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Sep 22

Waste as a Renewable Energy Source

Posted in Environment and Sustainability | Future Technology | Waste to Energy

Waste Energy Source The enormous increase in the quantum and diversity of waste materials generated by human activity and their potentially harmful effects on the general environment and public health, have led to an increasing awareness about an urgent need to adopt scientific methods for safe disposal of wastes. While there is an obvious need to minimize the generation of wastes and to reuse and recycle them, the technologies for recovery of energy from wastes can play a vital role in mitigating the problems. Besides recovery of substantial energy, these technologies can lead to a substantial reduction in the overall waste quantities requiring final disposal, which can be better managed for safe disposal in a controlled manner while meeting the pollution control standards.


Waste generation rates are affected by socio-economic development, degree of industrialization, and climate. Generally, the greater the economic prosperity and the higher percentage of urban population, the greater the amount of solid waste produced. Reduction in the volume and mass of solid waste is a crucial issue especially in the light of limited availability of final disposal sites in many parts of the world. Although numerous waste and byproduct recovery processes have been introduced, anaerobic digestion has unique and integrative potential, simultaneously acting as a waste treatment and recovery process.

Waste-to-Energy Conversion Pathways

A host of technologies are available for realizing the potential of waste as an energy source, ranging from very simple systems for disposing of dry waste to more complex technologies capable of dealing with large amounts of industrial waste. There are three main pathways for conversion of organic waste material to energy – thermochemical, biochemical and physicochemical.

Thermochemical Conversion

Combustion of waste has been used for many years as a way of reducing waste volume and neutralizing many of the potentially harmful elements within it. Combustion can only be used to create an energy source when heat recovery is included. Heat recovered from the combustion process can then be used to either power turbines for electricity generation or to provide direct space and water heating. Some waste streams are also suitable for fueling a combined heat and power system, although quality and reliability of supply are important factors to consider.

Thermochemical conversion, characterized by higher temperature and conversion rates, is best suited for lower moisture feedstock and is generally less selective for products. Thermochemical conversion includes incineration, pyrolysis and gasification. The incineration 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.

Biochemical Conversion

The bio-chemical conversion processes, which include anaerobic digestion and fermentation, are preferred for wastes having high percentage of organic biodegradable (putrescible) matter and high moisture content. Anaerobic digestion is a reliable technology for the treatment of wet, organic waste. Organic waste from various sources is composted in highly controlled, oxygen-free conditions circumstances resulting in the production of biogas which can be used to produce both electricity and heat. Anaerobic digestion also results in a dry residue called digestate which can be used as a soil conditioner.

Alcohol fermentation is the transformation of organic fraction of biomass to ethanol by a series of biochemical reactions using specialized microorganisms. It finds good deal of application in the transformation of woody biomass into cellulosic ethanol.

Physico-chemical Conversion

The physico-chemical technology 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. 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.

Factors affecting Energy Recovery from waste

The two main factors which determine the potential of recovery of energy from wastes are the quantity and quality (physico-chemical characteristics) of the waste. Some of the important physico-chemical parameters requiring consideration include:

  • Size of constituents
  • Density
  • Moisture content
  • Volatile solids / Organic matter
  • Fixed carbon
  • Total inerts
  • Calorific value

Often, an analysis of waste to determine the proportion of carbon, hydrogen, oxygen, nitrogen and sulfur (ultimate analysis) is done to make mass balance calculations, for both thermochemical and biochemical processes. In case of anaerobic digestion, the parameters C/N ratio (a measure of nutrient concentration available for bacterial growth) and toxicity (representing the presence of hazardous materials which inhibit bacterial growth), also require consideration.

Significance of Waste-to- Energy (WTE) Plants

While some still confuse modern waste-to-energy plants with incinerators of the past, the environmental performance of the industry is beyond reproach. Studies have shown that communities that employ waste-to-energy technology have higher recycling rates than communities that do not utilize waste-to-energy. The recovery of ferrous and non-ferrous metals from waste-to-energy plants for recycling is strong and growing each year. In addition, numerous studies have determined that waste-to-energy plants actually reduce the amount of greenhouse gases that enter the atmosphere.

Nowadays, waste-to-energy plants based on combustion technologies are highly efficient power plants that utilize municipal solid waste as their fuel rather than coal, oil or natural gas. Far better than expending energy to explore, recover, process and transport the fuel from some distant source, waste-to-energy plants find value in what others consider garbage. Waste-to-energy plants recover the thermal energy contained in the trash in highly efficient boilers that generate steam that can then be sold directly to industrial customers, or used on-site to drive turbines for electricity production. WTE plants are highly efficient in harnessing the untapped energy potential of organic waste by converting the biodegradable fraction of the waste into high calorific value gases like methane. The digested portion of the waste is highly rich in nutrients and is widely used as biofertilizer in many parts of the world.

