An Introduction to Biomethane

Biogas that has been upgraded by removing hydrogen sulphide, carbon dioxide and moisture is known as biomethane. Biomethane is less corrosive than biogas, apart from being more valuable as a vehicle fuel. The typical composition of raw biogas does not meet the minimum CNG fuel specifications. In particular, the COand sulfur content in raw biogas is too high for it to be used as vehicle fuel without additional processing.

Liquified Biomethane

Biomethane can be liquefied, creating a product known as liquefied biomethane (LBM). Biomethane is stored for future use, usually either as liquefied biomethane or compressed biomethane (CBM) or  since its production typically exceeds immediate on-site demand.

Two of the main advantages of LBM are that it can be transported relatively easily and it can be dispensed to either LNG vehicles or CNG vehicles. Liquid biomethane is transported in the same manner as LNG, that is, via insulated tanker trucks designed for transportation of cryogenic liquids.

Compressed Biomethane

Biomethane can be stored as CBM to save space. The gas is stored in steel cylinders such as those typically used for storage of other commercial gases. Storage facilities must be adequately fitted with safety devices such as rupture disks and pressure relief valves.

The cost of compressing gas to high pressures between 2,000 and 5,000 psi is much greater than the cost of compressing gas for medium-pressure storage. Because of these high costs, the biogas is typically upgraded to biomethane prior to compression.

Applications of Biomethane

The utilization of biomethane as a source of energy is a crucial step toward a sustainable energy supply. Biomethane is more flexible in its application than other renewable sources of energy. Its ability to be injected directly into the existing natural gas grid allows for energy-efficient and cost-effective transport. This allows gas grid operators to enable consumers to make an easy transition to a renewable source of gas. The diverse, flexible spectrum of applications in the areas of electricity generation, heat provision, and mobility creates a broad base of potential customers.

Biomethane can be used to generate electricity and heating from within smaller decentralized, or large centrally-located combined heat and power plants. It can be used by heating systems with a highly efficient fuel value, and employed as a regenerative power source in gas-powered vehicles.

Biomethane to Grid

Biogas can be upgraded to biomethane and injected into the natural gas grid to substitute natural gas or can be compressed and fuelled via a pumping station at the place of production. Biomethane can be injected and distributed through the natural gas grid, after it has been compressed to the pipeline pressure. In many EU countries, the access to the gas grid is guaranteed for all biogas suppliers.

One important advantage of using gas grid for biomethane distribution is that the grid connects the production site of biomethane, which is usually in rural areas, with more densely populated areas. This enables the gas to reach new customers. Injected biomethane can be used at any ratio with natural gas as vehicle fuel.

Biomethane is more flexible in its application than other renewable sources of energy.

The main barriers for biomethane injection are the high costs of upgrading and grid connection. Grid injection is also limited by location of suitable biomethane production and upgrading sites, which have to be close to the natural gas grid.

Several European nations have introduced standards (certification systems) for injecting biogas into the natural gas grid. The standards, prescribing the limits for components like sulphur, oxygen, particles and water dew point, have the aim of avoiding contamination of the gas grid or the end users. In Europe, biogas feed plants are in operation in Sweden, Germany, Austria, the Netherlands, Switzerland and France.

PSA System for Biogas Upgradation

Pressure swing adsoprtion, also known as PSA, is emerging as the most popular biogas upgradation technology in many parts of the world. A typical PSA system is composed of four vessels in series that are filled with adsorbent media which is capable of removing water vapor, CO2, N2 and O2 from the biogas stream.

During operation, each adsorber operates in an alternating cycle of adsorption, regeneration and pressure buildup. Dry biogas enters the system through the bottom of one of the adsorbers during the first phase of the process. When passing through the vessel, CO2, N2 and O2 are adsorbed onto the surface of the media. The gas leaving the top of the adsorber vessel contains more than 97% CH4

Biogas upgradation through PSA takes place over 4 phases: pressure build-up, adsorption, depressurization and regeneration. The pressure buildup is achieved by equilibrating pressure with a vessel that is at depressurization stage. Final pressure build up occurs by injecting raw biogas. During adsorption, CO2 and/or N2 and/or O2 are adsorbed by the media and the gas exits as CH4.

