Changes in some water quality conditions in recycling water using three types of biofiltration systems during the production of the sharptooth catfish Clarias gariepinus (Burchell): Part I: Relative efficiency in the breakdown of nitrogenous wastes by the different biofiltration units

A comparison is made of the relative efficiencies in the breakdown of nitrogenous wastes of three types of water recirculation biofiltration units used during the production of the sharptooth catfish Clarias gariepinus (Burchell). Two types of trickling filters were employed. One contained PVC shavings with a calculated surface contact area of 1 220 m. The second is a more sophisticated biofilter unit made up with Siporax porous sintered glass cylinders with a total surface water contact area of 32 000 m. The third filter consisted of a rotating biological contactor unit with a water contact surface area of 271.2 m. Investigations showed that the PVC shavings filter unit was clearly the most efficient of the three by transforming more than 96% of the NH-N into NO-N. This was followed by the rotating biological contactor with a 93% efficiency and lastly by the Siporax filter with an almost 93% efficiency. The outcome of the section on the production of Clarias gariepinus follows in Part 2 of this series