Solid waste treatment is a subdivision of Environmental Engineering that centers on the management of garbage. Unlike water treatment and air pollution, control solid waste management is much more complex because of the materials considered as refuse. Over the last three decades, major cities as well as other vibrant urban centers have seen an increase in solid waste. Municipal solid waste management is categorized into various sub-sections including collection, transport, processing, recycling or disposal, and monitoring of waste materials.
The diagram above is a comprehensive flow chart that highlights the processes of Municipal solid waste management. Different countries have dissimilar methods of managing solid wastes; however, the chart presented above is a standard procedural flow of the way non-digestible and organic wastes are managed effectively either for recovery or disposal purposes.
The first stage of solid waste megamenu is a collection. The collection is done in various stages with the first being the assortment of mixed solid waste. Over the years, households, as well as corporate entities, have been urged to separate the digestible and non-digestible wastes in order to help in the collection process. The garbage is later taken to transfer stations where the waste is further classified in accordance to the digestible period. The trucks used to collect these refuse have specific storage compartments for the organic and inorganic waste. Each truck then transports the waste to transfer stations where the refuse is mechanically sorted again so that it may be recycled or sent to the landfills.
Figure 2. Refuse Collection Flow Chart
For the organic wastes, each batch of refuse has a specific digestion period as shown in table one below. This chart is used in individual transfer station each having different capacities and purposes such as direct discharge to landfills of storage discharge for recovery or recycling. As indicated by Hoornweg, and Perinaz, there exists only two kinds of basic modes of operation- direct discharge meaning that the type of waste determines the disposal strategy; for example, agricultural refuse from households are the first to be sent to the landfill due to their digestion (15). On the other hand, in storage discharge, the refuse is emptied from the collection trucks into pit that are then classified for different types of recycling.
Table 1. Digestion Period Table
Processing of Solid Wastes
Processing solid wastes is the second central function of municipal solid waste management. Processing augments the productivity of solid waste disposal in addition to preparing solid waste for consequent recovery of materials as well as energy. Since the 1950s, disposal of solid wastes involved open dumping, sanitary land filling as well as disposal at sea. Due to the environmental problems associated with open dumps on land and sea, currently, the only standard method of solid waste disposal at land filling. Additionally,processing segregate solid waste components may be completed at the point of collection or at transfer facility. Onsite processing needs the collaboration of waste producer; homes, commercial establishments, as well as industries. As shown in table one, solid waste digests at different times. Organic waste materials for example plant material, food scraps as well as paper products, are increasingly being recycled through biological composting or digestion processes to decompose thus killing dangerous pathogens. The resulting organic material is then recycled as either mulch or compost useful for agricultural and landscaping purposes.
Mechanical Biological Treatment
Mechanical Biological Treatment (MBT) is described as a technology that combines mechanical sorting as well as biological treatment. MBT is also known as BMT (Biological Mechanical Treatment), nevertheless, this merely refers to the order of processing. The “mechanical” component is frequently a bulk handling mechanical sorting state.
Pyrolysis and Gasification
Pyrolysis and gasification are thermal treatment processes that involve heating solid waste at high temperatures in oxygen-depilated kilns. The process typically takes place in a sealed vessel under high pressure. The processes are known to be potentially more efficient than the direct burning of solid waste because more energy recovered and used in generating electricity. As indicated by Sabbas et al, the liquid oil, as well as gas, have been burnt to produce energy; nonetheless, the solid residue is refined into products such as activated carbon (81).
Solid waste management is currently considered a major branch of environmental engineering because of the different technologies that are used in every step of the process. From the first step of collection, environmental engineers are expected to develop strategies that guarantee proper separation and storage of organic and inorganic waste. In the processing stage, more techniques such as Mechanical biological treatment, and Pyrolysis and gasification are required to develop ways to improve recovery in order to maintain environmental sustainability.
Hoornweg, Daniel, and Perinaz Bhada-Tata. What a Waste: A Global Review of Solid Waste Management. Vol. 15. World Bank, Washington, DC, 2012.
Sabbas, Thomas, Alessandra Polettini, Raffaella Pomi, Thomas Astrup, Ole Hjelmar, Peter Mostbauer, Giovanna Cappai et al. “Management of Municipal Solid Waste Incineration Residues.” Waste Management 23, no. 1 (2013): 61-88.