Waste-to-Energy around the World

To an even greater extent than in the United States, waste-to-energy has thrived in Europe and Asia as the preeminent method of waste disposal. Lauding waste-to-energy for its ability to reduce the volume of waste in an environmentally-friendly manner, generate valuable energy, and reduce greenhouse gas emissions, European nations rely on waste-to-energy as the preferred method of waste disposal. In fact, the European Union has issued a legally binding requirement for its member States to limit the landfilling of biodegradable waste.

According to the Confederation of European Waste-to-Energy Plants (CEWEP), Europe currently treats 50 million ton of wastes at waste-to-energy plants each year, generating an amount of energy that can supply electricity for 27 million people or heat for 13 million people. Upcoming changes to EU legislation will have a profound impact on how much further the technology will help achieve environmental protection goals.

A Glance at Feedstock for Waste-to-Energy Plants

Agricultural Residues

Large quantities of crop residues are produced annually worldwide, and are vastly underutilised. The most common agricultural residue is the rice husk, which makes up 25% of rice by mass. Other residues include sugar cane fibre (known as bagasse), coconut husks and shells, groundnut shells, cereal straw etc. Current farming practice is usually to plough these residues back into the soil, or they are burnt, left to decompose, or grazed by cattle. A number of agricultural and biomass studies, however, have concluded that it may be appropriate to remove and utilise a portion of crop residue for energy production, providing large volumes of low cost material. These residues could be processed into liquid fuels or combusted/gasified to produce electricity and heat.

Animal Waste

There are a wide range of animal wastes that can be used as sources of biomass energy. The most common sources are animal and poultry manures. In the past this waste was recovered and sold as a fertilizer or simply spread onto agricultural land, but the introduction of tighter environmental controls on odour and water pollution means that some form of waste management is now required, which provides further incentives for waste-to-energy conversion. The most attractive method of converting these waste materials to useful form is anaerobic digestion which gives biogas that can be used as a fuel for internal combustion engines, to generate electricity from small gas turbines, burnt directly for cooking, or for space and water heating. Food processing and abattoir wastes are also a potential anaerobic digestion feedstock.

Sugar Industry Wastes

The sugar cane industry produces large volumes of bagasse each year. Bagasse is potentially a major source of biomass energy as it can be used as boiler feedstock to generate steam for process heat and electricity production. Most sugar cane mills utilise bagasse to produce electricity for their own needs but some sugar mills are able to export substantial amount of electricity to the grid.

Forestry Residues

Forestry residues are generated by operations such as thinning of plantations, clearing for logging roads, extracting stem-wood for pulp and timber, and natural attrition. Wood processing also generates significant volumes of residues usually in the form of sawdust, off-cuts, bark and woodchip rejects. This waste material is often not utilized and often left to rot on site. However it can be collected and used in a biomass gasifier to produce hot gases for generating steam.

Industrial Wastes

The food industry produces a large number of residues and by-products that can be used as biomass energy sources. These waste materials are generated from all sectors of the food industry with everything from meat production to confectionery producing waste that can be utilised as an energy source. Solid wastes include peelings and scraps from fruit and vegetables, food that does not meet quality control standards, pulp and fibre from sugar and starch extraction, filter sludges and coffee grounds. These wastes are usually disposed of in landfill dumps.

Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruit and vegetables, pre-cooking meats, poultry and fish, cleaning and processing operations as well as wine making. These waste waters contain sugars, starches and other dissolved and solid organic matter. The potential exists for these industrial wastes to be anaerobically digested to produce biogas, or fermented to produce ethanol, and several commercial examples of waste-to-energy conversion already exist.

Municipal Solid Waste (MSW)

Millions of tonnes of household waste are collected each year with the vast majority disposed of in landfill dumps. The biomass resource in MSW comprises the putrescibles, paper and plastic and averages 80% of the total MSW collected. Municipal solid waste can be converted into energy by direct combustion, or by natural anaerobic digestion in the landfill. At the landfill sites the gas produced by the natural decomposition of MSW (approximately 50% methane and 50% carbon dioxide) is collected from the stored material and scrubbed and cleaned before feeding into internal combustion engines or gas turbines to generate heat and power. The organic fraction of MSW can be anaerobically stabilized in a high-rate digester to obtain biogas for electricity or steam generation.

Sewage

Sewage is a source of biomass energy that is very similar to the other animal wastes. Energy can be extracted from sewage using anaerobic digestion to produce biogas. The sewage sludge that remains can be incinerated or undergo pyrolysis to produce more biogas.

