Initial Formation and Accumulation of Manganese Deposits inDrinking Water Pipes: Investigating the Role of Microbial-Mediated Processes

Microbial Mn(II) oxidation occurs in areas withinsufficient disinfectants in drinking water distribution systems.However, the overall processes of microbial-mediated Mn depositformation are unclear. This research investigated the initial Mn(II)oxidation, deposit accumulation, and biofilm development in pipeloops fed with nondisinfectedfinished water for 300 days. Theresults show that it took 20 days for microbial Mn(II) oxidationand deposition to be initiated visibly in new pipes continuouslyreceiving 100 mu g/L Mn(II). Once started, the deposit accumu-lation accelerated. A pseudo-first-order kinetic model couldsimulate the disappearance of Mn(II) in well-mixed pipe loopwater. The observed rate constant reached 2.81 h-1[correspond-ing to a Mn(II) half-life of 0.25 h] after 136 days of operation.Without oxygen, Mn(II) in the water also decreased rapidly to 1.0 mu g/L through adsorption to deposits, indicating that after theinitial microbial formation of MnOx, subsequent MnOxaccumulation was attributable to a combination of microbial andphysicochemical processes. Compared to the no-Mn condition, Mn(II) input resulted in 1 order of magnitude increase in biofilmformation. This study sheds light on the increasingly rapid processes of Mn accumulation on the inner surfaces of water pipesresulting from the biological activity of Mn(II)-oxidizing biofilms and the build-up of MnOxwith strong adsorption capacity.