Influence of aeration, plants, electrodes, and pollutant loads on treatment performance of constructed wetlands: A comprehensive study with septage

Abstract

This study reports the performance of non-aerated and aerated unplanted, planted, microbial fuel cell planted wetlands for stabilizing septage and treating the drained wastewater. The wetland systems of this study were dosed with septage for a relatively shorter period, i.e., 20 weeks, followed by 60 days of sludge drying period. The sludge loading rates across the constructed wetlands ranged between 259 and 624 kg total solids (TS)/m² per year. Organic matter, nitrogen, and phosphorus concentration of the residual sludge ranged between 8512 and 66,374 mg/kg, 12,950 and 14,050 mg/kg, 4979 and 9129 mg/kg, respectively. The presence of plants, electrode, and aeration improved sludge dewatering and decreased the organic matter and nutrient concentration of the residual sludge. The heavy metals (Cd, Cr, Cu, Fe, Pb, Mn, Ni, and Zn) concentration of the residual sludge fulfilled the guidelines for agricultural reuse in Bangladesh. Chemical oxygen demand (COD), ammoniacal nitrogen (NH₄-N), total nitrogen (TN), total phosphorus (TP), and coliform removal percentages from the drained wastewater ranged between 91 and 93 %, 88 and 98 %, 90 and 99 %, 92 and 100 %, and 75 and 90 %, respectively. NH₄-N removal from the drained wastewater depended upon aeration. The sludge treatment wetlands achieved metals removal percentages (from the drained wastewater) ranging between 90 and 99 %. Physicochemical and microbial routes in accumulated sludge, rhizosphere, and media contributed to pollutants removal. Input load and organic removal increment (from the drained wastewater) were positively correlated; nutrient removal showed a contradictory trend. The non-aerated and aerated microbial fuel cell planted wetlands produced maximum power densities ranging between 66 and 3417 mW/m³. Because of the shorter experimental duration, this study revealed preliminary but new information on the macro and micro pollutants removal pathways in septage sludge wetlands (with and without electrode) that could be utilized to design pilot or full-scale systems.

Keywords: Bioenergy; Effluent disposal; Pollutants removal; Reuse; Sludge.