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Reducing Water Footprint : Technologies for Industries & Civic Bodies
Surendra A Patwardhan, Technology Head (Water and Waste Solution Division) Thermax Limited Due to increasing scarcity of water and stringent pollution norms, there is a huge oppor tunity for the application of recycling technology. Under constant threat, owing to climate change, explosive population growth, and wastage, there is tremendous pressure on water, the most basic but valuable resource. So, recycling of water becomes impor tant for agricultural and landscape irrigation, industrial processes, reuse in housing colonies and societies, or replenishing groundwater basins etc., amongst other things.

With the deteriorating quality and quantity of water, communities and industries are having a difficult time managing their resources. Civic bodies in several parts of India are asking industries to treat sewage and use it for their processes, rather than draw from the scarce resources that can instead be used for drinking water and agricultural purposes. More and more companies are now looking at completely offloading their water and waste management.

In the current environment of water scarcity, companies are finding it profitable to recycle and reuse their treated effluents. Reverse osmosis, ultra-filtration systems and other tertiary treatment processes make this possible for industries keen on resource optimisation.

Today, Thermax has, in its portfolio, a host of technologies, suitable for varied customer requirements. These include Sequential Batch Reactor (SBR), Membrane Bio-Reactor (MBR) and Fluidised Aerobic Bio-Reactor (FAB, a proprietary technology from Thermax). Thermax provides industries with total water management solutions. It provides effluent treatment solutions for various types of industrial effluents and municipal sewage.

Besides its own indigenously developed technologies, Thermax has upgraded its expertise through technology partnerships with global majors such as GE Water for MBR, Wehrle Umwelt GmbH for difficult to degrade effluents, etc.

Industries and Recycling
Depletion of water due to its misuse and the rising cost of available water are persuading industry to opt for recycling. There are also two additional factors that go in favour of water recycle: the cost of treating the available raw water based on its source and quality, and the cost of disposal of effluents. Companies are well aware of the huge penalties, if they fail to adhere to the effluent disposal norms set by Pollution Control Boards (PCBs). Today, industries can make use of customised systems to suit the wide variety of effluents and maintain efficiency. These systems are based on physico-chemical and biological treatments and membrane separation. Thermax has the experience and capability to design and commission wastewater treatment plants for industries like chemicals, drugs, pharmaceutical, refineries, power, steel etc.

Generally, recycling finds its application in water intensive sectors like power, refineries, paper, textile, steel, etc. Effluents from sectors like pharmaceuticals, distillery and tannery are difficult to degrade using conventional process. The tie up with Wehrle Umwelt GmbH, the German company helps Thermax to treat such difficult to degrade effluents.

Different factors govern the use and cost of technology:
• Type of industry
• Nutrient load of the effluent
• Flow rate of effluent
• End application of recycling

There are different norms specified by the PCB, based on the application of recycled effluent. Treated waste can be used for gardening, flushing, washing and again for processing.

Recycling Sewage
Another major application of recycling is in sewage treatment and its recycle. Sewage is a resource that can be recycled for various uses like gardening, toilet flushing, car wash, cooling towers etc. In water stressed areas, treated sewage is used by industries too, for their requirements. Faced with the alarming fact that over 60 per cent of the sewage generated in our country goes untreated, and considering its negative impact on human health, the government is focusing on waste management through centralised/decentralised sewage treatment plants and by mandating large upcoming real estate projects to have their own treatment facilities.

Thermax offers both customised and standardised sewage treatment plants for municipal corporations, housing societies, commercial complexes, SEZs, hotels and hospitals. These systems reduce lifetime costs and occupy 1/5th of the space of any conventional system. These can be installed in basements or on terraces with the options of recycling, complete automation and connections to the municipal lines, facilitating sustainable solutions of decentralised sewage treatment. Though technologies are available to treat sewage to obtain potable water, people in India are reluctant to use this water for drinking purpose; which is common practice in developed countries.

Technologies Available for Recycling
Commonly used technologies for recycling are:
• Activated Sludge Process (ASP)
• Fluidised Aerobic Bio-Reactor (FAB)
• Membrane Bio-Reactor (MBR)
• Sequential Batch Reactor (SBR)

All these technologies, depending on the objective of recycling and end use, require some further treatment like Ultra-Filtration (UF), Reverse Osmosis (RO), Activated Carbon Filtration (ACF), Chlorination, etc.



General process flow can be drawn as Activated Sludge Process
This process is a traditional system, based on the concept of suspended growth of bacteria. It requires sludge recycling and micro-organism MLSS (Mother Liquor Suspended Solids) monitoring. To be effective, it needs a retention time of 16-24 hours, which is a rather time consuming process and also requires large spaces.

