Industry can improve
the technology to do so
exists. But does the will?
Water use in Indian industry is very high due to a combination of factors including
obsolete process technology, poor recycling and reuse practices and poor wastewater
treatment. Water once used is generally thrown without any further use, even if the water
is not much contaminated. Segregation of wastewater from various processes into clean
wastewater, (that can be reused) and contaminated water is not commonly done. The result
is that even the uncontaminated water gets contaminated after mixing and is discharged as
Indian industry, especially thermal power plants, consume majority of their water
for cooling requirements. Majority of industries use 'once-through cooling systems', in
which water once used for cooling is discharged. Similarly, reuse of non-contact steam
condensate is also not favoured in India, though it is virtually clean and can be reused
by reducing the total dissolved solids (TDS).
The wastewater treatment
system in Indian industry is essentially installed to meet the wastewater discharge norms.
The design principles do not consider the possibility of recycling and reusing the
wastewater. Inevitably, in all industries the wastewater discharged is seldom suitable for
reuse within the industry, though industry expects other users to reuse its wastewater
because it is 'treated'. Most industries have their water intake points upstream of their
wastewater discharge points. This itself exemplifies the quality and interest of
wastewater treatment by Indian industry.
the water problem
The key to the problem lies in effective management of water resources. An integrated
approach involving water treatment, source reduction, reuse of process water, effluent
treatment, recycling of treated effluent and waste-minimisation is urgently required.
process technology: Clean
and advanced process technologies can help industry reduce its water demand. For instance,
by replacing the conventional bleaching process with totally chlorine bleaching process,
pulp and paper companies can almost close their water cycle. But they are costly.
process water: This involves reusing water in a series, in an open system, for two
or more successive but different purposes. This enables use of poor quality water for more
than one purpose.
Indefinite reuse of same water after treatment for the same purpose. Makeup water is to be
used only to replace unavoidable losses. This is far cheaper than installing new process
technology and recent technological development has made sure that it can be used by any
type of industry.
harvesting: This helps industries meet a substantial part of their annual water
requirement even as demand on local sources is minimised.
is not the bottleneck
There are enough technologies to solve all water problems and what is more, the
prices of these technologies are gradually decreasing. In a nutshell, it quite feasible
today for an Indian industry to substantially reduce its water consumption and wastewater
discharge by putting efficient systems for recycling and reusing the process water. But
for this to happen government policy needs to be overhauled.
water in Indian Thermal Power Plants (TPPs)
According to CPCB's report
on Water Quality in India 1990-2001 status and trends of the total wastewater discharged
from all major industrial sectors, 80.3 per cent is cooling water generated just from
TPPs. Therefore, closing the cooling water cycle should be the priority of Indian industry
and the regulators alike.
cooling technologies are in use today:
Once-through cooling system: This system requires the intake of a
continual flow of cooling water. The water demand for the once-through system is 30 to 50
times that of a closed cycle system. Most Indian TPPs operate this system.
Closed-cycle systems: This system discharges heat through evaporation
in cooling towers and recycles water within the power plant. The water required to do this
is comparatively small since it is limited to the amount lost through the evaporative
process. Because of the expense associated with closed-cycle cooling, once-through systems
are far more common. Some recently commissioned Indian TPPs employ this technology.
In once-through cooling
system approximately 100 litres of water is required to produce 1 Kwh electricity. In
badly managed TPPs this could go up to 200 litres. In comparison in a closed-cycle system,
about 2-3 litres water is required to generate 1 Kwh electricity.
By converting all Indian TPPs to closed-cycle cooling system, by rough
estimation almost 65,000 mld or 24 billion m3 fresh water can be saved. This is roughly
equivalent to India's total domestic water requirement.
In closed-cycle cooling
towers water is lost due to evaporation, windage and drift and intentional blow down.
These losses are about 1.5-2 per cent of the recirculation rate. Currently fresh water is
used as makeup in Indian industry. But with proper treatment of process wastewater and
effective chemical treatment to control corrosion and fouling, wastewater can be easily
reused in the cooling towers, reducing the freshwater intake for cooling to zero.
In general, combined
primary (sedimentation) and secondary (biological oxidation, disinfection) treatment of
wastewater is sufficient to make it suitable for cooling towers. Currently most large and
medium scale Indian companies are required to treat their wastewater till secondary
treatment to meet the pollution norms. Therefore, in these companies no additional
investment is required for treating the wastewater and reusing it in cooling towers.
A wide range of chemicals
are available today which can reduce the danger of corrosion and scaling in the cooling
tower equipment thereby enabling the use of treated effluent as cooling water. Many
companies outside India are using treated effluent as cooling water quite successfully. In
places where fresh water is quite costly, use of treated effluent as cooling water
presents substantial financial gain for the companies.
RECYCLING AND REUSE
|Wastewater treatment and recycling at industrial level with RO
||Capital cost (Rs crore)
maintenance costs (Rs/kl)
Limited, Chennai Size: 15.12 MLD 12.24 MLD is recycled to the cooling towers
and from this plant 3.0 MLD fresh water is
being supplied to Chennai City
Corporation Limited (earlier known as Madras Refineries Limited) Size: 11.25 MLD
Treated water used for cooling towers
The quality of treated water is BOD-2 mg/l;
TDS- 30 mg/l; COD- 5.0 mg/l
|GMR Power corporation,
Chennai Size: 7. 2 MLD Treated water used for cooling towers
||Secondary and tertiary
treatment followed by Reverse Osmosis
Showing the world the way, EverythingAboutWater, May-June, 2001
ii Conserving Water at MRL, EverythingAboutWater, May-June, 2001
iii Generating Clean Power, EverythingAboutWater, May-June, 200
membrane is a thin layer of material separating substances when a driving force is applied
across it. Once considered a viable technology for desalination, membrane processes are
increasingly employed for removal of bacteria and other microorganisms, particulate
material, organic and inorganic chemicals and colour and other contaminants. As advances
are made in membrane production and module design, capital and operating costs continue to
decline. The pressure-driven membrane processes are essentially of four different kinds:
micro filtration, ultra filtration, nano filtration and reverse osmosis.
osmosis (RO): RO use for wastewater recycling and reuse process has become quite
common. O systems are compact, simple to operate, and require minimal labor, making them
suitable for all systems. RO can effectively remove nearly all inorganic contaminants,
nearly all contaminant ions and most dissolved non-ions from water. RO is particularly
effective when used in series. Water passing through multiple units can achieve near-zero
effluent contaminant concentrations.
pre-treatment section, where the feed is treated by chemical clarification (precipitation,
coagulation/flocculation or flotation) and subsequent filtration, or by filtration and
subsequent ultra filtration
membrane section, where high pressure is applied and the waste water is cross-flowed
across the membrane
post-treatment section, where the permeate is prepared for reuse or discharge, and the
concentrate brine is collected for further work-up or for disposal
The capital and operating
and maintenance cost of RO systems are become quite competitive with the increasing cost
of buying water in water-scarce areas. For instance, the cost of treating municipal sewage
water by RO in Chennai is in the range of Rs 25-50 per m3 (See: Wastewater treatment...).
This is similar (in cases even lower) to the cost of fresh water charged by the Madras
Water Supply & Sewage Board.