Bioaugmentation treatment of coal chemical reverse osmosis concentrate in biological contact oxidation system coupled with ozone pretreatment

With the zero discharge requirements of coal chemical industry in China, reverse osmosis technology and fractional crystallization technology have been applied to recover water and valuable salts. Organic matter significantly inhibits salt crystallization, therefore it is urgent to remove organic matter from coal chemical reverse osmosis concentrate (CCROC) efficiently and economically. Common biological systems have the bottlenecks of long start-up period and poor pollutants removal efficiency due to the inhibition of toxic compounds and high salinity to the microorganisms. In this work, a self-prepared halotolerant bacteria preparation (HBP, mixture of screened Bacillus, Pseudomonas, and Halomonas with strong degrading capacity of CCROC) was inoculated into different biochemical systems (activated sludge and biological contact oxidation in sequencing batch reactor) to try to enhance the pollutants removal of extremely refractory CCROC (BOD5/COD of 0.05). The results showed that HBP increased the total organic carbon (TOC) removal efficiency from 8% to 15% in activated sludge system. In addition, biological contact oxidation reactor (BCOR) could better retain the HBP, leading to a higher TOC removal efficiency (20%). Typically, the inoculation of HBP without activated sludge in BCOR contributed to the highest TOC removal (28%). The class Bacilli (genus Bacillus) was dominant during the start-up and stable period of this bioaugmented treatment process. To further increase the pollutants removal, ozone oxidation pretreatment was conducted prior to biological treatment to break the ring structures. The total TOC removal increased to 42% under the combined treatment, while the dominant classes in biofilms shifted to Actinobacteria, Gammaproteobacteria, Alphaproteobacteria, and Bacteroidia. This study provided an effective approach for CCROC treatment with industrial application potentials.