Ozonation of Source-Separated Urine for Resource Recovery and Waste Minimization: Process Modeling, Reaction Chemistry, and Operational Considerations
Bench-scale, semibatch experiments were performed to examine physical-chemical constraints on ozone (O-3) absorption and micropollutant oxidation during ozonation of source-separated hydrolyzed urine and the concentrate and diluate streams produced via electrodialysis of hydrolyzed urine. O-3 consumption by each matrix was found to occur within a fast pseudo-first-order kinetic regime, Critical constraints on micropollutant oxidation were found through mass transfer modeling to be (i) micropollutant diffusion from the bulk solution into the gas-liquid interfacial film for compounds recalcitrant toward O-3 (i.e., k(03,app)'' <= 10(3) M-1 s(-1)), and (ii) aqueous-phase mixing for compounds highly reactive toward O-3 (i.e., k(03,app)'' > 10(3) M-1 s(-1)), Homogeneous chemical reaction modeling indicated that aqueous reaction chemistry is significantly influenced by the degree to which incidentally produced hydroxyl radicals are consumed by NH3 in each matrix, in terms of (a) micropollutant oxidation efficiencies, and (b) potential yields of oxidation byproducts. On the basis of the experimental data reported here, per capita energy requirements were estimated for treatment of source-separated urine via (1) ozonation, (2) ozonation with postelectrodialysis, and (3) electrodialysis with postozonation. These estimates indicate that scenario (1) would likely be less energy efficient than ozonation of municipal wastewater effluent in achieving equivalent reductions in urine-derived micropollutant loads, whereas scenarios (2 and 3) could be more efficient than equivalent centralized wastewater treatment strategies in achieving equivalent levels of urine-derived nutrient and micropollutant attenuation. Furthermore, experimental and model data suggest that urine ozonation efficiency maybe substantially improved by optimizing aqueous-phase mixing and specific gas-liquid interfacial area.