The kinetic behaviors of simultaneous phosphorus release and denitrification on sludge for BNR processes

In this study, we investigated the kinetic behaviors of phosphorus release and denitrification on sludge for two biological nutrient removal (BNR) processes, i.e., suspension growth process (A(2)O) and combined suspension-biofilm growth process (TNCU) under anoxic condition. The readily biodegradable substrate and nitrate loadings, 20-180 mg HAc-COD/g MLSS and 4-25 mg NO3-N/g MLSS respectively, are controlled in a batch reactor for phosphorus release and denitrification of sludge taken from A(2)O and TNCU processes under various SRT (5, 10 and 15 days) operating conditions. Experimental results indicated that the occurrence of simultaneous phosphorus release and denitrification is a kinetic competition mode under anoxic condition in the presence of a readily biodegradable substrate. Moreover, the available substrate in bulk solution determined the kinetic behaviors of phosphorus release and denitrification. To prevent nitrate inhibition, the sludge is exposed to a C/N ratio higher than 6.1 for phosphorus release. The sludge's phosphorus content (as created by different SRT processes) and initial nitrate loading dominated the kinetics of phosphorus release and denitrification, respectivley. Moreover, the sludge of suspension gorwth process demonstrated a higher phosphorus release potential than the combined suspension-biofilm growth process. However, the nitrate inhibition is significant for A(2)O sludge also. Based on proposed phosphorus release rate equation, the rate constant would be reduced by denitrification about 31-67% and 20-45% for A(2)O and TNCU processes, respectively.