Category Archives: Biogas

The Need for Speciality Membrane Covers

  By | | ,
3 Comments

Biogas containment is a critical safety component. When handling biogas, you must ensure the storage area is properly covered to prevent contamination. Membrane covers are a reliable solution. They are made using polymers, such as polyvinyl, polyethylene and polypropylene. A biogas cover is also suitable in water treatment plants, where it’s necessary to prevent odour and gas from escaping. Waste-to-energy projects leverage uniquely designed membranes to collect biogas and use it as fuel. Whether you are storing liquids or gases, Biogas Membrane provides several benefits that make it a valuable investment, particularly for large-scale projects.

finding the right membrane cover for biogas projects

Improved Safety

Areas that handle chemicals and toxic gases have strict safety standards. Membrane covers are some of them. The linings are resistant to chemicals, meaning no hazardous compounds can get in or out of the storage section. In a case where a membrane covers water in an open area, rainwater can’t permeate the material. It gathers on top of the membrane, ensuring the covered water is safe to use. The cover also keeps out waste from avian life, dust, debris and other contaminants.

Biogas storage membranes are strong and tear-proof. Since they can resist punctures, you don’t have to worry about contamination, even when people walk on top of them. Additionally, they safeguard against UV rays, which can compromise the composition of various gases and liquids.

Low Maintenance

After installing a geomembrane, you won’t have to worry about servicing it regularly. Membrane covers for water silos, biogas digestors and water treatment plants are flexible, yet strong. Regardless if it’s a single or double membrane, expect a robust material that cleans easily. The covers are built to withstand extreme weather conditions. So, no matter how hot it cold it gets, the membrane provides excellent temperature control. Due to the minimal supervision and maintenance required, the membrane liners reduce costs.

Compared to the cost of acquiring and maintaining full storage tanks and closed cisterns, membranes are economical. The installation is uncomplicated, as well. Although some covers require peripherals, like inner support struts, the setup is not hard and doesn’t disrupt operations.

Diverse Applications

Perhaps the biggest advantage of membrane covers is their versatility. Through customisation, covers can serve different uses. They are suitable for collecting biogas to convert into green energy, capping landfills after they reach their capacities and controlling vapours and fumes in wastewater treatment plants. The specific requirements determine the ideal membrane. Therefore, you must understand particular storage needs before settling on a biogas liner.

biogas-crop

Finding the Right Membrane Covers

Geomembranes come in different materials. When picking a liner, learn how suitable a certain material is for your storage. For instance, the aggressive conditions of a biogas digestor demand a heavy-duty polypropylene cover that can take the punishment.

Consider the thickness because it dictates its durability. You want the cover to be as thick as possible without affecting flexibility or functionality.

The most important part of selecting a membrane lining is ensuring it matches the project. It should satisfy the product’s chemical composition and the necessary technical specifications.

Whether your project involves wastewater, clean water or biogas, you need reliable, durable and effective coverage solutions. With geomembranes or biogas membranes, you guarantee safety and quality.

Biogas in Agriculture Sector in India: Key Challenges

  By | | , ,
3 Comments

Although the conversion of agriculture waste – cattle dung and crop residues –  to biogas and digested slurry is an established and well-proven technology in India, 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 sector in India can restore agriculture productivity and strengthen revenue to make it attractive.

How Can You Produce Your Own Biogas?

  By | | , ,
4 Comments

The idea of biogas is anything but new. People have been experimenting with making biogas for many generations. Biogas is made by converting organic waste into energy. It’s a huge win for the environment because it utilizes what is otherwise considered waste, but it’s a big win for pocketbooks too.

Organic waste includes the byproducts of human food production (think potato peels, carrot peels, the tops of turnips, etc) but it also includes manure. Any manure is fair game, think about cows, pigs, chickens, rabbits, goats — virtually any farm animal produces mounds of this each day.

This manure produces very high levels of methane gas which is horrible for the environment. By using this manure to create biogas, we remove the danger of creating heat-trapping gases in our atmosphere that raises the temperature of the entire planet. Using it for biogas production can also help to reduce global warming.

How Do We Produce Biogas?

Biogas is produced from the breakdown of organic waste in an environment that is void of oxygen. We call this environment anaerobic and the process is process is called anaerobic digestion. Two products are created from this process. One is digestate. Digestate can be used for fertilizer and even as livestock bedding.  The other product is biogas. Biogas can be used for heating, electricity production and as a clean vehicle fuel.