Depressurization is performed by equalizing with a second pressurizing vessel, and regeneration is achieved at atmospheric pressure, leaving a gas that contains high concentrations of CH4 to be re-circulated. During the regeneration phase, the bed must be regenerated by desorbing (or purging) the adsorbed gases. Purging is accomplished by reducing the pressure in the bed and back-flushing it with some of the concentrated gas product. The gas pressure released from one vessel is used by the other, thus reducing energy consumption and compressor capital costs.

Special adsorption materials are used as a molecular sieve, preferentially adsorbing the target gas species at high pressure. The adsorbent media is usually zeolites (crystalline polymers), carbon molecular sieves or activated carbon. Aside from their ability to discriminate between different gases, adsorbents for PSA-systems are usually very porous materials chosen because of their large surface areas.

Food Waste Management and Anaerobic Digestion

Food waste is one of the single largest constituent of municipal solid waste stream. In a typical landfill, food waste is one of the largest incoming waste streams and responsible for the generation of high amounts of methane. Diversion of food waste from landfills can provide significant contribution towards climate change mitigation, apart from generating revenues and creating employment opportunities.

food-waste-biogas

Of the different types of organic wastes available, food waste holds the highest potential in terms of economic exploitation as it contains high amount of carbon and can be efficiently converted into biogas and organic fertilizer. Food waste can either be utilized as a single substrate in a biogas plant, or can be co-digested with organic wastes like cow manure, poultry litter, sewage, crop residues, abattoir wastes etc or can be disposed in dedicated food waste disposers (FWDs). Rising energy prices and increasing environmental concerns makes it more important to harness clean energy from food wastes.

Anaerobic Digestion of Food Wastes

Anaerobic digestion is the most important method for the treatment of food waste because of its techno-economic viability and environmental sustainability. The use of anaerobic digestion technology generates biogas and preserves the nutrients which are recycled back to the agricultural land in the form of slurry or solid fertilizer. The relevance of biogas technology lies in the fact that it makes the best possible utilization of food wastes as a renewable source of clean energy.

A biogas plant is a decentralized energy system, which can lead to self-sufficiency in heat and power needs, and at the same time reduces environmental pollution. Thus, the benefits of anaerobic digestion of food waste includes climate change mitigation, economic benefits and landfill diversion opportunities.

Anaerobic digestion has been successfully used in several European and Asian countries to stabilize food wastes, and to provide beneficial end-products. Sweden, Austria, Denmark, Germany and England have led the way in developing new advanced biogas technologies and setting up new projects for conversion of food waste into energy.

Codigestion at Wastewater Treatment Facilities

Anaerobic digestion of sewage sludge is wastewater treatment facilities is a common practice worldwide. Food waste can be codigested with sewage sludge if there is excess capacity in the anaerobic digesters. An excess capacity at a wastewater treatment facility can occur when urban development is overestimated or when large industries leave the area.

anaerobic_digestion_plant

By incorporating food waste, wastewater treatment facilities can have significant cost savings due to tipping fee for accepting the food waste and increasing energy production. Wastewater treatment plants are usually located in urban areas which make it cost-effective to transport food waste to the facility. This trend is catching up fast and such plants are already in operation in several Western countries.

The main wastewater treatment plant in East Bay Municipal Utility District (EBMUD), Oakland (California) was the first sewage treatment facility in the USA to convert post-consumer food scraps to energy via anaerobic digestion. EBMUD’s wastewater treatment plant has an excess capacity because canneries that previously resided in the Bay Area relocated resulting in the facility receiving less wastewater than estimated when it was constructed. Waste haulers collect post-consumer food waste from local restaurants and markets and take it to EBMUD where the captured methane is used as a renewable source of energy to power the treatment plant. After the digestion process, the leftover material is be composted and used as a natural fertilizer.

The first food waste anaerobic digestion plant in Britain to be built at a sewage treatment plant is the city of Bristol. The plant, located at a Wessex Water sewage works in Avonmouth, process 40,000 tonnes of food waste a year from homes, supermarkets and business across the southwest and generate enough energy to power around 3,000 homes.

A Glance at Biogas Storage Systems

Selection of an appropriate biogas storage system makes a significant contribution to the efficiency and safety of a biogas plant. There are two basic reasons for storing biogas: storage for later on-site usage and storage before and/or after transportation to off-site distribution points or systems. A biogas storage system also compensates fluctuations in the production and consumption of biogas as well as temperature-related changes in volume.

