The effect of changing inter process and final disinfection reagents on corrosion and biofilm growth in distribution pipes

Abstract

Anglian Water are currently up-rating the treatment process on all their surface water sources to include ozone to aid clarification and additional GAC contact time for the removal of micropollutants such as pesticides and trihalomethanes in the water. The final disinfection for the high quality water is by either chloramination or chlorination and pumped into a distribution network containing pipes of various materials. To investigate the effect on the distribution network of chanving from pre-chlorination to an advanced water treatment process, a pipe rig was constructed at Grafham Water Works which included sections of a 60 year old cast iron main and new plastic MDPE pipework. The work was carried out in conjunction with University College London and investigated parameters including assimilable organic carbon (AOC), total organic carbon (TOC) and temperature and monitored their effect on the biofilm growth and corrosion rates. The biofilm growth and corrosion rates on the coupons inserted into the cast iron pipes of the rig were found to be related to their orientation on the main. Temperature had a significant effect and correlated to bacterial activity. During the period of investigation Grafham main works also changed over from pre-chlorination to ozonation and samples were taken from the actual distribution system pre and post the process changes. The results from these findings agreed with the pipe rig model, with the overall conclusion that the change from pre-chlorination to ozonation would have little effect on the corrosion and biofilm growth in distribution.