Constructed wetlands for drained wastewater treatment and sludge stabilization: Role of plants, microbial fuel cell and earthworm assistance

This study reports drained wastewater treatment and sludge stabilization performance of an unplanted system and four Phragmites plant-based sludge treatment wetlands (without or with earthworm assistance and microbial fuel cells integration). Biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), nitrogen(N), phosphorus (P), solids, and coliform removal percentage from the drained wastewater (produced because of sludge stabilization) was 96, 99, 89, 99, 98 and 97%, respectively in the five systems. Electrochemically active or inactive organic decomposition, nitrification, denitrification, filter media-based adsorption, and other chemical-based mechanisms primarily contributed to wastewater organic, nitrogen, phosphorus removal. N and P accumulation percentage in plant tissues was not substantial: accumulation percentage (with respect to total removal) ranged from 3 to 9% and 0.2 to 1%, respectively. However, plants improved suspended solids and coliform removal (from the drained wastewater) because of root-based filtration. Total solids (TS %) content in the residual sludge ranged between 83 and 89% within the five systems; the planted-microbial fuel cell integrated sludge treatment wetland with earthworm assistance produced the highest TS (%) content in the residual sludge. Organic matter, N, P concentration in the residual sludge ranged between 23 and 42 mg/kg, 8 and 13 mg/kg, 1 and 1.1 mg/kg, respectively. Earthworm assistance and microbial fuel cell integration improved drained wastewater purification and sludge stabilization within the planted systems. Activation, ohmic, and concentration losses influenced current production in microbial fuel cell integrated wetlands. A maximum power density production rate of 60 mW/m³ was recorded. This study shows the potential application of planted, earthworm assisted microbial fuel cell-based constructed wetland for drained wastewater and sludge treatment.