Leaching of chromium and lead from the cement mortar lining into the flowing drinking water shortly after pipeline rehabilitation

Internal cement lining protection is used for both new and renovation of old cast iron water pipes. However, under unfavorable conditions, contaminants may be released from the cement lining into the drinking water shortly after the rehabilitation of old or installation of new water pipes. This paper proposes a mathematical model for the leaching of heavy metals from the inner cement lining of the pipe into the flowing water, taking sorption into account. Previously, mathematical models described in the literature for the leaching of contaminants from a cement coating into water only addressed static conditions or did not consider sorption. Experimental verification of the mathematical model under dynamic conditions showed very good agreement between calculated and measured results and confirmed the necessity of taking into account the sorption phenomenon. It also demonstrated the need for periodic water changes during laboratory experiments to describe the release of contaminants from the cement coating into the flowing water. Based on the results of laboratory experiments and the developed mathematical model, the concentrations of heavy metals at the ends of different lengths of drinking water supply pipeline sections after their eventual rehabilitation by cementation were calculated. Maximum lead concentrations at the end of 30, 23 and 13-km cemented sections of the pipeline were 2.0; 1.5 and 1.0 mg/m3, respectively. In contrast, chromium concentrations were 2.5; 1.6 and 0.9 mg/m3, respectively. Although all of these values are below the drinking limits, they can reach them if there is another additional source of contaminants or if the water stagnates periodically. The developed methodology and mathematical model allow to select the maximum length of the water main section that can be renovated or replaced at one time without significant impact on drinking water quality. © 2022 The Authors