Biomass Energy – An Introduction

Biomass is the material derived from plants that use sunlight to grow which include plant and animal material such as wood from forests, material left over from agricultural and forestry processes, and organic industrial, human and animal wastes. Biomass comes from a variety of sources which include:

  • Wood from natural forests and woodlands
  • Forestry plantations
  • Forestry residues
  • Agricultural residues such as straw, stover, cane trash and green agricultural wastes
  • Agro-industrial wastes, such as sugarcane bagasse and rice husk
  • Animal wastes
  • Industrial wastes, such as black liquor from paper manufacturing
  • Sewage
  • Municipal solid wastes (MSW)
  • Food processing wastes

In nature, if biomass is left lying around on the ground it will break down over a long period of time, releasing carbon dioxide and its store of energy slowly. By burning biomass its store of energy is released quickly and often in a useful way. So converting biomass into useful energy imitates the natural processes but at a faster rate.

Biomass wastes can be transformed into clean energy and/or fuels by a variety of technologies, ranging from conventional combustion process to state-of-the art thermal depolymerization technology. 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.

 Biomass waste-to-energy conversion reduces greenhouse gas emissions in two ways.  Heat and electrical energy is generated which reduces the dependence on 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 wastes.

Solutions for Major Issues arising in Biomass Energy Projects

This article makes an attempt at collating some of the most prominent issues associated with biomass technologies and provides plausible solutions in order to seek further promotion of these technologies. The solutions provided below are based on author’s understanding and experience in this field.

  1. Large Project Costs: The project costs are to a great extent comparable to these technologies which actually justify the cause. Also, people tend to ignore the fact, that most of these plants, if run at maximum capacity could generate a Plant Load Factor (PLF) of 80% and above. This figure is about 2-3 times higher than what its counterparts wind and solar energy based plants could provide. This however, comes at a cost – higher operational costs.
  2. Technologies have lower efficiencies: The solution to this problem, calls for innovativeness in the employment of these technologies. To give an example, one of the paper mill owners in India, had a brilliant idea to utilize his industrial waste to generate power and recover the waste heat to produce steam for his boilers. The power generated was way more than he required for captive utilization. With the rest, he melts scrap metal in an arc and generates additional revenue by selling it. Although such solutions are not possible in each case, one needs to possess the acumen to look around and innovate – the best means to improve the productivity with regards to these technologies.
  3. Technologies still lack maturity: One needs to look beyond what is directly visible. There is a humongous scope of employment of these technologies for decentralized power generation. With regards to scale, few companies have already begun conceptualizing ultra-mega scale power plants based on biomass resources. Power developers and critics need to take a leaf out of these experiences.
  4. Lack of funding options: The most essential aspect of any biomass energy project is the resource assessment. Investors if approached with a reliable resource assessment report could help regain their interest in such projects. Moreover, the project developers also need to look into community based ownership models, which have proven to be a great success, especially in rural areas. The project developer needs to not only assess the resource availability but also its alternative utilization means. It has been observed that if a project is designed by considering only 10-12% of the actual biomass to be available for power generation, it sustains without any hurdles.
  5. Non-Transparent Trade markets: Most countries still lack a common platform to the buyers and sellers of biomass resources. As a result of this, their price varies from vendor to vendor even when considering the same feedstock. Entrepreneurs need to come forward and look forward to exploiting this opportunity, which could not only bridge the big missing link in the resource supply chain but also could transform into a multi-billion dollar opportunity.
  6. High Risks / Low pay-backs: Biomass energy plants are plagued by numerous uncertainties including fuel price escalation and unreliable resource supply to name just a few. Project owners should consider other opportunities to increase their profit margins. One of these could very well include tying up with the power exchanges as is the case in India, which could offer better prices for the power that is sold at peak hour slots. The developer may also consider the option of merchant sale to agencies which are either in need of a consistent power supply and are presently relying on expensive back-up means (oil/coal) or are looking forward to purchase “green power” to cater to their Corporate Social Responsibility (CSR) initiatives.
  7. Resource Price escalation: A study of some of the successful biomass energy plants globally would result in the conclusion of the inevitability of having own resource base to cater to the plant requirements. This could be through captive forestry or energy plantations at waste lands or fallow lands surrounding the plant site. Although, this could escalate the initial project costs, it would prove to be a great cushion to the plants operational costs in the longer run. In cases where it is not possible to go for such an alternative, one must seek case-specific procurement models, consider help from local NGOs, civic bodies etc. and go for long-term contracts with the resource providers.

