Zero liquid discharge system
ZLD process typically involves the following steps: pretreatment, concentration and thermal treatment.
Pretreatment is used to reduce the amount of TSS (Total Suspended Solids), COD (Chemical Oxygen Demand) and turbidity. After removal or significant reduction of TSS, COD and turbidity of treated wastewater, other wastewater treatment processes can be used.
Concentration of dissolved solids in the ZLD system is usually accomplished by membrane technologies, such as reverse osmosis (RO), electrodialysis (ED) or by a combination of RO with ED. With the help of ED technology or the above-mentioned combination of RO + ED, we can achieve recovery of more than 98 % of treated water.
Thermal treatment - the last step of the ZLD process is usually consisting of evaporator and crystallizer. The output of this process are crystalline salts NaCl, Na2SO4, etc. These salts can be sold for further processing. Any unusable solid waste is landfilled at controlled landfills. Evaporated water can be reused as condensate.