sc7b03155_si_001.pdf (5.59 MB)
Phosphate Recovery from Human Waste via the Formation of Hydroxyapatite during Electrochemical Wastewater Treatment
journal contribution
posted on 2018-02-05, 00:00 authored by Clément
A. Cid, Justin T. Jasper, Michael R. HoffmannElectrolysis
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 treating toilet wastewater,
pilot-scale and bench-scale experiments demonstrated that electrolysis
can remove phosphate by cathodic precipitation as hydroxyapatite at
no additional energy cost. Phosphate removal could be predicted based
on initial phosphate and calcium concentrations, and up to 80% total
phosphate removal was achieved. While calcium was critical for phosphate
removal, magnesium and bicarbonate had only minor impacts on phosphate
removal rates at concentrations typical of toilet wastewater. Optimal
conditions for phosphate removal were 3 to 4 h treatment at about
5 mA cm–2 (∼3.4 V), with greater than 20
m2 m–3 electrode surface area to reactor
volume ratios. Pilot-scale systems are currently operated under similar
conditions, suggesting that phosphate removal can be viewed as an
ancillary benefit of electrochemical wastewater treatment, adding
utility to the process without requiring additional energy inputs.
Further value may be provided by designing reactors to recover precipitated
hydroxyapatite for use as a low solubility phosphorus-rich fertilizer.