| dc.description | Manganese (Mn) is a commonly occurring drinking water contaminant that poses a major problem to utilities across North America. Its presence often results in "dirty water" associated problems, distribution system fouling, and could indirectly cause health problems as it disrupts other treatment barriers and potentially acts as a sink for numerous toxic heavy metals. Widespread problems continue across North America even when drinking water utilities meet drinking water guidelines, which have been set at 0.05 mg/L for a maximum concentration of Mn in bulk water. In order for utilities to stop the Mn related problems they must have a better understanding of the main mechanisms responsible for the problems in distribution systems. Previous studies have typically been full-scale evaluations that are specific to a particular region. While these studies have provided valuable insight it is hard to apply their findings to a broader region. The main objective of this dissertation was to provide a more detailed picture of manganese in distribution systems through bench-scale experimentation, overcoming some of the shortcomings of previous full-scale studies. This novel approach examined many factors: Mn concentration, presence and concentration of chemical oxidants, the presence of manganese oxidizing bacteria (MOB), pipe material, organic matter, surface adsorption, and detachment. Annular reactors modeled the entire system over a yearlong period, considered all of the above factors, and examined numerous reactions in bulk water and on pipe surfaces. Batch tests looked specifically at reactions occurring only in bulk water considering all factors except for pipe material and MOB. Additional experiments looked at a single important aspect of this particular environment. Inactivation tests of MOB, by chlorine, in suspension and in a biofilm were run, which has never been done for this species of bacteria before ( Leptothrix discophora SP-6). Adsorption tests were also run of Mn onto different pipe surfaces, with varying Mn concentration, time, and oxidation state. It was concluded that in most chlorinated environments both chemical oxidation by chlorine, and microbial oxidation by MOB are dominant mechanisms for Mn oxidation and accumulation. In the absence of chlorine, MOB are the dominant oxidation and accumulation mechanism, with minimal to no surface adsorption of Mn to cast iron and polycarbonate surfaces respectively. Cast iron pipes in particular offer protection to MOB from disinfection. "Dirty water" problems will arise at concentrations as low as 0.02 mg/L. They results of these experiments are comparable to full-scale study, but are more comprehensive, showing how several factors interact with one another to affect Mn. Utilities should consider using an alternative disinfectant that will not chemically oxidize Mn, such as chloramines. They need to maintain a constant disinfectant residual since changes often result in sloughing of Mn and Fe oxides and it would help to control MOB biofilm growth. It is also pertinent that utilities strive to achieve greater removal of Mn during treatment, reducing the amount of dissolved Mn entering the distribution system, ideally as low as 0.01 mg/L. They should be aware that Mn2+ can enter the distribution system on organic matter, so removal of this material is essential as well. Utilities should also monitor their water and distribution system deposits periodically for harmful toxic metals since even small concentrations of Mn oxides can result in the accumulation of high concentrations of these toxins. | en_US |
