Electrolysis of toilet wastewater with TiO2-coated semiconductor anodes and stainless steel cathodes is a potentially viable onsite sanitation solution in parts of the world without infrastructure for centralized wastewater treatment. In addition to providing disinfection, chemical oxygen demand reduction, and removal of ammonium ion, onsite electrolysis can remove phosphate by cathodic precipitation. The formation of Mg-containing hydroxyapatite (MgxCa5-x(PO4)3OH, 0 ≤ x &lt;1) on stainless steel cathodes during toilet wastewater electrolysis at pilot- and bench-scales was observed. Phosphate removal levels up to 80% of the influent concentrations were achieved concomitant of electrochemical treatment. While initial Ca2+, phosphates, and carbonates concentrations were critical for phosphates removal, Mg2+ and Cl- concentrations had only minor impacts on phosphates removal rates in synthetic wastewaters at concentrations typical of toilet wastewater. Experiments suggested that the precipitation of hydroxyapatite at the cathode during toilet wastewater electrolysis may have been initiated by alkaline near-cathode pH values and migration of Ca2+ to the cathode. Onsite electrochemical reactors may be designed to recover precipitated hydroxyapatite for use as a phosphorus-rich fertilizer.

Formation of hydroxyapatite during toilet wastewater treatment by electrolysis

254th National Meeting (2017)

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