It’s essentially like composting all of the materials, but in an environment without oxygen and in the temperature range of around 35 to 40 degrees Celsius and pH of around 7. This is optimal to produce biogas. Biogas can be converted into an upgraded form of gas by removal of carbon dioxide that can be used like natural gas. It can be used as-is as an engine fuel. It can be used as fuel in a vehicle, sometimes without modification.

How Can You Produce Your Own Biogas?

Just imagine being on your own off-grid property, running a hundred head of cattle, growing your own food and canning it. You’ve got meat covered, your food is stocked and you are prepared for just about anything. But what about fuel? Imagine what a game-changer it could be if you were able to produce your own fuel from the waste from your cattle and your garden scraps or food residuals! You can!

The Biogas Digester makes it possible, and fairly easy, for you to start producing your own biogas. Buy a ready-made biodigester for around $700-$1000 dollars and start producing your own biogas to meet your fuel requirements. They are containers designed to do the work for you and help you collect the fruits of your composted and digested waste.

Build your own! China has approximately 30 million Biodigesters in use in its rural areas. Rural Chinese areas are far removed from cities that have gas stations. It simply isn’t accessible as it is in the US. Many rural people have learned to make their own biodigesters to fill their fuel needs.

offgrid-biodigester

You need a tank that is sealed with an access hole on one side for adding organic waste. You have another access to an outlet. That is where you collect the liquid run-off that can be used for fuel.

The bottom of the main unit is the digestion chamber. From that is an outlet where the digestate can be collected and used as fertilizer. The main chamber typically has a domed top to allow for the room that will be necessary for the expansion of the gases formed inside. By being sealed, the unit creates that all-important anaerobic environment.

Useful Links

A tank that demonstrates the size and simplicity of a tank that can be purchased and used in the backyard.

https://www.etsy.com/listing/705458580/portable-home-biogas?gpla=1&gao=1&

This is a very in-depth article with directions for creating your own biodigester from Science Direct – https://www.sciencedirect.com/topics/engineering/biogas-digester

Biogas from Crop Wastes vs Energy Crops: European Perspectives

  By | | , ,
8 Comments

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.

biogas-crop

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 energy 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.

Energy 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 Agricultural Waste

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

In Europe, the supply chain for biogas from agricultural waste 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 crop residues are 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 agriculture wastes 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.

Biomethane – The Green Gas

  By | | , , ,
1 Comment

Biomethane, also known as the green gas, is a well-known and well-proven source of clean energy, and is witnessing increasing demand worldwide, especially in European countries, as it is one of the most cost-effective and eco-friendly replacement for natural gas and diesel.

Advantages of Biomethane

The key advantage of biomethane is that it is less corrosive than biogas which makes it more flexible in its application than raw biogas. It can be injected directly into the existing natural gas grid leading to energy-efficient and cost-effective transport, besides allowing natural gas grid operators to persuade consumers to make a smooth transition to a renewable source of natural gas.

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.

The injected biomethane can be used at any ratio with natural gas as vehicle fuel. In many EU countries, the access to the gas grid is guaranteed for all biogas suppliers.

A major advantage of using natural 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 biogas to reach new customers.

Storage of Biomethane

Biomethane can be converted either into liquefied biomethane (LBM) or compressed biomethane (CBM) in order to facilitate its long-term storage and transportation. LBM can be transported relatively easily and can be dispensed through 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.

Applications of Biomethane

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, as a transportation fuel, is most suitable for vehicles having engines that are based on natural gas (CNG or LNG). Once biogas is cleaned and upgraded to biomethane, it is virtually the same as natural gas.

Because biomethane has a lower energy density than NG, due to the high CO2 content, in some circumstances, changes to natural gas-based vehicle’s fuel injection system are required to use the biomethane effectively.

Description of a Biogas Power Plant

  By | | , , ,
14 Comments

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. The key components of a modern biogas power (or anaerobic digestion) plant include: manure collection, anaerobic digester, effluent treatment, biogas storage, and biogas use/electricity generating equipment.

anaerobic_digestion_plant

Working of a Biogas Plant

The fresh organic waste 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 digester 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 Cleanup

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.

