工业废水,生活污水处理后再行利用,是解决城市水源缺乏、防止城市环境污染、保护城市水源的重要措施。废污水的研究和实践,国外一些工业发达国家不仅在理论、技术、设备上较为成熟,而且投资很多,城市废污水处理普及率相当高。国外一般多采用二级处理,经过处理后的废污水再用于农业灌溉、工业冷却、卫生设备冲洗、街道清洗、城市绿化等方面。国外在近二三十年中废污水处理率有较大提高。如瑞典50年代只有10个城市有污水处理厂,到1974年已发展到1540个污水处理厂,二级处理 Industrial wastewater, domestic sewage treatment before use, is to solve the lack of urban water, to prevent urban environmental pollution, an important measure to protect urban water. Wastewater research and practice, some foreign industrialized countries are not only mature in theory, technology and equipment, but also a lot of investment, urban sewage treatment penetration is quite high. Foreign countries generally use more secondary treatment, after treatment of waste water and then used in agricultural irrigation, industrial cooling, sanitation flushing, street cleaning, urban greening and so on. Abroad in the past two decades, the sewage treatment rate has been greatly improved. For example, in Sweden, only 10 cities had WWTPs in the 1950s. By 1974, they had grown to 1,540 WWTPs and secondary treatment