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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.

Concurrent hydrogen (H 2 ) production and phosphorus (P) recovery were investigated in dual chamber microbial electrolysis cells (MECs). The aim of the study was to explore and understand the influence of applied voltage and influent COD concentration on concurrent H 2 production and P recovery in MEC. P was efficiently precipitated at the cathode chamber and the precipitated crystals were verified as struvite, using X-ray diffraction and scanning electron microscopy analysis. The maximum P precipitation efficiency achieved by the MEC was 95%, and the maximum H 2 production rate was 0.28 m 3 -H 2 /m 3 -d. Response surface methodology showed that applied voltage had a great influence on H 2 production and P recovery, while influent COD concentration had a significant effect on P recovery only. The overall energy recovery in the MEC was low and ranged from 25 ± 1 to 37 ± 1.7 %. These results confirmed MECs capability for concurrent H 2 production and P recovery.Keywords: Bio-electrochemical System; Phosphorus Recovery; Microbial Electrolysis Cell; Struvite; Response Surface Methodology IntroductionDue to population growth, the global demand for unsustainable resources is rising. As a result, concerns around resource depletion are increasing. Phosphorus is one of the most 2 important unsustainable nutrients on our planet. Phosphorus is essential for all forms of life, especially for plant growth. Unfortunately, estimates show that phosphorus rocks will be depleted within the next 50-100 years (Cooper et al., 2011). Therefore, alternative sources of phosphorus should be discovered to balance the high demand for phosphorus. Magnesium ammonium phosphate (struvite) is one of most common phosphate fertilizers that can be recovered from different streams of wastewater. Struvite is an efficient slow release fertilizer that can be used for crop growth, and is an excellent alternative for phosphate rocks (Rahman et al., 2014).Struvite precipitation occurs in the equimolecular concentration of magnesium (Mg), ammonium (NH 4 ) and (P); these elements combine with water to form struvite. The precipitation of these components is also highly dependent on pH, where struvite starts to precipitate at pH > 8 (Doyle & Parsons, 2002). The most common methods for P recovery as struvite are chemical addition and carbon dioxide stripping through aeration. These processes are effective for struvite precipitation; however, the operation cost is too high. Using chemical addition to raise the solution's pH can account for up to 97% of struvite cost (Jaffer et al., 2002;Morales et al., 2013).Microbial electrolysis cells (MECs) are a new and promising approach for hydrogen (H 2 ) production from organic matter, including wastewater and other renewable resources. In MECs, electrochemically active bacteria oxidise organic matter and generate CO 2 , electrons and protons. The bacteria transfer the electrons to the anode and the protons are released into the solution. The electrons then travel through a wire to a cathode and combine wit...