Ammoniatoxicity is one of the major problems in zero water exchange intensive shrimpculture system. Optimum shrimp growth demands less than 0.1 mg/L unionizedammonia (NH3) in culture ponds (1.33 to 1.53 mg/L TAN at pH 8 and 28?– 30?C ) (Shan and Obbard 2001; Lin and Chen 2001, 2003). Its higherconcentration increases pH and reduces dissolved oxygen in blood, causes stressresulting in reduced feeding and disposition to diseases (Wickins 1976; Schuleret al. 2010). Themost widely used methods for addressing ammonia toxicity in aquaculture is theestablishment of biological nitrification using biological filters, biofilmreactors and nitrifiying bacteria as such.
Natural colonization of nitrifyingbacteria takes relatively longer time ( 4 to 8 weeks), and in intensive culturesystems naturally occurring nitrification may not be sufficient as it is beyondthe carrying capacity of the system, which is sensitive to physical and chemical changessuch as salinity and/or temperature (Maloneand Pfeiffer 2006; Emparanza 2009; Kuhn et al. 2010). In this context,bioaugmentation gains importance in bioremediation of TAN in intensive culturesystems. In this process immobilization of nitrifiers prior to application hasturned out to be an attractive proposition considering its effectiveapplication.
Immobilization technology has been used extensively in commercialbioreactor fermentations (Chen et al.2000; Nakano et al. 2004; Zala et al. 2004; Li and Logan 2004). Nitrosomonas europaea(ATCC 19718) immobilized on biofiltershave been successfully applied to the removal of NH3 (Chung andHuang 1998), for the treatment of mixtures ofH2S and NH3 with a two-stage biofilter (Chung et al. 2007) andin a biotrickling filter packed with polyurethane foam (Ramirez et al. 2009).
Several naturalmaterials (agar, agarose, collagen, alginates and chitosan, microbialcellulose) and synthetic polymer materials (polyacrylamide, polyurethane,polyethylene glycol and polyvinyl alcohol) have been used as the substrata forimmobilization (Jianlong et al. 1998;Fang et al. 2004; Rezaee et al. 2008;Boonpauk et al.
2011; Peirong and Wei2011). National Centre for AquaticAnimal Health (NCAAH) developed an economically viable and user friendlytechnology of bioaugmenting nitrification based on NBC (Achuthan et al. 2006) immobilized on wood powder asbiodegradable carrier, which would not leave any residue on degradation (Manju et al.
2009). Woodpowder from the plant species Ailanthus altissima was used for immobilization by adsorption. Subsequentlythe present work was undertaken for mass production of NBC immobilized on woodpowder and validation of the efficacy of the product for removal of TAN fromshrimp culture systems.