipment from abrasion and wear. It reduces the formation of deposits in pipelines and chan-nels. It also reduces the frequency of digester cleaning required due to accu-mulated grit. The grit chamber also separates the organic material from the grit. Types of grit chambers include the horizontal flow chamber, the detritus tank, the aerated grit chamber (involves a spiral flow pattern) and the vortex flow grit chamber.

Coagulation/Flocculation: aims include the removal of colloids and other charged suspended particles. This is done by the compression of the electric double layer of the particles. This causes the particle to be adsorbed and the charge is neutralized. The particles start to bridge together and are then en-meshed in a precipitate.

The primary focus of the coagulation/flocculation process is the removal of tur-bidity (cloudy appearance of water due to suspended particles). This process also removes bacteria and improves the colour of the water. The coagulant chemicals are added and the water is mixed violently to ensure that the chemi-cal is well spread. The water has to be mixed for the appropriate amount of time because if it is mixed too long, the blades will shear the newly formed pre-cipitate back into smaller particles. The next step is the coagulation. The elec-trical charged of the fine particles are neutralized which allow them to come closer together and form large clumps. Flocculation then occurs where the gen-tle mixing brings the clumps together. This floc then settles out in the sedimen-tation basin.

Biological Treatment: Advantages include a low operational cost as well as the removal of toxic pollutants in the final product. Disadvantages include a large footprint, the infeasibility of destroying all the toxic pollutants. Microorganisms produce more cells of microorganisms in waste water as well as CO2, CH4 and H2O. There are three types of microorganisms: aerobic (re-quire oxygen), anaerobic (don’t require oxygen) and anoxic (have electron ac-ceptors such as nitrate and nitrite).Microorganisms in waste water include:

· Bacteria – dominate in all biological processes and use soluble organics as food.

· Fungi – need less nitrogen source· Algae – photoautotrophs, popular in natural water treatment systems eg

lagoons, wetlands· Protozoa – use bacteria as food· Rotifers and Crustaceans – consume bacteria· Viruses – no contribution to pollutant removal

Microorganisms require a carbon source (organic matter), an energy source (oxidation or reduction reaction) as well as nutrients (N, S, P, K, Zn, Mn, Co) to grow.

Aerobic Oxidation:

The aerobic heterotrophic bacteria predominate in this process. The protozoa also play a role in consuming the bacteria and colloidal particles.

Anaerobic Treatment: The purpose of the anaerobic process is to convert sludge to liquid and gas products while producing as little biomass as possible. This process is more economical.

1. Hydrolysis: large polymers are broken down by enzymes2. Fermentation: production of CO2 and organic acids3. Acetogenesis: breakdown of volatile acids to acetate and hydrogen4. Methanogenesis: the acetate, hydrogen and CO2 are converted to meth-

ane and water.

Nitrification: Aerobic autotrophic bacteria must predominate to accomplish ni-trification. The pH must be controlled during this process.

Denitrification: Both heterotrophic and autotrophic organisms can take part in this process. pH is elevated as alkalinity is produced.

Anaerobic Processes: process in which organic materials are converted into CH4 and CO2 in the absence of O2 via the activity of groups of anaerobic microorganisms.

Temperature ranges for anaerobic digestion:· Psychrophilic: optimum temperatures 15-20C. Low efficiency but it is

highly desirable with economic trades in temperate climates. · Mesophilic: 30-37C. Most commonly employed anaerobic treatment

process. Often unstable. · Thermophilic: 55-60C. More efficient than mesophilic processes. Ther-

mophilic reactor can accept a higher organic loading and produce lower quantities of sludge. More energy is required to heat up the reactor. They produce high concentrations of VFA in their effluent. Useful in treating slurries of constant composition.

Covered anaerobic lagoon process: Advantages include a strong ability to han-dle a wide range of wastewater. The process is simple, has a low construction cost and will create high effluent quality and has a high residence time.Disadvantages include the fact that a large land area is required and the feed flow distribution is inefficient.

Anaerobic sequencing batch reactor: batch fed, decanted, suspended growth system and is operated in a cyclic sequence of four stages: feed, react, settle, decant.

