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2.2 Sewage Reclamation Using Reverse Osmosis
Industries in growing metropolitan areas may face production losses as a
result of excess demand for municipal water. Madras Fertilizers Limited
(MFL), Madras City, Tamil Nadu, India, has faced such a situation in 1983
and 1987 (see the Indian Case Study in Part C of this Source Book). As a
result, MFL has explored alternatives including the use of desalinated sea
water and treated wastewater to supply process and cooling water to its
operations. After detailed review of these alternatives, the Company
decided to reclaim water from city sewage using advanced waste water
treatment followed by Reverse Osmosis (RO) as an additional purification
step. The Company has a daily water requirement of 20.25 MLD, 68% of which
is required for cooling purposes.
Wastewater used by the plant is treated to tertiary standards using an
activated sludge process, with the treated water being further reclaimed
through excess lime addition, ammonia stripping, recarbonation,
chlorination, multimedia filtration, activated carbon filtration,
cartridge filtration, and reverse osmosis using thin film polyamide
Ammonia stripping is carried out in first-stage and second-stage counter
current flow ammonia strippers, which are similar to cooling tower cells.
Treated wastewater is sprayed from the top while air is sucked in from the
bottom of the tower by an induced draft (ID) fan located at top of the
tower. Free ammonia is blown out of water into the air. The
ammonia-stripped water is pumped to a first stage carbonation tower and
calcium carbonate clarifier, where the pH is brought drown to 7.0, and
chlorinated before being sent to storage. The excess sludge from the
clarifier is disposed of in sludge beds, and water drained from sludge is
recirculated into the inlet lagoon.
Although most undesirable constituents like BOD, hardness, and ammonia
are removed by tertiary treatment, the total dissolved solids (TDS)
content is generally higher than well water. This would increase overall
water consumption by making it necessary to add make up water regularly to
dilute the salinity, increase the corrosiveness of the recirculating
water, and increase chemical dosing needed to keep corrosion and sealing
problems in check; all of which result in increased operating costs. To
reduce these undesirable salinity-related costs, MFL selected Reverse
Osmosis (RO) treatment of the treated effluent as a convenient and viable
Extent of Use
Industries requiring large volumes of cooling water could use this
Operation and Maintenance
A qualified chemical engineer is required to supervise the treatment
process. Other operation and maintenance requirements include the
maintenance of the physical facilities, routine monitoring of the plant
operation, and oversight of the supply and circulation system.
Level of Involvement
This technology is typically implemented at the individual industry
The total capital cost of a 20 MLD reclamation and reuse facility is
estimated to be about $ 18 million. Annual operation and maintenance costs
are about 10% of the capital cost.
Effectiveness of the Technology
Reclaiming sewage releases an equivalent amount of potable water in the
municipal water system for domestic and other uses in the city.
This technology is suitable for use in areas where a large quantity of
sewage water is available nearby.
Use of reverse osmosis proved to be a less expensive alternative than
other alternatives such as sea water desalination, and resulted in a
savings in the drinking water supply.
The initial capital cost of an RO system may be high, especially if the
sewerage line is far away from the industry. This system is also expensive
to operate due to high power consumption requirements.
No problems are known as the reclaimed water is not for human
Further Development of the Technology
The technology is transferable and can be used by other industries. New
industries should consider integrating this technology into their overall
plant design to make it cost effective.
Rajappa, M.S. 1990. Reclaimed City Sewage as Industrial Water. Journal
of Indian Water Works Association, Jan-March, 95-100.