Energy Recovery from Waste: Meaning, and Examples Explained
Energy recovery from waste, also referred to as as waste-to-energy, is the act and process of extracting energy from waste, either through destruction or conversion, or both.
It is linked to sustainability concepts like soil conservation, water conservation, air quality conservation, carbon capture and storage, circular economy and renewable energy development.
This article discusses energy recovery from waste, according to the outline below;
-An Overview of How We Generate Energy from Waste
-Products of Energy Recovery from Waste
-Examples of Energy Recovery from Waste
An Overview of How We Generate Energy from Waste
We generate energy from waste by subjecting waste materials to thermal, chemical and biochemical processes which transform the waste into various energy products.
The above sentence summarizes the concept of energy recovery from waste, and describes how we can transform waste to energy, in order to recover energy from waste.
It also indicates that energy recovery from waste is a form of recycling and waste management, which is aimed at improving the quality of the ecosystem by conserving natural resources [4].
Aside energy products like biofuel and heat, other useful products can be derived when waste is subjected to energy-transformation processes.
The three main categories of such processes are discussed below;
1). Thermal Processes for Energy Recovery from Waste
Thermal processes for energy recovery from waste, include all methods or processes that are driven primarily by heat, and which involve significant changes in temperature.
The effect of heat on waste materials leads to mainly physical changes, although chemical changes can also occur.
All thermal waste-to-energy processes involve a reduction in mass and volume, of the substrate [3].
Energy recovery from thermal treatment processes usually involves cogeneration, water heating and the use of steam turbines for electricity generation.
Examples of thermal energy recovery processes include pyrolysis and incineration [6].
2). Chemical Processes
Chemical processes of energy recovery from waste include all processes involving the use of chemical reagents, and/or the occurrence of chemical changes in the substrate.
They may involve temperature changes or heat application as well. In such cases, these processes are referred to as ‘thermochemical’ processes.
Examples of chemical (and thermochemical) methods of energy recovery from waste are catalytic fermentation and gasification. Such processes commonly produce energy in the form of liquid and gaseous biofuel.
3). Biochemical Processes for Energy Recovery from Waste
Biochemical energy recovery mainly involves biological organisms and processes like microbial biodegradation which cause chemical changes in a substrate. Anaerobic digestion is a typical example [1].
Products of Energy Recovery from Waste
The two main products of energy recovery from waste are heat and fuel.
1). Heat as a Product of Energy Recovery
Heat is derived either directly as a product of thermal treatment, or as recovered waste heat.
Energy recovery involving waste heat is called ‘heat recovery’. The goal of heat recovery is to boost both energy conservation and energy efficiency, by minimizing energy losses [5].
Heat production within the context of waste management and energy recovery, can occur under a broad range of conditions and scenarios, including cogeneration, waste combustion, thermochemical conversion, and energy management systems.
The recovered heat can be used to generate electricity, among other purposes.
2). Fuel as a Product of Energy Recovery
Energy recovery processes involving waste materials may involve the production of fuels.
Gasification, anaerobic digestion and pyrolysis are good examples of such processes, while examples of fuels produced include biomethane, biobutanol and bioethanol [2].
Fuels produced through waste conversion are generally referred to as ‘waste-derived fuels’.
Examples of Energy Recovery from Waste
1). Energy Recovery from Solid Waste
Solid waste includes inorganic materials like plastics, and organic biomass in the form of agricultural residue, manure, sewage, paper products, and food waste.
Energy recovery from solid waste may employ any method that is capable of converting the substrate effectively. This includes chemical, biochemical and thermal approaches like gasification, catalytic digestion, and pyrolysis [6].
Energy recovery is a good method for managing municipal and agricultural waste, as well as for environmental conservation and landfill diversion.
2). Energy Recovery from Wastewater
Energy recovery from wastewater sludge is an important initiative and practice, in view of the increasing rate of waste water production in sewage and industrial systems.
Because wastewater contains organic compounds, it is a suitable substrate for biochemical treatment and biofuel production.
The fuel and energy derived from wastewater can be used to reduce the total amount of energy consumed in the process of wastewater management [7].
Conclusion
Energy recovery from waste refers to all methods, facilities and conditions that are used to convert waste to energy, or to capture and conserve waste energy.
We generate energy from waste through;
1. Thermal Processes
2. Chemical Processes
3. Biochemical Processes
Products of energy recovery include;
1. Heat Energy
2. Liquid and Gaseous Fuels
Examples of energy recovery from waste are;
1. Energy Recovery from Solid Waste
2. Energy Recovery from Wastewater
References
1). Adekunle, K.; Okolie, J. (2015). “A Review of Biochemical Process of Anaerobic Digestion.” Advances in Bioscience and Biotechnology, 6, 205-212. Available at: https://doi.org/10.4236/abb.2015.63020. (Accessed 17 September 2022).
2). Bhatt, A. K.; Bhatia, R. K.; Thakur, S.; Rana, N.; Sharma, V.; Rathour, R. K. (2018). “Fuel from Waste: A Review on Scientific Solution for Waste Management and Environment Conservation.” Prospects of Alternative Transportation Fuels (pp.205-233). Available at: https://doi.org/10.1007/978-981-10-7518-6_10. (Accessed 16 September 2022).
3). Bourtsalas, A.; Seo, Y.; Alam, T.; Seo, Y. (2019). “The status of waste management and waste to energy for district heating in South Korea.” Waste Management 85:304-316. Available at: https://doi.org/10.1016/j.wasman.2019.01.001. (Accessed 17 September 2022).
4). Ngusale, G.; Oloko, M.; Agong, G.; Nyakinya, B. (2017). “Energy recovery from municipal solid waste.” Energy Sources, Part A: Recovery, Utilization and Environmental Effects 39(16):1807-1814. Available at: https://doi.org/10.1080/15567036.2017.1376007. (Accessed 17 September 2022).
5). O’Rielly, K.; Jeswiet, J. (2014). “Improving industrial energy efficiency through the implementation of waste heat recovery systems.” Transactions- Canadian Society for Mechanical Engineering 39(1):125-136. Available at: https://doi.org/10.1139/tcsme-2015-0010. (Accessed 17 September 2022).
6). Palacio, J. C. E. , Santos, J. J. C. S. , Renó, M. L. G. , Júnior, J. C. F. , Monica Carvalho, M., Reyes, A. M. M. , & Rúa Orozco, D. J. (2018). “Municipal Solid Waste Management and Energy Recovery.” In (Ed.), Energy Conversion – Current Technologies and Future Trends. Available at: https://doi.org/10.5772/intechopen.79235. (Accessed.16 September 2022).
7). Stillwell, A. S.; Hoppock, D. C.; Webber, M. E. (2010). “Energy Recovery from Wastewater Treatment Plants in the United States: A Case Study of the Energy-Water Nexus.” Sustainability 2(4). Available at: https://doi.org/10.3390/su2040945. (Accessed 16 September 2022).
