Sodium hypochlorite pecularities in application for restoration of highly porous fillers after their use in biofiltration systems of recirculating aquaculture systems

Abstract

Purpose. Development of a method for the regeneration of highly porous fillers for biofilters after slagging of their pores with biofilm residues in the process of growing aquaculture objects in recirculating aquaculture systems (RAS). Methodology. Regeneration of fillers was performed with solutions of sodium hypochlorite of different concentrations (2.5%, 1%, 0.5% of active chlorine) after their exploitation for 6 months. The cleaning efficiency was monitored by the difference in fillers weights after cleaning. Findings. According to the study, the use of sodium hypochlorite for cleaning highly porous fillers for biofilters (using an example of porous ceramic filler and foamed glass «JBL Micromec») is efficient and cost-effective. A reduction in the weight of the test samples averaged 12.95% for porous ceramics and 15.01% for foamed glass. Based on the obtained data, aqueous solutions with different concentrations of sodium hypochlorite do not have a pronounced difference in efficiency, respectively; the optimal for use is a 0.5% solution. Originality. The use of highly porous fillers for biofilters has long been unprofitable in fish farming due to the rapid loss of their main advantages - a high specific area per unit volume as a result of micropore slagging with biofilm residues. As a result, complete regeneration of these filter materials was required annually, which, given the significantly higher cost compared to polymeric fillers, made their use unprofitable. The described technique allows the use of porous ceramics and foamed glass, after their restoration, for a long time, with replacement only after mechanical wear. Practical value. The described method allows using highly porous fillers for biofilters in the process of growing aquaculture objects without their main disadvantage - a rapid decrease in efficiency as a result of pore slagging with biofilm residues. Keywords: RAS, biofilter, filler, restoration, sodium hypochlorite.