Waste-to-energy is the use of combustion and biological technologies to recover energy from urban wastes. There are three major waste to energy conversion routes – thermochemical, biochemical and physico-chemical. Thermochemical conversion, characterized by higher temperature and conversion rates, is best suited for lower moisture feedstock and is generally less selective for products. On the other hand, biochemical technologies are more suitable for wet wastes which are rich in organic matter.
Thermochemical Conversion of Waste
The three principal methods of thermochemical conversion of waste are combustion in excess air, gasification in reduced air, and pyrolysis in the absence of air. The most common technique for producing both heat and electrical energy from household wastes is direct combustion.
Combined heat and power (CHP) or cogeneration systems, ranging from small-scale technology to large grid-connected facilities, provide significantly higher efficiencies than systems that only generate electricity.
Combustion technology is the controlled combustion of waste with the recovery of heat to produce steam which in turn produces power through steam turbines. Pyrolysis and gasification represent refined thermal treatment methods as alternatives to incineration and are characterized by the transformation of the waste into product gas as energy carrier for later combustion in, for example, a boiler or a gas engine. Plasma gasification, which takes place at extremely high temperature, is also hogging limelight nowadays.
Biochemical Conversion of Waste
Biochemical processes, like anaerobic digestion, can also produce clean energy in the form of biogas which can be converted to power and heat using a gas engine. Anaerobic digestion is the natural biological process which stabilizes organic waste in the absence of air and transforms it into biofertilizer and biogas.
Anaerobic digestion is a reliable technology for the treatment of wet, organic waste. Organic waste from various sources is biochemically degraded in highly controlled, oxygen-free conditions circumstances resulting in the production of biogas which can be used to produce both electricity and heat.
In addition, a variety of fuels can be produced from waste resources including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The resource base for biofuel production is composed of a wide variety of forestry and agricultural resources, industrial processing residues, and municipal solid and urban wood residues. Globally, biofuels are most commonly used to power vehicles, heat homes, and for cooking.
Physico-chemical Conversion of Waste
The physico-chemical conversion of waste involves various processes to improve physical and chemical properties of solid waste. The combustible fraction of the waste is converted into high-energy fuel pellets which may be used in steam generation.
The waste is first dried to bring down the high moisture levels. Sand, grit, and other incombustible matter are then mechanically separated before the waste is compacted and converted into fuel pellets or RDF.
Fuel pellets have several distinct advantages over coal and wood because it is cleaner, free from incombustibles, has lower ash and moisture contents, is of uniform size, cost-effective, and eco-friendly.
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.
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.
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
Amount of solid organic waste
Amount of organic wastewater
~ 1000 liters/day ganji (cooked rice water)
~ 120 – 135 m3/day
Equivalent LPG to replace
50 – 55 Kg/day (> 2.5 commercial LPG cylinders)
Fertilizer (digested leachate)
~ 1500 – 2000 liters/day
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 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.
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.
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.
Meeting an ever increasing demand for food/feed/energy and managing waste have become two of the major global challenges. The global world population is estimated to increase from 7.3 billion in 2015 to 9.7 billion in 2050. Approximately one third of the global food produced for human composition is wasted. Currently, approximately 1.3 billion metric tons of waste are disposed with significant environmental impact as far as greenhouse gases and economic footprints and the current waste management practices are not costly sustainable.
Increase in Global Energy Demand
Global energy demand is estimated to increase from 524 Quadrillion btu in 2010, to 820 Quadrillion btu by 2040 (a 56% increase). Similarly, global demand of food and animal products are projected to increase by 70-100% and 50-70%, respectively, by 2050. To cope up with the demand for animal products, a substantial increase in nutritious animal feed is needed.
On one hand, the production of conventional feedstuff such as soybean meal and fish meal is reported as the major contributor to land occupation, ocean depletion, climate change, water and energy consumption. Moreover, such conventional animal feedstuff are not only limited in supply but also are becoming more expensive over the years. Additionally, there is an already strong and increasing competition for resources such as food, feed and biofuel production.
