Analysis of the Impact of Citric Acid CIP Carryover on Disinfection By-Product Formation in Membrane Treatment Facilities

Contamination of membrane systems treated water from clean-in-place (CIP) chemicals is un-avoidable. Citric acid is of particular concern as it will react with chlorine disinfection in the downstream process resulting in formation of DBP. In order to estimate the quantity of citric acid carryover at a WTP, a series of bench-scale tests were conducted indicating a citric concentration of 1.8 mg/L to the plant clearwell with corresponding increase in THM (chloroform) from 39 g/L to 50 g/L and an HAA increase from 35 g/L to 63 g/L. Reduced citric acid concentration in the treated water resulted in even higher THM formation to a maximum of 56 g/L since the pH was not as low. For source waters with higher alkalinity, buffer capacity can mask the presence of citric acid carryover. A review of the existing CIP cleaning process was undertaken to identify options to reduce carryover and an improved method of flushing the CIP solutions from the membrane is proposed whereby the CIP solution is flushed by air-purge displacement, rather than traditional dilution flushing. The overall impact on the water supply due to CIP carryover is likely nominal on an annualized basis. However, short term spikes in THMs and HAAs may result in sample failure in the distribution system depending the pH and citric acid carryover. Changes to the CIP flushing procedures could reduce these spikes, risk of sample failure and potentially reduce the volume of flush water required.