Self Study Reort 1

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RASHTREEYA VIDYALAYA COLLEGE OF ENGINEERING

Renewable Energy Technology

Biogas from waste and Renewable sources1) Ashwanth Subramanian1

Rashtreeya Vidyalaya College of Engineering, Bangalore [email protected]

Abstract- This is a report on production and applications of organic natural gas or biogas, produced from renewable resources. In this report , the block diagram of the biogas generation process, the material balance- an example , the type of reactors, information on how the obtained crude gas is purified using pressure swing adsorption to improve the quality of the biogas and finally the environmental impact analysis of a biogas plant and how the liquid and solid waste from the biogas plant is utilized.

I. BLOCK DIAGRAM

Figure 1 : Block diagram for Biogas production

In the above block diagram of producing biogas, the first step is to select the right amount of feed then has to be pre-digested, that is, some of the tough contestants have to be broken down into simpler forms. For example, most plant material contains complex substances like Lignin, Cellulose and Hemi cellulose. These substances cannot be digested easily in a bioreactor, so we need to convert them to carbohydrate using specialised microbes in a specifically designed environment. This process takes anywhere between 48 to 72 hours depending on the type of feed and their cellulolignin characteristics.

The Pre-Digested feed has to be made suitable for the next stage of digestion. This process is called feed enrichment. Here the material is mixed to form the correct consistence, balance the pH and destroy any residual unwanted bacteria that may go to the next stage. This feed that contains high nutritional content is ready for the microbial army in the main digestion stage to produce biogas.

DEPARTMENT OF CHEMICAL ENGINEERING

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The Digestion Process is bio mimicry of the digestion system of animals. The process is highly controlled and balanced by on board computers. The technology used in the reactors for digestion is called Variable Hydraulic Microbe Incubated Auto balanced Anaerobic Bio-Reactor.

There are three stages of digestion:

In the first stage, the large organic polymers those are present in the feed that arrives from the previous processes are broken down into their smaller constituent parts to enable the bacteria in the subsequent stages of the reactors to ac- cess the energy potential. These constituent parts or monomers such as sugars are readily available to the large population of microbes. This process of breaking these long chains structures and dissolving the smaller molecules into solution is also called hydrolysis. Therefore hydrolysis of these high molecular weight polymeric components is the necessary first step in the biogas making process. Through this stage, the complex organic molecules are broken down into simple sugars, amino acids, and fatty acids. This stage also produces some quantity of Acetate and hydrogen, which can be directly used in the third stage of the process to form biogas. However there are other molecules such as volatile fatty acids that are compounds with chain length greater than acetates that needs to be catabolised into easily convertible compounds before it reaches the third stage of the process.

The Second stage of the process, uses a different group of microbes, and starts with further breakdown of the remaining components by fermentative bacteria. Here volatile fatty acids are converted along with ammonia, carbon dioxide and hydrogen sulphide as well as other by-products. This part of the second stage is similar to the way milk becomes curd. Simultaneously specific bacterium is made available to handle harmful hydrogen sulphide and convert it into hydrogen and elemental sulphur. Sulphur dissolves in water and hydrogen is used back in the process. A third set of bacterium would use the converted fatty acids, ammonia, carbon dioxide and hydrogen to produce largely acetic acid and some more carbon dioxide and hydrogen.

The Third and the terminal stage is where large amount of biogas is produced. Highly specialised microbial population, accurately acclimatised and finely placed utilise all the intermediate compounds from stage one and two and systematically convert them to methane, carbon dioxide and water. It is these compound that make-up the Crude biogas. The remaining, non-digestible material along with the mortal remains of bacterium and used-up water is excreted from the system.

The excreted material from the system is converted into high NPK fertiliser, which is nitrogen fixed and phosphate solubilised and an organic high alkaloid pest repellent.

