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.
Working of a Biogas Plant
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.
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.
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.
Qatar has one of the highest per capita waste generation rates worldwide. In 2012, Qatar generated 8,000 tons of solid waste daily (excluding construction and demolition waste which amounts to 20,000 tons additional waste per day). This number is predicted to reach 19,000 tons/day in 2032, with an annual growth rate of roughly 4.2%.
Most of these wastes end up in landfills – in 2012, more than 90% of Qatar’s solid waste were sent to landfills although the government is intensifying its efforts to reduce this amount. This percentage is extremely high compared to many industrialized countries in Europe and Asia (e.g. Austria, Denmark, Netherlands and Japan) where less than 10% of solid waste are disposed of in landfills. These countries have high recycling rates, have invested in technologies that convert waste into energy, and apply composting process to their organic waste, especially food wastes. In some of these nations, as much as 40% of their wastes are composted.
Composting in Qatar
Currently, composting in Qatar is mainly done at the Domestic Solid Waste Management Centre (DSWMC) in Mesaieed, which houses the largest composting facility in the country and one of the largest in the world. The waste that enters the plant initially goes through anaerobic digestion, which produces biogas that can power the facility’s gas engine and generators, followed by aerobic treatment which yields the final product.
Two types of compost are generated: Grade A (compost that comes from green waste, such as yard/park trimmings, leftovers from kitchen or catering services, and wastes from markets) and Grade B (compost produced from MSW). The plant started its operation in 2011 and when run at full capacity is able to process 750 tons of waste and produce 52 tons of Grade A compost, 377 tons of Grade B compost, liquid fertilizer which is composed of 51 tons of Grade A compost and 204 tons of Grade B compost, and 129 tons of biogas.
This is a significant and commendable development in Qatar’s implementation of its solid waste management plan, which is to reduce, reuse, recycle and recover from waste, and to avoid disposing in landfills as much as possible. However, the large influx of workers to Qatar in the coming years as the country prepares to host the World Cup in 2022 is expected to substantially increase solid waste generation and apart from its investments in facilities like the composting plant and in DSWMC in general, the government may have to tap into the efforts of organizations and communities to implement its waste management strategy.
Thankfully, several organizations recognize the importance of composting in waste management and are raising awareness on its benefits. Qatar Green Building Council (QGBC) has been actively promoting composting through its Solid Waste Interest Group. Last year, they were one of the implementers of the Baytna project, the first Passivhaus experiment in the country.
This project entails the construction of an energy-efficient villa and a comparative study will be performed as to how the carbon footprint of this structure would compare to a conventional villa. The occupants of the Passivhaus villa will also be made to implement a sustainable waste management system which includes composting of food waste and garden waste, which is meant to lower greenhouse gas emissions compared to landfilling.
Qatar Foundation is also currently developing an integrated waste management system for the entire Education City and the Food Services group is pushing for composting to be included as a method to treat food and other organic waste. And many may not know this but composting can be and has been done by individuals in their own backyard and can even be done indoors with the right equipment.
Katrin Scholz-Barth, previous president of SustainableQatar, a volunteer-based organization that fosters sustainable culture through awareness, skills and knowledge, is an advocate of composting and has some great resources on how to start and maintain your own composting bin as she has been doing it herself. A simple internet search will also reveal that producing compost at home is a relatively simple process that can be achieved with minimal tools. At present, very few families in Qatar are producing their own compost and Scholz-Barth believes there is much room for improvement.
As part of its solid waste management plan as stated in the National Development Strategy for 2011-2016, Qatar aims to maintain domestic waste generation at 1.6 kg per capita per day. This will probably involve encouraging greater recycling and reuse efforts and the reduction of waste from its source. It would also be worthwhile to include programs that will promote and boost composting efforts among institutions, organizations and individuals, encouraging them with the fact that apart from its capability of significant waste diversion from landfills, composting can also be an attractive source of income.
Note: The article is being republished with the permission of our collaborative partner EcoMENA. The original article can be viewed at this link.
Vermicomposting is a type of composting in which certain species of earthworms are used to enhance the process of organic waste conversion and produce a better end-product. It is a mesophilic process utilizing microorganisms and earthworms. Earthworms feeds the organic waste materials and passes it through their digestive system and gives out in a granular form (cocoons) which is known as vermicompost.
Simply speaking, vermicompost is earthworm excrement, called castings, which can improve biological, chemical, and physical properties of the soil. The chemical secretions in the earthworm’s digestive tract help break down soil and organic matter, so the castings contain more nutrients that are immediately available to plants.
Production of Vermicompost
A wide range of agricultural residues, such as straw, husk, leaves, stalks, weeds etc can be converted into vermicompost. Other potential feedstock for vermicompost production are livestock wastes, poultry litter, dairy wastes, food processing wastes, organic fraction of MSW, bagasse, digestate from biogas plants etc.
Earthworms consume organic wastes and reduce the volume by 40–60 percent. Each earthworm weighs about 0.5 to 0.6 gram, eats waste equivalent to its body weight and produces cast equivalent to about 50 percent of the waste it consumes in a day. The moisture content of castings ranges between 32 and 66 percent and the pH is around 7. The level of nutrients in compost depends upon the source of the raw material and the species of earthworm.
Types of Earthworms
There are nearly 3600 types of earthworms which are divided into burrowing and non-burrowing types. Red earthworm species, like Eiseniafoetida,and are most efficient in compost making. The non-burrowing earthworms eat 10 percent soil and 90 percent organic waste materials; these convert the organic waste into vermicompost faster than the burrowing earthworms.
They can tolerate temperatures ranging from 0 to 40°C but the regeneration capacity is more at 25 to 30°C and 40–45 percent moisture level in the pile. The burrowing types of earthworms come onto the soil surface only at night. These make holes in the soil up to a depth of 3.5 m and produce 5.6 kg casts by ingesting 90 percent soil and 10 percent organic waste.
Types of Vermicomposting
The types of vermicomposting depend upon the amount of production and composting structures. Small-scale vermicomposting is done to meet personal requirements and farmers/gardeners can harvest 5-10 tons of vermicompost annually.
On the other hand, large-scale vermicomposting is done at commercial scale by recycling large quantities of organic waste in modern facilities with the production of more than hundreds of tons annually.
Benefits of Vermicompost
The worm castings contain higher percentage of both macro and micronutrients than the garden compost. Apart from other nutrients, a fine worm cast is rich in NPK which are in readily available form and are released within a month of application. Vermicompost enhances plant growth, suppresses disease in plants, increases porosity and microbial activity in soil, and improves water retention and aeration.
Vermicompost also benefits the environment by reducing the need for chemical fertilizers and decreasing the amount of waste going to landfills. Vermicompost production is trending up worldwide and it is finding increasing use especially in Western countries, Asia-Pacific and Southeast Asia.
A relatively new product from vermicomposting is vermicompost tea which is a liquid produced by extracting organic matter, microorganisms, and nutrients from vermicompost. Unlike vermicompost and compost, this tea may be applied directly to plant foliage, reportedly to enhance disease suppression. Vermicompost tea also may be applied to the soil as a supplement between compost applications to increase biological activity.
Vermicompost may be sold in bulk or bagged with a variety of compost and soil blends. Markets include home improvement centers, nurseries, landscape contractors, greenhouses, garden supply stores, grocery chains, flower shops, discount houses, indoor gardens, and the general public.
Slaughterhouse 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.
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.
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.
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.
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