Nitrification treatment of swine wastewater with acclimated nitrifying sludge immobilized in polymer pellets

Nitrification of ammonia (NH4+) is a critical component for improved systems of animal wastewater treatment. One of the most effective processes uses nitrifying microorganisms encapsulated in polymer resins. It is used in Japan in municipal wastewater treatment plants for higher nitrification rates, shorter hydraulic retention times (HRT), and lower aeration treatment cost. We evaluated whether this technology could be adapted for treatment of higher-strength lagoon swine wastewaters containing -230 mg NH4-N L-1 and 195 mg BOD5 L-1. A culture of acclimated lagoon nitrifying sludge (ALNS) was prepared from a nitrifying biofilm developed in an overland flow soil using fill-and-draw cultivation. The ALNS was successfully immobilized in 3- to 5-mm polyvinyl alcohol (PVA) polymer pellets by a PVA-freezing method. Swine wastewater was treated in aerated, suspended bioreactors with a 15% (w/v) pellet concentration using batch and continuous flow treatment. Alkalinity was supplemented with inorganic carbon to maintain the liquid pH within an optimum range (7.7-8.4). In batch treatment, only 14 h were needed for nitrification of NH4+. Ammonia was nitrified readily, decreasing at a rate of 16.1 mg NH4-N L-1 h-1. In contrast, it took 10 d for a control (no-pellets) aerated reactor to start nitrification; furthermore, 70% of the N was lost by air stripping. Without alkalinity supplements, the pH of the liquid fell to 6.0-6.2, and NH4+ oxidation stopped. In continuous flow treatment, nitrification efficiencies of 95% were obtained with NH4+ loading rates of 418 mg-N L-reactor-1 d-1 (2.73 g-N g-pellet-1 d-1) and an HRT of 12 h. The rate of nitrification obtained with HRT of 4 h was 567 mg-N L-1 d-1. In all cases, the NH4-N removed was entirely recovered in oxidized N forms. Nitrification rates obtained in this work were comparable to rates obtained with municipal systems. This indicates that immobilized ALNS pellets were not greatly affected by high NH4+ or BOD concentration of swine wastewater. Thus, immobilized pellet technology can be adapted for fast and efficient removal of NH4+ contained in anaerobic swine lagoons using acclimated microorganisms.