sewage purification

例句：

1. 1. The city has implemented strict sewage treatment measures to reduce pollution.
   该市实施严格的污水处理措施以减少污染。
2. 2.The sewage treatment plant is the heart of the city's environmental protection efforts.
   污水处理厂是城市环境保护工作的核心。
3. 3. The process of sewage purification involves treating raw sewage to remove harmful substances before it is discharged into the environment.
   污水净化过程涉及对原始污水进行处理，以去除有害物质后再排放到环境中。