Contributed by Mr. Setu Goyal (TERI University, New Delhi) who can be reached at setu.goyal@gmail.com

Salman Zafar’s Articles in ISER

Renewable energy in South Africa

Issue 4 2010 / 13 December 2010 / Salman Zafar, Renewable Energy Advisor

South Africa, the most industrialised country in Africa, has a population of approximately 50 million living on a land area of 1.2 million km2. The country has large reserves of coal and uranium, and small reserves of crude oil and natural gas. Coal provides 75% of the fossil fuel demand and accounts for 91% of electricity generation. South Africa is enjoying sustained GDP growth of approximately 5% per annum. (more…)

Renewable Energy in Jordan

Issue 3 2010 / 14 October 2010 / Salman Zafar, Renewable Energy Advisor

The Hashemite Kingdom of Jordan is heavily dependent on oil imports from neighbouring countries to meet its energy requirements. The huge cost associated with energy imports creates a financial burden on the national economy and Jordan had to spend almost 20% of its GDP on the purchase of energy in 2008. Electricity demand is growing rapidly, and the Jordanian Government has been seeking ways to attract foreign investment to fund additional capacity. In 2008, the demand for electricity in Jordan was 2,260 MW, which is expected to rise to 5,770 MW by 2020. Therefore, provision of reliable and clean energy supply will play a vital role in Jordan’s economic growth.

(more…)

Biomass energy resources in the MENA region

Issue 4 2009Past issues / 22 December 2009 / Salman Zafar, Renewable Energy Advisor

The high volatility in oil prices in the recent past and the resulting turbulence in energy markets has compelled many MENA countries, especially the non-oil producers, to look for alternate sources of energy, for both economic and environmental reasons. The significance of renewable energy has been increasing rapidly worldwide due to its potential to mitigate climate change, to foster sustainable development in poor communities and augment energy security and supply.

The major biomass producing MENA countries are Sudan, Egypt, Algeria, Yemen, Iraq, Syria and Jordan. Traditionally, biomass energy has been widely used in rural areas for domestic purposes in the MENA region. Since most of the region is arid/semi-arid, the biomass energy potential is mainly contributed by municipal solid wastes, agricultural residues and agro-industrial wastes.

(more…)

 

Major Issues in Biomass Energy Projects

The issues enumerated below are not geography-specific and are usually a matter of concern for most of the biomass energy projects:

  1. Large Project Costs: In India, a 1 MW gasification plant usually costs about USD 1-1.5 million. A combustion-based 1 MW plant would need a little more expenditure, to the tune of USD 1-2 million. An anaerobic digestion-based plant of the same capacity, on the other hand, could range anywhere upwards USD 3 million. Such high capital costs prove to be a big hurdle for any entrepreneur or clean-tech enthusiast to come forward and invest into these technologies.
  2. Low Conversion Efficiencies: In general, efficiencies of combustion-based systems are in the range of 20-25% and gasification-based systems are considered even poorer, with their efficiencies being in the range of a measly10-15%. The biomass resources themselves are low in energy density, and such poor system efficiencies could add a double blow to the entire project.
  3. Dearth of Mature Technologies: Poor efficiencies call for a larger quantum of resources needed to generate a unit amount of energy. Owing to this reason, investors and project developers find it hard to go for such plants on a larger scale. Moreover, the availability of only a few reliable technology and operation & maintenance service providers makes these technologies further undesirable. Gasification technology is still limited to scales lesser than 1 MW in most parts of the world. Combustion-based systems have although gone upwards of 1 MW, a lot many are now facing hurdles because of factors like unreliable resource chain, grid availability, and many others.
  4. Lack of Funding Options: Financing agencies usually give a tough time to biomass project developers as compared to what it takes to invest in other renewable energy technologies.
  5. Non-Transparent Trade Markets: Usually, the biomass energy resources are obtained through forests, farms, industries, animal farms etc. There is no standard pricing mechanism for such resources and these usually vary from vendor to vendor, even with the same resource in consideration.
  6. High Risks / Low Pay-Backs: Biomass energy projects are not much sought-after owing to high project risks which could entail from failed crops, natural disasters, local disturbances, etc.
  7. Resource Price Escalation: Unrealistic fuel price escalation too is a major cause of worry for the plant owners. Usually, an escalation of 3-5% is considered while carrying out the project’s financial modelling. However, it has been observed that in some cases, the rise has been as staggering as 15-20% per annum, forcing the plants to shut down.

