Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2012
Publication Date: 4/2/2012
Citation: Magri, A., Vanotti, M.B., Szogi, A.A. 2012. Anammox sludge immobilized in polyvinyl alcohol (PVA) cryogel carriers. Bioresource Technology. 114(2):231-240.
Interpretive Summary: The use of the anaerobic ammonium oxidation (anammox) as a new pathway to biologically remove ammonia has created great expectations in the field of wastewater treatment because it can significantly reduce aeration needs and cost of treatment. However, due to the low growth rate of anammox bacteria, one of the main challenges for effective implementation of the anammox process is to develop methods that increase the bacterial cells’ retention inside the reactors. In this research we immobilized anammox bacteria NRRL B-50286 (Brocadia caroliniensis) by encapsulation in polymer gel pellets. The entrapping polymer used was polyvinyl alcohol (PVA), which was polymerized into sheets using a freezing method (cryogels) and then cut into 4-mm pellet cubes. The anammox pellets were added to stirred reaction tanks to remove ammonia from wastewater. They were successfully tested using both synthetic and swine wastewater. The PVA pellets were highly porous to ammonia and nitrite needed by the entrapped anammox bacteria and achieved > 93% removal efficiency. They were also porous to the dinitrogen gas produced by the bacteria and intense bubbling from the pellets was noticed throughout the experiments. The pellets removed the nitrogen pollutants at a rate of 3 g per kg of pellet per day. They could be used in the treatment tanks at a proportion of 20-30% (w/v) to more effectively treat wastewater using the anammox process.
Technical Abstract: This study evaluated the use of polyvinyl alcohol (PVA) cryogels to encapsulate slow-growing anammox bacteria for deammonification treatment of wastewater. The cryogel pellets were prepared by a freezing-thawing procedure at -8 oC. 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 PVA cryogels were highly porous to anammox substrates and N2 gas by-product; the process was not limited by substrate availability unless quite low N concentration (< 5 mg/L) achieving >93% ammonia and nitrite removal efficiency. The stoichiometry of anammox reaction was maintained for more than 5 months under non-sterile conditions. In mass balances, >80% of the potential N conversion activity (nitrite + ammonium) was achieved or 2,920 mg N/kg-pellet per day. In addition, the immobilized anammox bacteria was resilient to inhibition at high nitrite concentrations (244-270 mg nitrite-N/L).