A Zero Liquid Discharge System (ZLD) uses advance technology for treating water to reduce and eliminate the liquid waste produced at the end of an industrial process. A well-designed, high performing ZLD treatment system does the following:
Handles variations in waste contamination and flow
Allows for required chemical volumes adjustments
Recovers approximate 95% of liquid waste for re-use
Treats and retrieves valuable byproducts such as salt and brine from waste
Produces a dry, solid cake for disposal
A ZLD treatment system is one among the many available alternatives of water purification systems. It helps a facility meet its stringent effluent requirements.
The components of a ZLD treatment system largely depend on the:
1. Volume of dissolved material present in the waste
2. Required flow rate of the system
3. Specific contaminants present in the waste
Any basic ZLD treatment system typically consists of the following:
Clarifier and reactor to precipitate metals, hardness and silica
Chemical feed to facilitate the precipitation, flocculation, and coagulation of any metals or suspended solids
Ultrafiltration to remove the leftover trace amounts of suspended solids and prevent fouling, scaling, and corrosion down the line of treatment
Reverse Osmosis to limit the bulk of dissolved solids from the water stream during the primary phases of concentration
Brine concentrators to distillate the rejected RO stream to further decrease the waste volume
Evaporator to vaporise excess water in the final phases of waste concentration
Crystalliser to boil off any remaining liquid, leaving behind a dry, solid cake for disposal
Following are the steps involved in a ZLD treatment facility to purify water:
1)Pretreatment and conditioning
Pretreatment is done to remove contaminants from the wastewater stream that can be filtered or precipitated out. This step is important for conditioning water and reducing the suspended solids and materials that could otherwise harm the following steps of treatment. Sometimes coagulation with lime or caustic soda is added to this step. Once the coagulation process is complete, water is made to pass through a flocculation chamber where particles that have been coagulated are slowly stirred together to create visible particles.
Concentration in the earlier stages of this water treatment process is done using membranes such as reverse osmosis (RO), brine concentrators, or electro dialysis.
After concentration, evaporation is conducted to generate solid waste. Acid is added at this point to help neutralise the solution to avoid scaling and harming the heat exchangers during the heating process.
4)Recycled water distribution
Treated water that is being reused for an industrial process to meet the demands of a facility needs to be purified by the ZLD system. Solid waste enters a dewatering process at this stage where the water is removed from the sludge leaving a solid cake behind, which is later reused or used for a landfill.
This water treatment system can be employed in any facility, regardless of the size and needs. If you are looking for a leading provider of water purification systems in India, make sure to check Thermax and their offerings. They hold four decades of experience in offering end-to-end solutions for water treatment to many industries, commercial, rural, hospitality and defense establishments.