Abstract
Carbon/nitrogen ratio is an important parameter during the biological wastewater treatment. Our study emphasizes revealing the mechanisms of chemical oxygen demand/total nitrogen (COD/TN) ratio dependent improved greywater (GW) treatment in an oxygen based membrane biofilm reactor (O2-MBfR). Results showed that reducing COD/TN ratio from 40 to 20 g COD/g N by supplementing NH4Cl to GW improved the relative abundance of genera related to LAS-biodegradation (from 8.39% to 35.7%), nitrification (from 0.20% to 0.62%) and denitrification (from 3.01% to 7.59%). Reducing COD/TN ratio also led to an increase in the ammonia monooxygenase (AMO) activity (from 7.56 to 10.2 mg N/g VSS-h), as well as improved ammoxidation and linear alkylbenzene sulfonate (LAS) mineralization although the dissolved oxygen (DO) concentration and pH decreased. Much higher NH4+ − N at lower COD/TN ratio (10 units) led to lower DO (0.13 ± 0.01 mg/L) and pH (6.72 ± 0.02), but the continuously increased AMO activity (up to 12.9 mg N/g VSS-h) enabled the cometabolism of ammoxidation and LAS mineralization, leading to the efficient removal of organics and nitrogen under the low DO condition.