There are two broad categories of biogas storage systems: Internal Biogas Storage Tanks are integrated into the anaerobic digester while External Biogas Holders are separated from the digester forming autonomous components of a biogas plant. The simplest and least expensive storage systems for on-site applications and intermediate storage of biogas are low-pressure systems. The energy, safety, and scrubbing requirements of medium- and high-pressure storage systems make them costly and high-maintenance options for non-commercial use. Such extra costs can be best justified for biomethane or bio-CNG, which has a higher heat content and is therefore a more valuable fuel than biogas.

Low-Pressure Storage

Floating biogas holders on the digester form a low-pressure storage option for biogas systems. These systems typically operate at pressures below 2 psi. Floating gas holders can be made of steel, fiberglass, or a flexible fabric. A separate tank may be used with a floating gas holder for the storage of the digestate and also storage of the raw biogas. A major advantage of a digester with an integral gas storage component is the reduced capital cost of the system.

The least expensive and most trouble-free gas holder is the flexible inflatable fabric top, as it does not react with the H2S in the biogas and is integral to the digester. These types of covers are often used with plug-flow and complete-mix digesters. Flexible membrane materials commonly used for these gas holders include high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low density polyethylene (LLDPE), and chlorosulfonated polyethylene covered polyester. Thicknesses for cover materials typically vary from 0.5 to 2.5 millimeters.

Medium-Pressure Storage

Biogas can also be stored at medium pressure between 2 and 200 psi. To prevent corrosion of the tank components and to ensure safe operation, the biogas must first be cleaned by removing H2S. Next, the cleaned biogas must be slightly compressed prior to storage in tanks.

High-Pressure Storage

The typical composition of raw biogas does not meet the minimum CNG fuel specifications. In particular, the CO2 and sulfur content in raw biogas is too high for it to be used as vehicle fuel without additional processing. Biogas that has been upgraded to biomethane by removing the H2S, moisture, and CO2 can be used as a vehicular fuel. Biomethane is less corrosive than biogas, apart from being more valuable as a fuel. Since production of such fuel typically exceeds immediate on-site demand, the biomethane must be stored for future use, usually either as compressed biomethane (CBM) or liquefied biomethane (LBM).

Two of the main advantages of LBM are that it can be transported relatively easily and it can be dispensed to either LNG vehicles or CNG vehicles. Liquid biomethane is transported in the same manner as LNG, that is, via insulated tanker trucks designed for transportation of cryogenic liquids.

Biomethane can be stored as CBM to save space. The gas is stored in steel cylinders such as those typically used for storage of other commercial gases. Storage facilities must be adequately fitted with safety devices such as rupture disks and pressure relief valves. The cost of compressing gas to high pressures between 2,000 and 5,000 psi is much greater than the cost of compressing gas for medium-pressure storage. Because of these high costs, the biogas is typically upgraded to biomethane prior to compression.

Biogas Sector in India: Perspectives

Biogas is an often overlooked and neglected aspect of renewable energy in India. While solar, wind and hydropower dominate the discussion in the cuntry, they are not the only options available. Biogas is a lesser known but highly important option to foster sustainable development in agriculture-based economies, such as India.

What is Biogas

Briefly speaking, biogas is the production of gaseous fuel, usually methane, by fermentation of organic material. It is an anaerobic process or one that takes place in the absence of oxygen. Technically, the yeast that causes your bread to rise or the alcohol in beer to ferment is a form of biogas. We don’t use it in the same way that we would use other renewable sources, but the idea is similar. Biogas can be used for cooking, lighting, heating, power generation and much more. Infact, biogas is an excellent and effective to promote development of rural and marginalized communities in all developing countries.

This presents a problem, however. The organic matter is putting off a gas, and to use it, we have to turn it into a liquid. This requires work, machinery and manpower. Research is still being done to figure out the most efficient methods to make it work, but there is a great deal of progress that has been made, and the technology is no longer new.

Fossil Fuel Importation

India has a rapidly expanding economy and the population to fit. This has created problems with electricity supplies to expanding areas. Like most countries, India mainly uses fossil fuels. However, as oil prices fluctuate and the country’s demand for oil grows, the supply doesn’t always keep up with the demand. In the past, India has primarily imported oil from the Middle East, specifically Saudi Arabia and Iraq.