Contributed by Setu Goyal, TERI University (New Delhi) who can be reached at setu.goyal@gmail.com)

 

 

Biomass Combined Heat and Power (CHP) Systems

Combined Heat and Power (CHP) is the simultaneous generation of multiple forms of useful energy (usually mechanical and thermal) in a single, integrated system. In conventional electricity generation systems, about 35% of the energy potential contained in the fuel is converted on average into electricity, whilst the rest is lost as waste heat. CHP systems use both electricity and heat and therefore can achieve an efficiency of up to 90%.

CHP systems consist of a number of individual components—prime mover (heat engine), generator, heat recovery, and electrical interconnection—configured into an integrated whole. Prime movers for CHP units include reciprocating engines, combustion or gas turbines, steam turbines, microturbines, and fuel cells.

A typical CHP system provides:

  • Distributed generation of electrical and/or mechanical power.
  • Waste-heat recovery for heating, cooling, or process applications.
  • Seamless system integration for a variety of technologies, thermal applications, and fuel types.

The success of any biomass-fuelled CHP project is heavily dependent on the availability of a suitable biomass feedstock freely available in urban and rural areas.

Rural Resources Urban Resources
Forest residues Urban wood waste
Wood wastes Municipal solid wastes
Crop residues Agro-industrial wastes
Energy crops Food processing residues
Animal manure Sewage

Technology Options

Reciprocating or internal combustion engines (ICEs) are among the most widely used prime movers to power small electricity generators. Advantages include large variations in the size range available, fast start-up, good efficiencies under partial load efficiency, reliability, and long life.

Steam turbines are the most commonly employed prime movers for large power outputs. Steam at lower pressure is extracted from the steam turbine and used directly or is converted to other forms of thermal energy. System efficiencies can vary between 15 and 35% depending on the steam parameters.

Co-firing of biomass with coal and other fossil fuels can provide a short-term, low-risk, low-cost option for producing renewable energy while simultaneously reducing the use of fossil fuels. Biomass can typically provide between 3 and 15 percent of the input energy into the power plant. Most forms of biomass are suitable for co-firing.

Steam engines are also proven technology but suited mainly for constant speed operation in industrial environments. Steam engines are available in different sizes ranging from a few kW to more than 1 MWe.

A gas turbine system requires landfill gas, biogas, or a biomass gasifier to produce the gas for the turbine. This biogas must be carefully filtered of particulate matter to avoid damaging the blades of the gas turbine.  

Stirling engines utilize any source of heat provided that it is of sufficiently high temperature. A wide variety of heat sources can be used but the Stirling engine is particularly well-suited to biomass fuels. Stirling engines are available in the 0.5 to 150 kWe range and a number of companies are working on its further development.

A micro-turbine recovers part of the exhaust heat for preheating the combustion air and hence increases overall efficiency to around 20-30%. Several competing manufacturers are developing units in the 25-250kWe range. Advantages of micro-turbines include compact and light weight design, a fairly wide size range due to modularity, and low noise levels.

Fuel cells are electrochemical devices in which hydrogen-rich fuel produces heat and power. Hydrogen can be produced from a wide range of renewable and non-renewable sources. A future high temperature fuel cell burning biomass might be able to achieve greater than 50% efficiency.

Conclusions

CHP technologies are well suited for Clean Development Mechanism (CDM) and sustainable development projects, because they are, in general, socio-economically attractive and technologically mature and reliable. In developing countries, cogeneration can easily be integrated in many industries, especially agriculture and food-processing, taking advantage of the biomass residues of the production process. This has the dual benefits of lowering fuel costs and solving waste disposal issues.

