Introduction
Waste treatment is fundamental in the transition to a circular and sustainable economy because it facilitates both the efficient management of industrial waste and its conversion into clean energy. Through innovations in waste management processes, such as anaerobic digestion, gasification and pyrolysis, non-recyclable waste is transformed into renewable energy sources such as electricity, biogas and heat.
Technological advances help reduce dependence on fossil fuels, greenhouse gas emissions and their polluting effects. In this article, we discuss the issue of effective waste treatment management through innovative technologies to increase energy efficiency, and drive the development of a more sustainable future.
What is waste treatment and why is it important?
Definition
This process involves a set of operations designed to modify the physical, chemical or biological characteristics of waste, facilitating its management. These processes include collection, classification and processing, with the main objective being to reduce or neutralize hazardous substances, recover recover recoverable materials, and prepare waste for conversion into clean energy or final disposal in a safe and efficient manner.
Importance
Waste treatment is significant in reducing environmental impact through sustainability and conservation of natural resources. Efficient waste management minimizes pollution, prevents accumulation in landfills and facilitates the recovery of recovered materials. It also mitigates greenhouse gas (GHG) emissions, optimizes energy use and reduces the extraction of virgin raw materials, inspiring a more sustainable development model.
What types of waste can be energetically recovered?
Energy recovery consists of transforming waste into usable resources to generate renewable energy. This process reduces the negative effects associated with waste treatment, and also minimizes dependence on virgin resources. Waste recovery contributes to sustainable development by converting potential liabilities into assets, promoting a more balanced and stable economic system.
Types of waste that can be recovered include municipal solid waste (MSW), industrial waste, agricultural waste and sewage sludge. MSW, consisting of waste generated in households and businesses, can be incinerated with energy recovery or biogas production.
Industrial waste, on the other hand, presents a wide variety of options, from direct combustion to gasification, depending on its composition. Agricultural residues, such as crop residues and manure, are an excellent source of biogas, while sewage sludge is dried and used as a fuel in industrial processes.
The generation of clean energy from waste contributes to diversifying the energy mix, reducing dependence on conventional sources, and creating new business opportunities.
How waste-to-energy (WtE) plants work
Waste-to-Energy (WtE) plants convert non-recyclable waste into usable energy. The main objective of WtE plants is to generate renewable energy and to contribute to waste management by minimizing the volume and hazardousness of waste. Through these technologies, secondary raw materials are produced; which, helps to reduce GHG emissions. The stages include:
- Collection and classification: Waste, urban solid or industrial, is collected and sorted to separate recyclable materials from non-recyclable materials that are destined for energy valorization for processing in WtE.
- Pretreatment: Initially, waste is treated through a process, which includes shredding, drying, and homogenization, optimizing its combustion or conversion into clean energy.
- Conversion technologies: These include incineration, anaerobic digestion, gasification, and pyrolysis.
Waste-to-energy technologies
Incineration: This is one of the most widely used processes for waste-to-energy conversion. This technology burns waste at high temperatures in combustion chambers, generating heat that is converted into electricity by steam turbines. It is ideal for managing large volumes of non-recyclable waste but requires strict controls on pollutant emissions.
Anaerobic digestion (AD): A biochemical process that takes organic waste and places it in a reactor in the absence of oxygen and rich in microbial communities to generate biogas (composed of methane and carbon dioxide) and digestate. The biogas obtained is used to generate thermal or electrical energy. It is an old technology, but in constant evolution, however, AD is not as efficient as other methods, its energy efficiency is estimated at 40% at best1.
Gasification and pyrolysis: These are thermochemical reaction processes that drive feedstock conversion under high pressure and temperature conditions. They are used to transform low value-added industrial wastes into valuable products. In both processes, useful by-products are obtained, but in the case of gasification, energy is also generated during the conversion process. A description of each follows2:
- Gasification: A decomposition process that occurs at temperatures between 800 -1000°C in partially oxidized atmospheres, producing a synthesis gas (syngas) composed mainly of hydrogen, methane and carbon monoxide, with a high calorific value. It also produces biochar, a solid by-product that is rich in carbon and is used as a fertilizer, fuel or carbon sequestrant, contributing to GHG reduction.