Utilization of Biogas

Biogas is dried and vented into a CHP unit to a generator to produce electricity and heat. The size of the CHP system depends on the amount of biogas produced daily.

Treatment of Digestate

The digested substrate is passed through screw presses for dewatering and then subjected to solar drying and conditioning to give high-quality organic fertilizer.  The press water is treated in an effluent treatment plant based on activated sludge process which consists of an aeration tank and a secondary clarifier. The treated wastewater is recycled to meet in-house plant requirements.

Monitoring of Environmental Parameters

A chemical laboratory is necessary to continuously monitor important environmental parameters such as BOD, COD, VFA, pH, ammonia, C:N ratio at different locations for efficient and proper functioning of the process.

Control System

The continuous monitoring of the biogas plant is achieved by using a remote control system such as Supervisory Control and Data Acquisition (SCADA) system. This remote system facilitates immediate feedback and adjustment, which can result in energy savings.

Biogas from Kitchen Waste at Akshaya Patra Foundation

  By | | , ,
8 Comments

The Akshaya Patra Foundation, a not-for-profit organization, is focused on addressing two of the most important challenges in India – hunger and education. Established in year 2000, the Foundation began its work by providing quality mid-day meals to 1500 children in 5 schools in Bangalore with the understanding that the meal would attract children to schools, after which it would be easier to retain them and focus on their holistic development. 14 years later, the Foundation has expanded its footprint to cover over 1.4 million children in 10 states and 24 locations across India.

Akshaya-Patra-Kitchen-BioGas

The Foundation has centralised, automated kitchens that can cook close to 6,000 kilos of rice, 4.5 to 5 tonnes of vegetables and 6,000 litres of sambar, in only 4 hours. In order to make sustainable use of organic waste generated in their kitchens, Akshaya Patra Foundation has set up anaerobic digestion plants to produce biogas which is then used as a cooking fuel. The primary equipment used in the biogas plant includes size reduction equipment, feed preparation tank for hydrolysis of waste stream, anaerobic digester, H2S scrubber and biogas holder.

Working Principle

Vegetable peels, rejects and cooked food waste are shredded and soaked with cooked rice water (also known as ganji) in a feed preparation tank for preparation of homogeneous slurry and fermentative intermediates. The hydrolyzed products are then utilized by the microbial culture, anaerobically in the next stage. This pre-digestion step enables faster and better digestion of organics, making our process highly efficient.

The hydrolyzed organic slurry is fed to the anaerobic digester, exclusively for the high rate biomethanation of organic substrates like food waste. The digester is equipped with slurry distribution mechanism for uniform distribution of slurry over the bacterial culture.

Optimum solids are retained in the digester to maintain the required food-to-microorganism ratio in the digester with the help of a unique baffle arrangement. Mechanical slurry mixing and gas mixing provisions are also included in the AD design to felicitate maximum degradation of organic material for efficient biogas production.

After trapping moisture and scrubbing off hydrogen sulphide from the biogas, it is collected in a gas-holder and a pressurized gas tank. This biogas is piped to the kitchen to be used as a cooking fuel, replacing LPG.

Basic Design Data and Performance Projections

Waste handling capacity 1 ton per day cooked and uncooked food waste with 1 ton per day ganji water

Input Parameters                      

Amount of solid organic waste 1000 Kg/day
Amount of organic wastewater ~ 1000 liters/day ganji (cooked rice water)

Biogas Production

Biogas production ~ 120 – 135 m3/day

Output Parameters

Equivalent LPG to replace 50 – 55 Kg/day (> 2.5 commercial LPG cylinders)
Fertilizer (digested leachate) ~ 1500 – 2000 liters/day

Major Benefits

Modern biogas installations are providing Akshaya Patra, an ideal platform for managing organic waste on a daily basis. The major benefits are:

  • Solid waste disposal at the commercial kitchen site avoiding waste management costs
  • Immediate waste processing overcomes problems of flies, mosquitos etc.
  • Avoiding instances when the municipality does not pick up waste, creating nuisance, smell, spillage etc.
  • Anaerobic digestion of Ganji water instead of directly treating it in ETP, therefore reducing organic load on the ETPs and also contributing to additional biogas production.

