Corrosive Substances (pH)

Wastewater that is too acid or too alkaline can seriously corrode the sewerage system.

The letters pH followed by a number are used to express the acid or alkaline condition of a liquid.

A pH test shows acidity or alkalinity with numbers from 0 to 14. A pH of 7 indicates a neutral liquid, neither acid nor alkaline. Numbers below 7 ranging down to 0 show increasing acidity, with 0 being the most acid. Numbers above 7 ranging up to 14 show increasing alkalinity, with 14 being the most alkaline.

The photograph below is of a King County Industrial Waste investigator reading a pH meter.

In King County, the maximum limit for wastewater discharged into the sanitary sewer is pH 12. The instantaneous minimum limit is violated when any grab sample (a single, random sample) or continuous recording is less than pH 5. The daily minimum limit is violated when a recording of 15 minutes or longer remains below pH 5.5 or when four consecutive grab samples collected at 15-minute intervals or longer in a 24-hour period are all below pH 5.5.