II. PARAMETRIC CONTROLS

pH Temperature Humidity Flowrate Hydraulic retention time Total solids C:N Ratio Pathogens


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Feed poisoning Organic carbon content Microbial censusTypically, the desired C: N ratio of the feed substrates is between 25:1 and 30:1. uality and amount of input masses realized

III. MATERIAL BALANCE

Quality and amount of input masses realized in practice must meet the design assumptions ie. To check whether the Biogas production according to the theoretical value. Ex: consider the conversion efficiency within the CHP as important factor if no direct quantification of the biogas mass flow is available. We need mass balance for many purposes. Based on the mass balance calculations, we may have to decide the size of the reactor. If the reactor size is less there can be chances of explosion. If more, it is just waste of money. We need proper mass balance equations for finding out the composition of the outlet gas. Based on its composition, the required purification process is selected to increase the concentration of the methane content in the biogas so that it can be put to the right use. Also, the composition of the nutrients in the digestate is also important as its values determines its usage in the agriculture and farming industries.

Figure 2 : Mass balance, an example

Therefore the mass balance equation is used in checking:

Substrate quality Infeed amount Quantification of degree of degradation by means of a gas potential test of the digestate Stability of biological process (acid concentration) Inhibition effects Leackage of biogas within the gas collection system


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Table containing biogas potential values

An Example table, from which the size of reactor can be decided, based on the substrate present.

The above table has been taken from the book “Biogas from waste and renewable energy technology”- Dieter Dublin and Angelika Steinhauser. From the book the information that I have gained on how mass balance is done is that first only in type of feed is allowed to enter to find out how much is the biogas potential for one kind of feed alone. An example can be seen in the above table. In practical situation taking into cost constraints and biogas potential values, the best suitable mixture of different feeds are mixed in known quantity to get the maximum amount of biogas from the mixture in the particular condition.

The material balance aspect is very important for designing the reactor. Based on material balance the geometry of the reactor, the conversion in the reactor can be specified. Material balance also place an important role in gas purification, for the analysis of the crude gas and the purified biogas. Material balance can also be used in the analysis of the wastes produced from the reactor. Analysis on the waste will give information on the reusability of the waste.

IV. BIO REACTORS

The bio reactors used for generating the biogas in types are many in number. It is a highly controlled multistage polyculture anaerobic digestion process occurring in the absence of oxygen. The feed to the reactor is selected based on cost, and the quality of biogas and that it should have zero emission.

Slowly growing anaerobic bacteria require longer sludge retention times (SRT) in anaerobic reactors. Loading rates are therefore, primarily dictated by the concentration of active biomass in anaerobic reactors. Consequently, maintenance of a high SRT is the major point of interest in practical application of AD process. High rate anaerobic treatment could be achieved by employing efficient biomass retention methods. In anaerobic reactors to maintain higher biomass densities, SRT has to be in excess of HRT (hydraulic retention time). SRT>>HRT


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High biomass densities also provide greater resistance to any inhibitory substances in the influent. To accomplish the higher treatment efficiency and reliability associated with a long SRT, a number of novel anaerobic reactor configurations have been developed.

Types of reactors :

Anaerobic Sequencing Batch Reactor Anaerobic Filter (Packed Bed) Reactor Anaerobic Fluidized Bed Reactor (FBR) Upflow Anaerobic Sludge Blanket (UASB) Reactor Expanded Granular Sludge Bed (EGSB) Reactor Hybrid (UASB+Packed Bed) Reactor Anaerobic Baffled Reactor Leach Bed Reactor Anaerobic Membrane Bioreactor ……… And many more.

Anaerobic Sequencing Batch Reactor:

The batch operation allows good effluent quality control since the reactor draw can be made just when the compliance with legal standard has been attained. Operation of the Anaerobic Sequencing Batch Reactors consists of four steps: feeding, reaction, settling and treated effluent withdrawal. The main factors affecting the overall performance of the ASBR are: agitation, Substrate/Biomass ratio, geometric configuration of the reactor and the feeding strategy.

