Control Strategies for the Mitigation and Removal of Attached Manganese Biofilms

Abstract

Biofilm formation and manganese oxidizing bacteria (MOBs) in water transmission and distribution systems can lead to a wide array of water quality issues, operational problems, and negative hydraulic impacts. To investigate possible methods to control biofilm formation, a study using chlorine dioxide (ClO2) and sodium hypochlorite (NaOCl) was performed with rotating annular reactors (ARs). Results showed that low (.5 mg/L as ClO2) and high (1. mg/L as ClO2) doses of ClO2, and 2. mg/L as Cl2 of NaOCl, were effective at mitigating biofilm to different extents by oxidizing readily available dissolved manganese (Mn) and iron (Fe) and/or inactivating biofilm populations. The most effective biofilm control strategy tested was a 2. mg/L dose of NaOCl, which provided significant reductions of suspended bacteria (2.1 log reduction), established biofilm (2.5 log reduction), and new biofilm growth (3.2 log reduction). Results from this study suggest that the implementation of treatment strategies for the control of existing and future biofilms should consider both (1) the removal of readily available metals by oxidation, and (2) the direct inactivation of attached bacteria.