2 research outputs found
Phosphate Recovery from Human Waste via the Formation of Hydroxyapatite during Electrochemical Wastewater Treatment
Electrolysis
of toilet wastewater with TiO<sub>2</sub>-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<sup>–2</sup> (∼3.4 V), with greater than 20
m<sup>2</sup> m<sup>–3</sup> 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
Modular Advanced Oxidation Process Enabled by Cathodic Hydrogen Peroxide Production
Hydrogen
peroxide (H<sub>2</sub>O<sub>2</sub>) is frequently used
in combination with ultraviolet (UV) light to treat trace organic
contaminants in advanced oxidation processes (AOPs). In small-scale
applications, such as wellhead and point-of-entry water treatment
systems, the need to maintain a stock solution of concentrated H<sub>2</sub>O<sub>2</sub> increases the operational cost and complicates
the operation of AOPs. To avoid the need for replenishing a stock
solution of H<sub>2</sub>O<sub>2</sub>, a gas diffusion electrode
was used to generate low concentrations of H<sub>2</sub>O<sub>2</sub> directly in the water prior to its exposure to UV light. Following
the AOP, the solution was passed through an anodic chamber to lower
the solution pH and remove the residual H<sub>2</sub>O<sub>2</sub>. The effectiveness of the technology was evaluated using a suite
of trace contaminants that spanned a range of reactivity with UV light
and hydroxyl radical (HO<sup>•</sup>) in three different types
of source waters (i.e., simulated groundwater, simulated surface water,
and municipal wastewater effluent) as well as a sodium chloride solution.
Irrespective of the source water, the system produced enough H<sub>2</sub>O<sub>2</sub> to treat up to 120 L water d<sup>–1</sup>. The extent of transformation of trace organic contaminants was
affected by the current density and the concentrations of HO<sup>•</sup> scavengers in the source water. The electrical energy per order
(<i>E</i><sub>EO</sub>) ranged from 1 to 3 kWh m<sup>–3</sup>, with the UV lamp accounting for most of the energy consumption.
The gas diffusion electrode exhibited high efficiency for H<sub>2</sub>O<sub>2</sub> production over extended periods and did not show a
diminution in performance in any of the matrices