Moving Bed Bio-Reactor (MBBR or FAB)
Moving Bed Bio-Reactors are compact plants with high loading rates, self-regulating system and reduced power consumption. Other benefits also include:
• Simple operations and low maintenance requirements
• Non-clogging design and better oxygen transfer efficiency
• Almost odourless operations are possible
• Maximum removal of E.coli from the wastewater, thereby requiring the minimum amount of disinfectant for polishing

Sequential Batch Reactors (SBR)
Sequential Batch Reactors (SBR) are industrial processing tanks for the treatment of wastewater. Sequential batch reactors treat wastewater such as sewage or output from anaerobic digesters or mechanical biological treatment facilities in batches. Oxygen is bubbled through the wastewater to reduce biochemical oxygen demand (BOD) and chemical oxygen demand (COD) to make it suitable for discharge into sewers or for use on land. Some advantages of SBR are:
• Operates in both aerobic as well as anoxic conditions
• Ability to treat a wide range of influent volumes
• Lower investment and recurrent cost, as secondary settling tanks and sludge return systems are not required
• Improved operational reliability
• Almost odourless operations
• Better temperature control

Membrane Bio-Reactors (MBR)
Membrane bio-reactor (MBR) is a combination of a membrane process such as microfiltration or ultra-filtration with a suspended growth bio-reactor. When used with domestic wastewater, MBR processes could produce wastewater treated to levels suitable for discharge into coastal, surface or brackish waterways or to be reclaimed for urban irrigation. Recent technical innovations and significant membrane cost reductions have made MBRs an established and attractive process option to treat and reuse industrial and municipal wastewater. Benefits of MBR include:

• Produces high quality treated water that can be directly fed for reverse osmosis
• Eliminates secondary clarifier, filtration and disinfection units
• No sludge settling problems
• Reduced tank volumes – almost 25 per cent of extended aeration based ASP and up to 50 per cent of that of SBR
• Can be made fully automated with zero manual intervention

Ultra-Filtration
Ultra-filtration is based on membrane technology, consisting of several membrane modules that efficiently remove a wide range of microscopic particles, colloidal matter and pathogens, including viruses and bacteria. These systems are extremely effective for treating heavy surface water. Ultra-filtration treated water can be sent for reverse osmosis and recycled, or further taken for portable application. Also, costly and unreliable methods of water waste pre-treatment before reverse osmosis are not required; which means, considerable savings in terms of pre-treatment and increased RO availability factor.

Reverse Osmosis
Reverse Osmosis (RO) is a process of physical separation of dissolved solids and minerals present in water. This technology uses the principle of osmosis, wherein the mineral concentration of raw water is reduced by applying high pressure through a semipermeable membrane.

References
Among the several industrial installations, there is Arvind Mills, Santej, Gujarat, where Thermax successfully commissioned and operated an effluent recycle plant. The Arvind plant was situated in an area where water was scarce and costly. Thermax supplied an effluent treatment recycle plant with a flow rate of about 10 MLD. The treated effluent is used in processes as well as make-up water for boiler feed, reducing the unit’s operating cost.

Thermax has done sewage treatment with recycle for the Municipal Council of Chandrapur in Maharashtra. Here, Thermax has supplied two plants of capacity 25 MLD and 45 MLD, with FAB reactors and teritiary treatment. The treated effluent from the plant will be reused for industrial process application after some apropriate post-treatment. Some of the other sewage treatments installations commissioned by Thermax are for the Greater Vizag Municipal Corporation, Uttar Pradesh Jal Nigam, Pratapgarh, UP, and the Chandigarh Municipal Corporation, to name a few. In these plants, the treated effluent, after post-treatment, can be reused for industrial process applications. A sewage treatment and recycle installation was also commissioned for a municipality by Thermax.

Challenges Before Recycling Technology
While recycling, 'operation and maintenance’ of the plant needs to be taken care of. There is the need to monitor the quality, flow rate and nutrient load at various points of operation. Increase in COD - BOD quantities and change in ratios between the two can result in fouling of membranes and other problems. In such cases, the efficiency of the recycle plant goes down. Problems like these need to be tackled immediately to keep the cost of operation well under control.

Conclusion
Due to increasing scarcity of water and stringent pollution norms, there is a huge opportunity for the application of recycling technology. The Government has taken positive steps to promote this technology. Today, many industries are opting to recycle their effluent and use the same in their processes or for gardening, washing, flushing, etc. Sewage recycling can be seen as good option for optimum utilisation of available water resources. In coming years, recycle systems will be adopted by almost every industry and even by municipalities.