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.

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As the name implies, carbon capture removes CO2 from emissions streams. Conventionally, the captured gas then goes to storage deep underground or helps oil companies extract more from their wells. However, these applications carry environmental concerns of their own. Thankfully, several alternate uses for captured CO2 have emerged that could be better long-term solutions.

Building Materials

One of the most promising uses for carbon capture is to store it in building materials. The world already produces a substantial amount of concrete, bricks and similar resources, providing ample storage space. Using it to hold — and thereby reduce — emissions from other sources could also lower the construction industry’s massive carbon footprint.

A recent study found that this method could remove more than 16 billion tons of CO2 from the atmosphere annually. While savings that high are unlikely, even a fraction of that total would be a substantial improvement.

This method works by holding CO2 in biomass or artificial rocks and using those resources to make bricks, concrete aggregates or bioplastics. Unlike conventional carbon capture strategies, it doesn’t require much specialized equipment or new workflows, so it has little impact on overall energy consumption. As a result, the benefits are more impactful.

Refrigeration

Another way to use captured carbon is to use it as a refrigerant. Refrigeration systems have used CO2 for years, as the gas has high thermal conductivity and is relatively easy to compress and manage. Sourcing this CO2 from existing industrial sources would provide the same benefits while making it greener.

Refrigeration units are contained systems, so they do not release gases into the atmosphere. Leaks are possible, but even in these scenarios, CO2 is preferable to older refrigerants, which are often hydrofluorocarbons. These compounds have global warming potentials in the thousands, making them several times more destructive than CO2.

Sourcing refrigerants from waste streams also reduces the need to produce CO2 through other means. As a result, overall process-related emissions may fall as this use case grows.

Efficient Heating Solutions

Captured greenhouse gases can heat as well as cool. Organizations can sequester CO2 by growing plant matter, which naturally absorbs the gas through photosynthesis. Then, they can turn this biomass into heating pellets to replace alternatives like propane.

While biomass pellets do release some greenhouse gases when they burn, they still have advantages over other emissions-producing heat sources. Firstly, they’re a renewable resource, so they reduce material extraction-related strain on the environment. Secondly, they cost just $19.05 per million British thermal units of energy, which is more than twice as cost-effective as propane.

Biomass pellets also burn hot for their size, so consumers can use less of them to achieve desired temperatures. Consequently, they can be a more efficient way to heat an area compared to fossil fuels.

Fertilizer

Other businesses have diverted their captured carbon toward fertilizer production. Making fertilizer with conventional means is an emissions-heavy process, emitting 12.5 million tons of CO2 annually. However, a different approach that directly uses CO2 instead of releasing it as a by-product is a promising alternative.

The process works by combining captured CO2 with nitrate and water to create urea, a key component in fertilizers. Doing this instead of making urea from energy-intensive ammonia-based methods would consume more CO2 than it emits. It would also reduce nitrate pollution, which is a key concern in wastewater management.

This application is so beneficial because it addresses multiple problems simultaneously. The world needs fertilizer to ensure food security, but it must also reduce CO2 emissions from industrial and fertilizer-producing processes. Creating urea from captured carbon helps in both areas.

Food and Beverage Products

Many food and beverage products also require CO2. As a result, carbon capture is an ideal way to provide this resource while mitigating harmful emissions elsewhere.

Beer, soda and other carbonated beverages need CO2 to create their trademark bubbles. The gas is also common in snack production, where injecting it into dough can create puffy, crispy textures in chips and corn-based foods. Traditionally, this CO2 comes from fossil fuel combustion, so sourcing it from other, existing processes can reduce overall emissions.

Beverages are already the world’s largest consumer of CO2, so the sector provides plenty of demand for carbon capture. While sequestered carbon must undergo purification for use in these products, the environmental benefits are worth the added complexity, given the market size.

Remaining Challenges in Carbon Capture and Usage

As these five use cases show, carbon capture and usage can benefit many industries and applications. However, it still faces some obstacles and downsides that stop it from being a perfect environmental solution.

The biggest problem with carbon capture is that it does not eliminate emissions. While it can mitigate the effects of CO2 emissions, some gases still enter the atmosphere, and it may dissuade some companies from switching to carbon-free energy sources. As a result, it can lead to greenwashing and hinder needed progress in sustainable energy, even if it is better than fossil fuel usage without carbon capture.

Uneven supply and demand may also pose an issue. The market for CO2 is generally smaller than generation levels, so even if factories capture all their carbon emissions, they may struggle to find buyers to sell it to. Finding new use cases, like using CO2 in construction materials, can help, but growth in these areas may still be slow, impacting the financial performance of carbon capture equipment.

High upfront costs are another barrier. Additional research and growth will make these expenses fall, but it can hinder carbon capture and usage in the short term.

Captured CO2 Can Serve Many Uses

No single use for captured carbon will be enough to make a meaningful difference. It will take a combination of all of these uses for the market to be rich enough to support large-scale improvements.

While challenges remain, the potential for carbon capture and storage across industries is hard to ignore. Such applications must happen alongside investments in carbon-free energy to achieve desired results, but the ability to mitigate current emissions in the meantime is promising.

The post Turning Carbon Into Cash: Innovative Ways to Utilize Captured CO₂ first appeared on BioEnergy Consult.

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.

Future Outlook

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.

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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 Eisenia foetida, 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.

Vermicompost Tea

A relatively new product from vermicomposting is vermicompost tea which is a liquid fertilizer 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.

Potential Market

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.

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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.

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