Upflow anaerobic sludge blankets (UASB): Critical elements of this process in-clude the influent distributor, the gas, liquid and solid separator and the efflu-ent withdraw system. It is an incredible high strength wastewater treatment process. Granular sludge is fed as the influent; 1-3 microns in size. There is a high concentration at the bottom of the tank and low conc at the top. High vol-ume of organic loading and setteability level. While designing the UASB, a few factors need to be kept in mind. The upflow velocity determines the formation of the granular sludge and sludge separa-tion. The reactor volume and dimensions.

Anaerobic Baffled Reactor (ABR): Advantages include its simplicity; there is no special separation device or mechanic mixing. There is a low residence time and wastewater of different constituents can be treated. This process is also stable with regards to shock loads.

Membrane separation anaerobic treatment process: Advantages include a higher biomass concentration which in turn will reduce the size of the reactor required. This process has high removal efficiency. Membrane fouling can be caused by a high concentration of sludge or the accu-mulation of colloidal materials and sludge on the membrane surface. Precipita-tion of inorganic salts can also cause fouling. In order to control/prevent foul-ing, there needs to be a high liquid velocity and the loss of active sludge.

Anaerobic filter: a matric provides an attachment surface that supports anaero-bic microorganisms. It’s a form of a biological wastewater treatment process. A fluidized bed reactor can also be used; in this case, the matrix is fluidized. This can handle fine suspended solids without the potential of blocking.

Process for BOD removal nitrification using an aeration tank: the air is used to mix the activated sludge with the water. The air also provides the oxygen de-mand needed for the organisms to oxidise the organic compounds. This process can be done in five ways: 1) a plug flow activated sludge 2) step aera-tion activated sludge 3) a complete mix activated sludge 4) oxidation ditch and 5) a sequencing batch reactor

Process for biological nitrogen removal: this process uses an anoxic mix to re-move nitrogen in the waste water. Preanoxic methods of removal include 1) a modified Ludzack-Ettinger 2) a sequencing batch reactor. Post anoxic method involves the anoxic stage after the aerobic stage.

Activated sludge process model: Biomass in influent + net biomass growth = biomass in effluent + biomass wasted

While designing a biological treatment process, a few considerations need to be taken:

· Selection of reactor type based on the nature of waste water, the local environmental conditions, the presence of toxic substances, cost and fu-ture plans.

· Sludge retention time· Organic loading· Food to microorganism ratio· Sludge production· Oxygen requirements· Nutrient requirements

Aerobic lagoon advantages include a low operational cost and easy mainte-nance. Disadvantages include low biological organism removal efficiency, a long reaction time and a large footprint. A larger size of the lagoon means a higher BOD removal.

Filters: a rock media could possibly cause the problem of plugging and has a low surface to volume ratio. A synthetic media trickling filter has a high surface to volume ratio and is considerably lighter.

Nitrification: BOD removal and nitrification can be accomplished in trickling fil-ters operated at low organic loading.

Recirculation is done to increase the contact efficiency between the biofilm and the waste water. This process also helps to dilute the influent. Improves distri-bution over the surface, thus reducing the tendency to clog and also reduce fil-ter flies. Prevents biological slime.

Design considerations: the filter has to be low cost and high durability + poros-ity. Needs to have adequate airflow. Loading criteria.

Rotating Biological Contactors (RBSs): advantages include the simplicity of the process and low energy costs, BOD removal is comparable to well operated ac-tivated sludge process and denitrification could be achieved if the process is well designed.

Combined aerobic treatment processes:· Integrated Fixed-Film activated Sludge (IFAS): an activated sludge sys-

tem that has a fixed film media in a suspended growth reactor. The pur-pose of the film media is to increase the biomass in the reactor. Media types include a sponge, plastic carriers or honeycomb polyester fabrics.

· Moving Bed Biofilm Reactor (MBBR): this process uses small plastic ele-ments (7-22mm) to support the growth of biofilm in the reactor. The sus-pended growth portion of the hybrid is designed as a complete mix reac-tor.

Attached growth vs activated sludge: activated sludge is more economical, flexible and easy to operate/maintain.

Secondary Clarifier: in the upper, discrete floc particles start to settle (Type I), as the particles start to sink, they begin to flocculate (Type II) and in the lower zones, hindered settling occurs and compression settling (Type III).

If too much sludge builds up, there is poor settling and a low separation effi-ciency.