Need for alternative non-conventional source of food, feed, and fuel
Thus there is a pressing need for identifying and exploring the potential of alternative non-conventional source of food, feed, and fuel, which are economically viable, environmentally friendly, and socially acceptable.
By 2030 the Bio-based Economy is expected to have grown significantly. A pillar of this is biorefining, the sustainable processing of biomass into a spectrum of marketable products and energy. To satisfy this demand biorefineries need to be better integrated, flexible and operating more substantially. This means that a major yield, more efficient use of nutrients and water and greater pest and disease resistance should be achieve.
Zena Fly: A Startup Worth Watching
In this context an Italian-based start-up, Zena Fly, designed an innovative process for the future integrated biorefinery by mimicking nature’s ability. In fact, Zena Fly utilizes the natural insect life cycle to manage large quantity of organic waste produced in urban and industrial context, in order to generate sustainable and valuable by-products. The project of three young entrepreneurs foresees a combined bio-refinery where waste is turned into high-quality by-products by the anaerobic insect digestion.
The basic concept is to convert waste into high-valuable products utilizing the black soldier flies (H. illucens), a now globally distributed insect. With a modern technique, the typical insect life cycle of these insects can be utilized in order to manage urban and industrial waste. The voracious larvae can reduce by more than 40-70% (based on the nature of the substrate-waste) the substrate where reared (waste) within 12-14 days.
From the anaerobic waste digestion, large quantity of fine protein meal for feed composition (more than 50-60% in protein), fat, fertilizing oil and other by-products of great interest such as chitin, and high-quality biofuel are then extracted.
Since the adult fly do not feed, and do not fly around for feeding, these animals are exceptionally valuable from a sanitary perspective (larvae has been demonstrate to reduce/eliminate E.coli and Salmonella).
Zena Fly business model foresees to replicate their integrated biorefineries next to any waste management companies or industrial production areas where large quantity of waste need to be reduced and transformed. This is a win/win operation, where the waste management cost would be cut in half and the process will generate appealing opportunities for investments in a market where the increasing demand is already way higher than the products availability.
Zena Fly is now seeking for the right partner-investor in order to scale up quickly. For more information, please visit www.zena-fly.com or email us on email@example.com
The impact of human activities on the environment is rapidly changing. One such activity gaining much attention is waste disposal. A lot of waste products go to landfills despite constituting a reasonable fraction of organic matter, such as paper materials, food wastes, and pet droppings.
The new preferred way to dispose of organic waste is composting. Composting refers to the process through which materials biodegrade. It is a means by which organic waste can be safely recycled. Composting can be effectively done with compost systems.
Take note that this process of waste disposal is still in its early stages, especially when adopted in homes. Still, here are 7 benefits of composting:
1. Improved Soil Quality
Composted materials become humus, a known nutrient-rich constituent of soil. The newly formed humus replenishes soil nutrients and improves water retention in loose soil. Thus, soil quality considerably improves as a result of composting.
Composted materials are also rich in fungi and bacteria. These microbes prevent insect infestation and suppress weed growth. With these nutrient draining agents out of the way, your soil quality dramatically improves, too.
2. Saves Time and Money
It is a waste of time and money when a yard being cultivated does not experience normal growth, nor does it yield the expected harvest. Fortunately, you can save money and time in the long term with composting practices. This is possible because of the compost’s ability to fight insect infestation, weed growth, and to replenish the soil of lost nutrients.
The three nutrients that are sought in chemical fertilizers, Nitrogen, Phosphorus, and Potassium (NPK), are made available by humus. This directly saves you the cost of purchasing fertilizers. Without the presence of compost, farmers need to spend a lot of money to buy pesticides and weed killers.
3. Environment Friendliness
Composting is an environmentally friendly option compared to landfills. Landfills are currently the most common destination for organic waste. In landfills, organic waste cannot decay properly, so they generate a specific greenhouse gas called methane.
Methane is known to cause harmful effects on the environment – similar to that of carbon dioxide but even more dangerous. The more organic waste ends up in landfills, the more methane gas that is produced.