Without a steady and sustainable fossil fuels supply, India has looking more seriously into renewable sources they can produce within the country. Biogas is an excellent candidate to meet those requirements and has been used for this goal before.

Biogas in India

There are significant differences between biogas and fossil fuels, but for India, one of the biggest is that you can create biogas at home. It’s pretty tricky to find, dig up and transform crude oil into gas, but biogas doesn’t have the same barriers. In fact, many farmers who those who have gardens or greenhouses could benefit with proper water management and temperature control so that plants can be grown year round, It still takes some learning and investment, but for many people, especially those who live in rural places, it’s doable.

This would be the most beneficial to people in India because it would help ease the strain of delivering reliable energy sources based on fossil fuels, and would allow the country to become more energy independent. Plus, the rural areas are places where the raw materials for biogas will be more available, such animal manure, crop residues and poultry litter. But this isn’t the first time most people there are hearing about it.

Biogas in India has been around for a long time. In the 1970’s the country began a program called the National Biogas and Manure Management Program (NBMMP) to deal with the same problem — a gas shortage. The country did a great deal of research and implemented a wide variety of ideas to help their people become more self-sufficient, regardless of the availability of traditional gasoline and other fossil fuel based products.

The original program was pioneering for its time, but the Chinese quickly followed suit and have been able to top the market in biogas production in relatively little time. Comparatively, India’s production of biogas is quite small. It only produces about 2.07 billion m3/year of biogas, while it’s estimated that it could produce as much as 48 billion m3/year. This means that there are various issues with the current method’s India is using in its biogas production.

Biogas_Animal

Biogas has the potential to rejuvenate India’s agricultural sector

The original planning in the NBMMP involved scientists who tried to create the most efficient biogas generators. This was good, but it slowed people’s abilities to adopt the techniques individually. China, on the other hand, explicitly worked to help their most rural areas create biogas. This allowed the country to spread the development of biogas to the most people with the lowest barriers to its proliferation.

If India can learn from the strategy that China has employed, they may be able to give their biogas production a significant boost which will also help in the rejuvenation of biomass sector in the country. Doing so will require the help and willingness of both the people and the government. Either way, this is an industry with a lot of room for growth.

Biogas from Slaughterhouse Wastes

slaughterhouse-wasteSlaughterhouse waste (or abattoir waste) disposal has been a major environmental challenge in all parts of the world. The chemical properties of slaughterhouse wastes are similar to that of municipal sewage, however the former is highly concentrated wastewater with 45% soluble and 55% suspended organic composition. Blood has a very high COD of around 375,000 mg/L and is one of the major dissolved pollutants in slaughterhouse wastewater.

In most of the developing countries, there is no organized strategy for disposal of solid as well as liquid wastes generated in abattoirs. The solid slaughterhouse waste is collected and dumped in landfills or open areas while the liquid waste is sent to municipal sewerage system or water bodies, thus endangering public health as well as terrestrial and aquatic life. Wastewater from slaughterhouses is known to cause an increase in the BOD, COD, total solids, pH, temperature and turbidity, and may even cause deoxygenation of water bodies.

Anaerobic Digestion of Slaughterhouse Wastes

There are several methods for beneficial use of slaughterhouse wastes including biogas generation, fertilizer production and utilization as animal feed. Anaerobic digestion is one of the best options for slaughterhouse waste management which will lead to production of energy-rich biogas, reduction in GHGs emissions and effective pollution control in abattoirs. Anaerobic digestion can achieve a high degree of COD and BOD removal from slaughterhouse effluent at a significantly lower cost than comparable aerobic systems. The biogas potential of slaughterhouse waste is higher than animal manure, and reported to be in the range of 120-160 m3 biogas per ton of wastes. However the C:N ratio of slaughterhouse waste is quite low (4:1) which demands its co-digestion with high C:N substrates like animal manure, food waste, crop residues, poultry litter etc.

Slaughterhouse effluent has high COD, high BOD, and high moisture content which make it well-suited to anaerobic digestion process. Slaughterhouse wastewater also contains high concentrations of suspended organic solids including pieces of fat, grease, hair, feathers, manure, grit, and undigested feed which will contribute the slowly biodegradable of organic matter. Amongst anaerobic treatment processes, the up-flow anaerobic sludge blanket (UASB) process is widely used in developing countries for biogas production from abattoir wastes.

