浮渣

例句：

1. 1. Thefactory discharged a lot of sludge into the river.
   工厂向河流排放了大量污泥。
2. 2. The scum on the surfaceof the lake was caused by the pollution.
   湖泊表面的浮渣是由于污染造成的。
3. 3. Theresidue left after the chemical reaction is importantfor further analysis.
   化学反应后留下的残余物对进一步分析很重要。