Date of Graduation


Document Type


Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level



Civil Engineering


Wen Zhang

Committee Member

Julian Fairey

Second Committee Member

Franck Carbonero


Bacteria, Chlorine, Chlorine Dioxide, Water Treatment


Microbial communities resistant to common oxidants can cause concerns for water treatment plants (WTPs). If a bacterium is not fully oxidized during disinfection, these species can impede upon filtration processes or seed biofilms in the distribution system. In an effort to minimize disinfection by-products (DBP's) that result from the reaction of chlorine (Cl2) with natural organic matter, water treatment plants have the option to change their primary oxidant to chlorine dioxide (ClO2). The following study examines the change in microbial communities during the sedimentation process under differing oxidation regimes, specifically chlorine (Cl2) and ClO2 at the local water treatment plant (Beaver Water District, Lowell, AR). Both water and biofilm samples taken from the sedimentation basin were investigated using a PCR approach targeting 16S rRNA coupled with denaturing gradient gel electrophoresis (DGGE). It is shown that the biofilm community in this environment exhibits higher diversity indices when compared to planktonic communities. Cl2 oxidation decreased the diversity index biofilms and basin waters that were previously under ClO2 treatment. Pelagibacter ubique, a common bacteria was observed within the basin biofilm during both Cl2 and ClO2 application. Novosphingobium aromaticivorans was also observed persistent in basin biofilms under both applications and has been linked to primary biliary cirrhosis if no defense barrier exists in the following treatment steps. This study provided valuable information for WTPs when making the decision to change primary oxidants.