Micropollutant-Free Nutrient Recovery: Adsorption of Micropollutants on Ion Exchangers and Biosolids-Derived Biochar
Date of Award
Doctor of Philosophy (PhD)
Civil, Construction, and Environmental Engineering
Mayer, Brooke K.
McNamara, Patrick J.
Zitomer, Daniel H.
The presence of excessive nutrients in treated wastewater effluent is a growing concern in terms of water quality and ecological balance. Thus, removal of nutrients is of great interest. Moreover, the removed nutrients can be recovered in forms amenable for agricultural reuse, which yields a sustainable supply of nonrenewable phosphorus that can be used to support global food production. As nutrient recovery gains interest, it is essential that the products be free of harmful contaminants. One class of contaminants of great concern is organic micropollutants. To help address these issues, this study evaluated the fate and impact of micropollutants during nutrient recovery via an ion exchange-regeneration-precipitation process. The adsorptive behavior of the micropollutants was evaluated for the ion exchangers and for a sustainable biosolids-derived biochar that may be useful for separating micropollutants from nutrients prior to ion exchange. Bench-scale batch reactors were operated for ion exchange-regeneration and adsorption tests. The surface properties of ion exchangers and biochar were characterized to help assess the mechanisms of micropollutant adhesion on solid adsorbents. The presence of micropollutants in water reduced the kinetic rates of nutrient exchange onto ion exchangers. Micropollutants were adsorbed to the phosphate exchangers and were released with phosphate ions during ion exchange regeneration. To remove micropollutants from water prior to ion exchange, biosolids-derived biochar was used since micropollutants were adsorbed to the biochar, but ionic nutrients were not. Biochar produced at higher pyrolysis temperatures increased adsorption capacity, as did higher ambient temperatures for batch sorption experiments. Under multi-solute conditions, not all target micropollutants demonstrated suppressed adsorption. Biochar, ammonium, and phosphate exchangers were accordingly arranged in sequence in a flow-through system. The biochar column removed more than 80% of influent hydrophobic micropollutants and 50% of hydrophilic micropollutants, thereby reducing the presence of micropollutants in the nutrient removal/recovery process. Thermodynamic parameters indicated an endothermic adsorption reaction and heterogeneity in adsorption site distribution on the biochar surface. The binding energy and entropy change of adsorption were not affected by the presence or absence of other solutes in the matrix. The underlying binding mechanism for biosolids-derived biochar adsorption was potentially dominated by non-specific hydrophobic interaction and non-covalent interaction including hydrogen bonding and π-stacking.