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Full Circle – LiquidWaste
Management
Liquid waste includes effluents of industries,
fertiliser and pesticide solutions from
agricultural fields, leachate from landfills,
urban run-off of untreated waste water and
garbage, mining wastes etc. Tata Consulting
Engineers provided consultancy solutions to
the Bangalore Water Supply and Sewerage
Board (BWSSB). Typically, about 1100 MLD of
sewage is generated daily in Bangalore city.
BWSSB had existing sewage treatment plants
(STP) capacities of about 730 MLD capacity
and about 330 MLD additional STP was
added on under JICA-BWSSP (II) project.
The Vrishabhavathi Valley (V Valley) STPs
were upgraded periodically and the capacity
was augmented over time. Under separate
project, V Valley STP capacity augmentation
is taken up by BWSSB yet again, with Tata
Consulting Engineers providing sustainable
solutions in managing liquid waste.
Brownfield confines,
Greenfield value engineering
As consultants for the V Valley project, TCE
had the challenge of working in Brownfield
conditions. Along with the sewage treatment
process, the capacities were increased with
available limited footprint, that is, within the
given plant area confines. TCE had the task of
also evaluating the best technology for liquid
waste treatment and solid stream treatment.
The liquid waste contains both toxic and
non-toxic substances and treatment releases
green house gases.
TCE team proposed a conventional
Activated Sludge Process (ASP) secondary
and Tertiary treatment of new 150 MLD
STP capacity with biological nutrient
removal (BNR) facility to meet new Central
Pollution Control Board / Karnataka
State Pollution Control Board treated
sewage discharge norms for Bangalore.
Using the anaerobic digestion process,
the sludge from the STP is designed to
generate energy from the biogas. Through
value engineering solutions, the sludge
handling system is designed to handle
increased capacities (Sludge from 300 MLD
plant capacity including existing plant
of 150 MLD capacity) such that sludge
from the new and existing STP could be
processed using advanced technology.
The solutions planned will also reduce
the volume of dewatered sludge by about
40-45% compared to conventional sludge
treatment. The process also ensures better
quality of sludge product (Class A biosolids)
which is a sustainable solution and is very
environmental friendly.
The sludge generated from the plant is
proposed to be treated with Advanced
Sludge Treatment to achieve United State
Environmental Protection Agency (USEPA)
Class A Biosolids treatment and disposal
standards. The USEPA Class A Biosolids
reduce the level of pathogens to below
detectable levels (i.e. Fecal coliform 1,000
MPN/gm of DS) compared to Fecal coliform
2,000,000 MPN/gm of DS of Class B bio solids
standards. This is a hygienic and healthy
option as there is no risk of infectious disease
transmission through casual contact or
indigestion, no site restrictions are required
for storage of Class A biosolids and there
is less odour from solids which ensures
hygienic transporting and disposing of Class
B Biosolids, etc.
For achieving USEPA Class A
Biosolids in the STP solids output,
Thermal Hydrolysis Process (THP)
is recommended. It is pre-treatment
technology before anaerobic digestion
of sludge. It optimizes digestion
and dewatering (30-33% dry solids
compared to typically 20% DS),
reduces digester volume (about 30-
Energy recovery from the sludge
helps reduce green house gas
emissions. The waste to energy
solution, is designed to contribute
to about 35% of the total energy
requirement for the operation of
sewage treatment plant.
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