Abstract：
Low temperatures limit the denitrification wastewater in activated sludge systems, but this can be mitigated by addition of redox mediators (RMs). Here, the effects of chlorophyll (Chl), 1,2-naphthoquinone-4-sulfonic acid (NQS), humic acid (HA), and riboflavin (RF), each tested at three concentrations, were compared for denitrification performance at low temperature, by monitoring the produced extracellular polymeric substances (EPS), and characterizing microbial communities and their metabolic potential. Chl increased the denitrification rate most, namely 4.12-fold compared to the control, followed by NQS (2.62-fold increase) and HA (1.35-fold increase), but RF had an inhibitory effect. Chl promoted the secretion of tryptophan-like and tyrosine-like proteins in the EPS and aided the conversion of protein from tightly bound EPS into loosely bound EPS, which improved the material transfer efficiency. NQS, HA, and RF also altered the EPS components. The four RMs affected the microbial community structure, whereby both conditionally abundant taxa (CAT) and conditionally rare or abundant taxa (CRAT) were key taxa. Among them, CRAT members interacted most with the other taxa. Chl promoted Flavobacterium enrichment in low-temperature activated sludge systems. In addition, Chl promoted the abundance of nitrate reduction genes narGHI and napAB and of nitrite reduction genes nirKS, norBC, and nosZ. Moreover, Chl increased abundance of genes involved in acetate metabolism and in the TCA cycle, thereby improving carbon source utilization. This study increases our understanding of the enhancement of low-temperature activated sludge by RMs, and demonstrates positive effects, in particular by Chl.
摘要：
低温限制了活性污泥系统中的反硝化废水，但这可以通过添加氧化还原介体(RM)来缓解。这里,叶绿素（Chl）的影响，1,2-萘醌-4-磺酸(NQS)，腐殖酸（HA），和核黄素（RF），每个在三个浓度下测试，比较了低温脱氮性能，通过监测产生的胞外聚合物(EPS)，并表征微生物群落及其代谢潜力。Chl提高反硝化速率最多，即与对照相比4.12倍，其次是NQS（增加2.62倍）和HA（增加1.35倍），但RF有抑制作用。Chl促进EPS中色氨酸样和酪氨酸样蛋白的分泌，并有助于蛋白质从紧密结合的EPS转化为松散结合的EPS，提高了材料的输送效率。NQS,HA,和RF也改变了EPS组件。四个RM影响微生物群落结构，其中条件丰富的分类单元（CAT）和条件稀有或丰富的分类单元（CRAT）都是关键分类单元。其中,CRAT成员与其他分类群的互动最多。Chl促进低温活性污泥系统中黄杆菌的富集。此外,Chl促进了硝酸盐还原基因narGHI和napAB以及亚硝酸盐还原基因nirKS的丰度，norBC,NosZ此外，Chl增加了参与乙酸代谢和TCA循环的基因的丰度，提高碳源利用率。这项研究增加了我们对RM增强低温活性污泥的理解，并显示出积极的效果，特别是Chl。
