Waste-to-Energy

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 [WM, 2023].  In the same year, Brazil produced 81.8 million tons, or 224,000 tons per day [EX, 2023].  Goiás state, in turn, produced 3.349 million  tons in 2019, or 9,175 tons per day [MR, 2021].

  

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 also into a fuel (an interesting way of energy storage for later use).  WtE is an integral part to reach 100% renewable energy in future along with other renewable sources.

  

Landfill reduction

  

WtE provides a cost effective & 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 (by burning waste, reducing the solid mass of the original waste by 80–85% and the volume by 95–96%), gasification, pyrolization, anaerobic digestion, and landfill with gas recovery.

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Common techs for the combustion of municipal solid waste (MSW) include mass burn facilities & refuse derived fuel (RDF), which is 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.  It consists of everyday items we use and then throw away.  Typically, this type of waste includes household waste, commercial waste and may also contain demolition and construction waste (construction & demolition debris - C&D).  Figure 2 and Figure 3 shows the gravimetric composition of MSW in the Region of Central Macedonia (RCM), Greece, and in Brazil, respectively, where organic waste stands out.

  

MSW has always been an undesirable asset in society, which grows every year.  Inadequate waste disposal causes air pollution, water & soil contamination.  Open & 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.

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WtE plants

 

A WtE 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 electricity & heat.  Figure 4 shows a typical WtE incineration plant and the waste management hierarchi (WMH).

  

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.

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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 tech.  In general, pyrolysis of organic substances produces volatile products and leaves char, a carbon-rich solid residue.  Pyrolysis process is a viable option for a highly organized waste system [ICLEI, 2021].