The sustainable treatment of chemical polishing wastewater under low-carbon economy: Pollutants removal, resource recovery and energy generation

A two-step approach, first by iron-air fuel cell and then by adjusting pH, was developed to treat chemical polishing wastewater, aiming at resource recovery and energy generation. The removal efficiencies of main pollutants, i.e. PO43- and Al3+ were 77.87% and 100%, the corresponding volumetric removal rates were 1.81 and 0.36 kg/(m(3)center dot d). The approach also showed removal abilities to COD, SS, NO3- and NH4+ with 77.87%, 100%, 22.96%, 16.67%, 100% and 61.53%, respectively. Nearly all of Al3+ was precipitated by PO43- in step I. Meanwhile, plenty of Fe2+ was accumulated for the following PO43- removal. In step II with pH being adjusted from 3.0 to 7.0, PO43- was supposed to be precipitated to form vivianite (Fe-3(PO4)(2)center dot 8H(2)O). By SEM-EDS, XRD, FITR and Mossbauer analysis, precipitate in step I was determined as AlPO4, while in step II it was mainly vivianite with a grade of 60%. The yield of AlPO4 and vivianite was 5.13 and 13.22 kg/t chemical polishing wastewater. Besides, electricity was generated by two-step approach. The total output energy was calculated as 0.33 kW h/t wastewater, with maximum output voltage at 0.19 V. This novel approach has potential economic advantages and will promote the sustainable development of chemical polishing wastewater treatment.