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氮素是导致水体富营养化的重要营养物质之一,污水处理厂总氮排放标准为15~20 mg L−1,远高于地表水环境质量标准(GB 3838-2002)。过量的氮排入地表水会造成水体富营养化。因此,对污处理水厂的二级处理出水进行再处理尤为迫切,而潜流型人工湿地因其处理效率高和具有多重生态服务功能而在污水再处理中得到广泛应用[1]。潜流型人工湿地是通过植物、微生物、基质间的协同作用实现氮去除。有研究[2-5]表明,植物吸收和基质吸附对氮去除的贡献较小,微生物对氮的转化利用才是主要的脱氮途径。潜流型人工湿地微生物脱氮主要依靠硝化和反硝化过程[6],介导硝化反应的细菌主要是好氧的自养微生物,而介导反硝化过程的微生物主要是厌氧的异养微生物[7],且该过程需要碳源提供电子受体。传统的人工湿地中总氮去除率为40%~55%[8],很多人工湿地总氮处理效率均低于50%[9]。氮去除主要受氧气和有机碳不足的限制[10],因此,亟需采取强化措施提高人工湿地脱氮效率。LAI等[11]对曝气条件下的垂直流人工湿地的脱氮效果进行了研究并发现,在C/N由3增加到12的过程中,TN、
${\rm{NO}}_3^ - $ 、COD去除率随C/N增加而增加,但C/N过高会抑制${\rm{NH}}_4^ + $ 的去除。CHEN 等[12]的研究表明,在无曝气、碳源缺乏条件下(C/N=1.6),因${\rm{NO}}_3^ - $ 与${\rm{NO}}_2^ - $ 竞争电子受体,导致${\rm{NO}}_2^ - $ 积累;而在C/N增加到2.8时,在种植植物下TN去除率可达99%,且无${\rm{NO}}_2^ - $ 积累。曝气和C/N对低C/N污水中氮转化途径具有重要影响,然而,曝气条件下低C/N污水处理效果和微生物对不同C/N的响应仍不清楚。在植物生长旺盛期,植物根系分泌物中的可溶性糖和小分子有机酸(乙酸、草酸、琥珀酸等)可以为反硝化微生物提供部分碳源[13]。已有文献中,多采用5∶1、10∶1、15∶1等较高的C/N研究不同C/N对人工湿地污水处理效果[14-15]。然而在高C/N条件下,虽然氮去除效率较高,但也会消耗更多的可溶性氧,会限制好氧硝化过程;同时,过量的碳源也会增加二次污染的风险[16-17]。因此,只有平衡碳源和可溶性氧的需求才能实现最佳的氮去除效果,节能减耗。本研究在芦苇旺盛期开展,评价了在曝气条件下不同低C/N(0.9∶1,2∶1,4∶1)对污水的处理效果,阐明了在低C/N污水处理中氮去除的微生物机制,以期为水平潜流型人工湿地的节能运行提供参考。
曝气条件下进水C/N对水平潜流型人工湿地脱氮效果和氮转化功能微生物丰度的影响
Influence of C/N ratio on the nitrogen removal and functional microbial abundance under aeration condition in horizontal subsurface flow constructed wetlands
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摘要: 为提高潜流型人工湿地在低C/N条件下的污水处理效果,考察了在植物生长旺盛期曝气条件下不同C/N(0.9∶1、2∶1、4∶1)对污水的脱氮效率、微生物群落结构和功能微生物丰度的影响。结果表明:
${\rm{NO}}_3^ - $ 去除率为57.48%~83.19%且随C/N的增加而增加;当C/N为2和4时,可提高COD和TN的去除率,COD和TN去除率均达到80%以上。当C/N为2和4处理组的nirK、nosZ、厌氧氨氧化细菌16S rRNA基因丰度均显著高于当C/N为0.9时的处理组(P<0.05);nxrA基因丰度随C/N增加而降低。物种数、Shannon-Wiener指数、Simpson指数、Chao1指数均随C/N的增加而增加。在不同处理组中相对丰度较高的细菌均为变形菌门和酸杆菌门,其占总细菌序列的62.89%~69.66%。对细菌群落结构进行PCoA分析,发现不同处理组间微生物群落组成结构差异较大。由此可见,在植物生长旺盛期,调节C/N为2和4均可显著提高污水处理效果,曝气和添加碳源强化措施可通过改变基质中氮转化功能微生物丰度和微生物群落结构来提高低C/N污水处理效率。Abstract: To improve the removal efficiency of the low C/N ratio sewage by subsurface flow constructed wetland, the influences of C/N ratios(0.9∶1, 2∶1, 4∶1) on the nitrogen removal rate, microbial community structure and functional microbial abundance under aeration condition in horizontal subsurface flow constructed wetlandsat the vigorous stage of plant growth were studied. The results were as follows: the removal rate of${\rm{NO}}_3^ - $ was 57.48%~83.19%, and increased with the increase of C/N ratio. The removal rates of COD and TN increased as the C/N ratio increased to 2 and 4, and both of them were above 80%. The gene abundance of nirK, nosZ and anammox bacterial 16S rRNA of the treatments with C/N ratios of 2 and 4 were significantly higher than that of the treatment with low C/N ratio (C/N=0.9) (P<0.05); the gene abundance of nxrA decreased as the C/N ratio increased. The bacterial species number, Shannon-Wiener index, Simpson index and Chao1 index increased with the increase of C/N ratio. The Proteobacteria and Acidobacteria were the dominant bacteria in all treatments, which accounted for 62.89%~69.66% of the total bacteria sequences. Principle coordinate analysis of bacterial communities showed that there were huge differences of microbial community among the three treatments. Thus, adjusting the C/N ratio to 2 and 4 could improve the removal efficiency of the sewage in the horizontal subsurface flow constructed wetland during the vigorously stage of plant growth. Adding carbon source and changing aeration condition could change the functional gene abundance and microbial community structure in the substrate to improve the removal efficiency of contaminants. -
表 1 目的基因定量PCR引物
Table 1. Primers of target genes used in quantitative PCR
基因 引物 引物序列 (5′~3′) 扩增长度/bp anammox 16S rRNA AMX809F GCCGTAAACGATGGGCACT 257 AMX1066R AACGTCTCACGACACGAGCTG amoA amo598f GAATATGTTCGCCTGATTG 120 amo718r CAAAGTACCACCATACGCAG nxrA F1norA CAGACCGACGTGTGCGAAAG 322 R1norA TCYACAAGGAACGGAAGGTC nirK nirK583F TCA TGGTGCTGCCGCGKGACGG 326 nirK909R GAA CTTGCCGGTKGCCCAGAC nirS nirScd3aF GT(C/G)AACGT(C/G)AAGGA(A/G)AC(C/G)GG 425 nirSR3cd GA(C/G)TTCGG(A/G)TG(C/G)GTCTTGA nosZ nosZ1527F CGCTGTTCHTCGACAGYCA 250 nosZ1773R ATRTCGATCARCTGBTCGTT 表 2 不同处理的微生物群落丰富度和多样性指数
Table 2. Richness and diversity indices of the microbial communities in different treatments
处理 物种数 Shannon-Wiener Simpson Chao1 CW0 2 186 9.738 0.994 3 616.17 CWH 2 353 9.742 0.995 4 103.56 CWC 2 478 9.819 0.996 4 326.24 -
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