The
population of India is estimated to reach between 1.5 - 1.8 billion by year
2050. To avoid our country from becoming a water scarce country, availability
of 3060 billion m3 fresh water is required. The average annual surface water
flows in India has been estimated as 1869 billion m3 of which only 690 billion
m3 can be utilized considering monsoon climate and topographical and geological
reasons. The available groundwater resource due to various recharges is 432
billion m3. The country will be water stressed even if the total available
water i.e. 2301 billion m3 is taken into account. Ensuring uninterrupted supply
of water of adequate quality and quantity at affordable cost will be the
biggest challenge for the municipalities and industries due to the huge demand
and pollution caused by discharge of untreated or partially treated used
waters.
In
recent years, with the development of industries, increase in population and
improved living standard, demand of water has remarkably increased.
Municipalities are not able to provide uninterrupted water supply to the
citizens. The communities in many Indian cities have to purchase drinking water
at a high cost of Rs. 50 – 150 per m3. Since water has become a scarce
commodity, availability of water of adequate quality and quantity at affordable
cost is possibly the biggest challenge faced by the industries today. It is
necessary for all the industries to positively implement all kind of programs
and measures for effective utilization of water resources.
Chennai
Petroleum Corporation Ltd., Chennai for example have invested large sum of
money in desalination of Sea water and in laying a pipeline to convey the
desalinated water all the way to their refinery. Earlier, when faced with a
severe water shortage, the refinery was the first to invest in a plant to
recover water from treated municipal sewage and effluent from the refinery.
Madras Fertilizers Limited followed their example. In Mumbai, Rashtriya
Chemical Fertilizers have also set up a plant to recover water from municipal
sewage and used the recovered water for cooling applications.
Water
can no longer be taken for granted. It
needs to be managed judiciously through measures to conserve, recover, and
reuse, especially in industries that consume large quantities of water. Water
is used in the industry for a number of applications that include cooling,
steam production to generate power and other process applications besides
drinking and sanitation.
Water
Audit
The
first step in Water Conservation and Management Programme is comprehensive
water Audit to arrive at a realistic water balance for the entire factory and
colony. Water audits at regular intervals help the management to take stock of
the situation and act before the problem escalates and threatens closure due to
non availability of water. The objectives of carrying out a water audit is not
only to identify areas of excessive use
(and its abuse) but also assess the quality of water being supplied for each
application and compare it with the actual requirement and optimize the cost of
treating water. This involves following exercise-
- Measurement
of water consumption at user points by calibrated instruments. Flow through
closed pipes can be measured by an Ultrasonic flow measuring instrument and
flow through open channels through V-Notch weirs.
- The
quality and quantity of effluents generated from each section should also be
assessed. Conscious efforts shall be made to effect savings in cost of treating
the effluent.
- The
next step is to establish bench marks for water consumption based on
international practices for similar industries and identify areas of excess
consumption.
- An
action plan should then be drawn for reducing the consumption of water in those
areas. With good housekeeping discipline and perseverance it should be possible
to achieve the results.
Conservation
of Water for Cooling
A
major portion of industrial water is utilized for cooling applications in majority
of industries and hence provides an opportunity to conserve the water by
optimizing the operations of cooling towers and following the best practices as
given below-
- It
is essential to check the cooling water treatment programme, which enables us
to operate the tower at optimum cycles of concentration. The quantity of
make-up water decreases significantly with increasing cycles of concentration.
Water meters should be installed at cooling water make-up as well as blow down
line.
- Use
of cooling water for other purposes like floor washing should be stopped. There
should be no overflows from the basin.
- One
should also look for any leak through the bottom floor of the tower basin and
if detected the leak should be plugged during the annual shut down.
- Loss
of water due to evaporation is around 2% of the water in circulation and hence
in areas of water scarcity, the feasibility of using air cooled towers should
be explored.
- Side
stream filtration should be adopted to keep cooling water free of suspended
solids. Backwash water from side stream filter can be recovered by installing a
plate type clarifier. The quantum of water recovered can be significant in
large industries like fertilizer, steel etc.
Water
Conservation in Pretreatment Plant
Almost
all the plants utilizing surface water will have a clarifier and filter
beds. Blow down from the clarifier must
be treated through the sludge thickener and sludge dewatering unit (centrifuge
/ filter press). The clear water from sludge thickener and the filtrate from
sludge dewatering unit should be pumped back to the clarifier. This will not
only help in water conservation but also reduces the cost incurred in sludge
handling and disposal.
The
entire quantity of water used for backwashing the filters must be collected and
returned to the clarifier.
Water
Conservation in Softening Plants
Softening
plants offer scope both for water conservation as well as for a reduction in
salt consumption by opting for salt recycling. Salt recycle is effectively used
in almost all the power stations in Maharashtra as the entire quantity of water
used for cooling is softened and the salt consumption is high. For salt
recycling, it will be necessary to install an additional brine measuring tank
(BMT 2) identical to the existing one (BMT 1) and modify the frontal piping.
