Research and demonstration on reclaimation of chemical industrial wastewater with high salinity and hardness and purification of reverse osmosis concentrates

The demonstration is specifically designed to achieve the reclaimation of integrated chemical industry park wastewater (CIPWW) with high levels of hardness and salinity and the standardized discharge of concentrates generated during the reclaimation period by effectively composing dual-membrane technology combined by microfiltration (MF) and reverse-osmosis (RO) with multiple water treatment techniques. Concerning the concentrates generated by RO, the full-scale calcium-sulfate (CaSO4) crystallizer is creatively applied as the pretreatment unit for hardness removal with doubled catalytic ozonation-high performance biological aerated filter (O3-HBAF) and ultrafiltration (UF) as subsequent treatment technologies. Considering the characteristics of RO concentrates as high permanent hardness, high sulfate concentration and high refractory organic matter (ROM) content, pilot tests were conducted particularly focusing on the CaSO4 crystallizer and O3-HBAF unit which verified the reasonability of the technological process, and relevant operating parameters were optimized including flocculant dosage, catalyst dosage, etc. A series of adjustments were also made for the agent-addition devices of RO in order to stabilize the differential pressure facing variable influent circumstances. During over one-year of full-scale operation, the treated CIPWW was innovatively supplied for chemical fiber factories which established rigorous limitations on the impurity content of reuse water, and the water quality of purified RO concentrates partially met the requirements of class IV of Environmental Quality Standard for Surface Water (GB3838–2002, China). The application of CaSO4 crystallizer approximately saved the operation cost by 57.04 % compared with that of Na2CO3 softening process, and sufficiently recycled calcium ions from RO concentrates as CaSO4·2H2O products.