反硝化深床滤柱深度脱氮效果及反硝化功能基因分析

采用石英砂、活性炭双层滤料反硝化深床滤柱处理城镇污水处理厂二沉池出水中硝酸盐氮（NO₃^--N），研究了深床滤柱反硝化脱氮性能以及主要反硝化功能基因对进水碳氮比（化学需氧量/总氮，即COD/TN，简称C/N）的响应。结果表明，NO₃^--N平均转化率随着C/N升高，由46.5%升高至90.0%，化学需氧量（COD）平均去除率由97.2%降至76.5%。低碳氮比（C/N<6）条件下，出水亚硝酸盐氮（NO₂^--N）出现明显的积累，在C/N=4.2时，积累率达41.5%，在高碳氮比（C/N ≥ 6）条件下，NO₂^--N积累量逐渐减少，直至出水无NO₂^--N。研究表明，反硝化深床滤柱对污染物的转化主要发生在前35cm滤料深度，COD去除率和NO₃^--N转化率分别为94.0%、81.2%。采用荧光实时定量PCR技术在C/N分别为4.2、6和7条件下，对深床滤柱中反硝化功能基因napA、narG、nirK、nirS和nosZ数量进行分析，结果表明，随着C/N升高，各反硝化功能基因拷贝数也随之升高，说明增加碳源投加量可以为反硝化细菌提供更好的生长环境，有利于其生长繁殖，促进反硝化过程的进行；当narG基因拷贝数大于（nirS+nirK）基因拷贝数时，NO₂^--N会产生积累。

Nitrogen removal performance of deep-bed denitrification filter and analysis of denitrifying genes

The denitrification performance and the change of denitrifying genes under different chemical oxygen demand (COD)/total nitrogen (TN) (C/N) conditions in a deep bed denitrification filter which used dual medium of quartz sand and activated carbon were investigated, when the filter treated the nitrate (NO₃^--N) of effluent from the secondary sedimentation tank in urban wastewater treatment plant. The result showed that the average of NO₃^--N conversion rate and COD removal efficiency increased from 46.5% to 90.0% and from 97.2% to 76.5%, respectively. Nitrite (NO₂^--N) accumulated under low C/N (C/N<6). When C/N was 4.2, NO₂^--N accumulation ratio reached 41.5%. With the increase of C/N (C/N ≥ 6), the accumulation of NO₂^--N gradually decreased until no NO₂^--N was detected in the effluent of the filter. The pollutants removal in the deep-bed denitrification filter mainly occurred in the first 35cm, which allowed for COD removal efficiency and NO₃^--N conversion rate of 94.0% and 81.2%, respectively. When C/N was 4.2, 6 and 7, the abundance of napA, narG, nirK, nirS and nosZ genes in the deep-bed denitrification filter was investigated by real-time quantitative PCR (qPCR). The number of denitrifying genes copies increased with the increase of C/N. It was found that the increase of carbon source could provide better environment for denitrifying bacteria and be beneficial to the growth and reproduction of denitrifying bacteria and then promote the denitrification process. Moreover, it was concluded that when the number of narG copies was higher than the sum of nirS and nirK copies, there was nitrite accumulation.