Slaughterhouse waste is a protein-rich substrate and may result in sulfide formation during anaerobic degradation. The increased concentration of sulfides in the digester can lead to higher concentrations of hydrogen sulfide in the biogas which may inhibit methanogens. In addition to sulfides, ammonia is also formed during the anaerobic digestion process which may increase the pH in the digester (>8.0) which can be growth limiting for some VFA-consuming methanogens.

Anaerobic Digestion of Animal Manure

Animal manure is a valuable source of nutrients and renewable energy. However, most of the manure is collected in lagoons or left to decompose in the open which pose a significant environmental hazard. The air pollutants emitted from manure include methane, nitrous oxide, ammonia, hydrogen sulfide, volatile organic compounds and particulate matter, which can cause serious environmental concerns and health problems. In the past, livestock waste was recovered and sold as a fertilizer or simply spread onto agricultural land. The introduction of tighter environmental controls on odour and water pollution means that some form of waste management is necessary, which provides further incentives for biomass-to-energy conversion.

Anaerobic digestion is a unique treatment solution for animal manure as it can  deliver  positive  benefits  related  to  multiple  issues,  including  renewable  energy,  water pollution, and air emissions. Anaerobic digestion of animal manure is gaining popularity as a means to protect the environment and to recycle materials efficiently into the farming systems. Waste-to-Energy (WTE) plants, based on anaerobic digestion of cow manure, are highly efficient in harnessing the untapped renewable energy potential of organic waste by converting the biodegradable fraction of the waste into high calorific gases.

The establishment of anaerobic digestion systems for livestock manure stabilization and energy production has accelerated substantially in the past several years. There are thousands of digesters operating at commercial livestock facilities in Europe, United States,  Asia and elsewhere. which are generating clean energy and fuel. Many of the projects that generate electricity also capture waste heat for various in-house requirements.

Important Factors

The main factors that influence biogas production from livestock manure are pH and temperature of the feedstock. It is well established that a biogas plant works optimally at neutral pH level and mesophilic temperature of around 35o C. Carbon-nitrogen ratio of the feed material is also an important factor and should be in the range of 20:1 to 30:1. Animal manure has a carbon – nitrogen ratio of 25:1 and is considered ideal for maximum gas production. Solid concentration in the feed material is also crucial to ensure sufficient gas production, as well as easy mixing and handling. Hydraulic retention time (HRT) is the most important factor in determining the volume of the digester which in turn determines the cost of the plant; the larger the retention period, higher the construction cost.

Process Description

The fresh animal manure is stored in a collection tank before its processing to the homogenization tank which is equipped with a mixer to facilitate homogenization of the waste stream. The uniformly mixed waste is passed through a macerator to obtain uniform particle size of 5-10 mm and pumped into suitable-capacity anaerobic digesters where stabilization of organic waste takes place.

In anaerobic digestion, organic material is converted to biogas by a series of bacteria groups into methane and carbon dioxide. The majority of commercially operating digesters are plug flow and complete-mix reactors operating at mesophilic temperatures. The type of digester used varies with the consistency and solids content of the feedstock, with capital investment factors and with the primary purpose of digestion.

Biogas contain significant amount of hydrogen sulfide (H2S) gas which needs to be stripped off due to its highly corrosive nature. The removal of H2S takes place in a biological desulphurization unit in which a limited quantity of air is added to biogas in the presence of specialized aerobic bacteria which oxidizes H2S into elemental sulfur. Biogas can be used as domestic cooking, industrial heating, combined heat and power (CHP) generation as well as a vehicle fuel. The digested substrate is passed through screw presses for dewatering and then subjected to solar drying and conditioning to give high-quality organic fertilizer.

Renewable Energy from Food Residuals

Food residuals are an untapped renewable energy source that mostly ends up rotting in landfills, thereby releasing greenhouse gases into the atmosphere. Food residuals are difficult to treat or recycle since it contains high levels of sodium salt and moisture, and is mixed with other waste during collection. Major generators of food wastes include hotels, restaurants, supermarkets, residential blocks, cafeterias, airline caterers, food processing industries, etc.