Black Liquor

Pulp and Paper Industry is considered to be one of the highly polluting industries and consumes large amount of energy and water in various unit operations. The wastewater discharged by this industry is highly heterogeneous as it contains compounds from wood or other raw materials, processed chemicals as well as compound formed during processing. Black liquor can be judiciously utilized for production of biogas using anaerobic UASB technology.

Conclusions

Waste-to-energy plants offer two important benefits of environmentally safe waste management and disposal, as well as the generation of clean electric power. Waste-to-energy facilities produce clean, renewable energy through thermochemical, biochemical and physicochemical methods. The growing use of waste-to-energy as a method to dispose off solid and liquid wastes and generate power has greatly reduced environmental impacts of municipal solid waste management, including emissions of greenhouse gases. Waste-to-energy conversion reduces greenhouse gas emissions in two ways. Electricity is generated which reduces the dependence on electrical production from power plants based on fossil fuels. The greenhouse gas emissions are significantly reduced by preventing methane emissions from landfills. Moreover, waste-to-energy plants are highly efficient in harnessing the untapped sources of energy from a variety of wastes.

An environmentally sound and techno-economically viable methodology to treat biodegradable waste is highly crucial for the sustainability of modern societies. A transition from conventional energy systems to one based on renewable resources is necessary to meet the ever-increasing demand for energy and to address environmental concerns.

Written by Salman Zafar, Renewable Energy Expert.

  • Derek

    This information is priceless! I can’t wait to contribute to the cause. Thank you so much for this information!

  • Salman

    Thanks a lot for your comment, Derek. I am glad you liked it.

  • lynnji izzle

    I’m in debate and we’re doing a case about alternative energy sources so hopefully this goes through! 🙂

  • Salman

    Thats great to know!! Hope the article was helpful to you in more ways than one.

  • Ravi Soparkar

    Dear Mr. Salman Zafar,

    I am impressed with your article on ‘Waste to Energy’ on ‘alternative-energy-news’ website.

    I am Ravi Soparkar from Pune India.

    I am working on decentralized samll capacity renewable enrgy projects for benefit of rural population in India.

    I request you for any tech material on user friendly process on renewable energy which may be useful for my work.

    Dear Mr salman Zafar, I am Ravi Soparkar from Pune India. I am impressed with your article on ‘Waste to Energy’. I am working on decentralized small renewable energy systems for benefit of rural population in India. May request you for info. on small scale user fiendly process for waste to energy generation. I would also like to be on your mailing list.Do mail me your mail id, so I can write you in detail.
    Kindly let me know anything I can do for you from India.

    Regards
    Ravi Soparkar Pune India +91 9325014999

  • Salman

    Dear Mr. Soparkar
    I am glad to hear that you found my article quite informative. You would be surprised to know that I am also from India.I will definitely tell you if I need any help from Pune.
    I appreciate your interest in renewable energy for rural areas. Keeping in view the raw materials available in rural India, biomass gasification, anaerobic digestion, pelletization and CHP are the best technology options. I will give you more details about these processes in subsequent mails if you are interested.
    Please let me know whether you are working for some company or independently.
    You may write back to me at salman.alg@gmail.com
    Have a nice day!
    Salman

  • Roar Olsen

    Dear Mr. Salman,

    Thanks for a very good article. I am representing a company, delivering small scale as well as large scale systems in the Middle east, located in Dubai. Do not hesitate to contact me if further information regarding our technology, prices and structures can be achieved.

    Best regards,
    Olsen

  • Roar Olsen

    All,
    My email address is roar.olsen[AT]gmail.com

    Best regards,
    Olsen

  • Salman

    Dear Mr. Olsen
    Thanks for writing. I have replied through an email.
    Best wishes
    Salman

  • Blake

    Waste to energy can also be done at a smaller scale even consumer level. Biomass gasification is a good technology which is being used at a commercial or village level scale in places like India. There are free plans or really good videos and information on gasifiers and gasification at http://www.Victorygasworks.com

  • Gutenberg

    Are there any commercial companies that can establish a waste to energy plant on a smaller scale for a local rubbish dump?

  • Chukwudi

    Dear Mr Salman Zafar,

    I am very impressed with your article on “Waste As A Renewable Energy Source”.

    My name is Chukwudi Nduba. I am from Nigeria.
    I am actually working on a project/proposal for “a way to generate electricity using waste as its feedstock” because of the present situation of electricity in our country. I am looking forward to constructing a good proposal of the above mentioned project that will generate electricity for a state (for instance,Lagos state) here in Nigeria.

    I humbly request you for any technical material on a best processing path for the conversion of waste to energy/electricity that will be cost effective, low capital and operating costs, which may be useful for my project/proposal. Also, what kind of waste will be the feedstock for the plant or can all the listed kinds of waste mentioned in your article be used as the feedstock for the plant.

