(Source: Grobelak, et al., 2019)
Both sludge and wastewater include organic pollutants that are high in three nutrients (NPK), which may be recovered and used in a variety of ways. Because nutrients are concentrated in sewage flows arising from urine (the richest), human excreta, and detergents (both rich in P), the sludge is accurately referred to as ’organic concentrates.’. These nutrients can be utilized for agriculture and other reasons, while the organic carbon can be used as a soil conditioner or a natural fertilizer (Karamina et al., 2020).
Sludge Processing
Thickening is frequently the initial stage in sludge treatment which is carried out in a tank known as a gravity thickener (Pahl et al., 2013). A thickener may decrease sludge volume to less than half of its original size. The sludge digesting process begins once all the solids from the sewage sludge have been collected. This is a process that decomposes the organic materials in the sludge into stable chemicals. The sludge then flows into the second tank where it is converted by other bacteria to produce a mixture of carbon dioxide (CO2) and methane (Gurjar, 2021). The leftover sludge is dewatered before ultimate disposal after valuable gases and other byproducts have been extracted. Despite its hardened appearance, dewatered sludge frequently includes a large quantity of water, up to 70% in certain situations. Depending on its chemical makeup, sludge can be buried underground in a sanitary landfill or utilized as fertilizer once it has been adequately dewatered (Lee et al., 2018). If the sludge is too poisonous to be reused or buried, it can be incinerated and turned into ash (Zhou et al., 2020). While sewage sludge is typically treated with a standard plan of action, it is critical to consider factors such as the source of the sewage, the treatment process used to reduce the sewage to sludge, and the possible byproducts that can be recovered from it for further use before deciding on a sludge treatment plan.
Pathogen removal is another big task in the sludge treatment. Sludge pathogenicity can be lowered significantly using stabilizing procedures like as aerobic or anaerobic digestion. In wastewater treatment, the term digestion refers to the stabilization of organic materials by bacteria under contact with sludge in circumstances that are advantageous for their development and reproduction. Anaerobic, aerobic, or a mix of both digestion processes are possible. There is different process involved in the pathogenesis treatment which are incorporated in tabular form (Table 5) with the mark of their importance.
Table 5 . Comparison of various sludge pathogens removal technologies