Wash water is treated so that it can be used as a fertiliser

After distillation the wash water contains only potassium, the last step of the wash water treatment is neutralization with nitric acid to obtain potassium saltpetre as a fertilizer.

That is why it is necessary to determine the pH value. The easiest way to measure the pH value is to use litmus indicator strips. Multi range test strips are available and will colour after contact with water and the colour will indicate the pH value.

The pH value is measured and neutralised by adding nitric acid (HNO3). Nitric acid is mainly used in the neutralisation of biodiesel wash water to form potassium saltpetre (KNO3) as a fertiliser.

It is a widely used crop fertilizer.