(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