城市污水生物脱氮系统中DNRA的检测与分析

Detection and Genetic Analysis of Dissimilatory Nitrate Reduction to Ammonium in Biological Nitrogen Removal System for Municipal Sewage

在污水生物脱氮过程中,硝化阶段产生的硝酸盐在反硝化阶段被还原为氮气从而达到脱氮目的,此外,硝酸盐还可能被还原为铵(DNRA过程),但在污水处理中是否存在这一过程尚有争议。为此,以西安市某污水处理厂A^2/O工艺中的厌氧池为研究对象,在氮平衡分析的基础上,对污泥进行连续培养,探讨DNRA现象。现场检测结果表明,在6500 m^3的厌氧池中TN的平均损失量为177.6 kg/d,硝态氮的平均损失量为235.2 kg/d,TN损失量低于硝态氮损失量,说明可能存在DNRA过程。在进水NO3^-N和COD浓度分别为20、200mg/L的条件下,对活性污泥进行了50个周期的连续富集培养,出水氨氮浓度达到了10 mg/L,证明城市污水生物脱氮系统中确实存在DNRA过程;接种污泥和培养污泥的16SrRNA和nrfA功能基因测序结果显示,进行DNRA的主要菌属为变形菌门中的Thauera、Hydrogenophaga和Geobacter。

The nitrate produced in the nitrification stage is reduced to N2 in the denitrification stage to achieve the purpose of denitrification in the biological nitrogen removal process of sewage. In addition, nitrate may also be reduced to ammonium ( dissimilatory nitrate reduction to ammonium, DNRA), but whether the process takes place in the sewage treatment is still controversial. Therefore, nitrogen equilibrium analysis was carried out in an anaerobic tank in A^2/O process of a sewage treatment plant in Xi' an. On this basis, the sludge was continuously cultured to explore the phenomenon of DNRA. Field measurement results showed that the average loss of total nitrogen was 177. 6 kg/d, and the average loss of nitrate nitrogen was 235. 2 kg/d in the anaerobic tank with a volume of 6 500 m^3. The loss of total nitrogen was lower than that of nitrate nitrogen, indicating that DNRA process might exist. Under the condition of NO3^-- N concentration of 20 mg/L and COD concentration of 200 mg/L, activated sludge was continuously enriched and cultured for 50 cycles, and the ammonia nitrogen concentration of the effluent reached 10 mg/L, which proved that DNRA process indeed existed in the municipal sewage biological nitrogen removal system. Sequencing results of 16S rRNA and functional genes of nrfA in inoculated sludge and cultured sludge showed that the major genera for DNRA were Thauera, Hydrogenophaga and Geobacter in phylum of Proteobacteria.