    I would also like to be on your mailing list. You may write back to me at chudynduba2002[AT]yahoo.com. Please, do mail me your mail id, so I can write you in detail.
    Kindly let me know anything I can do for you from Nigeria.
    Have a nice day!

    Chukwudi Nduba

  • Vaibhav Chaturvedi

    Dear Mr.Salman Zafar,

    I congratulate you for this very informative article.
    I am an MBA student in India, and have keen interest in waste-to-energy implementation at small scale. I would like to read more of this and help you in your cause.
    Regards,
    Vaibhav

  • http://www.bioenergyconsult.com Salman

    Dear Vaibhaw
    Glad to hear from you.I am also based in India. You may write to me at salman.alg@gmail.com and I would be happy to help in your endeavors.
    Best wishes
    Salman
    salman.alg@gmail.com

  • dr.areej

    Dear Mr. Salman Zafar,

    Thank you for this informative article. I am an ophthalmologist by profession, an Indian based in Jordan, middle-east. Me and my husband will be glad to receive such articles from you as we wish to have such plants in Jordan too.

    Regards,
    Ahid and Areej

  • Salman

    Dear Dr. Areej,

    Thanks so much. I am glad to know that you liked my article. I would be glad to help in the promotion of sustainable energy systems in Jordan. You may write to me at salman.alg[AT]gmail.com so that I can share my other articles with you.

    Best wishes,
    Salman

  • Ngoni

    Dear Mr. Salman
    Your article is very informative and i have really liked it. Do you have any documentation on how to convert solid waste to energy. I am in Zimbabwe and currently developing a project proposal on that so i am not very sure on other things that might be needed to make this successful. In Zimbabwe we have had problems with sewerage and solid waste resulting in cholera issues so i hope with your informative articles i can work out something. Will appreciate if you email me on ngoni@nedico.co.zw Thanks

  • Suchindra

    Dear Mr Salman,

    I thank you very for the wonderful & informative article, I would like to know more about Municipal waste to energy . Kindly keep me posted.

    One thing I would like to know is , Will this kind of project work in India, & does any advanced country successfully implemented the project & operational, If yes
    please share the companies details . We are planning to start in Bangalore. Also i would like to know the cost involved in setting up 100 tons plant as pilot project.

  • http://www.enext-energy.com Jeroen van der Kooij

    I am representing a Belgian company, Enext Environmental Protection and Renewable Energy bvba. You can find them on: http://www.enext-energy.com

    Enext has developed a patented process in which from Municipal Solid Waste (MSW) a solid fuel pellet is made with handling and burning characteristics (LHV app. 23 MJ/kg) similar as high bituminous coal. In The Netherlands this process and resulting product was granted a certificate and is labelled as Coal Comparable Fuel (CCF). This is a very interesting concept since this solid fuel pellet can be used in modern coal fired electricity plants unlike older existing technologies which produce Refuse Derived Fuels (RDF).

    Composition of these solid fuel pellets is a mixture of dry organic waste (like paper, card-box, wood, cellulose, rubber, fabrics, etc) and plastics. Depending on the type of MSW, the biogenic part of these pellets could be around 60%, and thus by avoiding the use of coal an important amount of CO2 emission reduction is achieved. Besides the Carbon content of the pellets is about 20 % less compared to coal giving a direct lower C02 emission. No need to built expensive Waste Incinerators, but existing modern coal fired electricity plants can be used, in which these solid fuel pellets can be burned instead of coal.

    If anyone has any questions, send me an email on: jmvdkooij [AT] gmail.com

    Greetz Jeroen

  • anne Sahondo

    Dear Mr Salman

    This information is very enlightening, i am a chemical engineering student in Zimbabwe and would like to find out more about other energy sources, as we are facing many difficulties, it would be good to know what else we have that we can use to help our economy.

  • Salman

    Dear Anne,

    Thanks for your kind words regarding my article. I appreciate your interest in exploring alternate energy sources. You may write directly to me at salman.alg [AT] gmail.com so that I can send you relevant material.

    Thanks again
    Salman

  • jazz

    is it possible to make a miniature energy converter in ur own home?

  • lala

    So what happens with the dioxin and furan when you use thermo-chemical conversion?

  • Surendra G

    Well written Salman Sir,
    Sir I need a help regarding “Convertion of Agri Waste into Energy”,This topic is choosen for seminar which is to be given by me.This has to be related with Thermodynamics,Fluid Mechanics,Production technology and Mechanics of Materials.plz help me Sir to co-relate.

  • Renter204

    Food, Fiber Fuel. Its far better to find productive uses of waste than to burn them,

  • Pat

    Jeroen.

    Can you contact me as soon as possible as i’m very interested in the above. i know its a long time ago but thats not a problem.

    regards

    Pat


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