Composting solves this problem in a whiff by reducing the amount of methane produced while organic matter decays. Composting allows carbon to be retained in the soil, which lowers the carbon footprint caused by decaying matter.
The ability of compost to bypass the incineration of yard waste also makes it a preferred option for organic waste in yards.
4. Improved Human Health
There are several ways for composting to indirectly enhance human health. The reduction of greenhouse gas emissions, as mentioned above, by composting is not only good for the environment but also for people – a reduction of greenhouse gas means a healthier environment to live in.
Organic food production credited to composting also improves human health in significant ways. It reduces the number of chemicals from fertilizers and pesticides that end up in meals, translating to healthier humans.
5. Higher Agricultural Yield
A higher yield of crops is very important to farmers. Through its ability to increase soil quality, composting achieves a higher return in agricultural products. More plant yield accounts for more plants to be sold, which also means more money to be made.
Soil quality also translates to the quality of the food which is produced. Food produced from high-quality, organic soil is free from all toxins from chemical fertilizers and pesticides.
6. Reduced Erosion
Erosion is harmful to the soil because it makes soil matter and nutrients to be washed away. This is compounded by the fact that soils are loose.
Compost averts erosion by remedying the existing structure of the soil. It further prevents erosion by:
Aiding water infiltration in the soil structure.
Aiding water retention, thereby slowing runoff and loss of soil matter.
Allows for quicker vegetation growth.
7. Aids Biodiversity
Microorganisms present in the soil, such as bacteria, fungi, and protozoa, will cause the decay of organic material. Their presence is important because they aid soil aeration. Soil aeration on its own accelerates the composting process, making nutrients available in their usable state as quickly as possible.
Other organisms that are present in composted soil include worms and beneficial insects. All these aids the process of plant growth.
Composting is a sustainable and environmentally friendly way to dispose of organic waste. It is particularly important even now as the world struggles with creating solutions to waste disposal.
Composting results in better soil quality. It is also a process that saves them time and money of farmers. Humans can benefit from composting through improved health. There is a higher yield of farm produce as a result of composting. Erosion is significantly reduced, and biodiversity is achieved in the soil through composting.
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.
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.
A tank that demonstrates the size and simplicity of a tank that can be purchased and used in the backyard.
Waste management systems can be divided into a number of steps from collection, storage, transportation, processing, treatment, recycling and final disposal. Integrated solid waste management refers to this entire process and aims to maximise resource use efficiency, with minimal amounts ending up in final disposal sites. During Practical Action’s recent work in the South Asia region, we have gained particular experiences in terms of firstly waste collection, storage and transportation; and secondly waste processing in particular of organic waste.
Collection and Transportation
In many cities, waste collection services fail to reach all areas of the town or city. People are left to manage their own waste, which they do by burning and burying it, or dumping on open spaces. Sometimes large bins or skips are provided but they may be irregularly emptied, and also overflow when the contents is picked over by waste pickers and animals.
In Bangladesh, in order to help increase the overall capacity for collecting household waste, Practical Action has promoted a door-to-door collection service run by local NGOs. Residents pay a service charge in addition to their municipal rates, but in return they receive a regular service, leading to a cleaner neighbourhood.
In Faridpur, the local NGO, WORD, with technical backstopping from Practical Action serves more than 5,000 customers with waste collection. There are three main types of customer, non-slum households, slum households and institutions. Slum-based households are charged the lowest tariffs (minimum BDT 10) while the institutional rate is highest (minimum BDT 150).
The numbers of slum households is small because the alternative option of localized composting (with a barrel system) was widely taken up. This is easier than collection through vans and is useful for slum people as they can use the compost later. Waste collectors use small rickshaw vans for the collection service. Recently we have also introduced small small rickshaw vans and small motorized versions for the collection service.
The waste is taken to a composting facility where it is sorted and the organic portion is separated for composting, and in some cases for generating biogas. In 2008, WORD started the waste collection business with only 525 customers. In the last 8 years, the number has increased more than tenfold (5,100 customer per month) making the solid waste management a viable business. It has not only contributed to a better living environment, but also generated green and dignified jobs for 21 waste workers.
