Whether it is a chemical plant or a power plant, water management must be a high priority. There are many factors that raise this concern, like severe environmental regulations on wastewater discharge, and a shortage of water. Both these industries are notorious for substantial water consumption and the generation of wastewater with high pollutant levels.
The Zero Liquid Discharge has emerged as an effective solution by wastewater treatment plants to address these environmental challenges and promote sustainability. The ZLD in power plant eliminates discharge at the end of the wastewater treatment cycle and allows the resultant treated water to be reused within the plant in a myriad of ways.
In this article, we will explore the significance and working of Zero Liquid Discharge in the power and chemical plants along with its process, and the benefits it delivers in achieving sustainability goals. Although helpful in reusing water, the major role in implementing ZLD is to prevent the environment from polluted wastewater discharge from chemical and power plants.
In the power plants, a huge quantity of water is used in cooling systems, which is around 2.5 to 3.5 cubic meters per megawatt-hour (MWh) for new plants, while older plants may consume more depending on their technology and cooling systems. On the other side, chemical plants also require freshwater for various operational works like cooling, cleaning, and reaction mixtures. The consumption amount depends on significant factors like the type of reaction or the chemicals.
Both these industries generate high amounts of wastewater that contain pollutants, chemicals, high BOD, COD and high levels of salinity. The untreated wastewater discharge in the environment poses a high risk to the sustainability of flora and fauna. It disrupts the ecosystem and contaminates the freshwater bodies. That’s the reason power plant water treatment is being exercised with maximum action.
Now let’s understand the ZLD water treatment plant process and its importance in power plants as well as in chemical plants. Zero Liquid is a highly advanced wastewater treatment technology that eliminates any liquid discharge from a chemical or power plant.
The Zero Liquid Discharge system employs a comprehensive approach to wastewater treatment generated during operational processes. It includes various stages of treatment such as reverse osmosis, evaporation, and crystallization for the separate of water from contaminants and dissolved solids to make it clean for further use.
The treated wastewater will be used within the plant while the remaining will be disposed of in an environmentally-safe manner. The Zero Liquid Discharge thus helps chemical and power plant companies to significantly reduce their freshwater consumption, minimize wastewater generation, and ensure compliance with stringent environmental regulations.
The working of Zero Liquid Discharge is almost the same in chemical and power plants. Here are the major stages of its working:
Pre-treatment is simply the removal of items which can be easily separated out before the wastewater goes for the further treatment process. This step is essential to ensure that no items in the wastewater scale or foul the further steps of treatment. Generally, this treatment stage consists of a clarifier or a reactor that can remove metals, hardness, and silica. It may also include screening, sedimentation, and oil-water separation.
In the primary treatment stage, the wastewater will enter into clarifiers and settling tanks. At this stage, the suspended solids and organic matter will settle as sludge. This sludge is separated from the wastewater and sent for further treatment or disposal.
In the secondary treatment stage, the partially treated wastewater is further treated using biological processes like activated sludge, extended aeration, or sequencing batch reactors (SBR). All these biological processes use micro-organisms for the breakdown of dissolved biological contaminants and consume organic pollutants, further reducing their concentration in the water.
Generally, after the secondary treatment, the water is of good quality to be discharged into freshwater bodies or used for other purposes. However, for industries like power and chemicals, it also undergoes advanced treatment to achieve zero liquid discharge. It involves a combination of various processes like Reverse Osmosis (RO), Evaporation, Crystallization, and Drying.
Let’s understand each of these processes in brief:
In the reverse osmosis process, the water is passed through semi-permeable membranes under high pressure. The membranes obstruct the path of the contaminants and impurities and allow clean water to pass through. This method is highly efficient in removing dissolved salts, inorganic compounds, and other contaminants. The resultant water, which is also known as permeate, is comparatively pure and can be used for further purposes.
The remaining concentrated water, i.e. brine or concentrate, is subjected to evaporation. The water is evaporated by applying heat, and it leaves behind a highly concentrated solution.
The leftover concentrated solution is passed through a crystallization process in which the dissolved solids and minerals solidify into crystals. These crystals are then separated and collected for proper disposal.
To get rid of any last traces of moisture, the solid residue left over from the crystallization process is further dried. The resultant dry solids can either be disposed of or put to good use as energy or for land application.
In the whole process of zero liquid discharge, the treated water is recovered and recycled for various purposes within the chemical or power plant. It can be used as process water, cooling water, or for equipment cleaning. ZLC minimizes the water intake by maximizing water recovery.
The implementation of Zero Liquid Discharge in chemical and power plants will be a crucial step towards environmental sustainability, water savings, and mitigating the harmful impacts of wastewater discharge on the environment. The companies can conserve water, prevent pollution, ensure regulatory compliance, and even recover valuable resources from their wastewater.
Wipro Water has vast experience of custom-designing and manufacturing industrial wastewater treatment plants with ZLD technology. We can help you achieve zero liquid discharge by developing the proper solution and realistic cost for your ZLD wastewater treatment system needs.