Anaerobic sequencing batch reactor (ASBR) process is a batch-fed, batch-decanted, suspended growth system and is operated in a cyclic sequence of four stages: feed, react, settle and decant. Since a significant time is spent in settling the biomass from the treated wastewater, reactor volume requirement is higher than for continuous flow processes. However, it requires no additional biomass settling stage or solids recycle. No feed short-circuiting is another advantage of ASBRs over continuous flow systems. Operational cycle-times for the ASBR can be as short as 6 hours if biomass granulation is achieved.

The treatment of four different distillery wastewaters was carried out using a pilot scale reactor (Figure 1) of 180 l working volume, the reactor has a length to diameter ratio, L/D, of 6 m/0.194 m, maintained at 35°C by a thermostatically regulated heating cable. In the upper part of the reactor was placed an inert (polyurethane) support (total height of 0.20 m) for cell immobilization to improve the solid retention. The reactor was equipped with six sampling ports (at 0.75m intervals from the bottom to the top of the reactor), two pH probes and two temperature probes.

A volumetric pump (Hydra EM24) was used to fill the reactor; agitation was provided by recycling the mixed liquor from an intake below the inert support and injecting it upwards from the bottom of the reactor. The produced biogas was measured by an Elkro gas (BK-P) meter.


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Figure 3 : Anaerobic Sequencing batch reactor

Packed Bed Reactor:

Anaerobic filter is a fixed-film biological wastewater treatment process in which a fixed matrix (support medium) provides an attachment surface that supports the anaerobic microorganisms in the form of a biofilm. Treatment occurs as wastewater flows upwards through this bed and dissolved pollutants are absorbed by biofilm. Anaerobic filters were the first anaerobic systems that eliminated the need for solids separation and recycle while providing a high SRT/HRT ratio.

Various types of support material can be used, such as plastics, granular activated carbon (GAC), sand, reticulated foam polymers, granite, quartz and stone. These materials have exceptionally high surface area to volume ratios (400 m2/m3) and low void volumes. Its resistance to shock loads and inhibitions make anaerobic filter suitable for the treatment of both dilute and high strength wastewater.

Limitations of anaerobic filter are mostly physical ones related to deterioration of the bed structure through a gradual accumulation of non-biodegradable solids. This leads eventually to channelling and short-circuiting of flow, and anaerobic filters are therefore unsuitable for wastewaters with high solids contents. Additionally, there is a relatively high cost associated with the packing materials.


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Figure 4 : Packed Bed Reactor

Fluidized Bed Reactor (FBR):

FBR is a biological reactor that accumulates a maximum active attached biomass yet still handling fine suspended solids without blocking. By maximizing the surface area available for microbial attachment and minimizing the volume occupied by the media, a maximum specific activity of attached biomass may be achieved for a given reactor volume. A filter containing extremely small particles (0.5 mm) provides adequate surface area to achieve these benefits.

In order to achieve fluidization of the biomass particles, units must be operated in an upflow mode. Rate of liquid flow and the resulting degree of bed expansion determines whether the reactor is termed a fluidized bed or expanded bed system. Expanded bed reactors have a bed expansion of 10% to 20% compared to 30% to 90% in fluidized beds.

In FBR, biomass is attached to surface of small particles (anthracite, high density plastic beads, sand etc.) which are kept in suspension by upward velocity of liquid flow. Effluent is recycled to dilute incoming waste and to provide sufficient flow-rate to keep particles in suspension. Large surface area of support particles and high degree of mixing those results from high vertical flows enable a high biomass conc. to develop and efficient substrate uptake. Biomass concentration: 15-40 g/l.

The greatest risk with FBR is the loss of biomass particles from the reactor following sudden changes in particle density, flow rate or gas production. If flow is interrupted and the bed allowed to settle, there is a tendency once flow is restarted for the entire bed to move upward in plug-flow rather than fluidizing. In practice, considerable difficulties were experienced in controlling the particle size and density of flocks due to variable amounts of biomass growth on particles.Therefore FBRs are considered to be difficult to operate.


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Figure 5 : Fluidized Bed Reactor

An Example reactor :

Figure 6 : Images of Reactor at Scalene

The above are the images of a bio reactors which was seen at the scalene greenergy corporation part of Scalene research energy institute.

