Construction of simple movable bio-filters and their nitrification performance during biofilm development

Abstract:

This paper describes the construction of the simple moveable bio-filters. Additionally, the feasibility of biofilm developed through using tank water for raising prawn broodstock and its nitrification performance were evaluated in a recirculating system stocked with Macrobrachium rosenbergii. Common media such as zeolite, fiber ball and biochemical ring (Total weight 30.9 kg) were put into plastic barrel (Total volume 70 L) to make a simple bio-filter. The two same bio-filters named Ⅰ and Ⅱ were used in current research that served as the recirculation filter. It should be noted that the bio-filter can be placed in a trolly transporting to any tank in aquaculture workshop to treat water. Two culture tanks were used as the main system in which Macrobrachium rosenbergii were grown as a source of waste nutrients. Tank water flowed out of overwintering ponds (4 m³) for broodstock and was mechanically filtered through the simple bio-filters Ⅰ (0.231 m³/h) and Ⅱ (0.138 m³/h) by pumps. The results showed that the biofilm can be developed after about 17 days through using tank water for raising prawn broodstock. Concentrations of TAN and NO₂^--N can be effectively reduced by the simple moveable bio-filters. Resulting average removal rates were 40.23%, 45.3% in TAN and 58.4%, 65.1% in NO₂^--N in 37 d by the two filters Ⅰ and Ⅱ. Average removal rates were 0.138 mg, 0.081 mg TAN/ (m²·d), while 0.053 mg, 0.035 mg NO₂^--N/ (m²·d) by filtersⅠ and Ⅱ. The results of this study showed that filters Ⅰ and Ⅱ have high nitrification efficiency in removing TAN and NO₂^--N, and no significant differences were observed between Ⅰ and Ⅱ (P>0.05).