In United States, food scraps is the third largest waste stream after paper and yard waste. Around 12.7 percent of the total municipal solid waste (MSW) generated in the year 2008 was food scraps that amounted to about 32 million tons. According to EPA, about 31 million tons of food waste was thrown away into landfills or incinerators in 2008. As far as United Kingdom is concerned, households throw away 8.3 million tons of food each year. These statistics are an indication of tremendous amount of food waste generated all over the world.

The proportion of food residuals in municipal waste stream is gradually increasing and hence a proper food waste management strategy needs to be devised to ensure its eco-friendly and sustainable disposal. Currently, only about 3 percent of food waste is recycled throughout U.S., mainly through composting. Composting provides an alternative to landfill disposal of food waste, however it requires large areas of land, produces volatile organic compounds and consumes energy. Consequently, there is an urgent need to explore better recycling alternatives.

Anaerobic digestion has been successfully used in several European and Asian countries to stabilize food wastes, and to provide beneficial end-products. Sweden, Austria, Denmark, Germany and England have led the way in developing new advanced biogas technologies and setting up new projects for conversion of food waste into energy.

Anaerobic Digestion of Food Waste

Anaerobic digestion is the most important method for the treatment of organic waste, such as food residuals, because of its techno-economic viability and environmental sustainability. The use of anaerobic digestion technology generates biogas and preserves the nutrients which are recycled back to the agricultural land in the form of slurry or solid fertilizer.

The relevance of biogas technology lies in the fact that it makes the best possible use of various organic wastes as a renewable source of clean energy. A biogas plant is a decentralized energy system, which can lead to self-sufficiency in heat and power needs, and at the same time reduces environmental pollution. Thus, anaerobic digestion of food waste can lead to climate change mitigation, economic benefits and landfill diversion opportunities.

Of the different types of organic wastes available, food waste holds the highest potential in terms of economic exploitation as it contains high amount of carbon and can be efficiently converted into biogas and organic fertilizer. Food waste can either be used as a single substrate in a biogas plant, or can be co-digested with organic wastes like cow manure, poultry litter, sewage, crop residues, slaughterhouse wastes, etc.

A Typical Energy Conversion Plant

The feedstock for the food waste-to-energy plant includes leftover food, vegetable refuse, stale cooked and uncooked food, meat, teabags, napkins, extracted tea powder, milk products, etc. Raw waste is shredded to reduce to its particle size to less than 12 mm. The primary aim of shredding is to produce a uniform feed and reduce plant “down-time” due to pipe blockages by large food particles. It also improves mechanical action and digestibility and enables easy removal of any plastic bags or cling-film from waste.

Fresh waste and re-circulated digestate (or digested food waste) are mixed in a mixing tank. The digestate is added to adjust the solids content of the incoming waste stream from 20 to 25 percent (in the incoming waste) to the desired solids content of the waste stream entering the digestion system (10 to 12 percent total solids). The homogenized waste stream is pumped into the feeding tank, from which the anaerobic digestion system is continuously fed. Feeding tank also acts as a pre-digester and subjected to heat at 55º to 60º C to eliminate pathogens and to facilitate the growth of thermophilic microbes for faster degradation of waste.

From the predigestor tank, the slurry enters the main digester where it undergoes anaerobic degradation by a consortium of Archaebacteria belonging to Methanococcus group. The anaerobic digester is a CSTR reactor having average retention time of 15 to 20 days. The digester is operated in the mesophilic temperature range (33º to 38°C), with heating carried out within the digester. Food waste is highly biodegradable and has much higher volatile solids destruction rate (86 to 90 percent) than biosolids or livestock manure. As per conservative estimates, each ton of food waste produces 150 to 200 m3 of biogas, depending on reactor design, process conditions, waste composition, etc.

Biogas contains significant amount of hydrogen sulfide (H2S) gas that needs to be stripped off due to its corrosive nature. The removal of H2S takes place in a biological desulphurization unit in which a limited quantity of air is added to biogas in the presence of specialized aerobic bacteria that oxidizes H2S into elemental sulfur. The biogas produced as a result of anaerobic digestion of waste is sent to a gas holder for temporary storage. Biogas is eventually used in a combined heat and power (CHP) unit for its conversion into thermal and electrical energy in a co­generation power station of suitable capacity. The exhaust gases from the CHP unit are used for meeting process heat requirements.

