Sustainable removal of ammonia from anaerobic-lagoon swine waste effluents using an electrochemically-regenerated ion exchange process

A new process, based on ion-exchange and electrochemical regeneration, was tested for removing ammonia from effluents of swine-waste anaerobic lagoons. The process, consisting of a daily sequential operation of adsorption (180 min), chemical regeneration (125 min) and electrooxidation of ammonia in the regeneration solution (8 h, applied during low-cost electricity hours), was shown feasible for reducing the ammonia concentration in the wastewater from similar to 1000 to similar to 60 mg/L with a total cost estimated at similar to$3/kg N. The work focused on identifying the best operational conditions enabling continuous operation of the ion-exchange column and recycling of the regenerant solution without the need for replenishment of either. Chemical additions were restricted to in-line addition of NaOH to maintain constant pH during the electrolysis step and periodical addition of NaCl to compensate for Cl- and Na+ losses. It was found that removing NH4+ (by chabazite-zeolite) from swine wastewater characterized by NH4+:K+:Ca2+:Mg2+:Na+ ratio of 1:0.66:0.1:0.06:0.30 (g/g) could be carried out by the proposed treatment sequence at conditions of pseudo steady state, with an adsorption stage of 12.5 bed volumes and 14.5 mm hydraulic retention time. Applying such conditions, the concentration of K+ (the main competing cation) stabilized both in the regenerant solution and on the chabazite, enabling >90% NH4+ removal without need for replacing the regenerant solution. Electrooxidation efficiency constantly exceeded 90% due to the high Cl- concentration (>17 g/L) maintained in the regeneration solution and because only a small mass of organic matter was transferred to the regenerant solution following the adsorption step. (C) 2012 Elsevier B.V. All rights reserved.