Page 339 - Industrial Wastewater Treatment, Recycling and Reuse

Urban Wastewater Treatment 311

• Sand filter
• Pressure filter
• Cartridge filters
• Reverse osmosis
• Degasification to remove CO 2
• Reuse in industry.
It is reported that the plant cost was nearly Rs. 40 crores in 1998, and the
3
operating cost as reported in 2005 came to Rs. 39 per m . With the passage
of time and the success of reuse schemes, the municipal taxes levied also
3
became higher at Rs. 6 per m of raw sewage. Some additional treatment
steps, such as the use of ultrafiltration, became necessary in order to improve
the quality of the water reaching the RO system (keeping the silt density
index, SDI, <3.0), owing to the more polluted nature of the influent waste-
water (MoEF, 2011). It is to be noted that the overall scheme here empha-
sizes primary treatment followed by secondary in the form of conventional
ASP and finally tertiary treatment using RO to make water recyclable for
reuse. A number of process modifications and/or alternatives can be possible
to increase effectiveness and to reduce overall cost of treatment.

7.4.2 Tertiary Treated Municipal Sewage Reuse, Madras
Refineries Ltd. (MRL) and Madras Fertilizers Ltd., Chennai, India
A similar case study has been reported under the treatment scheme
employed at MRL and Madras Fertilizers Ltd. for recycling and reuse of
municipal sewage for nonpotable uses in the refinery and fertilizer plant.
MRL and the Madras Fertilizer Ltd. (MFL) are consumers of a very large
quantity of water for their processing requirements. The treatment plant
encompasses a tertiary treatment plant (TTP) unit for reusing the secondary
municipal sewage to minimize the water demand from the source and
become self-supporting in water availability to compensate for the increasing
process water requirements (MoEF, 2011).

7.4.2.1 Salient Features
It is evident from the report that since 1991, MRL initiated the reuse of
municipal sewage, generating 12 MLD of reusable water. MFL produced
16 MLD of reusable water. The operation of these TTPs was facilitated
by the Chennai Metro Water and Sewerage Board to ensure a secondary
treated sewage with a biochemical oxygen demand of 120 mg/L. The TTPs
of MRL and MFL, which received secondary treated wastewater from the
Chennai, consisted of the following treatment units (Figure 7.7):
• Additional secondary biological treatment