The ZLD system by using of coagulation-evaporation combined method

At ilam petrochemical, high TDS (Total Dissolved Solid) waste water should be sent to the evaporation pond (E.P), but at the time of the project implementation, due to lack of space, the construction of E.P has been out of scope. So, wide field studies were conducted on E.P alternative designs, which in addition to solving environmental problems by recovering major fraction of wastewater will save water. Since High TDS Waste Water treatment using evaporation creates problems such as sedimentation in the system, at first it is necessary to remove the water hardness. So the combination method was used to remove Hardness and TDS. In order to remove hardness (calcium and silica) a complete process was used to chemical softening the waste water. This process was consist of flocculation and coagulation. After the softening, treated waste water will be concentrated by Multi-Effect Distillation to achieve saturated sodium chloride. The treated water is collected in a storage tank and brine water also enters thermal crystallizer for crystallization. Last step, to crystallize sodium chloride concentrate will be send to crystallization system composed by thermal crystallizer and pusher centrifuge to obtain crystals of sodium chloride. In thermal crystallizer, due to high concentrations of effluent, evaporation should be performed by force circulation. Therefore, Ilam petrochemical waste water that is harmful to the environment, is recovered by nearly 95% recovery and is came back to the industry cycle and it saves a lot in water and energy consumption.