For power plant owners, water management is a top priority!
Many variables, such as tougher environmental controls on wastewater discharge, regional water shortages, and public opinion of power plants, might make it a special problem.
Zero Liquid Discharge (ZLD) can assist in resolving these concerns. The ZLD technique eliminates wastewater discharge at the end of the treatment cycle, allowing the treated water to be retrieved and reused in a variety of ways.
ZLD for power plants
While beneficial in terms of water reuse, the decision to deploy ZLD is most likely motivated by concerns about the plant's challenging environmental discharge.
When water contains difficult-to-dispose-of contaminants, it is frequently chosen. It may also be possible to do away with the necessity for discharge permits. Because coal-fired power plants have a high-water demand and difficult water discharge, zero liquid discharge is especially important for the steam electric power industry. Cooling towers, bottom ash quenching, and flue-gas scrubbing all require large amounts of water. Because of the flue-gas desulfurization process, power plant effluent can contain a lot of heavy metals (FGD).
How is ZLD technology beneficial for power plants?
According to public perception, ZLD technology not only solves the environmental problem of removing wastewater, but it also reduces the amount of water a power plant needs to draw from other sources, such as rivers, lakes, or aquifers, in order to keep running.
The method can assist plants in achieving environmental stewardship goals and improving their public perception, alleviating public worry about the plant's impact on the impacted water supply.
Globally, wastewater treatment rules are growing more stringent, with all regions expected to tighten governance in the future years. To receive government clearance, any new power plant industry must incorporate ZLD water treatment technology.
How does ZLD work?
A traditional ZLD system is a water and wastewater treatment system that takes a holistic approach. It usually entails a review of all wastewater sources as a potential resource for the plant, as well as a valuation of the water that can be reused at the end of the ZLD process.
Pre-treatment with clarifying, softening, filtration, reverse osmosis (RO), and related thickening and dewatering is common in a ZLD method.
Reverse osmosis removes dissolved solids from wastewater by concentrating the bulk of the stream via a series of membranes, resulting in a waste stream with high TDS but less overall wastewater that needs to be treated. The size of the crystallizer can be reduced by using a reverse osmosis system. However, in order to avoid membrane scaling, the RO concentrate is usually pre-softened.
Cold lime softening and filtration are recommended as two steps in the pre-treatment procedure. The lime softening lowers the pH of the water, which is caused by substances like calcium, magnesium, and silica in the water, which can create fouling or scaling of the reverse osmosis equipment. Clarifier can be used to eliminate hardness from the water in the first step. The clarifier's activity prolongs the life of downstream ultrafiltration membranes and minimises the number of cleaning cycles required. In a single unit, it combines mixing, internal solids recirculation, moderate flocculation, and gravity sedimentation.
Filtration is another step in the pre-treatment process. To remove any leftover solid particles, filtration membrane systems can be used. Backwash water is recirculated via the clarifier. If the initial salinity is not too high, reverse osmosis is then employed to remove the majority of dissolved particles from the wastewater stream during the first phases of concentration.
Sludge treatment is a phase in the ZLD process. The underflow is pushed into a thickening, which increases the concentration of the sludge, and clarifier can be utilised at this stage. The thickened underflow is directed to a filter press or pressure dewatering filter, while the overflow is returned to the clarifier. Since it eliminates the waste stream, evaporation is important in ZLD. This reduces the expense of solidified waste removal.
True, ZLD is a highly sophisticated procedure that necessitates more energy and capital than traditional wastewater treatment and disposal methods. Decision makers will push regulatory incentives in reaction to public opinion, which could make ZLD a fundamental choice in the future.