The Cosmic Poet: Top 5 “Waste-to-Energy” Technologies

With the unprecedented pace of growing population implicating the growing rates of trash generation. In the year 2012, the world generated 1.3 billion tons of solid waste. According to a report of the World Bank, waste is set to hit 3.4 billion tons by 2050. [1] Instead, landfills that are not sustainable have harmful environmental consequences due to substantial emission of greenhouse gas such as methane and production of leachates (liquid pollution, containing many toxins and pathogens that are formed when water seeps through waste piles). [2] The need of the hour is ‘Waste-to-Energy’ technologies that process non-renewable waste which would serve two purposes: waste management and energy production. Major technologies used worldwide are:

5. Pyrolysis/Gasification (alternative technologies): It is the process of degassing waste under oxygen-controlled conditions, during which pyrolysis gas and a solid coke are formed. It can substitute incineration and is more pollution-free. Pyrolysis could be an option for the treatment of specific waste such as contaminated soil, clinical waste, or mono hazardous industrial/commercial waste. However, it is not recommended for either heterogeneous solid municipal waste. Moreover, Dendro Liquid Energy (DLE), is a zero-waste technology from Germany in which all kinds of mixed waste, including plastics and wooden logs, are treated in a reactor to produce carbon monoxide and hydrogen further generating electric power. Syngas – This method leverages the process of gasification. It converts solid and liquid waste into a gas called Syngaswhich is then used to generate energy or heat. Gasification is seen as upcoming prominent technology to be used worldwide.

4. Landfill Gas (LFG): It is an essential component to partially mitigate negative ecological impacts from the operation of sanitary landfills. Sanitary landfilling is widely used to treat and store the collected waste in a controlled manner. Although it is an improvement on unregulated and open dumping, it still has negative long-term environmental impacts like emission of greenhouse gas methane in landfill gas into the atmosphere. The methane is formed by the anaerobic digestion of organic matter in the landfill body. To reduce greenhouse gas emissions from landfill sites into the atmosphere, trapping methane gas becomes crucial. This is possible through LFG capture. But some losses occur during the start-up phase before the methane capturing system is installed and in operation. However, it is not possible to capture all of the gas emitted by the landfill even amidst operation. Over 200 LFG collection projects were successfully realized under the Clean Development Mechanism of the Kyoto protocol for mitigation of climate gas emissions [3]

3. Anaerobic Digestion for Biogas Production: It is the process of decomposition of organic matter through microorganisms in the absence of oxygen. Anaerobic digestion occurs naturally under oxygen-deprived conditions but can be used under controlled conditions to produce biogas. For this, a gas-tight reactor, an anaerobic digester, provides favorable conditions for microorganisms to turn organic matter into biogas and a solid-liquid residue called digestate which can be utilized as an organic fertilizer.

Biogas is a mixture of different gases which can be converted into thermal or electrical energy. The flammable gas methane (CH4) is the main component in biogas and its content ranges between 50 – 75% depending on feedstock and operational conditions [4]. Due to its lower methane content, the calorific (heating) value of biogas is about two-thirds that of natural gas. This method uses small-scale digesters in developing countries for a long time for biogas or ‘gobar gas’ (as called in India) in rural areas. The primary input is from agriculture, especially animal manure, which is relatively easy to operate and can be well applied at small scales. At the municipal level, it is seen as a viable option for energy recovery from waste in urban areas. A major challenge to this process is to guarantee a consistently well-separated organic waste fraction because Organic waste is often mixed with inorganic matter such as plastics, metals, and other contaminants which often hampers the successful operation of Anaerobic digestion. However small-scale biogas plants are a viable and economical option for developing countries.

2. Co-processing: It is the use of waste-derived materials to replace natural mineral resources, fossil fuels such as coal, fuel oil, and natural gas through different pre-treatment processes waste can be transformed into so-called refuse-derived fuel in industrial processes. It is used worldwide mainly in the cement industry and thermal power plants; also, in the steel and lime industry. In thermal plants where only energy recovery takes place, this is called co-incineration. In the European cement industry, the thermal substitution rate of traditional fuels by waste could be up to 80%, while the average substitution rate across the EU amounts to about 39%. [5] The share of Municipal solid waste used in co-processing is still low compared to waste such as used tires, hazardous industrial waste, contaminated soil, biomass residues, or sludge from wastewater treatment plants.

1. Incineration/combustion: this is the major technology used for handling especially plastic waste in many countries. Example Japan and Singapore have been incinerating their municipal solid waste since 2017 and 2015, respectively.[6] Even in China, incineration has been vastly used since 2017. Sweden began importing waste from other European countries in 2016 for its waste-to-energy operations. The calorific value is 7 Megajoules per kg of waste using this technology.

References

https://openknowledge.worldbank.org/handle/10986/17388
https://journals.sagepub.com/doi/abs/10.1177/0734242X16675683
UNFCCC, “United Nation Framework Convention on Climate Change,” [Online]. Available: https://cdm.unfccc.int/Projects/projsearch.html
A. Wellinger, J. D. Murphy and D. Baxter, The Biogas Handbook. Science, Production and Applications, Cambridge: Woodhead Publishing, 2013.
CEMBUREAU, “Activity Report 2015,” The European Cement Association, Brussel, 2015.
https://www.unep.org/ietc/resources/publication/waste-energy-considerations-informed-decision-making