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| Environmental risk and influencing factors of effluent from three-compartment septic tanks |
| Received:October 26, 2020 |
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| KeyWord:three-compartment septic tank;environmental risk;microbial community;potential pathogens;soil |
| Author Name | Affiliation | E-mail | | KUAI Wei | Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China | | | LI Hou-yu | Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China | | | GAO Yi | Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China | | | YANG Bo | Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China | | | ZHANG Chun-xue | Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China | | | XU Yan | Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China | xuyan@aepi.org.cn | | ZHENG Xiang-qun | Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China | |
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| Abstract: |
| In order to understand the effects of three-compartment septic tanks on feces disposal and their influence on the surrounding environment, a study was conducted to investigate the effluent quality characteristics from the second and third tanks of three-compartment septic tanks in the typical rural area of Guangxi, China. Horizontal and vertical soil samples around three-compartment septic tanks were collected to explore the changes in their physical and chemical indicators and the microbial community's structure to determine the environmental risks arising from three-compartment septic tanks. The study also sought to clarify the key factors influencing potential pathogenic bacteria changes in the horizontal and vertical soil around the three-compartment septic tanks. The results indicated that the average removal rates of organic matter(TOC), total nitrogen(TN), and total phosphorus(TP) in three-compartment septic tanks were 66.77%、61.82% and 26.64%, respectively. However, the TOC, TP, and TN contents in the third tank were as high as 219.0, 32.9 mg·L-1, and 226.0 mg·L-1, respectively, with the TOC content exceeding the irrigation standard requirements of GB5084-2005 Farmland Irrigation Water Quality Standard. The concentrations of TOC, TN, and TP in the soils surrounding the three-compartment septic tanks decreased with an increase in septic tank distance and profile depth. The concentrations of TOC, TN, and TP of the soil at a 10 m distance from the septic tank were 23.2 g·kg-1, 131.0 g·kg-1, and 72.3 mg·kg-1, respectively, while at 40 cm vertically, they were 22.9 g·kg-1, 89.0 g·kg-1, and 80.3 mg·kg-1, respectively. The TOC, TP, and TN content of surface soil at a 10 m distance from the septic tank was higher than that of TOC(22.3 g·kg-1), TN(79.9 g·kg-1), and TP(71.3 mg·kg-1) in the background soil. PLS-DA analysis indicated that effluent from the septic tank could affect the surrounding soil environment's microbial structure. Potential pathogenic bacteria were detected in the effluent and the soil surrounding the three-compartment septic tank. Spearman and RDA analysis indicated that TP in the horizontal soil was a key factor affecting pathogenic bacteria distribution(P<0.01). In the vertical soil, TOC was positively correlated with individual bacteria, such as Clostridiales and Bacteroidales(P<0.05). These findings showed that the three-compartment septic tanks could affect the surrounding soil' s physical and chemical properties and microbial community structure, which might be due to leakage or dripping during feces transport, thereby polluting the surrounding soil. |
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