Environmental Engineering Reference
In-Depth Information
Solid waste may comprise municipal solid wastes, such as food waste, rubbish,
treated waste (industrial and sewage sludge), construction waste, industrial wastes
(e.g., chemicals, scrap products, glass, ly ash, resins, industrial sludge, etc.), and
hazardous wastes (e.g., volatile organic chemicals and pathological, biomedical, and
pharmaceutical wastes). About 48 million tons of municipal solid waste is generated
annually in India (Agarwal et al.
2005
). Per capita waste generation in major cities of
India ranges from 0.2 to 0.6 kg (Devi and Satyanarayana
2001
). Urban local bodies
spend approximately Rs. 500-1,500 per ton for solid waste collection, transporta-
tion, treatment, and its disposal. With increasing urbanization and consequent boost
in the urban population, wastewater generation has increased tremendously. Water is
the most essential natural resource of Earth, without which life would be impossible.
Water resources are becoming increasingly contaminated from anthropogenic activi-
ties that result in its pollution. Although water pollution has both human and natural
causes, pollution caused by human activities (e.g., industrial and urban efluents,
tube well water withdrawal, agricultural runoff, etc.) is generally more widespread.
A particularly egregious example of serious human-related pollution is that most
sewage generated in towns and cities that are located on the banks of a river is con-
veniently allowed to low into the river (
Bhargava
2006
; Singh and Agrawal
2008
).
Stricter regulations on discharge of efluents and sewage into the rivers have been
passed and have increasingly resulted in the construction of new sewage-efluent
treatment plants. About 22,900 million liters per day (MLD) of domestic wastewa-
ter is generated from urban centers, whereas industrial wastewater generation is
13,500 MLD (CPCB
2005
). The total treatment capacity in India for domestic
wastewater is 5,900 MLD, whereas this value for industrial wastewater is 8,000 MLD.
Total wastewater generation, i.e., industrial as well as domestic, has increased from
7,007 MLD in 1978-1979 to 26,254 MLD in 2003-2004, in class I cities (at least
100,000 population - one lakh - and above). However, wastewater treatment capac-
ity has increased from 2,755.94 MLD in 1978-1979 to 7,044 MLD in 2003-2004
(CPCB 2005). Presently, only 26% of total wastewater released from all activities is
treated before discharge.
The insoluble solid residue remaining after sewage is inally processed is referred
as biosolids, domestic wastewater residuals, or sewage sludge. The prime objective
of treatment of wastewater in a sewage treatment plant is to remove pathogens and
disinfect efluent prior to its discharge into water bodies. The treatment eficiency of
such plants is dependent on the particular treatment processes used. However,
removal of solids in the form of sludge, during wastewater treatment, displaces
pathogens from the water stream and concentrates them on the sludge solids (Gerba
and Smith
2005
). Concentration of pathogens in wastewater and sewage sludge is
directly associated with an increased incidence of enteric infections at the treatment
plant source area of wastewater. Such infections usually result from certain patho-
genic forms of
Escherichia coli
, which are ubiquitous and normally exist in the
intestines of humans and other vertebrates.
The term biosolids (referring to that solid fraction that remains after sewage treat-
ment) is regarded to emphasize the beneicial nature of this product. The safe dis-
posal of sewage sludge is one of the major environmental challenges throughout the
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