Anammox sludge immobilized in polyvinyl alcohol (PVA) cryogel carriers

This study evaluated the use of PVA cryogels to encapsulate slow-growing anammox bacteria for deammonification treatment of wastewater. The cryogel pellets were prepared by freezing-thawing at -8 °C. On average, pellets contained 11.8 mg-TSS/g-pellet of enriched anammox sludge NRRL B-50286 (Candidatus Brocadia caroliniensis) in 4-mm cubes. They were tested with synthetic and partially nitrified swine wastewater using continuous stirred-tank reactors packed at 20% (w/v). The immobilized gel was retained inside the reactor by a screen that eliminated the need of sludge recycling. The stoichiometry of anammox reaction was maintained for more than 5 months under non-sterile conditions. The process was not limited by substrates availability unless quite low N concentration (<5 mg/L) achieving >93% removal efficiency. In mass balances, >80% of the potential N conversion activity was achieved (2920 mg-N/kg-pellet/d). In addition, the immobilized bacteria were resilient to inhibition at high nitrite concentrations (244-270 mg-N/L).