Electrochemical treatment of human waste coupled with molecular hydrogen production†
We have developed a wastewater treatment system that incorporates an electrolysis cell for on-site wastewater treatment coupled with molecular hydrogen production for use in a hydrogen fuel cell. Herein, we report on the efficacy of a laboratory-scale wastewater electrolysis cell (WEC) using real human waste for the first time with semiconductor electrode utilizing a mixed particle coating of bismuth oxide doped titanium dioxide (BiOx/TiO2). A comprehensive environmental analysis has been coupled together with a robust kinetic model under the chemical reaction limited regime to investigate the role of various redox reactions mediated by chloride present in human waste. The oxidative elimination of the chemical oxygen demand (COD) and ammonium ion can be modelled using empirical, pseudo-first-order rate constants and current efficiencies (CE). In combination with an anaerobic pre-treatment step, human waste containing high-levels of COD, protein, and color are eliminated within 6 hours of batch treatment in the WEC. The reactor effluent has a residual inorganic total nitrogen (TN) concentration of ∼40 mM. The CE and specific energy consumption were 8.5% and 200 kWh per kgCOD for the COD removal, 11% and 260 for kWh per kgTN for the TN conversion. The CE and energy efficiencies (EE) for hydrogen production were calculated to be 90% and 25%, respectively.