Concern over eutrophication caused by excess nutrient loading in surface waters has led to increasingly stringent regulations for nutrient concentrations in wastewater effluent. Additionally, many wastewater treatments plants are shifting their emphasis from purely wastewater treatment to also include resource recovery. Toward this aim, ion exchange processes can be employed to both remove and recover nutrients (phosphorus and nitrogen). Ion exchange processes can be used to concentrate nutrients from the wastewater into a regenerant stream, from which nutrient-rich products amenable to reuse in agricultural fertilizer applications can be recovered. Using both precipitation and adsorption processes to recover products from the regenerant stream facilitates recovery of a portfolio of more customizable nutrient-content products. In this study, phosphate and ammonium-selective ion exchangers (LayneRT resin and clinoptilolite, respectively), were tested in a synthetic nutrient solution and in secondary wastewater. Adsorption could be modeled using zero order kinetics, with maximum capacities of 12.0 mg phosphate/g LayneRT resin and 9.74 mg ammonium/g clinoptilolite. The ions were recovered via regeneration using 5% potassium hydroxide. The regenerant streams were combined together with magnesium to precipitate struvite (NH4MgPO4-6H2O). Additionally, a biosolids-derived biochar was found to be effective at directly adsorbing ammonium from clinoptilolite regenerant. Biochar is the solid product generated by pyrolysis, or heating of biomass in the absence of oxygen. Biochar has been used as a soil amendment, and after ammonium adsorption, may be used as an N-rich agricultural product. Moreover, ammonium-laden biochar can be mixed with struvite in varying ratios to produce customizable nutrient content products. Accordingly, the use of ion exchange followed by precipitation and/or adsorption could assist wastewater treatment plants in achieving lower effluent nutrient concentrations as well as recovering nutrients.

Customizable nutrient products recovered using ion exchange technology

253rd National Meeting (2017)

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