Abstract
This study investigated the mechanism and key factors influencing concurrent phosphorus (P) recovery and energy generation in microbial fuel cells (MFC) during wastewater treatment. Using a mediator-less dual chamber microbial fuel cell operated for 120 days; P was shown to precipitate as struvite when ammonium and magnesium chloride solutions were added to the cathode chamber. Monitoring data for chemical oxygen demand (COD), pH, oxidation reduction potential (ORP) and aeration flow rate showed that a maximum 38% P recovery was achieved; and this corresponds to 1.5 g/L, pH > 8, −550 ± 10 mV and 50 mL/min respectively, for COD, pHcathode, ORP and cathode aeration flow rate. More importantly, COD and aeration flow rate were shown to be the key influencing factors for the P recovery and energy generation. Results further show that the maximum P recovery corresponds to 72 mW/m2 power density. However, the energy generated at maximum P recovery was not the optimum; this shows that whilst P recovery and energy generation can be concurrently achieved in a microbial fuel cell, neither can be at the optimal value.
Highlights
Microbial fuel cells (MFCs) are systems that convert chemical energy in an organic substrate in wastewater into electrical energy
The precipitation occurs in equimolecular concentration of magnesium (Mg), ammonium (NH4 ) and P; and these combine with water to form struvite [3]
The maximum power density was achieved at chemical oxygen demand (COD) = 0.7 g/L, and the system achieved a maximum power density of 198 mW/m2 of (324 mA/m2 ) and decreased with2 time until the end of each batch
Summary
Microbial fuel cells (MFCs) are systems that convert chemical energy in an organic substrate in wastewater into electrical energy. There is increasing interest in finding new sustainable sources of P. Wastewater is a rich source of nutrients that can be used as a sustainable source of P. Magnesium ammonium phosphate hexahydrate (MAP or struvite) is an efficient slow release fertilizer [2]. The precipitation occurs in equimolecular concentration of magnesium (Mg), ammonium (NH4 ) and P; and these combine with water to form struvite [3]. P can be recovered as struvite from different waste streams including reject wastewater and digester effluent; and it can be achieved using several methods, including: chemical addition, carbon dioxide stripping or electrolysis [4,5,6]. The chemical addition is a costly process and the chemicals used to raise the pH can account for up to 97% of struvite cost [6,7]
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