The municipal conservancy department continues to play a regulatory and coordinating role through the Waste Management Steering Committee. This meets regularly to discuss any emerging issues and review the progress of door-to-door collection services. The conservancy department continues to manage the sweeping of streets and drains, and collection of waste from some areas of the town, from vegetable markets and slaughter houses. The only recycling and reuse of organic waste is done by WORD, as all municipal waste for now continues to be disposed at an open dumping site where no further treatment, sorting or reuse takes place.
In Nepal, Practical Action has facilitated organic waste management under a public-private partnership model. For example, in Butwal Municipality, a private firm, Marry Gold Concern, collects and manages wastes from 400 households with a monthly service fee of NPR 50 (GBP 0.33) in an area called Ramnagar. The company employs three operators for collecting and managing waste from low income communities. A compost plant has been set up which processes up to 10 metric tonnes of organic waste and generate 5 metric tonnes of compost per month. In addition, recyclable waste, mainly plastic, is sold to scrap dealers, creating another source of income.
Recycling and Disposal by Forming Associations and Enterprises
In Bangladesh, collection services have been organised through existing local NGOs. In Nepal, Practical Action has instead helped to form different groups of Informal Waste Workers (IWW) such as street waste pickers, waste segregators, pheriya (dry waste pickers), scrap owners and door to door collectors.
We have worked intensively with IWW from five municipalities of Kathmandu Valley. We have facilitated the establishment of a IWWs association called Samyukta Safai Jagaran (SASAJA), and the first waste workers’ cooperative with the same name. These organisations have distributed identity cards to members to increase their recognition as an ‘official’ part of the waste management system. We provided basic safety equipment to 5,622 IWWs, including rain boots/shoes, gloves, masks, raincoats, windcheaters with trouser and wrapper, aprons, cap etc. to minimize health risks.
Basic safety equipment is essential to minimize health risks to informal recycling sector.
Following capacity building and skill enhancement training from Practical Action, many of the IWW group members have established waste-based enterprises. For example, plastic tearing (PET bottle and carton crushing or pressing) for recycling and reuse; paper recycling and mechanical composting of organic waste. This approach has been scaled up in other municipalities in Chitwan and Rupadehi districts reaching around 350 IWWs there.
Reducing Waste through Home Composting
In Nepal and Sri Lanka, and in some slum communities in Bangladesh, we have promoted barrel composting of organic waste. This has the dual benefit of producing compost locally which can be used for home gardening, and reducing the amount of waste that needs to be collected and disposed of elsewhere.
It can reduce the amount of organic waste coming in to the waste collection stream by about 20-30%. It requires community involvement in waste management system as well as frequent monitoring and troubleshooting. This process ensures source segregation of waste, a necessary condition for proper implementation of the 3R system (reuse, reduce and recycle).
Practical Action has distributed more than 2,000 compost bins in Sri Lanka. Especially in Galle, Kurunegala and Akkaraipattu cities where we have distributed about 1,500 home composting bins from 2006 to 2016. More than 65% of the bins are being regularly used.
Our experience shows that once a locality is provided with home composting, the volume of organic waste into the municipal collection system is reduced around 20-30%. However, this varies greatly by locations. If the local authority strictly monitors the compost bin usage and provides troubleshooting support, waste reduction can reach up to 30%.
Both Kurunegala and Galle municipal councils have upscaled the distribution of bins city-wide with the support of national government funding. This technology was taken up by the private sector and other municipal councils. It has been used widely in the country as a solution for reducing organic waste coming in to the waste collection system. For example, Kandy municipal council has adopted the technology with strict restriction on organic waste collection in the municipality collection system.
The Provincial Agriculture department in Kurunegala and the Coconut cultivation board in Akkaraipattu are both promoting organic agriculture with the usage of composting and are using Practical Action’s work as examples for expansion. The central government has provided seeds and fertilizer to city dwellers, including the urban poor, to promote home gardening.
This has been further expanded by Kurunegala municipal council which has distributed potted plants. Some of the vertical gardening structures promoted by Practical Action are now included in urban gardening models of the Western Province Urban Agriculture unit.
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