Identifying key parameters in a novel multistep bio-ecological wastewater treatment process for rural areas

Abstract

With the goals of enhancing the removal of pollutants while reducing the cost of treatment, a novel, multistep bio-ecological A2O-H system for rural wastewater treatment consisting of a biological unit (modified anaerobic/anoxic/oxic, A2O) and an ecological post-treatment unit (hydrophyte filter bed, HFB) was developed. Four reactors, including two series large height/diameter ratio upflow anaerobic biofilm reactors (LUAB), an anoxic biofilm reactor (ABR), a five-cell water-dropping aeration submerged biofilm reactor (WDASB), and the HFB, were employed in the A2O-H system. Key parameters for each step were identified based on their performances for further application in the project. Concerning rural domestic sewage, the LUAB presented good organic removal and gas generation rates under a hydraulic retention time (HRT) of 3 d or within an organic load rate (OLR) of 0.10–0.15kg COD/(m3d). The HRT and OLR for the WDASB were evaluated to be 2–3h and 1.0–1.5kg COD/(m3d), respectively, for organic matter and ammonia removal. Complete nitrogen removal through denitrification occurred in the ABR with a reflux ratio of 100% and a HRT of 6h. The HFB presented a higher nutrient removal for the hydraulic load rate (HLR) of 0.2–0.3m3/(m2d) without clogging. Furthermore, the experimental results of the A2O-H system for the consecutive flow model condition showed that average removal efficiencies were 88% for COD, 85% for ammonia, 66% for TN, 89% for TP, and 87% for TSS. The pollutant concentrations of the effluent from the bio-ecological A2O-H system were lower than the rigorous regulated values of the Class 1A in the China National Standard GB18918-2002. Therefore, the multistep bio-ecological A2O-H system is a promising alternative for rural wastewater treatment.