The country’s industrial water requirement is significant, only next to that for municipal and irrigation purposes. Heavy industries such as power, iron and steel, and oil as well as others including sugar, textiles, and pulp and paper are the major consumers of water. A steady growth in these sectors over the past few years has increased the demand for water. There have also been positive developments on the technology front. Industrial units are shifting to advanced membrane-based technologies to improve treatment capabilities, reduce dependence on freshwater sources, and manage operational costs. More recently, a new technology, zero liquid discharge (ZLD), has gained prominence.
In the next few years, growing awareness among industrial units regarding the need to reduce their water footprint and the declining freshwater availability are expected to increase the demand for advanced technologies, digitalisation and the use of innovative equipment, thus expanding the market for global as well as local technology and equipment suppliers.
Indian Infrastructure takes a look at two leading companies and wastewater treatment technologies and practices …
Arvind Limited has been taking a number of water management initiatives such as wastewater treatment and recycling, desalination and ZLD to meet its water requirements efficiently.
It has the single largest textile effluent ZLD plant in Asia with a capacity of 17,000 cubic metres per day. ZLD is an important water treatment technology employed by Arvind Limited to treat effluents from textile industries. It deploys an advanced water treatment process that purifies and recycles wastewater at the end of the industrial process with zero liquid waste discharged. The solids produced as by-products at the end of the ZLD process are either reused or sold. For example, salt and brine are by-products from the last stage of ZLD which can be reused in the textile process. Approximately 95 per cent of the liquid can be recovered from the liquid waste fed to the system for treatment.
ZLD techniques used by Arvind Limited are more energy efficient because they employ a patented polymeric film technology. The technology uses polymeric films in heat exchangers instead of metal. The polymeric film requires a lower amount of heat and a smaller boiler size. The resultant operating cost of the system is low and there is energy saving of nearly 80 per cent as compared to conventional metallic wastewater evaporators used in this technology. The system uses two processes, namely, mechanical vapour recompression evaporator (MVRE) and multi-effect evaporator (MEE) to reduce the total dissolved salt (TDS) concentration of the influents.
MVRE operates on an energy recovery evaporator that compresses low pressure vapour, in turn producing a low volume of vapour with high pressure and temperature. The influent wastewater is heated with steam after which the vapours produced are compressed and sent to a heat exchanger where it gets condensed and gives water as a by-product. The pure water received at the outlet can be reused in the process. It is a fully automated system that requires no dedicated manpower. This process is also advantageous as it helps reduce maintenance costs. Generally, MVRE precedes MEE.
The MEE process consists of a sequence of vessels in which the water is boiled. Each vessel is kept at a lower pressure than the previous one. This is done because the boiling point of water decreases as the pressure decreases, therefore the boil-off vapour in one vessel can be used to heat the next one. This ensures that only one vessel requires an external source of heat. The evaporated water in the last stage is condensed in the steam condenser with the help of cool water. The effluent fed into the MEE has very high TDS. The process recovers approximately 95 per cent of the water, which is reusable. The concentrated mass from each vessel is filtered in a carbon filter and the filtrate is recycled back into the process.
Deepak Fertilisers and Petrochemicals Corporation Limited
Deepak Fertilisers and Petrochemicals Corporation Limited (DFPCL) is a leading producer of fertilisers and industrial chemicals. The company has manufacturing facilities in Taloja, Srikakulam, Panipat and Dahej. These manufacturing facilities have their own effluent treatment plants (ETPs) for recycling industrial effluent. In addition to ZLD and MEE, DFPCL has deployed other technologies for wastewater treatment. It uses reverse osmosis (RO) and ultrafiltration (UF) to recycle wastewater with some innovation to achieve better results.
UF is a type of treatment process involving a membrane filtration process wherein hydrostatic pressure forces the liquid against a semi-permeable membrane. The semi-permeable membrane is a thin layer of material that is capable of separating substances when force is applied across it. The UF system works on a micro level and segregates all suspended solid from the wastewater.
On the other hand, RO is a water treatment system that works by using a high pressure pump to increase the pressure on the salt side of the RO and forces the wastewater across the semi-permeable RO membrane, leaving behind 95-99 per cent of the dissolved salts/matter in the rejected stream.
DFPCL has introduced some changes in its wastewater treatment system so as to obtain better results. These include the use of RO for raw water instead of treated effluents from the ETP. Further, the use of permeate from the RO process as feed for the demineralisation (DM) plant was done and the DM plant regeneration was treated at the ETP. The major benefits achieved through this were improved performance of the DM plant, reduced regeneration of DM by 45 per cent, reduction in the effluent load, reduced chemical treatment at the DM plant and ETP, and improvement in the boiler feed water quality. Moreover, the facilities stopped discharging high TDS to the ETPs. The facilities also witnessed water savings as a result of these initiatives, as the requirement of water in the process reduced proportionately.
There has been an increasing focus on developing alternative sources of water supply through practices such as recycling and reuse of treated wastewater and desalination. Wastewater treatment is important for both water conservation and recycling as it allows the maximum amount of wastewater to be recycled and reused. New technologies like ZLD and MVRE further produce by-products that can be sold or reused, thereby reducing costs and increasing operational efficiency. Sustainable industrial water and effluent management with a focus on identification of alternative water sources along with the adoption of advanced technologies will thus be critical for averting the looming water crisis facing industries at present. w
Based on presentations by Naresh Verma, Chief Operating Officer, Arvind Limited; and Deepak Pande, Head Environmental Health & Safety, DFPCL, at a recent India Infrastructure conference