An anoxic-aerobic system combined with integrated vertical-flow constructed wetland to highly enhance simultaneous organics and nutrients removal in rural China

Abstract

The biggest problem in the treatment of rural domestic sewage is that the existing treatment projects require the big investment and the high operation and maintenance costs. To overcome this problem, cost-effective, low-consuming, resource-recovering and easy-maintenance technologies are urgently demanded. To this end, a novel anoxic-aerobic system combined with integrated vertical-flow constructed wetland (IVFCW) with source separation was proposed for treating rural sewage in this study. The anoxic-aerobic system contained the anoxic filter (ANF), two-stage waterwheel driving rotating biological contactors (ts-WDRBCs). Key parameters of ts-WDRBCs were identified to be 0.6 m drop height and 4 r/min rotational speed found on oxygenated clean water experiments. Then, the optimal operating parameters were determined to be 200% reflux ratio and 3 h hydraulic retention time of ts-WDRBCs. During the 80-day operation, 91.58 ± 1.86% COD, 96.17 ± 0.92% NH4+-N, 82.71 ± 3.92% TN and 92.28 ± 2.78% TP were removed under the optimal operating parameters. Compared with other treatment technologies, this combined bio-ecological system could achieve the higher simultaneous organics and nutrients removal. The effluent NO3−-N/NH4+-N concentration ratio of ts-WDRBCs was 2.15 ± 0.54, which was proved to be beneficial for plants growth. The microbial communities coexisted in each section ensured the desired removal performance of combined bio-ecological system. Summarily, high performance together with low investment costs and cheap operation costs are characteristics that make this system a promising and competitive alternative for rural sewage treatment.