Competitive Inhibition Of DNRA And Denitrification In Activated Sludge System

Dissimilatory nitrate reduction to ammonium（DNRA）process is to convert nitrate and other nitrogen-containing pollutants into ammonia that can be used as resources,thereby reducing nitrate emissions and maintaining ecological balance.It is of great significance to the nitrogen cycle in nature and the recycling of nitrate and nitrogen oxides in wastewater and waste gas.The DNRA ability of mixed bacteria in activated sludge system was studied in this paper.A strain with DNRA ability was successfully isolated from activated sludge samples and its nitrate reduction characteristics were studied.A sequencing batch reactor（SBR）was used to evaluate the efficiency of nitrate reduction and ammonium production under mixed conditions.The main findings are as follows:（1）The DNRA capability of the inoculated sludge was validated in a variety of externally applied carbon source environments and it was concluded that:The effect of C/N on ammonium production is greater.DNRA is more likely to dominate in the environment with higher C/N,and DNRA tends to occur in the environment with weaker oxidation degree.DNRA functional strain was obtained after qualitative detection of nitrogen forms in the crystals precipitated from the mixed bacteria under low temperature conditions.The strain was identified as Pseudomonas,and the gene accession number was OQ711934.The strain was named Pseudomonas.LZ-1.（2）The DNRA activity of Pseudomonas LZ-1 was significantly affected by carbon source C/N p H temperature and S/N.When sodium citrate was used as carbon source and C/N was 8,the strain had the strongest DNRA ability and the highest efficiency.The yield of NH₄⁺-N was21.56 mg/L and the conversion rate was 15.64%.When the initial p H was 9,the highest NH₄⁺-N production was 22.49 mg/L,and the conversion rate was 17.21%.When the initial p H was increased to 10,the DNRA ability of the strain decreased,indicating that the growth of Pseudomonas.LZ-1 would be affected in a strong alkaline environment.The DNRA ability of Pseudomonas.LZ-1 was enhanced,and the highest NH₄⁺-N production was 26.21 mg/L at 30℃,with a conversion rate of 19.88%.However,when the temperature increased to 35℃,the DNRA ability decreased,and the conversion rate of NH₄⁺-N decreased by 1.77%.Compared with the control,the addition of S^2-and SO₄^2-inhibited the DNRA process.With the increase of S/N(S^2-)ratio from 0.25 to 1,the inhibition of DNRA was weakened,the yield of NH₄⁺-N increased from 16.77 mg/L to 23.69 mg/L,and the conversion rate of NH₄⁺-N increased by5.48%.When the S/N(SO₄^2-)ratio increased from 0.5 to 4,the inhibition of DNRA was weakened,the yield of NH₄⁺-N increased from 19.69 mg/L to 29.86 mg/L,and the conversion rate of NH₄⁺-N increased by 7.37%.（3）The reactor was operated for 115 days,and the removal rate of nitrate was maintained at a high level during the operation of the reactor.In the fifth stage of the reactor operation,there was no nitrate nitrogen in the effluent.Increasing the nitrate concentration in the influent,increasing the C/N ratio and changing the HRT are helpful to reduce the nitrate to ammonia in the reactor,which can promote the DNRA process of the reactor.The addition of functional strains can also promote the ammonia production efficiency of the reactor.The highest conversion rate of NO₃^--N to NH₄⁺-N was increased from 12.98%to 19.85%by adding functional strains.The results of 16S r RNA high-throughput sequencing showed that Pseudomonas was the most abundant genus in the fourth and fifth stages,accounting for 23.94%and 32.58%,respectively.