The digested substrate leaving the reactor is rich in nutrients like nitrogen, potassium and phosphorus which are beneficial for plants as well as soil. The digested slurry is dewatered in a series of screw presses to remove the moisture from slurry. Solar drying and additives are used to enhance the market value and handling characteristics of the fertilizer.

Diverting Food from Landfills

Food residuals are one of the single largest constituents of municipal solid waste stream. Diversion of food waste from landfills can provide significant contribution towards climate change mitigation, apart from generating revenues and creating employment opportunities. Rising energy prices and increasing environmental pollution makes it more important to harness renewable energy from food scraps.

Anaerobic digestion technology is widely available worldwide and successful projects are already in place in several European as well as Asian countries that makes it imperative on waste generators and environmental agencies to root for a sustainable food waste management system.

Biogas in Agriculture Sector in India: Key Challenges

Although the conversion of agriculture waste – cattle dung and crop residues –  to biogas and digested slurry is an established and well-proven technology, it has been under-used, probably because until recently, firewood was easily available and chemical fertilizer was relatively affordable to most of the farmers in India.

The National Biogas and Manure Management Programme (NBMMP) was put in place to lower the environmental degradation and prevent greenhouse gas emissions, like carbon dioxide and methane, into the atmosphere. However, this objective of the program is less likely to motivate the farmers and their families to install biogas plants.

This program rolled out by Ministry of Non-Conventional Energy Sources (now Ministry of New and Renewable Energy), New Delhi, with heavy subsidies for family-type biogas plants to increase adoption, was successful with lakhs of biogas plants being installed across the country till now.

It was realised that due to poor dissemination of information and unsatisfactory communication about the plant operation & application of the digested biogas slurry, and unable to perceive the return in terms of value resulted in discontinuation of lakhs of biogas plants across the country.

The entire biogas technology marketing efforts failed to highlight major advantage – an increased revenue from agriculture with the use of high quality and a low-cost homegrown digested biogas slurry as fertiliser. Another advantage was to help farmers’ understand that their land quality and output per acre will increase over the years by the use of digested biogas slurry which has been degraded from the rampant use of chemical fertiliser and pesticides.

Challenges to be addressed

The farmer’s communities today are required to made to understand that their revenue from agriculture is decreasing year on year due to increasing deforestation, degradation of land quality, rampant use of chemical fertiliser and pesticides, lack of farm cattle, injudicious use of water for irrigation, and use heavy vehicles for ploughing.

These ill-advised decisions have made the farmers poorer, impacted the health of their families and the rural environment of villages. The years ahead are crucial if this trend is not reversed.

Unending benefits of biogas technology

Most of the rural and semi-urban areas have a poor perception of the Anaerobic Digestion (or biogas or biomethanation) technology. This technology offers benefits to all spheres of society but have a particular emphasis on the needs of the farmers in rural areas.

Farmers with dairy animals generally have free access to animal waste (dung), which provide input feed for the biogas digesters. Normally, these farmers stock-pile the dung obtained from their cattle as a plant fertilizer, but this has lower nitrogen content than the digested biogas slurry created by the biogas digestion process, which is odorless and makes a better fertilizer to substitute chemical fertilizers. They can use the gas for cooking or heating, for running power generators. The biogas technology helps farmers reduce their burden to buy LPG and harmful chemical fertilizers and pesticides.

In short, biogas technology is an integrated solution for sustainable agriculture, improving health and lowering environment degradation.

The promise of biogas technology

Biogas technology can help in the following manner:

  • Enhance bio-security for dairy animals – being fully fermented, bio-slurry is odorless and does not attract flies, repels termites and pests that are attracted to raw dung.
  • Provides high quality and low-cost homegrown fertiliser for sustainable agriculture.
  • Reduce energy poverty and ensure energy security.
  • Digested biogas slurry is an excellent soil conditioner with humic acid.
  • Save time for women for education and livelihood activities.
  • Increase forest cover as less firewood would be needed on a daily basis.
  • Reduce weed growth

Importance of Government Efforts

The agriculture sector is playing a major role in India economy and it comprises a huge vote bank. Our government has launched various initiatives like GOBAR-DHAN (Galvanizing Organic Bio-Agro Resources Dhan), Sustainable Alternative towards Affordable Transportation (SATAT), and New National Biogas and Organic Manure Programme (NNBOMP) in attempt to revive interest in biogas technology for farmers and entrepreneurs.

rice-straw-biogas

Agricultural residues, such as rice straw, are an important carbon source for anaerobic digestion

These initiatives are aimed at developmental efforts that would benefit the farmers, vehicle-users, and entrepreneurs. These initiatives also hold a great promise for efficient solid waste management and tackling problems of indoor air pollution caused by use of firewood, deforestation and methane gas release in the atmosphere due to open piling of cattle dung.