The decentralized model of biogas based waste-to-energy plants at Akshaya Patra kitchens ensure waste destruction at source and also reduce the cost incurred by municipalities on waste collection and disposal.

akshayapatra-kitchen

An on-site system, converting food and vegetable waste into green energy is improving our operations and profits by delivering the heat needed to replace cooking LPG while supplying a rich liquid fertilizer as a by-product.  Replacement of fossil fuel with LPG highlights our organization’s commitment towards sustainable development and environment protection.

The typical ROI of a plug and play system (without considering waste disposal costs, subsidies and tax benifts) is around three years.

Future Plans

Our future strategy for kitchen-based biogas plant revolves around two major points:

  • Utilization of surplus biogas – After consumption of biogas for cooking purposes, Akshaya Patra will consider utilizing surplus biogas for other thermal applications. Additional biogas may be used to heat water before boiler operations, thereby reducing our briquette consumption.
  • Digested slurry to be used as a fertilizer – the digested slurry from biogas plant is a good soil amendment for landscaping purposes and we plan to use it in order to reduce the consumption of water for irrigation as well as consumption of chemical fertilizers.

Biomass Energy in Vietnam

  By | | , ,
5 Comments

Vietnam is one of the few countries having a low level of energy consumption in the developing world with an estimated amount of 210 kg of oil equivalent per capita/year. A significant portion of the Vietnamese population does not have access to electricity. Vietnam is facing the difficult challenge of maintaining this growth in a sustainable manner, with no or minimal adverse impacts on society and the environment.

Being an agricultural country, Vietnam has very good biomass energy potential. Agricultural wastes are most abundant in the Mekong Delta region with approximately 50% of the amount of the whole country and Red River Delta with 15%. Major biomass resources includes rice husk from paddy milling stations, bagasse from sugar factories, coffee husk from coffee processing plants in the Central Highlands and wood chip from wood processing industries. Vietnam has set a target of having a combined capacity of 500 MW of biomass power by 2020, which is raised to 2,000 MW in 2030.

Rice husk and bagasse are the biomass resources with the greatest economic potential, estimated at 50 MW and 150 MW respectively. Biomass fuels sources that can also be developed include forest wood, rubber wood, logging residues, saw mill residues, sugar cane residues, bagasse, coffee husk and coconut residues.

Currently biomass is generally treated as a non-commercial energy source, and collected and used locally. Nearly 40 bagasse-based biomass power plants have been developed with a total designed capacity of 150 MW but they are still unable to connect with the national grid due to current low power prices. Five cogeneration systems selling extra electricity to national grid at average price of 4 US cents/kWh.

Biogas potential is approximately 10 billion m3/year, which can be collected from landfills, animal excrements, agricultural residues, industrial wastewater etc. The biogas potential in the country is large due to livestock population of more than 30 million, mostly pigs, cattle, and water buffalo. Although most livestock dung already is used in feeding fish and fertilizing fields and gardens, there is potential for higher-value utilization through biogas production.

It is estimated that more than 25,000 household biogas digesters with 1 to 50 m3, have been installed in rural areas. The Dutch-funded Biogas Program operated by SNV Vietnam constructed some 18,000 biogas facilities in 12 provinces between 2003 and 2005, with a second phase (2007-2010) target of 150,000 biogas tanks in both rural and semi-urban settings.

Municipal solid waste is also a good biomass resource as the amount of solid waste generated in Vietnam has been increasing steadily over the last few decades. In 1996, the average amount of waste produced per year was 5.9 million tons per annum which rose to 28 million tons per in 2008 and expected to reach 44 million tons per year by 2015.

Biological Desulphurization of Biogas

  By | | , ,
7 Comments

The most valuable component of biogas is methane (CH4) which typically makes up 60%, with the balance being carbon dioxide (CO2) and small percentages of other gases. However, biogas also contain significant amount of hydrogen sulfide (H2S) gas which needs to be stripped off due to its highly corrosive nature. Hydrogen sulfide is oxidized into sulfur dioxide which dissolves as sulfuric acid. Sulphuric acid, even in trace amounts, can make a solution extremely acidic. Extremely acidic electrolytes dissolve metals rapidly and speed up the corrosion process.

The corrosive nature of H2S has the potential to destroy expensive biogas processing equipment. Even if there is no oxygen present, biogas can corrode metal. Hydrogen sulphide can become its own electrolyte and absorb directly onto the metal to form corrosion. If the hydrogen sulphide concentration is very low, the corrosion will be slow but will still occur due to the presence of carbon dioxide.

