Biofilm Drinking Water Treatment

Using biofilms to produce biologically stable drinking water while removing pollutants

PictureA map of the decay of chloramine in a medium-sized city shows that it is impossible to suppress bacterial growth when the water is biologically unstable, even with a very high disinfectant concentration at the treatment plant.

The past decade has seen the drinking-water industry in the United States join the international consensus that biofilm processes are of high value for producing high-quality drinking water.  Dr. Rittmann pioneered this concept beginning in the 1980s, and Swette Center research has been a steady force for sound applications of biofilm treatment of potable water.  Biofilm treatment addresses two major water-quality challenges.

The first challenge is to produce water that is biologically stable, which means that it does not support excessive growth of bacteria as it is being distributed to the customers.  Biodegradable organic matter and ammonium are the main causes of biological instability.  In the past, the U.S. drinking water industry applied very high doses of chlorine to suppress growth of bacteria even though the water contained significant instability.  This is no longer possible, because hyper-chlorination is no longer allowed due to it causing disinfection by-products, corrosion, taste, and odor.  Biofilm treatment is the natural means to rid the water of biodegradable substrates – by biodegrading them with carefully controlled conditions in a biofilm processes.  Biofilm processes include biologically active rapid filters, slow sand filters, and various moving-bed options.

The second challenge is to remove one or several of the oxidized pollutants the plague so many water supplies today:  e.g., nitrate, perchlorate, selenate, and TCE.  Swette Center research focuses mainly (although not exclusively) on the H2-based Membrane Biofilm Reactor (MBfR), which provides simple, reliable, and cost-effective reduction of all of the oxidized pollutants.



Two typical bench-scale MBfRs used to reduce oxidized pollutants

Two upflow fixed-bed biofilm reactors used of heterotrophic denitrification