Because drainage oil processing is simple: put it in a huge pot and heat it up, then add some chemicals, the residues and impurities in the waste oil are separated and sink to the bottom of the pot.

因为地沟油加工程序简单：放到大锅中加热，再加入某种化学原料，废油中的残渣和杂质就被分离出来，沉淀在锅底。

youdao

The waste will add more nutrients to the soil as the pot breaks down.

VOA: special.2010.06.01