Stability of a lab-scale biofilm for simultaneous removal of phosphorus and nitrate

A lab-scale biofilm reactor for simultaneous removal of phosphorus and nitr ate was operated for one and a half years. Despite using only well defined synthetic wastewater and well defined operation, the activity varied signif icantly over the months. It was speculated that microbial population shifts were causing this phenomenon. This could also explain a sudden break down of the process following a slight change in the operation. Over shorter per iods of time (time-scale: days), the biofilm could be considered stable eno ugh to perform series of comparable batch experiments. Batch experiments wi th different start concentrations of acetate, nitrate or phosphate were con ducted. These verified 0.5 and 0 order removal rates in the bulk water depe nding on the concentration. This was taken as an indication of a zonation o f the biofilm. Due to the measured Variability in the activity and due to t he importance of the history of the bacteria when considering biological P removal, an-line measurements are strongly recommended for research on this subject. Microbial characterisation methods are recommended as an assistin g tool in further research.