Date of Award
Summer 2022
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Civil, Construction, and Environmental Engineering
First Advisor
Mayer, Brooke
Second Advisor
McNamara, Patrick
Third Advisor
Starke, Jeffrey
Abstract
Soluble non-reactive nutrient species, i.e., dissolved organic nitrogen (DON) and soluble non-reactive phosphorus (sNRP), are not effectively removed and recovered. Unfortunately, the non-reactive species can cause eutrophication in receiving waterbodies. Thus, removal and recovery of soluble non-reactive nutrients is critical for reducing nutrient discharge and advancing the national goal of enhanced nutrient recovery. Transformation of non-reactive nutrients to more readily removable/recoverable species using ozonation and UV/H2O2 for enhanced nutrient recovery has been reported in literature. Electrooxidation (EO) may outperform these processes in transforming nutrients as EO can utilize multiple oxidation pathways, e.g., in-situ generated oxidants or direct electron transfer (DET). This research evaluated EO for DON and sNRP transformation into more reactive dissolved inorganic nitrogen and soluble reactive phosphorus, respectively. The efficacy of EO for DON and sNRP transformation into more reactive species was first evaluated in synthetic water matrices. Transformation using EO increased with current density. DON showed less susceptibility towards EO-based transformation compared to sNRP; accordingly, subsequent EO tests focused on sNRP. Compared to UV/H2O2, EO transformation consumed up to 2.4 times less energy. The role of sorbed and dissolved in-situ generated oxidants in EO-based transformation was investigated using quenchers. These results, along with chronoamperometry tests, confirmed that DET was the dominant mechanism for EO-based nutrient transformation. Removal of sNRP using ion exchange improved up to 1.6 times after EO treatment. However, the ion exchanger’s affinity for EO-treated sNRP did not improve, suggesting that centrate sNRP removal improved after EO due to decreased organics after EO treatment. Since EO can be highly energy demanding, selective adsorption might be beneficial for enhanced nutrient recovery. Previous studies reported highly selective orthophosphate adsorption on a phosphate-binding protein (PBP), but sNRP adsorption on PBP has not yet been studied. Thus, adsorption of sNRP using PBP was assessed, showing that 95% of equilibrium sNRP adsorption on PBP takes place within 4 minutes. The sNRP compounds likely bind at PBP’s phosphate-selective binding site, and compounds with higher P content were removed to a greater extent.