Some observed characteristics of the reactor:

Length was about 12-15ft long diameter of 5-8ft One inlet for feed on one side and an exit of waste on the other side. Two outlets in the middle of the reactor at the top for the biogas generated. Pumps were used for pumping the feed. Stainless steel body coated with green paint. There was another outlet at the top for CO2 from the CO2 rebreather.


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V. CRUDE GAS PURIFICATION (MASS TRANSFER ASPECTS)

A number of different technologies for the major biogas upgrading step are commercially available. This major step comprises the drying of the raw biogas and the removal of carbon dioxide, and thus, the enhancement of the heating value of the produced gas.

Crude Biogas Composition:

Purified biogas composition :

Table containing Composition of the biogas (crude and purified)Source of table: Scalene Energy Research Institute

There are several techniques for purifying the crude gas some of the methods are :

Pressure swing adsorption:

Gas separation using adsorption is based on different adsorption behaviour of various gas components on a solid surface under elevated pressure. Usually, different types of activated carbon or molecular sieves (zeolites) are used as the adsorbing material. These materials selectively adsorb carbon dioxide from the raw biogas, thus enriching the methane content of the gas. After the adsorption at high pressure the loaded adsorbent material is regenerated by a stepwise decrease in pressure and flushing with raw biogas or biomethane. During this step off gas is leaving the adsorber.

Afterwards, the pressure is increased again with raw biogas or biomethane and the adsorber is ready for the next sequence of loading. Industrial scale upgrading plants implement four, six or nine


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adsorber vessels in parallel at different positions within this sequence in order to provide a continuous operation. During the decompression phase of the regeneration the composition of the offgas is changing as the also adsorbed methane is released earlier (at higher pressures) and the bulkof carbon dioxide is preferentially desorbed at lower pressures. Thus, the offgas of the first steps of decompression is typically piped back to the raw biogas inlet in order to reduce the methane slip. Offgas from later steps of regeneration could be led to a second stage of adsorption, to the offgas treatment unit or could be vented to the atmosphere. As water and hydrogen sulphide contents in the gas irreversibly harm the adsorbent material these components have to be removed before theadsorption column.

Figure 7 : Pressure Swing Adsorption

The application of this technology to biomethane production is advantageous if:

Methane content of biomethane stream (95,0-99,0vol%) is suitable for further utilisation Projected plant capacity is small or medium Biomethane stream can directly be utilised at delivery pressure and no further compression is needed Heat demand of the biogas plant can be (partly) covered by offgas treatment

Chemical absorption: amine scrubbing:

Chemical absorption is characterised by a physical absorption of the gaseous components in a scrubbing liquid followed by a chemical reaction between scrubbing liquid components and absorbed gas components within the liquid phase. As a result, the bonding of unwanted gas components to the scrubbing liquid is significantly stronger and the loading capacity of the scrubbing liquid is several times higher. The chemical reaction is strongly selective and the amount of methane also absorbed in the liquid is very low resulting in very high methane recovery and very low methane slip. Due to the high affinity of especially carbon dioxide to the used solvents (mainly aqueous solutions of


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Monoethanolamine MEA, Diethanolamine DEA and Methyldiethanolamine MDEA) the operating pressure of amine scrubbers can be kept significantly smaller compared to pressurised water scrubbing plants of similar capacity.

Typically, amine scrubbing plants are operated at the slightly elevated pressure already provided in the raw biogas and no further compression is needed. The high capacity and high selectivity of the amine solution, although an advantage during absorption, turns out to be a disadvantage during the regeneration of the scrubbing solution. Chemical scrubbing liquids require a significantly increased amount of energy during regeneration which has to be provided as process heat. The loaded amine solution is heated up to about 160°C where most of the carbon dioxide is released and leaves the regeneration column as a considerably pure offgas stream. As a small part of the scrubbing liquid is lost to the produced biomethane due to evaporation, it has to be replenished frequently. Hydrogen sulphide could also be absorbed from the raw biogas by chemical absorption but higher temperatures during regeneration would be needed. That is why it is advisable to remove this component prior to the amine scrubber.

