Pilot-scale treatment of hypersaline coal chemical wastewater with zero liquid discharge

Abstract

Coal to chemical processes produce substantial quantities of hypersaline organic wastewater. Zero liquid discharge (ZLD) is a strategy designed to minimize the wastewater discharge. Here, a pilot-scale ZLD system, consisting of nanofiltration (NF), disc tube reverse osmosis (DTRO), chemical softening, electro-oxidation (EO) and multiple-effect evaporator/crystallizer, was built for the treatment of coal chemical wastewater. The hybrid ZLD process is capable to treat 72 m3 influent per day and reached about 98% water recovery. First, bivalent and monovalent ions were separated from the raw water by a NF-DTRO process. Then the hardness and organic substances of the wastewater were removed by the chemical softening and the EO techniques. Eventually, industrial-grade salts of Na2SO4 and NaCl were recovered through an evaporator-crystallizer. The total operating cost is estimated to be 2.3 $ m−3 influent. This pilot-scale ZLD system is applicable to the treatment and reuse of hypersaline wastewater. The work will provide insights in large-scale application of the ZLD process for wastewater treatment.