Study on performance and mechanism of enhanced biological nitrification by zero-valent iron

doi:10.11949/0438-1157.20210310

Abstract

Abstract:

Emerging contaminants such as triclosan (TCS) and nano-copper (CuNPs) will enter the sewage treatment system and inhibit the biological nitrification performance, and long-term exposure to sludge microorganisms might cause the risk of enrichment and spread of antibiotic resistance genes. The nitrification inhibited by contaminants is improved by adding zero-valent iron in this study. Under the single and combined exposure of TCS and CuNPs, the enhanced effect of zero-valent iron on sludge nitrification was explored by measuring the concentration of ammonia nitrogen in the effluent, and the mechanism of enhanced biological nitrification efficiency by zero-valent iron was investigated by measuring pollutant concentration, nitrification enzyme activity, nitrification functional gene abundance and microbial population structure. Additionally, the influence of zero-valent iron on the fate of TCS resistance gene (mexB) and copper resistance gene (copA) was studied. When nitrification was inhibited by TCS and CuNPs, the introduction of zero-valent iron could increase (0.5%—6.7%) the removal efficiency of ammonia nitrogen in one reaction cycle to a certain extent, and the zero-valent iron was beneficial to the improvement and recovery of nitrification efficiency during long-term operation. Mechanism studies have shown that zero-valent iron could reduce the concentration of Cu²⁺ and TCS in the system, thereby reducing the toxicity of pollutants. In addition, zero-valent iron could increase the activity of two nitrification enzymes—AMO enzyme and NXR enzyme, and increased the abundance of amoA enzyme functional genes, besides, the abundance of Nitrospira and Lacibacter bacteria was increased by the addition of zero-valent iron, thus enhancing the nitrification performance of the sludge. It was worth noting that exposure of TCS and CuNPs would cause the enrichment of mexB and copA genes, meanwhile zero-valent iron would increase the abundance of mexB, copA genes as well, and increase the risk of transmission of resistance genes.

Key words: triclosan, copper nanoparticles, nitrification, antibiotic resistance genes, microbial community, enzyme, aeration, pollution

摘要：

三氯生（TCS）、纳米铜（CuNPs）等新型污染物进入污水处理系统后会抑制生物硝化效果，且对污泥微生物的长期暴露可能引发抗性基因的富集与传播风险，本研究通过添加零价铁改善受污染物抑制的生物硝化作用。在TCS、CuNPs的单独及联合暴露下，通过测定出水氨氮浓度探究零价铁对污泥硝化的强化作用，通过测定污染物浓度、硝化酶活力、硝化功能基因丰度及微生物种群结构探究零价铁强化生物硝化效能的机理；此外，探究了零价铁对TCS抗性基因（mexB）及铜抗性基因（copA）富集规律的影响。在硝化作用受到TCS、CuNPs抑制时，零价铁的引入可一定程度提高（0.5%~6.7%）一个反应周期内氨氮的去除效率，且长期运行中零价铁有利于硝化效率的提高与恢复。机理研究表明零价铁可降低系统中Cu²⁺和TCS的浓度，从而减轻污染物的毒性，此外，零价铁可提高两种硝化酶——AMO酶和NXR酶的活性，增加amoA酶功能基因的丰度，促进Nitrospira和Lacibacter的增长，因此强化了污泥的硝化性能。值得注意的是，TCS和CuNPs的暴露会引起mexB基因及copA基因的富集，而零价铁亦会增加mexB、copA基因的丰度，提高抗性基因的传播风险。

关键词: 三氯生, 纳米铜, 硝化, 抗性基因, 微生物群落, 酶, 曝气, 污染

CLC Number:

Q 939.99

Hong CHEN,Jing XIE,Yuying CHENG,Xin YU,Shanping CHEN,Gang XUE,Meilin WANG,Yi LUO,Xiangyu HE. Study on performance and mechanism of enhanced biological nitrification by zero-valent iron[J]. CIESC Journal, 2021, 72(10): 5372-5383.

陈红,谢静,成钰莹,于鑫,陈善平,薛罡,王美琳,罗意,贺向宇. 零价铁强化生物硝化效能及机理研究[J]. 化工学报, 2021, 72(10): 5372-5383.

Figures/Tables 7

Fig.1 The change of ammonia nitrogen concentration with time when short-term exposure (a) and long-term exposure (b) to pollutants and changes of nitrate nitrogen concentration with time under long-term exposure of pollutants (c) (The data in Fig. (b) when long-term exposure without adding iron were quoted from Ref.[4])

Fig.2 Concentrations of Cu2+ (a) and TCS (b) in sludge and liquid phases

Fig.3 XPS spectra of Fe in activated sludge in the Control group (a) and Control+Fe group (b) and the Fe3+ concentration in the four reactors in the Sludge-Fe group (c)

Fig.4 AMO enzyme activity(a), NXR enzyme activity(b) and amoA gene abundance(c) in each reactor

Fig.5 Abundance of related resistance genes in each reactor

Fig.6 Differences in microbial community structure between Sludge group (a) and Sludge-Fe group (b) (phylum level)

Fig.7 Differences in microbial community structure between Sludge group (a) and Sludge-Fe group (b) (genus level)

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