Reactive nitrogen and phosphorus removal from aquaculture wastewater effluents using polymer hydrogels

We have developed poly(allyl amine hydrochloride) (PAA . HCl) polymer hydrogels, that efficiently remove nitrate (NO3-), nitrite (NO2-), and orthophosphate (PO43-) nutrient anions from the aquaculture wastewater. The hydrogels were prepared by chemically crosslinking linear PAA . HCl chains with epichlorohydrin (EPI). The anion binding capacity of the pH sensitive polymer gels was measured in standard solutions and studied as a function of gel synthesis parameters. Equilibrium NO3-N, NO2-N, and PO4-P loading of 15, 1.6, and 17 mg/g of dry gel, respectively, were calculated from the measurement of decrease in anion concentration in aqueous solutions using UV-vis spectrophotometry. Batch experiments showed that nutrient concentrations in aquaculture wastewater effluents decreased with regard to PO4-P by 98 + %, NO3-N by 50 + % and NO2-N by 85 + % within 3 h of reaction. The regeneration of the hydrogels was demonstrated by the release of bound nutrient anions upon washing the gels with a 1 N NaOH solution. These results have demonstrated that the hydrogels are appropriate materials for treating aquaculture wastewater effluents, and reducing the nutrient anion concentrations to levels, less than 10 mg/l NO3-N, 0.08 mg/l NO2-N, and 0.3 mg/l PO4-P, suitable for discharge into natural surface waters. (C) 2000 Elsevier Science B.V. All rights reserved.