Part
of the water used for slow rinsing and practically the entire quantity used for
final rinsing can be recovered and reused partly for preparation of salt
solution and partly for slow rinse. Salt recovery can be made by collecting the
latter half of the effluent during salt injection in a separate brine measuring
tank and using it to partially regenerate the resin during the next cycle.
Water
Conservation in Demineralization Plant
Demineralization
by the ion exchange process generates strong effluents which require dilution
with fresh water or other streams low in dissolved solids prior to discharge.
However water can be recovered from the effluents generated in a DM plant by
installing a water recovery plant for reuse in the plant. Some plants use the
strongly acidic effluents in cooling water for pH control in place of acid.
There is considerable scope to conserve water in DM plant which can be achieved
by following measures-
- Almost
all the final rinse water during Mixed Bed regeneration can be recycled back to
the filtered water tank. Part of the water used for final rinsing can be
recycled back to the raw water tank as soon as its conductively reaches the
value equal to that of raw water.
- Good
housekeeping can significantly contribute to conservation of water in a DM
plant. Leaky valves and taps must be fixed immediately. Water flowing through
pH and conductivity sensors must be routed to the raw water tank.
- Whenever
rinse water volumes increase, the reasons for long rinse should be ascertained.
If it is established that the problem is due to fouling agent in water, action
must be taken to fix the problem either by addition of some equipment or change
over to non fouling resins or both.
- Presence
of non-reactive (colloidal) silica in boiler feed water high pressure boilers
may result in increased blow-down. In case presence of excessive amount of
colloidal silica is suspected it may be prudent to remove it from boiler feed
water by installing an Ultra filtration unit after the Mixed Bed. In case the raw water is high on organics as
well, the ultra filtration unit may be located ahead of MB unit to take care of
both issues.
Treatment
of Condensate
Conservation
of condensate not only saves water but also the huge cost incurred in high
purity water production and chemical conditioning. This can be achieved by
arresting the leakages in the lines and installing suitable treatment units
(condensate polishing units) for removal of undesirable components. Condensates
with traces of hydrocarbons can be treated through the use of Oil Coalescers or
specially designed Activated Carbon Filters
Effluent
Treatment
Use
of water in the industry produces an effluent which needs to be treated before
it can be discharged into a public sewer or a receiving stream. Treatment of
effluent is necessary to protect the receiving water bodies and ensure safe
water availability to the downstream habitation. Moreover, the effluent after
minimal treatment can be utilized for low end applications. Efforts should be
made to treat, recycle, and reuse the effluent in the premises so that the
industry could approach towards zero liquid discharge concepts and
uninterrupted water supply for production can be ensured. Often it is possible
to recover a valuable byproduct for reuse in the process and remaining effluent
is now more amenable for recovery of water economically.
In
Tirupur, group of industries had installed a combined effluent treatment plant
for treating their effluents with an option to recover the salt (Na2SO4) and
water which is again recycled back to the process. This approach not only
solved a potential problem of high TDS effluent disposal but also resulted in
practically ‘Zero-Discharge’ with significant savings in the cost of treatment
of effluent.
Water
Conservation in Offices and Residential Colony
As
far as possible, electronically operated proximity devices or at least press to
open type of valves should be provided to reduce wastage. These types of
installations result in water consumption of around 30%.
Supply
of potable water to residential colony and other user points should be under
gravity by installing water tanks on roof tops. Supply under gravity (through
overhead storage tanks) will minimize wastage through splashing. Again
restricting the supply to fix periods will also help in conserving water.
Almost
all colonies housing the factory employees will have a dedicated sewage
treatment plant. Water can be recovered by installing a tertiary treatment
plant and can used for low end applications like green belt development,
gardening, flushing the toilets etc., thus conserving fresh water. Needless to say this will involve separate
storage and plumbing to ensure that there is no accidental contamination with
potable water in other lines like washbasins and shower fountains. The
recovered water can also be used as cooling tower make-up by installing
membrane Bio reactor that will produce clear filtered water.
Rain
Water Harvesting
Rain
water harvesting is yet another opportunity for the industries to ensure that
the ground water gets recharged and the borewells do not run dry. The system is
relatively inexpensive and the benefits are many. Water falling on the roof top
is collected through channels, filtered and infiltration wells.
Water
is a scarce resource and it needs to be treated with all the respect it
deserves. Conservation, recovery and reuse must be practiced by all industries
on a continuous basis to ensure availability of adequate quantity of fresh
water for use. With the available technologies the fresh water consumption can
be minimized and is not very much difficult. Future efforts must be to maximize
recycling of water by adopting the latest technologies available.
(PIB
Features.)