Membrane bioreactor (MBR): biological process in which the secondary clarifier is replaces by a membrane filtration unit. Advantages include a high quality of permeate, longer SRT, less sludge production, higher sludge concentration, shorter HRT, small footprint and a higher hydraulic loading. The effluent of the MBR is low in BOD, COD, Ammonia, total nitrogen and turbidity. The smaller

plant size means less sludge and high quality of water. Lower production cost and longer membrane life makes MBR a more competitive option. Disadvantages include high capital cost, high replacement cost, high energy cost and possible maintenance issues. Types of MBR include the side stream MBR and the immerged MBR.

MBR Process: 1. Preliminary Treatment – removal of grit and materials that can be

screened. 2. Primary Treatment – generally not required for a MBR. 3. Solids Retention Time (SRT): benefits nitrification4. Mixed Liquor Suspended Solids (MLSS): immersed MBRs have mixed

liquor concentrations.

Types of membrane fouling: · Biofouling – formed due to deposition and growth of microorganisms on

membrane surfaces. · Organic fouling – caused by the deposition of proteins, polysaccharides,

acids and other organic substances (soluble or colloidal) that originates from feed water or microbial secretion.

· Inorganic fouling – results from chemical precipitation of inorganic crys-tals and/or biological precipitation of inorganic complexes.

Disinfections: purpose is to reduce pathogen concentrations to acceptable lev-els, rather than completely remove them.

Chemical methods:1. Chlorination using free chlorine, sodium hypochlorite or chlorine dioxide

The chlorine (which forms hydrochloric acid and hypochlorous acid) must penetrate into the bacterial cell to cause cell inactivation. The chlorine dioxide causes the disruption of protein synthesis which leads to inactiva-tion. Sodium hypochlorite or calcium hypochlorite is less toxic and only available in the liquid phase. This method is expensive and requires spe-cial handling.

2. Ozonation causes physical damage to DNA which leads to inactivation. Free radicals are formed, hydroxyl superoxide and ozone itself.

Physical methods: ultraviolet radiation. The DNA absorbs the light (200-300nm) which causes damagesMechanical methods: membrane filtration

Factors that influence disinfection: contact time, concentration of the disinfec-tant and the characteristics of the water.

Formation of disinfection byproducts (DBPs): · Trihalomethanes are a group of four chemicals that are formed when

chlorine and other disinfectants are used to control microbial contami-nants in drinking water with naturally occurring organic matter. The four chemicals are chloroform, bromodichloromethane, dibromocloromethane and bromoform.

· Haloacetic acids · Chlorite is a byproduct of chlorine dioxide

Factors that affect DBP formation: presence of organic precursors (remove as much organic material as possible before disinfection), free chlorine concentra-tion (replace chlorine with chloramine), bromide concentration (remove bro-mide before disinfection), pH and temperature. Dechlorination can be done by a few compounds, sulphur dioxide gas, sodium sulfite, bisulphite and metabisulphite.

Formation of DBPs in ozonation: bromate is the main chemical formed when ozone is used to disinfect drinking water. The ozone reacts with bromide which is naturally occurring in source water. Ozone depletes rapidly, so ozone residu-als are not likely to be found in the effluent. Oxygen concentration is usually high, so there is no need for reaeration.

UV Practice: quartz sleeves are used to isolate the lamps from direct water con-tact and to control the wall temperature. Regular cleaning is required for these sleeves. Advantages: no residual toxicity, high efficiency with regards to most bacteria and viruses, no formation of DBPs, small footprint and improved safety com-pared to the use of chemical disinfectants. Disadvantages: less effective in inactivating some viruses, spores, energy in-tensive, capital cost is high; acid washing is required to remove the scale on the sleeves, hydraulic design of the UV system is mandatory.

Significance of wastewater reuse: for population growth, in case of contamina-tion of water resources and periodic droughts.

Water for industrial purposes can either be recycled externally at a waste water treatment plant or internally using on site treatment facilities. One issue re-garding in-plant reuse is the accumulation of salt.The recycled water could be used for cooling tower water, however there could be some issues regarding calcium, magnesium and silica deposits. Precipitation could also occur. The wastewater could also cause metallic corrosion in the piping due to TDS, dissolved oxygen and some metals. This could be solved by adding chemical corrosion inhibitors and reducing TDS and metals.

