使用过的油需按要做滴定法来确定正确的氢氧化纳使用量。

For used oil, you should do a titration to determine the correct amount of NaOH to use.

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其将用过的油去除颜色及不纯颗粒，然后该油使用达10多天。

It removes color and impure bits from used oil, which is then used for up to 10 more days.

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共查获百余吨非法食用油，均收集自餐馆已经使用过的油和从下水道中所刮的油。

The police found hundreds of tons of illegal cooking oil, collected from oil already used in restaurants and scraped from the gutters.

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