Synergistic energy recovery and removal of organics and ammonium from moderate-strength wastewater through an MEC–flue gas–anammox system
摘要
The treatment of wastewater characterized by high levels of NH4+-N and a moderate organic strength with a low ratio of chemical oxygen demand (COD) to total nitrogen, poses significant challenges to conventional biological processes. In this study, an energy-harvesting microbial electrolysis cell (MEC)–flue gas–anaerobic ammonium oxidation (anammox) system was proposed to treat manure-free piggery wastewater (707 ± 8 mg/L COD and 321 ± 3 mg/L NH4+-N). The MEC first effectively removed wastewater organics and recovered chemical energy in the form of H2 (with trace CH4 production). Flue gas-derived nitrogen oxides were subsequently absorbed by MEC effluent, providing a sustainable nitrite source for the anammox process. The residual NO3−-N generated from anammox metabolism and flue gas absorption could be further removed through hydrogenotrophic denitrification using in situ MEC-derived H2. The integrated system eliminates the need for energyintensive aeration (required in aerobic processes) while also addressing the inefficiency of anaerobic treatment in handling moderate-strength wastewater. The system demonstrated an outstanding performance, with effluent concentrations of COD < 40 mg/L, NH4+-N < 0.8 mg/L, NO2−-N < 0.5 mg/L, and NO3−-N < 0.8 mg/L. Moreover, the MEC enabled the continuous production of H2 (0.50–0.91 m3/(m3·d)) and CH4 (0.01–0.14 m3/(m3·d)) with an energy recovery efficiency of ∼249% (the ratio of the energy content of the produced H2 and CH4 to the input electrical energy). This study provides an energy-effective strategy for the highly efficient treatment of moderate-strength wastewater.