A new modified anoxic-anaerobic-membrane bioreactor for treatment of real wastewater with a low carbon/nutrient ratio and high nitrate

Abstract

A new modified configuration of pilot-scale anoxic-anaerobic-membrane bioreactor (MAA-MBR) was designed for excellent organic and nutrient removal from real urban wastewater with a low carbon/nutrient ratio and notable nitrate concentration. Eight different runs of mixed liquor recycle (MLR) ratio of 100–600 % and hydraulic retention time (HRT) of 2–12 h were used to identify the optimal operating conditions of the MAA-MBR system. Statistical analysis (ANOVA) of the results showed that the food to microorganism ratio and degradation performance of the system were significantly independent of the aerobic HRT of 3–12 h. However, chemical oxygen demand (COD) and total nitrogen (TN) removal dropped by 7 % at 2 h aerobic HRT. The results also highlighted that TN and total phosphorus (TP) removal were significantly affected by the MLR ratio. Additionally, the MAA-MBR system was able to improve TP removal by 21.6 % comparing to the A2O-MBR system at the same operating conditions without any chemical addition. The maximum five-day biochemical oxygen demand, COD, TN, and TP removal were 99.2 %, 96.9 %, 88.1 %, and 75.8 %, respectively, at total HRT of 8.1 h and MLR ratio of 400 %. Moreover, TP removal improved to 92.0 % when methanol was added to the anaerobic reactor. In addition, more than 87 % of the maximum TP and TN removal occurred via the enhanced biological nutrient removal (EBNR) and the remaining removal happened via the assimilation mechanism. In conclusion, the proposed MAA-MBR system is highly efficient for EBNR of wastewater with a high nitrate concentration.