The wastewater could also have biological growth due to the warm and moist environments and the fact that organics and nutrients are available. This would cause problems with regards to heat transfer and create corrosion. To control this, the pH needs to be controlled and biocides need to be added.

In some cases, the recycled waste water can have a significant impact on crop yield and soil properties. The accumulation of salt results in deterioration of the soil. Ion toxicity can accumulate in the crop itself and excess nitrogen can re-duce the quality of the crop.

Groundwater recharge: the purpose of groundwater recharge is to reduce, stop or reverse declines of groundwater levels. It protects the underground freshwa-ter against saltwater and it stores reclaimed water. It is done by surface spreading and direct injection. Contaminants in the groundwater are removed

by soil filtration and retained in the soil matrix. Biodegradation of organic mat-ters takes place in the soils and pathogen removal isn’t efficient.

Advanced Wastewater Treatment: some of the residual constituents in treated wastewater include suspended solids, dissolved organic matter, ammonia, ni-trogen and phosphorous. Technologies that can be used for advanced treatment: depth filtration, mem-brane filtration, adsorption, ion exchange, chemical oxidation, chemical precipi-tation, air stripping

Membrane Filtration: involves a semipermeable membrane. Reverse osmosis occurs when the filter is too small. Pretreatment is required to remove chemi-cal precipitation or ion exchange, chemical oxidation to limit bacterial activity and the removal of residual organics.

Adsorption: is done by activated carbon - powdered activated carbon (PAC) or granular activated carbon (GAC). Carbon regeneration: chemicals are used to oxidise the adsorbed materials. Steam drives off the materials and solvents are used to let the adsorbed mate-rials redissolve. Thermal methods are used to reactivate the adsorbed materi-als.

GAC Column: Fixed bed, expanded bed, moving bed.

Ion Exchange: a strong acid cation, weak acid cation, strong base anion. Ion Ex-change helps in the removal of nitrogen, heavy metals and TDS.

Solid Waste Disposal: sources of solid wastes include woods and plastics from the screening units, sands and other inorganics from the grit chamber, undis-solved organics from the primary clarifier and microorganisms from the sec-ondary clarifier. In the advanced treatment, activated carbon is left over from adsorption, polymers from the ion exchange and organic matters/chemicals from filtration.

Disposal methods of solid wastes: - Landfill: suitable for most solid wastes except toxic matters, the resources and energy are wasted. - Incineration: suitable for organic solids, energy is recovered and the wa-

ter content should be low. This method has a high capital cost- Anaerobic Digestion: energy is recovered and is suitable for biodegrad-

able solids- Application of biosolids to land: utilising the nutrients available.

Sludge Processing Steps:I. Preliminary Operations: involve grinding (to cut or shear large materials

into small particles to prevent clogging and wrapping). Screening is an al-ternative to grinding. Grit removal, blending and storage

II. Thickening: to increase the solid content of the sludge by removing a portion of liquid. Can be done by gravity, centrifugal, gravity belt.

III. Stabilisation: to reduce the amount of pathogens, eliminate odours and to inhibit the potential putrefaction. Can be done by anaerobic digestion (cylindrical or egg-shaped)

Cylindrical Advantages: allows relatively large volume for has storage, low profile, convention constructional techniques. Disadvantages include ineffi-cient mixing, grit accimulation, large surface area provides space for scum ac-cumulation, regular cleaning is required

Egg-Shaped Advantages: minimal grit accumulation, higher mixing effi-ciency. More homogeneous biomass is obtained, lower operating and mainte-nance costs, smaller footprint and foaming is minimalised. Disadvantages in-clude little gas storage volume, high profile structure, difficulty in accessing the top mounted equipment, higher construction costs. IV. Conditioning: to reduce the incoming moisture content and improve the

dewatering characteristics. Can be done by chemical conditioning or heat treatment.

V. Dewatering: to reduce the moisture content of the sludge and biosolids. Dewatered sludge is easier to handle and is required prior to incineration and landfilling

VI. Heat DryingVII. Thermal Reduction

Final Desposal: - Land Application (Composting): process in which the organic material un-

dergoes biological degradation to a stable end product. The volatile solids are converted to carbon dioxide and water. Pathogens are destroyed due to high operation temperature. The composted biosolids can be used as soil condi-tioners and fertilisers.

- Incineration Plant (electricity generation)- Landfill