Biogas_Cleanup-H2S

The obvious solution is the use of a biogas cleanup process whereby contaminants in the raw biogas stream are absorbed or scrubbed. Desulphurization of biogas can be performed by biological as well as chemical methods. Biological treatment of hydrogen sulphide typically involves passing the biogas through biologically active media. These treatments may include open bed soil filters, biofilters, fixed film bioscrubbers, suspended growth bioscrubbers and fluidized bed bioreactors.

Biological Desulphurization

The simplest method of desulphurization is the addition of oxygen or air directly into the digester or in a storage tank serving at the same time as gas holder. Thiobacilli are ubiquitous and thus systems do not require inoculation. They grow on the surface of the digestate, which offers the necessary micro-aerophilic surface and at the same time the necessary nutrients. They form yellow clusters of sulphur. Depending on the temperature, the reaction time, the amount and place of the air added the hydrogen sulphide concentration can be reduced by 95 % to less than 50 ppm.

Most of the sulphide oxidising micro-organisms belong to the family of Thiobacillus. For the microbiological oxidation of sulphide it is essential to add stoichiometric amounts of oxygen to the biogas. Depending on the concentration of hydrogen sulphide this corresponds to 2 to 6 % air in biogas. Measures of safety have to be taken to avoid overdosing of air in case of pump failures.

Biofiltration

Biofiltration is one of the most promising clean technologies for reducing emissions of malodorous gases and other pollutants into the atmosphere. In a biofiltration system, the gas stream is passed through a packed bed on which pollutant-degrading microbes are immobilized as biofilm. A biological filter combines water scrubbing and biological desulfurization.

Biogas and the separated digestate meet in a counter-current flow in a filter bed. The biogas is mixed with 4% to 6% air before entry into the filter bed. The filter media offer the required surface area for scrubbing, as well as for the attachment of the desulphurizing microorganisms. Microorganisms in the biofilm convert the absorbed H2S into elemental sulphur by metabolic activity. Oxygen is the key parameter that controls the level of oxidation.

The capital costs for biological treatment of biogas are moderate and operational costs are low. This technology is widely available worldwide. However, it may be noted that the biological system is capable to remove even very high amounts of hydrogen sulphide from the biogas but its adaptability to fluctuating hydrogen sulphide contents is not yet proven.

Role of Biogas in Rural Development

  By | | , ,
4 Comments

Anaerobic digestion has proven to be a beneficial technology in various spheres for rural development. Biogas produced is a green replacement of unprocessed fuels (like fuel wood, dung cakes, crop residues). It is a cost effective replacement for dung cakes and conventional domestic fuels like LPG or kerosene. Biogas technology has the potential to meet the energy requirements in rural areas, and also counter the effects of reckless burning of biomass resources.

Biogas has the potential to rejuvenate India’s agricultural sector

An additional benefit is that the quantity of digested slurry is the same as that of the feedstock fed in a biogas plant. This slurry can be dried and sold as high quality compost. The nitrogen-rich compost indirectly reduces the costs associated with use of fertilizers. It enriches the soil, improves its porosity, buffering capacity and ion exchange capacity and prevents nutrient depletion thus improving the crop quality. This means increased income for the farmer.

Further, being relatively-clean cooking fuel, biogas reduces the health risks associated with conventional chulhas. Thinking regionally, decreased residue burning brings down the seasonal high pollutant levels in air, ensuring a better environmental quality. Anaerobic digestion thus proves to be more efficient in utilization of crop residues. The social benefits associated with biomethanation, along with its capacity to generate income for the rural households make it a viable alternative for conventional methods.

The Way Forward

The federal and stage governments needs to be more proactive in providing easy access to these technologies to the poor farmers. The policies and support of the government are decisive in persuading the farmers to adopt such technologies and to make a transition from wasteful traditional approaches to efficient resource utilization. The farmers are largely unaware of the possible ways in which farm and cattle wastes could be efficiently utilised. The government agencies and NGOs are major stakeholders in creating awareness in this respect.

Moreover, many farmers find it difficult to bear the construction and operational costs of setting up the digester. This again requires the government to introduce incentives (like soft loans) and subsidies to enhance the approachability of the technology and thus increase its market diffusion.