Advanced treatment of petrochemical wastewater by combined ozonation and biological aerated filter

The secondary effluent from a petrochemical wastewater treatment plant was treated by biological aerated filter (BAF) before and after ozonation, namely BAF1 and BAF2, respectively. The results showed that BAF2 fed with the ozonized secondary effluent exhibited a high efficiency in degrading organic pollutants. The removal efficiency of COD and NH4-N was 6.0 +/- 3.2 and 48.2 similar to 18.6% for BAF1 and 12.5 +/- 5.8 and 62.1 similar to 40.9% for BAF2, respectively, during the whole operation. The integration system of ozonation and BAF could tolerate a higher organic loading rate. When HRT decreased from 4 to 1 h, COD removal efficiency decreased from 12 to 4% for the BAF1 system, but it kept almost unchanged at high levels of 27-32% for the ozonation-BAF2 system, with around 20% removal by ozonation. The biomass in BAF2 exhibited a higher activity of protease, DHA, and SOUR than that in BAF1. The organic pollutants in influent and effluent of BAF were mainly ester compounds, which were difficult to biodegrade by BAF. The predominant genera in BAF1 were Gemmatimonadaceae uncultured, Thauera, and Thiobacillus, while the dominant genera in BAF2 were Nitrospira, Gemmatimonadaceae uncultured, and Flexibacter, respectively. Overall, BAF2 performed better than BAF1 in organic pollutant removal and microbial activity. The ozonation process was vital for BAF to treat petrochemical secondary effluent.