Effect of anoxic transformation processes in municipal wastewater on pH and oxidation reduction potential

This paper presents findings of an investigation into the relationships between nitrate utilization rate (NUR), pH and oxidation reduction potential (ORP) during anoxic transformation processes in municipal wastewater. The study utilized municipal wastewater obtained from a wastewater treatment plant located within Shah Alam, Malaysia. Denitrification was observed by monitoring the change in nitrate and nitrite concentrations in a bench-scale reactor during anoxic transformation processes. It was found that the decrease in nitrate concentration was correlated with the increase of pH. The nitrite concentration gradually increased at the onset of the experiment and reached an optimum value of approximately 3 mg/L before it was reduced and removed from solution at approximately 5 hours of residence time. It was clear that the ORP reduced as the experiment progressed indicating a parallel relationship between ORP and denitrification. These results showed that pH increased while the ORP decreased during denitrification of municipal wastewater. It was established that the optimum pH and ORP for denitrification was from 6.5 to 8.5 and -40mV to -160mV respectively.