- Pyrolysis: Unlike gasification, this process is carried out at temperatures between 400-800ºC in an inertized atmosphere (without oxygen), which avoids combustion. This process breaks down waste into three fractions: pyrolytic gas, a mixture of CO, H₂, CO₂ and CH₄; biooil, a liquid with high energy potential and is used as a substitute for fossil fuels; and biochar, similar to that generated in gasification, with applications as a fertilizer and solid fuel.
The following video shows a 3D animation of the Beston BLL-30 continuous pyrolysis plant. It can process tires, plastics, oily sludge and convert them into pyrolysis oil, syngas. Source: Grupo Beston Co., Ltd.
Beston’s continuous pyrolysis plant.
Types of waste that can be used to generate energy
Different types of waste can be used to generate energy, depending on their composition and origin. Organic waste includes food waste, gardening waste, manure, and slurry, together with by-products from the agri-food industry, all of which are rich in organic matter. Agricultural and forestry waste, such as crop residues and wood, also represent an important source for energy production.
Municipal solid waste, which includes paper and cardboard, plastics, and textiles, is also important for energy production. As for industrial waste, wood, sewage sludge, and waste from the chemical and oil industries stand out for their capacity for energy use. Finally, special wastes, such as used tires and electronic wastes, represent a potential source of materials that, with proper treatment, contribute to energy production.
Types of clean energy obtained by waste treatment
Waste-to-energy technologies generate different types of clean energy, depending on the process used:
- Electricity: obtained by incineration or gasification of waste, transforming heat into electrical energy. Gasification is cleaner as it reduces emissions.
- Biogas: Generated by anaerobic digestion of organic waste, it is used for electricity or as biomethane, a substitute for natural gas.
- Heat: Produced as a by-product of incineration, used in industries or district heating through cogeneration.
- Liquid fuels: Through pyrolysis, waste is converted into bio-oil for engines or chemicals.
- Hydrogen: Synthesis gas from gasification is used to produce hydrogen, a clean fuel.
Technological innovations for waste management and waste-to-energy conversion
Plasma arc gasification: This is a technology that decomposes waste, including hazardous materials, at extreme temperatures (up to 7,000°C), generating syngas, which can be used as a clean fuel after purification. It also produces slag, a glass-like by-product that is reusable in construction. Although it releases small amounts of dioxins during gas quenching, these are minor compared to traditional incineration3.
Dendroelectric liquid energy (DLE) technology: This is an innovation with near-zero emissions and high energy efficiency. Operating at moderate temperatures of between 150°C and 250°C, these plants are up to four times more efficient than DA, generating clean fuels such as hydrogen and carbon monoxide without combustion, eliminating the need for costly anti-emission technologies. With 80% efficiency and low operating costs, it is an affordable and sustainable solution for converting waste into clean energy.
Conclusions
Waste treatment is fundamental for the generation of clean energy and the transition to a more sustainable energy system. Processes such as energy recovery from industrial, urban, and agricultural waste are transformed through waste-to-energy (WtE) technologies such as gasification and anaerobic digestion, allowing the generation of electricity, biogas, and other energy resources.
Adopting these technologies promotes more sustainable waste management and boosts the circular economy, optimizing the use of energy materials and contributing to the closure of circular systems.
References
- Valuer, The Top Innovations in Waste-To-Energy Technology; accessed on September 10, 2024 at https://www.valuer.ai/blog/top-innovative-technologies-in-waste-to-energy
- RETEMA, Gasificación y pirólisis como solución para la gestión y valorización de subproductos; accessed on September 10, 2024 at https://www.retema.es/actualidad/gasificacion-y-pirolisis-como-solucion-para-la-gestion-y-valorizacion-de-subproductos
- Revolutionized, Top 6 Waste-to-Energy Technologies and Innovations in 2023; accessed on September 10, 2024 at https://revolutionized.com/waste-to-energy-technologies/
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