Under the global green initiative, Zero Liquid Discharge solutions help industries not only to use water efficiently but to implicate that there is no discharge of wastewater into the water bodies. Rajul Parikh from Alfaa UV discourses the benefit of the system in detail.
Zero Liquid Discharge (ZLD) is being talked about more frequently in the manufacturing industry where wastewater is produced. Businesses across the world are becoming increasingly concerned about water use and pollution reduction. This is mostly inspired by a larger “Green” or sustainable initiative, which companies are incorporating into their mission statements and corporate objectives. The goal of these Green initiatives is to adopt a more environmental friendly and socially responsible approach to the firm’s business and manufacturing processes. A potential solution that a number of organizations have employed is not just to improve water use efficiency and reduce liquid effluents, but to discharge no water at all, that is Zero Liquid Discharge (ZLD). While most industrial processes generate a waste water stream, the objective of a ZLD system is to recover and reuse all water, thereby avoiding any emissions or wastage. The concept at first seems unreasonable; surely water ‘in’ must lead to the discharge of at least some liquid effluent? ZLD systems employ the most advanced wastewater treatment technologies to purify and recycle virtually all of the wastewater produced.
Typically, ZLD systems are used where there are environmental limitations such as water insufficiency and/or where strong environmental regulations are obligatory; either because water resources are scarce or an industry’s activity is highly polluting.
In principle, the end goal of ZLD is to eliminate (to the extent feasible) the discharge or disposal of liquid waste from a facility, wherein no wastewater gets discharged to surface water bodies. This is ultimately accomplished by recycling, reusing or reducing the volume of waste stream, primarily including water-based streams. The non-water components of a wastewater come from either the manufacturing process itself or from a cleaning process and can include any number of materials, chemicals, oils or solids. Today, most of the ZLD facilities are primarily industrial and power plant applications. Typical waste streams that produce large volumes of wastewater include cooling tower blowdown, gas scrubbler blowdown, ion-exchange regeneration effluent and rinses, plant wash down and rain water runoff, and process wastes. These come from a wide variety of industries, including but certainly not limited to:
- Metal Working
- Metal Finishing
- Water Treatment
- Material Recycling
- Food and Beverage
Typical process of a hybrid ZLD system includes pretreatment, reverse osmosis, evaporation, crystallization and recovery. Pre treatment involves physical and chemical treatment followed by biological system to remove the organic load. The treated effluents are then subject to concentration and evaporation. The concentration method most often involves Reverse Osmosis (RO) methods.
Evaporation involves incineration/drying/evaporation of effluent in multi effect evaporators. The idea is to be left with little or no water (high purity water for reuse) and to be able to separate the dissolved particles from the wastewater/effluent, completing the ZLD cycle in the crystallization and recovery stage. Because the waste stream is so varying it is impossible to design a general ZLD-system. Some sources generate high concentrations of organic compounds, salts, metals and suspended solids. Others are relatively clean, such as condensate and storm water, and require less cleaning. Every ZLD-system is unique and has to be custom made each time.
Water scarcity, ground &surface water pollution, water economics and regulatory pressures are the main drivers of ZLD in India, and will determine the financial viability of ZLD.
While the benefits of ZLD are noteworthy, adoption of the technology has two key environmental considerations: energy consumption for the evaporation process and disposal of the solid waste. On the challenges front, high capital and operating costs of ZLD make it unattractive to many industries where the process is intense or the volume of wastewater is large and a near ZLD process will suffice. The addition of evaporators and crystallizers may increase the cost of a traditional wastewater system by 2 times. In general, with an eye on both capital and running costs, it may be a good idea to do a water audit and see for which applications non-potable water is required; for example- fire water, utility water or cooling water. By matching requirements with waste streams it may be possible to reduce the amount of water entering the ZLD system.
Signalling trends for the future, in a directive in 2015, Central Pollution Control Board in India released Guidelines on Techno-Economic feasibility of implementation of Zero Liquid Discharge (ZLD) for water polluting industries, clearly demonstrating that regulatory pressures will force heavily polluting industries to adopt ZLD, in the near future.