Effect of Hg on nitrogen removal performance of wastewater treatment system in low-pressure conditions

doi:10.11949/0438-1157.20231393

Abstract

Abstract:

The presence of mercury (Hg) in wastewater treatment systems in low-pressure areas can potentially reduce the efficiency of wastewater treatment. In a laboratory-scale study using a sequencing batch reactor (SBR), the impact of Hg under low-pressure conditions on wastewater treatment systems was investigated. It was found that Hg significantly lowered the removal rate of ammonia nitrogen (NH₄⁺-N), particularly at high concentrations. The removal rate of NH₄⁺-N decreased from 89.73% to 38.71% with increased Hg concentrations. Hg had a detrimental effect on the nitrogen transformation process within the SBR cycle. At an influent Hg concentration of 250 µg/L, the specific ammonium oxidation rate (SAOR) and the nitrite reduction rate (SNIR) decreased by 96.74% and 96.91%, respectively, and the activities of related functional enzymes decreased by 100.00% and 97.87%, respectively. Furthermore, Hg altered the morphology and structure of the activated sludge, leading to the disintegration of the overall sludge structure and changes in surface characteristics. It also inhibited the production of extracellular polymeric substances (EPS), particularly affecting the protein content. In terms of the microbial community, the addition of Hg significantly altered the structure of the activated sludge community, especially affecting functional genera related to the nitrification process, such as Nitrosomonas and Nitrospira. Therefore, attention needs to be paid to the impact of the presence of Hg in the sewage treatment system under low-pressure conditions.

Key words: mercury, low-pressure, wastewater, environment, microbial community, bioprocess

摘要：

汞（Hg）在低气压地区污水处理系统中的存在可能会降低污水处理效率。在实验室规模下以SBR为例，通过研究Hg对低气压条件下污水处理系统的影响发现，Hg显著降低了氨氮（NH₄⁺-N）的去除率，尤其是高浓度Hg的影响更显著，NH₄⁺-N去除率从89.73%下降至38.71%。Hg对SBR周期内的氮转化过程产生了负面影响，当进水Hg浓度为250 µg/L时，活性污泥氨氧化速率（SAOR）和亚硝酸盐还原速率（SNIR）分别下降96.74%和96.91%，与之相关的功能酶活性分别降低100.00%和97.87%。此外，Hg改变了活性污泥的形态和结构，导致污泥整体结构的瓦解和表面特征的变化，同时对EPS的生成产生抑制作用，特别是蛋白质含量受到影响。在微生物群落方面，Hg的加入使活性污泥群落结构发生了显著变化，尤其是和硝化过程相关的功能菌属Nitrosomonas和Nitrospira。因此，低气压条件下需对污水处理系统中Hg存在带来的影响给予关注。

关键词: 汞, 低气压, 废水, 环境, 微生物群落, 生物过程

CLC Number:

X 703

Lei GAO, Wen DAI, Zhonglian YANG, Shuping LI, Gangyin YAN, Qi SUN, Yongze LU, Guangcan ZHU. Effect of Hg on nitrogen removal performance of wastewater treatment system in low-pressure conditions[J]. CIESC Journal, 2024, 75(5): 2036-2046.

高磊, 戴闻, 杨忠莲, 李淑萍, 闫刚印, 孙琪, 陆勇泽, 朱光灿. 汞对低气压条件下污水处理系统脱氮性能的影响研究[J]. 化工学报, 2024, 75(5): 2036-2046.

Figures/Tables 11

Fig.1 Schematic diagram of the SBR experimental setup

Table 1 Composition of microelement solution

组分	浓度/（g/L）	组分	浓度/（g/L）
FeCl₃·6H₂O	1.5	CoCl₂·6H₂O	0.15
EDTA	10	MnCl₂·4H₂O	0.12
KI	0.18	NaMoO₄·2H₂O	0.06
H₃BO₄	0.15	CuSO₄·5H₂O	0.06

Fig.2 COD and NH4+-N removal effects of different SBR systems

Fig.3 Nitrogen transformation in different SBR systems

Fig.4 Changes in the activities of nitrogen transformation and key functional enzymes of nitrogen metabolism in different SBR systems before and after Hg addition

Fig.5 SEM images of sludge before and after Hg addition in different SBR systems

Fig.6 Changes of sludge EPS and its protein and polysaccharide contents before and after Hg addition in different SBR systems

Table 2 Diversity index

样品	OTU数	Shannon 指数	Chao指数	Simpson 指数	Coverage/%
R2-60d	814	5.379	829.80	0.811	99.9
R3-60d	709	5.407	709.00	0.823	99.9
R2-90d	660	4.125	698.52	0.712	99.8
R3-90d	844	6.117	882.29	0.931	99.8

Fig.7 NMDS analysis of sludge microbial community before and after Hg addition in different SBR systems

Fig.8 Phylum level microbial community structure in SBR

Fig.9 Genus level microbial community structure in SBR

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