Figure 8 : Chemical absorption: amine scrubbing:


High methane recovery is desired and consequently, no further offgas treatment to reduce the methane emissions is necessary

High methane content of biomethane stream is desired Projected plant capacity is medium or large Biomethane stream can be utilised at the almost atmospheric delivery pressure and no further

compression is needed Heat demand of regeneration step can be covered by infrastructure available at biogas plant


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Membrane technology: Gaspermeation:

Membranes for biogas upgrading are made of materials that are permeable for carbon dioxide, water and ammonia. Hydrogen sulphide, oxygen and nitrogen permeate through the membrane to a certain extent and methane passes only to a very low extent. Typical membranes for biogas upgrading are made of polymeric materials like polysulfone, polyimide or polydimethylsiloxane. These materials show favourable selectivity for the methane/carbon dioxide separation combined with a reasonable robustness to trace components contained in typical raw biogases. To provide sufficient membrane surface area in compact plant dimensions these membranes are applied in form of hollow fibers combined to a number of parallel membrane modules.

After the compression to the applied operating pressure the raw biogas is cooled down for drying and removal of ammonia. After reheating with compressor waste heat the remaining hydrogen sulphide is removed by means of adsorption on iron or zinc oxide. Finally, the gas is piped to a single- or multi-staged gaspermeation unit. The numbers and interconnection of the applied membrane stages are not determined by the desired biomethane quality but by the requested methane recovery and specific compression energy demand. Modern upgrading plants with more complex design offer the possibility of very high methane recoveries and relatively low energy demand. Even multi-compressor arrangements have been realised and proved to be economically advantageous. The operation pressure and compressor speed are both controlled to provide the desired quality and quantity of the produced biomethane stream.

Figure 9 : Membrane technology: Gaspermeation:



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High flexibility towards process layout and adaption to the local biogas production facility as well as flexible partial load behaviour and plant dynamics are desired

Methane content of biomethane stream (95,0-99,0vol%) is suitable for further utilisation Projected plant capacity is small or medium

Biomethane stream can directly be utilised at delivery pressure and no further compression is needed

Heat demand of the biogas plant can be (partly) covered by offgas treatment or Additional chemicals and other consumables have to be avoided Fast Start-up from cold standby and Start/Stop operation have to be realised

Physical absorption: Pressurised water scrubbing:

The absorbed gas components are physically bound to the scrubbing liquid, in this case water. Carbon dioxide has a higher solubility in water than methane and will therefore be dissolved to a higher extend, particularly at lower temperatures and higher pressures. In addition to carbon dioxide, also hydrogen sulphide and ammonia can be reduced in the biomethane stream using water as a scrubbing liquid. The effluent water leaving the column is saturated with carbon dioxide and is transferred to a flash tank where the pressure is abruptly reduced and the major share of the dissolved gas is released. As this gas mainly contains carbon dioxide, but also a certain amount of methane (methane is also soluble in water, but to a smaller extent) this gas is piped to the raw biogas inlet. If the water is to be recycled back to the absorption column, it has to be regenerated and is therefore pumped to a desorption column where it meets a counter current flow of stripping air, into which the remaining dissolved carbon dioxide is released. The regenerated water is then pumped back to the absorber as fresh scrubbing liquid.

Figure 10 : Physical absorption: Pressurised water scrubbing:


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The drawback of this method is that the air components oxygen and nitrogen are dissolved in the water during regeneration and thus, transported to the upgraded biomethane gas stream. Therefore, bio methane produced with this technology always contains oxygen and nitrogen. As the produced biomethane stream is saturated with water, the final step in upgrading typically is gas drying, for example by the application of glycol scrubbing.


Oxygen and nitrogen content in biomethane together with a reduced heating value is tolerable Projected plant capacity is medium or large Biomethane stream can directly be utilised at delivery pressure and no further compression is

needed Heat demand of the biogas plant can be (partly) covered by offgas treatment

VI. ENVIRONMENTAL IMPACT ANALYSIS

Biogas plants are in a way helping in solid waste management to a large extent from the household which generate a large amount of organic waste which can be used for biogas production.

