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. 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.
- National Institute of Hydrology, Roorkee.
The population of India is estimated to reach between 1.5 – 1.8 billion by year 2050. To avoid India from becoming a water scarce country, availability of 3060 billion m3 fresh water will be 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 m3is taken into account. Ensuring uninterrupted supply of water of adequate quality and quantity at affordable cost will be the biggest challenge for the urban local bodies (ULBs) 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. ULBs 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.
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.
- 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 Pre-treatment 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 and 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
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 Colonies
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.Odisha industry-2014
The article has been contributed by
National Institute of Hydrology, Roorkee,
Ministry of Water Resources,
Govt. of India.