Page 432 - Industrial Wastewater Treatment, Recycling and Reuse

404 Industrial Wastewater Treatment, Recycling, and Reuse

technology, followed by UASB and WSP technology. ASP and UASB are
mostly used as the main treatment system coupled with primary or tertiary
treatment units. ASP technology is the most suitable for large cities because it
requires less space as compared to UASB technology and WSP technology,
and as both of these technologies employ land-intensive ponds in treatment
schemes. Air blower/compressor and sludge recycle pump of ASP are major
power intensive components which demand for additional operating
expenses in comparison to UASB technology. In treatment schemes based
on conventional versions of ASP technology, both primary and secondary
sludge are commonly treated in anaerobic sludge reactors. This reduces
the required area of sludge beds.
Most of the sewage treatment systems using UASB technology include a
grit chamber as a preliminary treatment unit and terminal polishing unit.
This treatment scheme is simple to operate and has a low-operating cost with
an added advantage of biogas generation. Ideally, this makes UASB technol-
ogy the most favorable treatment option for various cities. However, UASB
technology is very sensitive to environmental changes and operational
parameters. Shifts in temperature, and variations in volumetric organic loads,
toxicity, and inhibitors cause operational difficulties in UASB. These factors
affect the retention of a microbial population in the bioreactor and lead to
frequent failures in UASB.
A series of WSP technology is being considered for the treatment in
class-II towns due to low-operating cost and area availability. The WSP
technology is also one of the most economical technologies; however,
unlike UASB technology, no resources in the form of biogas are recovered.
The advantages of WSP technology over UASB technology include less
sensitive operation and greater improvement in bacteriological quality.
The most frequently employed configuration of WSP technology uses
two parallel streams of at least three stages of ponds, the first stage being
the anaerobic pond, the second stage the facultative pond, and the third stage
the maturation pond. However, because the class-II towns are getting over-
populated, land availability for WSP is becoming major constraint in
employing this technology.

10.2.1 Latest Treatment Technologies Adopted in India
A number of newer treatment technologies have come into practice in
recent times and are becoming more popular for sewage treatment. These