Ill Impacts of improper way of solid waste management :

Increase disease transmission or otherwise threaten public health: Rotting organic materials pose great public health risks, including, as mentioned above, serving as breeding grounds for disease vectors. Waste handlers and waste pickers are especially vulnerable and may also become vectors, contracting and transmitting diseases when human or animal excreta or medical wastes are in the waste stream. (See the discussion on medical wastes below and the separate section on “Healthcare Waste: Generation, Handling, Treatment, and Disposal” in this volume.) Risks of poisoning, cancer, birth defects, and other ailments are also high.

Contaminate ground and surface water: Municipal solid waste streams can bleed toxic materials and pathogenic organisms into the leachate of dumps and landfills. (Leachate is the liquid discharge of dumps and landfills; it is composed of rotted organic waste, liquid wastes, infiltrated rainwater and extracts of soluble material.) If the landfill is unlined, this runoff can contaminate ground or surface water, depending on the drainage system and the composition of the underlying soils.

Create greenhouse gas emissions and other air pollutants: When organic wastes are disposed of in deep dumps or landfills, they undergo anaerobic degradation and become significant sources of methane, a gas with 21 times the effect of carbon dioxide in trapping heat in the atmosphere.

Garbage is often burned in residential areas and in landfills to reduce volume and uncover metals. Burning creates thick smoke that contains carbon monoxide, soot and nitrogen oxide, all of which are hazardous to human health and degrade urban air quality. Combustion of polyvinyl chlorides (PVCs) generates highly carcinogenic dioxins.

Damage ecosystems: When solid waste is dumped into rivers or streams it can alter aquatic habitats and harm native plants and animals. The high nutrient content in organic wastes can deplete dissolved oxygen in water bodies, denying oxygen to fish and other aquatic life form. Solids can cause sedimentation and change stream flow and bottom habitat. Siting dumps or


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landfills in sensitive ecosystems may destroy or significantly damage these valuable natural resources and the services they provide.

Injure people and property: In locations where shantytowns or slums exist near open dumps or near badly designed or operated landfills, landslides or fires can destroy homes and injure or kill residents. The accumulation of waste along streets may present physical hazards, clog drains and cause localized flooding.

Discourages tourism and other business: The unpleasant odor and unattractive appearance of piles of uncollected solid waste along streets and in fields, forests and other natural areas, can discourage tourism and the establishment and/or maintenance of businesses.

Major points to be discussed in the EIA of a biogas plant

Impacts on atmosphere.(odour, desulphurization unit) Noise Impacts on the surface and ground water Impacts on the soil Impacts on landscape And other impacts

Impacts on atmosphere:

The major point source of pollution in a biogas station is the cogeneration unit combustion biogas. Emissions from a biogas stations are comparatively negligible. In order to achive maximum reduction of negative impacts on the environment, a desulphurization unit is accommodated. Odour is one of the most disputable environmental impacts. If only carbon dioxide, methane and water are the only products, then there would not be any problem. But other by products such as hydrogen sulphide, ammonia, siloxanes are also liberated which lead to the negative odour. But in today’s versions of the biogas plants there are ways to treat the gas in order to reduce the negative odour of the biogas.

Noise:

It refers to the noise from the biogas plant which affects the nearest built up area. This noise from the biogas pant is majorly due the various instruments present in the biogas plant as a whole like cogeneration unit, heat exchanger, exhaust muffle, mechanical feed cutter etc. different countries have different set of standards.Impacts on the surface and ground water :

The liquid waste produced in the biogas reactor is rich in many nutrients. Most of the liquid is reused in the reactor. The excess of the liquid can be taken for reverse osmosis and can be used as public water supply.

Impacts on soil and landscape:

The biogas plants are usually situated in the agricultural or industrial are and thus they do not have that much impact on the landscape. The are brought in places where the soil is worn out. The fertilizer produced in the solid waste can be used in regeneration of the soil.


