A Pilot Study on Phosphate and Nitrate Removal from Secondary Wastewater Effluent Using a Selective Ion Exchange Process

Abstract

A pilot study was conducted at a wastewater treatment plant (WWTP) in Easton, Pennsylvania, for the removal of varying concentrations of phosphate (HPO4 2-) and nitrate NO3 - using a newly developed ion exchange material referred to as Polymeric Ligand Exchanger (PLE). The PLE was prepared by immobilizing copper (II) ions onto a commercially available chelating resin, DOW-3N. The loaded copper ions act as ligand exchanger sites that selectively bind with target ligands such as phosphate and nitrate. This pilot study was the final experimental testing phase of the PLE toward the full process development for the selective removal of both phosphate and nitrate using secondary effluent from a fully operational WWTP. In order to establish the effectiveness of the PLE, a commercially available activated alumina (AA) was also tested for comparison. Effluent phosphorus and nitrate concentration of less than 0.1 mg l-1 were achieved for up to 500 bed volumes; phosphorous was reduced from an average concentration of 4.0 mg l-1 and nitrate from average concentration of 16.4 mg l-1. In accord with prior laboratory observations, the pilot test results showed that the PLE could selectively remove phosphate from secondary municipal wastewater effluent under normal conditions (pH, ionic strength, dissolved organic carbon content). In addition, the pilot study provided new evidence that nitrate could be removed from secondary municipal wastewater effluent and concurrently with phosphate. The selective ion exchange process provides an alternative for concurrent removal of the eutrophic-enhancing nutrients, phosphate and nitrate.