Waste Water Treatment
“Wastewater,” also known as “sewage,” originates from
household wastes, human and animal wastes, industrial wastewaters,
storm runoff, and groundwater infiltration. Wastewater, basically, is
the flow of used water from a community. It is 99.94% water by
weight.The remaining 0.06% is material dissolved or suspended in the
water. It is largely the water supply of a community after it has been
fouled by various uses.
2.Characteristics of waste water
?An understanding of physical, chemical, and
biological characteristics of wastewater is very important in design,
operation, and management of collection, treatment, and disposal of
wastewater. The nature of waste-water includes physical, chemical, and
biological characteristics which depend on the water usage in the
community, the industrial and commercial contributions, weather, and
infiltration/inflow.
3.Physical properties of wastewater
When fresh, wastewater is gray in color and has a
musty and not unpleasant odor. The color gradually changes with time
from gray to black. Fouland unpleasant odors may then develop as a
result of septic sewage. The most important physical characteristics of
wastewater are its temperature and its solids concentration. Temperature
and solids content in wastewater are very important factors for
wastewater treatment processes. Temperature affects chemical reaction
and biological activities. Solids, such as total suspended solids (TSS),
volatile suspended solids (VSS), and settleable solids, affect the
operation and sizing of treatment units.
?Solids. Solids comprise matter
suspended or dissolved in water and wastewater. Solids are divided into
several different fractions and their concentrations provide useful
information for characterization of waste-water and control of treatment
processes.
?Total solids. Total solids (TS) is
the sum of total suspended solids and total dissolved solids (TDS). Each
of these groups can be further divided into volatile and fixed
fractions. Total solids is the material left in the evaporation dish
after it has dried for at least 1h or overnight (prefer-ably) in an oven
at 103 to 105°C and is calculated according to Standard Methods.
?Total suspended solids. Total
suspended solids (TSS) are referred to as nonfilterable residue. The TSS
is a very important quality parameter for water and wastewater and is a
wastewater treatment effluent standard. The TSS standards for primary
and secondary effluents are usually set at 30 and 12 mg/L, respectively.
TSS is determined by filtering a well-mixed sample through a 0.2 mm
pore size, 24 mm diameter membrane; the membrane filter is placed in a
Gooch crucible, and the residue retained on the filter is dried in an
oven for at least 1h at a constant weight at 103 to 105°C.
T.P.Sivanandan on February 11th, 2009
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