 

Anaerobic Digestion of Tannery Wastes

Anaerobic digestion is a favorable technological solution which degrades a substantial part of the organic matter contained in the sludge and tannery solid wastes, generating valuable biogas, contributing to alleviate the environmental problem, giving time to set-up more sustainable treatment and disposal routes. Digested solid waste is biologically stabilized and can be reused in agriculture.

The application of an anaerobic treatment for the break down of COD from tannery waste water is an attractive method to recover energy from tannery wastewater. Until now it was considered that the complexity of the waste water stream originating from tanneries in combination with the presence of chroming would result in the poisoning of the process in a high loaded anaerobic reactor.

When the locally available industrial wastewater treatment plant is not provided by anaerobic digester, a large scale digestion can be planned in regions accommodating a big cluster of tanneries, if there is enough waste to make the facility economically attractive. In this circumstance, an anaerobic co-digestion plant based on sludge and tanneries may be a recommendable option, which reduces the quantity of landfilled waste and recovers its energy potential. It can also incorporate any other domestic, industrial or agricultural wastes. Chrome-free digested tannery sludge also has a definite value as a fertilizer based on its nutrient content.

Hydrogen Sulphide Removal from Biogas

Depending on the use of the biogas, most trace components must be removed from the biogas. Water vapour can be particularly hazardous because it is highly corrosive when combined with acidic components such as hydrogen sulfide and to a lesser extent, carbon dioxide. The major contaminant in biogas is H2S. This component is both poisonous and corrosive, and causes significant damage to piping, equipment and instrumentation.

The concentration of various components of biogas has an impact on its ultimate end use. While boilers can withstand concentrations of H2S up to 1000 ppm, and relatively low pressures, internal combustion engines operate best when H2S is maintained below 100 ppm.

Most commonly used methods for hydrogen sulphide removal are internal to the digestion process:

  • air/oxygen dosing to digester biogas and
  • iron chloride dosing to digester slurry.

Biological desulphurization

Desulphurization of biogas can be performed by micro-organisms. Most of the sulphide oxidising micro-organisms belong to the family of Thiobacillus. For the microbiological oxidation of sulphide it is essential to add stoichiometric amounts of oxygen to the biogas. Depending on the concentration of hydrogen sulphide this corresponds to 2 to 6 % air in biogas.

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

Measures of safety have to be taken to avoid overdosing of air in case of pump failures. Biogas in air is explosive in the range of 6 to 12 %, depending on the methane content). In steel digesters without rust protection there is a small risk of corrosion at the gas/liquid interface.

Iron chloride dosing to digester slurry

Iron chloride can be fed directly to the digester slurry or to the feed substrate in a pre-storage tank. Iron chloride then reacts with produced hydrogen sulphide and form iron sulphide salt (particles). This method is extremely effective in reducing high hydrogen sulphide levels but less effective in attaining a low and stable level of hydrogen sulphide in the range of vehicle fuel demands. In this respect the method with iron chloride dosing to digester slurry can only be regarded as a partial removal process in order to avoid corrosion in the rest of the upgrading process equipment. The method need to be complemented with a final removal down to about 10 ppm.

The investment cost for such a removal process is limited since the only investment needed is a storage tank for iron chloride solution and a dosing pump. On the other hand the operational cost will be high due to the prime cost for iron chloride.

Organic Waste Management

Most of the organic waste generated in developing countries is dumped into the landfills. It is a sheer waste of such biodegradable waste capable of generating energy to be sent into the landfills. There it is not only responsible for large scale green house gas emissions, but also becomes a health hazard and creates terrestrial pollution.

There are numerous places which are the sources of large amounts of food waste and hence a proper food-waste management strategy needs to be devised for them to make sure that either they are disposed off in a safe manner or utilized efficiently. These places include hotels, restaurants, malls, residential societies, college/school/office canteens, religious mass cooking places, airline caterers, food and meat processing industries and vegetable markets which generate organic waste of considerable quantum on a daily basis.