These initiatives aren’t marketing the value which solves a major challenge – degradation of agriculture land for farming in rural India. The initiative and efforts are majorly focused on waste management, environment and towards behavioral change. These changes are of global importance and can be managed effortlessly by generating tangible results for farmers.

India has an aspiring young workforce which is moving to urban settlements in hope for better opportunities, therefore, productivity and revenue from agriculture needs to grow. The biogas technology can restore agriculture productivity and strengthen revenue to make it attractive.

Note: This article was first published by author on LinkedIn.com. The link to this article – https://www.linkedin.com/pulse/bio-gas-misunderstood-agri-technology-zahir-kapasi/

Biogas from Crop Wastes: European Perspectives

Most, if not all of Europe has a suitable climate for biogas production. The specific type of system depends on the regional climate. Regions with harsher winters may rely more on animal waste and other readily available materials compared to warmer climates, which may have access to more crop waste or organic material.

Regardless of suitability, European opinions vary on the most ethical and appropriate materials to use for biogas production. Multiple proponents argue biogas production should be limited to waste materials derived from crops and animals, while others claim crops should be grown with the intention of being used for biogas production.

Biogas Production From Crops

Europeans in favor of biogas production from crops argue the crops improve the quality of the soil. Additionally, they point to the fact that biogas is a renewable energy resource compared to fossil fuels. Crops can be rotated in fields and grown year after year as a sustainable source of fuel.

Extra crops can also improve air quality. Plants respire carbon dioxide and can help reduce harmful greenhouse gasses in the air which contribute to global climate change.

Biogas crops can also improve water quality because of plant absorption. Crops grown in otherwise open fields reduce the volume of water runoff which makes it to lakes, streams and rivers. The flow of water and harmful pollutants is impeded by the plants and eventually absorbed into the soil, where it is purified.

Urban residents can also contribute to biogas production by growing rooftop or vertical gardens in their homes. Waste from tomatoes, beans and other vegetables is an excellent source of biogas material. Residents will benefit from improved air quality and improved water quality as well by reducing runoff.

Proponents of biogas production from crops aren’t against using organic waste material for biogas production in addition to crop material. They believe crops offer another means of using more sustainable energy resources.

Biogas Production From Waste Materials Only

Opponents to growing crops for biogas argue the crops used for biogas production degrade soil quality, making it less efficient for growing crops for human consumption. They also argue the overall emissions from biogas production from crops will be higher compared to fossil fuels.

Growing crops can be a labor-intensive process. Land must be cleared, fertilized and then seeded. While crops are growing, pesticides and additional fertilizers may be used to promote crop growth and decrease losses from pests. Excess chemicals can run off of fields and degrade the water quality of streams, lakes and rivers and kill off marine life.

Once crops reach maturity, they must be harvested and processed to be used for biogas material. Biogas is less efficient compared to fossil fuels, which means it requires more material to yield the same amount of energy. Opponents argue that when the entire supply chain is evaluated, biogas from crops creates higher rates of emissions and is more harmful to the environment.

Agricultural residues, such as rice straw, are an important carbon source for anaerobic digestion

The supply chain for biogas from agricultural waste materials is more efficient compared to crop materials. Regardless of whether or not the organic waste is reused, it must be disposed of appropriately to prevent any detrimental environmental impacts. When the waste material is then used for biogas production, it creates an economical means of generating useful electricity from material which would otherwise be disposed of.

Rural farms which are further away from the electric grid can create their own sources of energy through biogas production from waste material as well. The cost of the energy will be less expensive and more eco-friendly as it doesn’t have the associated transportation costs.

Although perspectives differ on the type of materials which should be used for biogas production, both sides agree biogas offers an environmentally friendly and sustainable alternative to using fossil fuels.