"Waste is a matter of perspective"
The world generated about 2.4 billion tons of solid waste in 2022. With a steady increase of 1.55% per year, landfill will reach 3.4 billion tons by 2050. The good news is that 70% of this mass is suitable for energy recovery in waste-to-energy (WtE) industries [WM, 2023].
In the WtE process, waste that is neither recycled nor re-used is converted to energy in the form of heat, steam or electricity, or into a fuel for later use. WtE is an integral part to reach 100% renewable energy in future along with other renewable sources.
WtE provides a cost effective and hygienic alternative to treat residual waste, and can reduce landfill volumes by more than 90%. Moreover, It prevents one ton of CO2 release for every ton of waste burned and eliminates methane that would have leaked with landfill disposal. But at the moment we are only tapping into 11% of this vast storehouse [WM, 2023].
Energy recovery from waste is the conversion of non-recyclable waste materials into usable heat, electricity, or fuel through a variety of processes, including incineration (combustion), gasification, pyrolization, anaerobic digestion and landfill with gas recovery.
Common technologies for the combustion of municipal solid waste (MSW) include mass burn facilities and refuse derived fuel (RDF), a drop-in low-carbon substitute for fossil fuels. Mass burn units burn MSW in a single combustion chamber under conditions of excess air [EPA, 2023]. RDF systems use mechanical methods to shred incoming MSW, separate out non-combustible materials, and produce a combustible mixture that is suitable as a fuel in a dedicated furnace or as a supplemental fuel in a conventional boiler system (Figure 1).
Municipal solid waste - MSW
MSW is a mixture of energy-rich materials such as paper, plastics, yard waste, and products made from wood. Typically, this type of waste includes household waste, commercial waste, and demolition or construction waste.
MSW has always been an undesirable asset in society, which grows every year. Inadequate waste disposal causes air pollution, water & soil contamination. Open and unsanitary landfills contribute to contamination of drinking water and can cause infection and transmit diseases. The dispersal of debris pollutes ecosystems and dangerous substances from electronic waste or industrial garbage puts a strain on the health of urban dwellers and the environment.
WtE processes represent a better destination for MSW, not only by taking advantage of the energy potential that would be discarded in waste, but also by offering a sanitation solution for large urban centers that do not have the physical capacity to allocate a sanitary landfill close to their territory.
Waste to energy plant is a facility accepting organic waste and producing energy from it. The prevalent number of wastes to energy plants existing in the world are incinerators: they use steam cycle and turbine to produce the electricity and heat. Figure 2 shows a typical WtE incineration plant.
Wastes that are generally burned in a WtE plant include MSW, human sludge, hazardous industrial, medical, and biological waste. Modern plants have a sophisticated gas cleaning system conforming to the strictest air pollution standards.
Alternatives to incineration
Some technologies such as anaerobic digestion, pyrolysis, and gasification are better suited for homogeneous waste types after removing non-combustibles, recyclables and inert materials from the waste stream [SD, 2022].
Compared to incineration, pyrolysis, the most efficient technique for the conversion of biomass-based waste in manufacturing renewable fuels & chemicals, is an alternative solution referred to as non-pollutant technology. Pyrolysis process is a viable option for a highly organized waste system [ICLEI, 2021].
Figure 1: Refused derived fuel (RDF)
Figure 2: Typical WtE plant