The design of trickling biological periwinkle shells filter for closed recirculation catfish systems

Abstract

The design efficiency and economics of biofilter in reirculating aquaculture systems using local material as biofilter was carried out for 12 weeks. The type of trickling biofilter selected was vertical flow. The local, natural material selected as biofilter medium was periwinkle shells. The designed biofilter and other system components were constructed, assembled and commissioned for pilot fish production using catfish-Clarias gariepinus. The system with the designed biofilter served as the treatment system, while the system without biofilter served as the control system. Results of the biofilter design were 2.0 m depth, 150 m² surface area, 226 m²/m³ specific surface area and 0.35 m² cross sectional area. The specifications of the fish tank were 0.29 m radius, 0.90 m height, 0.21 m³ volume and 0.10 m free board. The results of the design of the sedimentation tank were 1.40 m length, 1.0 m width, 1.0 m depth, 2.0 hours detention time, 0.42 mm/sec settling velocity and 600 angle of inclination of the settling plates. The lift pump selected had the following specifications, 0.50 Hp power, 2.10 m³/hr discharge and 35.00 m head. The diameter of the perforation on the bottom of the distribution plate was 6.00 mm, while clearance was 0.3 m. The selected system recirculation rate was 10 times per hour, while the selected system recirculation ratio was 90% per day. Data from pilot fish production showed that mean values of final total length (TL) and weight of fish stocked in the treatment system were significantly (p<0.05) higher than that of the control. The result of the total ammonia-nitrogen (TAN), for the treatment system ranged from 0.00 to 4.00 ppm with a mean of 1.26+0.92 ppm, while that of the control varied from 0.00 to 6.80 ppm with a mean of 2.23+1.80 ppm. The nitrite-nitrogen values for the treatment system ranged from 0.00 to 1.80 ppm with a mean of 0.66+0.49 ppm while that of the control ranged from 0.00 to 2.50 ppm with a mean of 1.18+0.79 ppm. The unionized ammonia-nitrogen value (UAN) for the treatment system ranged from 0.000 to 0.022 ppm with mean of 0.007+ 0.006 ppm, while that of the control system ranged from 0.000 to 0.036 ppm, with a mean of 0.015+0.016 ppm. The mean values of nitrite-nitrogen and unionized ammonia-nitrogen for the treatment systems were significantly (p<0.05) lower than that of the control, while TAN mean value in the treatment system was not significantly (p>0.5) lower than that of the control system. Result of biofilter efficiency ranged from 0.00 to 100.00%, with a mean of 54.78+23.95%. Data on other water quality parameters such as DO, pH, temperature, BOD₅, Seechi transparency, total alkalinity, free carbon dioxide, chloride, etc. in the treatment system were not significantly (p>0.05) different from that of the control system. We concluded that periwinkle shell is a suitable trickling filter medium for closed recirculation catfish system.

Keywords: Periwinkle shells medium, closed recirculating catfish system, biofilter design

International Journal of Natural and Applied Sciences, 6(3): 272-280, 2010