The anaerobic digestion technology is highly apt in dealing with the chronic problem of organic waste management in urban societies. Although the technology is commercially viable in the longer run, the high initial capital cost is a major hurdle towards its proliferation. The onus is on the governments to create awareness and promote such technologies in a sustainable manner. At the same time, entrepreneurs, non-governmental organizations and environmental agencies should also take inspiration from successful food waste-to-energy projects in other countries and try to set up such facilities in Indian cities and towns.

Contributed by Mr. Setu Goyal, TERI University, New Delhi

Woody Biomass Utilization and Sustainability

Harvesting practices remove only a small portion of branches and tops leaving sufficient biomass to conserve organic matter and nutrients. Moreover, the ash obtained after combustion of biomass compensates for nutrient losses by fertilizing the soil periodically in natural forests as well as fields. The impact of forest biomass utilization on the ecology and biodiversity has been found to be insignificant. Infact, forest residues are environmentally beneficial because of their potential to replace fossil fuels as an energy source.

Plantation of energy crops on abandoned agricultural land will lead to an increase in species diversity. The creation of structurally and species diverse forests helps in reducing the impacts of insects, diseases and weeds. Similarly the artificial creation of diversity is essential when genetically modified or genetically identical species are being planted. Short-rotation crops give higher yields than forests so smaller tracts are needed to produce biomass which results in the reduction of area under intensive forest management. An intelligent approach in forest management will go a long way in the realization of sustainability goals.

Improvements in agricultural practices promises to increased biomass yields, reductions in cultivation costs, and improved environmental quality. Extensive research in the fields of plant genetics, analytical techniques, remote sensing and geographic information systems (GIS) will immensely help in increasing the energy potential of biomass feedstock.

Bioenergy systems offer significant possibilities for reducing greenhouse gas emissions due to their immense potential to replace fossil fuels in energy production. Biomass reduces emissions and enhances carbon sequestration since short-rotation crops or forests established on abandoned agricultural land accumulate carbon in the soil. Bioenergy usually provides an irreversible mitigation effect by reducing carbon dioxide at source, but it may emit more carbon per unit of energy than fossil fuels unless biomass fuels are produced unsustainably.

Biomass can play a major role in reducing the reliance on fossil fuels by making use of thermo-chemical conversion technologies. In addition, the increased utilization of biomass-based fuels will be instrumental in safeguarding the environment, generation of new job opportunities, sustainable development and health improvements in rural areas. The development of efficient biomass handling technology, improvement of agro-forestry systems and establishment of small and large-scale biomass-based power plants can play a major role in rural development. Biomass energy could also aid in modernizing the agricultural economy.

A large amount of energy is expended in the cultivation and processing of crops like sugarcane, coconut, and rice which can met by utilizing energy-rich residues for electricity production. The integration of biomass-fueled gasifiers in coal-fired power stations would be advantageous in terms of improved flexibility in response to fluctuations in biomass availability and lower investment costs. The growth of the bioenergy industry can also be achieved by laying more stress on green power marketing.

Socio-economic and Environmental Benefits of Waste-to-Energy

Waste-to-energy technologies hold the potential to create renewable energy from waste matter, including municipal solid waste, industrial waste, agricultural waste, and industrial byproducts. 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. Waste-to-energy systems can contribute substantially to GHG mitigation through both reductions of fossil carbon emissions and long-term storage of carbon in biomass wastes. Modern waste-to-energy systems options offer significant, cost-effective and perpetual opportunities for greenhouse gas emission reductions.

Additional benefits offered are employment creation in rural areas, reduction of a country’s dependency on imported energy carriers (and the related improvement of the balance of trade), better waste control, and potentially benign effects with regard to biodiversity, desertification, recreational value, etc. In summary, waste-to-energy can significantly contribute to sustainable development both in developed and less developed countries. Waste-to-energy is not only a solution to reduce the volume of waste that is and provide a supplemental energy source, but also yields a number of social benefits that cannot easily be quantified.