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Environmental benefits:

Typically, animal waste management systems utilize anaerobic or facultative lagoons for treatment of liquid waste streams, such as flush water and runoff, and land application to dispose of solids. The solids may be stockpiled for a period of time before application can be made. Manure stockpiles and improperly operating lagoons can be sources of odors and insect pests which are nuisances for neighbours. Effluents from lagoons contain substantial nitrogen and phosphorus nutrient loads and must be applied to land for disposal. Effluents from well-designed and properly operated systems constitute a very low potential for nonpoint source pollution of water resources; however, unfavourable weather may significantly increase the pollution potential from these systems. Enclosed anaerobic digestion systems for biogas production are not subject to pronounced influences of the weather, making effluents from digesters more stable and uniform than effluents from anaerobic lagoons. Additionally, odors are controlled since all the gas is burned prior to release into the atmosphere.

Anaerobic digestion processes result in source strength reduction by converting incoming organic matter to methane, carbon dioxide and small amounts of microbial biomass; pathogens and weed seeds are destroyed; and odors are reduced. Total nitrogen, phosphorus and other minerals remain largely unchanged; therefore, effluent from a digester must be retained in a holding pond and used either as recycled flush water or for irrigation. The potential for nonpoint source pollution resulting from heavy rainfall is lessened since the influent to the holding pond will have undergone complete digestion.

Another environmental benefit from using biogas as an energy resource is that there is no net production of greenhouse gases. The carbon dioxide released during biogas combustion originally was organic plant material and so is just completing a cycle from atmosphere to plant to animal and back to the atmosphere. Methane is a more severe greenhouse gas than carbon dioxide and capture of biogas as a fuel prevents the release of methane into the atmosphere. Land application of solids and anaerobic lagoon treatment of liquid wastes releases a substantial amount of methane to the atmosphere. Capture of the methane for use as a fuel would significantly reduce the net greenhouse gas production from CAFOs.

Utilization of the waste generated in the biogas reactor unit:

Waste from reactor are of two types:1. Liquid waste : is rich in alkaloids released by leafy material like water hyacinth, tomato

leaves, brinjal leaf etc during the digestion process of feedstock. It also contains some fatty acid salts. Alkaloids and FAS are natural pest repellent widely used by plants to fight against pests and insects. When sprayed on plants in dilutions of 1: 5 with water, pest repellent is especially effective in the control of Helliothis, Spodoptera and other larvae. Pest repellent is neither toxic nor corrosive and does not contaminate ground water, since SERIPEST is non-systemic, it does not enter the food chain through agricultural produce.

2. Solid waste: Phosphorus is one of the major plant nutrients, second only to nitrogen in requirement. However a greater part of soil phosphorus, approximately 95 –99% is present in the form of insoluble phosphates and hence cannot be utilized by the plants. To increase the availability of phosphorus for plants, we use large amounts of fertilizer on a regular basis. But after application, a large proportion of fertilizer phosphorus is quickly transferred to the


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insoluble form. Therefore, very little percentage of the applied phosphorus is used, making

continuous application necessary. solid material is nitrogen fixed and phosphate solubilized.

Nutrition value of the fertilizer per kg of the fertilizer:

Table containing the composition per kg of fertilizer produced at SERI

VII. APPLICATIONS

Domestic Cooking Fuel:

Biogas is buoyant at –71 degrees; it has a flammability bandwidth between 5 and 15%, Ignites at 650 degrees centigrade, yet very high calorific value. This makes SERIGAS as the most efficient and safest fuel for domestic cooking purposes. Complete burning does not produce dirty carbon monoxide that mixes with food causing change in its colour and flavour. In fact biogas has the efficiency of LPG and safety of firewood, when it comes to cooking at home. Further it should be the cheapest cooking gas you can ever get. And finally by using SERIGAS, you contribute in saving the planet.

