Page 341 - Industrial Wastewater Treatment, Recycling and Reuse

Urban Wastewater Treatment 313

more emphasis on primary treatment involving clarification and secondary in
the form of biological treatment, with generation of both chemical as well as
biological sludge. The final tertiary treatment again is in the form of RO to
make water suitable for recycle and reuse. The overall concern remain same
and it would be advisable to reduce/eliminate sludge, especially chemical
sludge.Theoverallcostofoperationagaincanbereducedsignificantlybyintel-
ligent combination of various treatment methodologies.

7.4.3 RO Plant for Wastewater Reuse, Vadodara, Gujarat, India
Another case study for industrial wastewater treatment and recycling/reuse
is the RO-based plant in Gujarat, which is used for treating the highly pol-
luted wastewater consisting of various industrial effluent streams for recy-
cling and reusing for industrial uses for its nonpotable purposes. The plant
uses highly polluted wastewater from an effluent disposal channel into which
several industries—refineries, fertilizer, petrochemical—discharge their raw
wastes. The successful operation of the plant demonstrated that at least 75%
of the wastewater could be made available for reuse at a treatment cost of Rs.
36 per 1000 L as per the 1999 estimates. The remaining 25% consists of the
rejects and sludge from the RO plant and needs to be disposed of separately.

Primary + secondary

Service
water
Lime solution Polyelectrolyte Soda-ash
tank and storage tank and solution tank and
ejector pump pump
HCI tank and
pump Sodium
bisulphite
Waste- Wastewater solution tank
water Pressure
storage pump Sludge blanket sand filter
clarifier
Back wash
water tank
and pump
Sludge to
Sludge pit
drying bed
Micron
cartridge filter RO membrane Permeate CO 2
block Purified water
Water recycle and
reuse
Tertiary
Rejected water
Degasser tower
Overall concern-total cost (mainly in RO) & sludge disposal
Figure 7.8 Flow diagram of the three MLD reverse osmosis plant for wastewater reuse
at Vadodara, Gujarat. From MoEF (2011).