污水处理厂出水的环境质量和农业再利用

Environmental Quality of Treated Wastewater and Its Reuse for Irrigation

对上海市正在运作的四家污水处理厂的出水质量进行监测,研究了污水厂出水的环境质量与农业再利用问题。由于处理后的生活污水和工业污水在性状上仍有很大差异,在文中分别进行讨论:(1)生活污水厂出水氮、磷负荷很高,大肠杆菌指标也严重超标。若直接用于农业灌溉,应重视营养盐和病菌对环境的污染问题。选用适当的灌溉方式,可减轻或避免这类污染。生活污水厂出水重金属含量并不高,用于农业灌溉,在短期内对土壤和蔬菜的重金属污染风险并不大;但由于重金属元素易累积等原因,这类风险还不能完全排除。(2)处理后的化工污水,仍有很高的有机污染负荷;Cl-约是《农田灌溉水质标准》中最大允许值的2倍;Zn和Cd等重金属也明显偏高。在污水厂改进处理工艺、降低各类污染物负荷前,还不能直接用于农业灌溉,以免给农业生态环境带来灾难性后果。

In order to reuse of treated water from wastewater treatment plants, we monitored the quality of outlet waters from 4 wastewater treatment plants in Shanghai. The treated domestic wastewater and industrial wastewater were discussed separately as they differed in the characteristics. The results showed: (1) High contents of N, P and microorganisms were found in the treated domestic wastewater. Therefore, proper patterns of irrigation, such as trickle irrigation, should be selected when it was reused for agriculture to avoid pathogen and nutrient pollution to crops and environment. Because of low heavy metal contents in the treated domestic wastewater, neither soil nor crops have potential of pollutants from heavy metals in a short period. However, risk of heavy metal pollution could not be prevented as heavy metals are easily accumulated in soil. (2) Organic pollutant contents in the treated chemical wastewater was high; Cl- was as high as two times the recommended limit value in《Water Quality Standards for Agricultural Irrigation》; and Zn and Cd et al were also higher than expected. To prevent from disastrous consequence to the agricultural ecological environments, such secondary wastewater should not be used for irrigation unless it is treated by more advanced processes.