摘要:

This study developed a two-stage biofilter utilizing pyrite/sawdust composites to treat actual secondary effluent with high dissolved oxygen (DO) concentrations (3-8.5 mg/L) over a period of 169 days. The findings demonstrated that the two-stage pyrite-based biofilters achieved advanced purification of the real secondary effluent, maintaining effluent concentrations of total nitrogen (TN) and total phosphorus (TP) below 2.0 mg/L and 0.5 mg/L, respectively, with an influent TN of 10 mg/L and a temperature of >21 degrees C. The Rhodocyclaceae family is the predominant mixotrophic denitrifying bacteria in both the first-class (FC) and second-class (SC) systems. Sulfate-reducing bacteria (i.e., Desulfrispora and Desulfatirhabdium) might be keystone species in the SC system, underscoring that the sulfate reduction process enhanced denitrification under low DO conditions. Differential functional gene analysis exposed that high DO might suppress the activity of Complex III, NAR, NIR, NOR, and NOS, leading to slow-unstable electron transport and consumption in the denitrification process. Moreover, the diminished expression of S and Fe cycling genes (soxA/B/Z/X, aprA/B, dsrA/B, ABC.FEV<middle dot>S, and korA/B/C) in the FC system indicated that high DO predominantly might inhibit the Sox pathway, dissimilatory sulfate reduction process, Fe2+/Fe3+ transfer, and biological Fe2+ oxidation system. The dormancy of the S and Fe cycles induced by high DO levels primarily accounted for the diminished performance of the pyrite-based biofilters. This study offers novel insights into the extensive application of pyrite-based composites and enhances the understanding of DO effects on S and Fe cycles in the nitrogen removal process of municipal tailwater.