Interactions between heterotrophic and autotrophic bacteria in fixed-film biological processes used in drinking water treatment

iological nitrification in water treatment is largely used in Europe to remove ammonia before the final disinfection step. In order to simulate this process in the laboratory, a scaling procedure for biofilm processes was developed and evaluated. Experiments conducted with these laboratory-scale reactors simulating nitrification in water treatment showed that in addition to remove ammonia, biological treatment can be used to remove easily biodegradable organic compounds such as acetate, and some trace concentrations of common micropollutants, such as phenol, monochlorophenol and chlorinated benzenes. Whereas phenol and monochlorophenol are removed immediately, chlorinated benzenes are removed after an adaptation period attributed to the time required for enzyme inductions. The biodegradation of high-molecular-weight organic compounds was estimated by challenging the laboratory scale reactors with two proteins of similar molecular weight but opposite net charge and a polysaccharide. While the proteins were hydrolyzed and assimilated the biofilm, the polysaccharide was not hydrolyzed. These results demonstrated the presence of proteolytic enzymes and the absence of polysaccharadase in an unacclimated biofilm.;A steady-state biofilm model, describing the species distribution profile in a biofilm and incorporating the accumulation of inert biomass, was derived to predict the performance of biofilm processes fed with more than one substrate oxidized by more than one species. Evaluation of this model in experimental conditions relevant to water treatment showed a good agreement between theoretical and experimental fluxes. Modeling predictions and experimental data showed that for a completely mixed reactor, the growth of acetate utilizers do not significantly affect the growth of nitrifying bacteria for a range of acetate concentration of 0 to 179...