Removal of ammonia-nitrogen (NH3-N) and nitrate (NO3-) by modified conventional activated-sludge system to meet new D.O.E regulations

The recent amendment of the Environmental Quality (Sewage) Regulations 2009 has significantly reduced the discharge limit of ammonia-nitrogen and nitrate in the domestic effluent discharge from treatment plants. However, the conventional activated-sludge processes employed in the domestic sewage treatment plants are not able to meet the new regulations, as nitrification is inhibited due to
insufficient solids retention time and sludge age of the biomass. Thus, the purpose of this study is to enhance the conventional activated-sludge process through a modified, laboratory scale biological reactor. To achieve this, a modified biological reactor with pre-installed continuous narrow baffle walls operating at extended aeration (SRT = 40 days) was designed to intentionally create a number of complete-mix activated-sludge zones. In addition, a pre-anoxic compartment was also provided prior to the aerobic chamber for denitrification purpose. In order to compare the performance, a control reactor (SRT = 2 days) operating at conventional aeration was created to simulate the conventional activated-sludge process in the domestic STP.
Synthetic wastewater was produced by using dissolved grinded cats food to imitate medium strength domestic wastewater and to create more consistent organic loading. During the operation stage, biological sludge was added into the reactors and 10 days of acclimatization period was set to stabilize the biomass, the performance of the reactors was monitored for 10 days continuously until the readings were stabilized. By comparison, both of the reactors managed to achieve above 80% of reduction for both COD and BOD