Concurrent hydrogen production and phosphorus recovery in dual chamber microbial electrolysis cell

Abstract

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...

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“…9 Struvite has been researched by many authors, but the process has the disadvantage that Mg addition is needed, which makes the process inefficient and expensive. 9,10…”

Microbial electrolysis cell as an emerging versatile technology: a review on its potential application, advance and challenge

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