Automotive Fuel:

High Calorific value of biogas is comparable to LPG, thus making it an excellent automotive fuel that produces practically no harmful carbon monoxide and other polluting gases. SERIGAS can be compressed to high pressure of 200 to 250 kgs for large vehicles and at 20 to 30 kg using NPMC technology developed by SERI for smaller vehicles like Cars, motor cycles.

Industrial Applications:

Industrial applications for biogas are many. Waste treatment and incineration, metals preheating (particularly for iron and steel), drying and dehumidification, glass melting, food processing, and fuelling industrial boilers. biogas may also be used as a feedstock for the manufacturing of a number of chemicals and products. In addition to these uses, there are a number of innovative and industry specific uses of biogas. biogas desiccant systems, can be used for dehumidification, and can be popular in the plastics, pharmaceutical, candy, and even recycling industries. In each of these


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industries, moisture filled air can lead to damage of the end product during its manufacture. For example, in the plastics industry, moisture can cause cracks and blemishes during the manufacture of certain types of plastics. Adding a biogas desiccant system to the manufacturing or drying environment allows industrial users to regulate more closely the amount of moisture in the air, leading to a more consistent and high-quality product. Biogas absorption systems can also be used extensively in industry to heat and cool water in an efficient, economical, and environmentally sound way.

Biogas co-firing technologies can also help in increasing industrial energy efficiency, and reduce harmful atmospheric emissions. Co-firing is the process in which biogas is used as a supplemental fuel in the combustion of other fuels, such as coal, wood, and other biomass materials. For example, a traditional industrial wood boiler would simply burn wood to generate energy. However, in this type of boiler, a significant amount of energy is lost, and harmful emissions are very high. Adding biogas to the combustion mix can have a two-fold effect. Biogas emits fewer harmful substances into the air than a fuel such as wood. Since the energy needed to power the biogas boiler remains constant, adding biogas to the combustion mix can reduce harmful emissions

REFERENCES

1. Barber WP and Stuckey DC (1999) The use of the anaerobic baffled reactor (ABR) for wastewater treatment: a review. Wat. Res., 33 (7), 1559-1578.

2. Ruiz C., Torrijos M., Sousbie P., Lebrato Martinez J., Moletta R., Delgenes J. P. (2002) Treatment of winery wastewater by an anaerobic sequencing batch reactor. Wat. Sci. Technol., 45 (10), 219-224 Sung

3. Viessmann group handbook on pressure swing adsoption.4. Vladimir lapcik, Marta Lapcikova “Biogass stations and their environmental impacts”(2011),

vol-23,str9-14.

5. Braun , R. : Neue Entwicklungen im Bereich der Biogaserzeugung, lecture held at the Symposium Biogas – Brennstoffzellensysteme am Museum Arbeitswelt in Steyr ( Ös terreich), 2 001

6. Ernst , C. : Biologische Arbeitsstoffe in abwassertechnischen Anlagen – Gef ä hrdungsbeurteilung und Schutzma ß nahmen , Entsorgung 1 , 2001 .

7. Langhans , G. : Some aspects of rheology in bioorganic suspensions and anaerobic fermentation broth, Paper presentation at Conference, Microbiology of Composting, Innsbruck, 2000

8. Yin , X. : Biogas; Thesis at the University of Applied Sciences in Munich, 2005 9. Biogas from Waste and Renewable Resources by Dieter Deublein and Angelika Steinhauser-

ISBN 978-3-527-31841-4-- 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim10. http://en.wikipedia.org/wiki/Biogas 11. http://en.wikipedia.org/wiki/Anaerobic_digestion 12. Renewables - Based Technology Sustainability Assessment—by-- ewulf, J., Van

Langenhove, H. (eds.)-- ISBN 978 - 0 - 470 - 02241 – 2---200613. http://www.biogas.ch/f+e/arasieg.htm 14. Scalene handbook on Seri organic natural gas technology.


http://www.biogas.ch/f+e/arasieg.htm

http://en.wikipedia.org/wiki/Anaerobic_digestion

http://en.wikipedia.org/wiki/Biogas

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