Refuse-Derived Fuel (RDF) from Municipal Solid Wastes

  • Solid waste is a growing problem in all countries, and a critical problem in almost all the cities of the developing world. Developed countries have in recent years reduced the environmental impact of solid waste through sanitary landfills and high-temperature incineration, as well as conserving natural resources and energy through increased recycling, but the volume of waste generated in developing countries is rising astronomically. Very few cities have adequate solid waste collection and disposal systems, and the accumulating waste threatens health, damages the environment, and detracts from the quality of life. Therefore, it is necessary to make use of all possible waste management technologies to arrest the degradation of environment and foster waste-to-energy technologies.
  • Urban areas of Asia produce about 760,000 tonnes of municipal solid waste (MSW) per day, or approximately 2.7 million m3 per day. In 2025, this figure will increase to 1.8 million tonnes of waste per day, or 5.2 million m3 per day. These estimates are conservative; the real values are probably more than double this amount. Most common method of disposing of wastes is to dump them in low-lying areas on the outskirts of towns which is very haphazard and unscientific. This has serious environmental impacts like water pollution, methane emissions, and soil degradation.
  • The advantages of the refuse-derived fuel plant type are focused mainly on the relatively higher energy content of the RDF fuel, which originates from the pre-combustion separation processing.
  • RDF plant employs mechanical processes to shred incoming MSW separating the non-combustibles in order to produce a high-energy fuel fraction and thus improved efficiency.
  • One of the most appealing aspects of RDF is that it can be employed as a supplementary fuel in conventional boilers. Furthermore, RDF’s energy content is around half that of UK’s industrial coals and nearly two thirds that of low grade US coal.
  • Pelletization scores over mass-burning, anaerobic digestion and composting because the pellets’ energy content is close to that of coal and can be substituted in local industry.
  • A number of widely employed industrial and utility-scale coal utilisation technologies have the potential to co-utilise RDF and coal, such as large-scale pulverised coal-fired power plant boilers, cement kilns, fluidised bed or stoker-fired boilers, coal gasification plant
  • Due to reduction in fuel particle size and reduction in non-combustible material, RDF fuels are more homogeneous and easier to burn than the MSW feedstock.
  • RDF has been successfully burned in a variety of stoker boilers and in suspension as a stand-alone fuel in bubbling and circulating fluidized bed combustion technology boilers. It needs lower excess air and hence works at better efficiency. Also, handling is easier since non-combustibles have been already removed.
  • In utilizing MSW through a pelletization process, additional tonnage of recyclables will be positively selected to take to that market, assisting the developing regions to work towards sustainable development goals, while positively selecting appropriate materials to mix with purchased high BTU materials in the production of the high BTU pellets, that can be used either to replace coal or coke in industrial processes.
  • RDF is a much more uniform fuel than MSW with regard to fuel particle sizing and heating value resulting in a more efficient combustion process. In addition, a majority of the non-combustible material is removed from the RDF before the fuel is fed into the boiler which reduces the size of both the fuel and ash handling systems. These fuel characteristics result in a RDF boiler system which is generally less expensive than a mass-burn system, thereby offsetting the cost of the RDF processing equipment.
  • It is much easier to transport and store fuel pellets to power plants or industries than raw MSW.
  • Advanced thermal technologies like gasification, pyrolysis, and depolymerization are unattractive to developing countries due to their prohibitive costs.
  • Technologies to control the release of air contaminants have improved substantially in the past decade and that, therefore, the releases from modern RDF plants are not high enough to have negative impacts on human health.
  • Air emissions from incinerators should be compared with air emissions from other methods of generating energy. When such comparisons are made, it is found that natural gas power plants are the cleanest way to generate energy but that emissions from waste incinerators are equivalent to or less than the emissions from a coal or oil power plant.
  • Incinerator proponents also assert that the health risks from exposure to the releases from a RDF power plant are substantially less than the risks from many other common activities.

Waste-to-Energy Conversion Pathways

The conversion of organic waste material to energy can proceed along three main pathways – thermochemical, biochemical and physicochemical. 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.

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 biological treatment method that can be used to recover both nutrients and energy contained in organic wastes such as animal manure. The process generates gases with a high content of methane (55–70 %) as well as biofertilizer. Alcohol fermentation is the transformation of organic fraction of waste to ethanol by a series of biochemical reactions using specialized microorganisms.

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. The waste is first dried to bring down the high moisture levels. Sand, grit, and other incombustible matter were then mechanically separated before the waste is compacted and converted into pellets. 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.