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 nitro genous wastes of three types of water recirculation biofiltration units use d during the production of the sharptooth, catfish Clarias gariepinus (Burc hell). Two types of trickling filters were employed. One contained PVC shav ings with a calculated surface contact area of 1 220 m(2). The second is a more sophisticated biofilter unit made up with Siporax porous sintered glas s cylinders with a total surface water contact area of 32 000 m(2). The thi rd filter consisted of a rotating biological contactor unit with a water co ntact surface area of 271.2m(2). Investigations showed that the PVC shaving s filter unit was clearly the most efficient of the three by transforming m ore than 96% of the NH3-N into NO3-N. This was followed by the rotating bio logical contactor with a 93% efficiency and lastly by the Siporax filter wi th an almost 93% efficiency. The outcome of the section on the production o f Clarias gariepinus follows in Part 2 of this series.