Biological Nitrogen Removal by Alternating Anoxic/aerobic CAST Treating Municipal Wastewater With a Low ρ_COD/ρ_TN Ratio

This study investigates the effects of continuous-feeding and step-feeding patterns on the nitrogen removal performance and the aeration rate under the anoxic/aerobic(A/O) condition of cyclic activated sludge technology(CAST) process treating low ρ_COD/ρ_TN wastewater,and analyzes the profiles of pH,DO and ORP under the step-feed mode.Resultsshow that the average removal rate of ρ_TN is 75.1% and SVI is 229 mL/g when the system runs under the continuous feeding mode,and activated sludge bulking occurs because of the operation under long-term condition of a low influent load.However,the average removal rate of ρ_TN increases to 81.5% and the average SVI decreases when the system runs under the step-feeding mode.Meanwhile,the aeration rate of the continuous-feeding mode is 0.56 m³/h but 0.24 m³/h under the step-feeding mode when the removal rate of ρ(NH₄⁺-N) is above 99%.Consequently,the operation cost can be significantly reduced by using the step-feeding mode.Furthermore,pH,DO,ORP curves have an observe variation during a cycle under the step-feed,which also have a better correlation with the variation of contamination in the system.