Reutilization of wastes is mainly focusing on dissolved substances. Non-dissolved, particulate waste is often discharged, as sludge, leaving a signiamount of nutrients un-used. Heterotrophic bacteria can convert these nutrients into bacterial biomass, which can potentially be used as feed and thereby reduce the waste discharge. A major constraint for this approach is the low carbon/nitrogen ratio in waste. If sufamounts of carbon are made available, e.g. by direct carbon supplementation bacteria production is enhanced in aquaculture systems. In this study, crude protein production by bacteria on solid waste was determined. Two bacterial reactors were connected to the screen outlet (mesh size 60of a semi-farm scale recirculation system, in which African catwas produced. The efcomprising solid waste and backwash water, was into a buffer tank, where the slurry was aerated and agitated. From the buffer tank the sludge was continuously pumped into the bacterial culture reactors at 7ml/min, which gives a hydraulic retention time in the reactors of 8h. Pure oxygen was diffused into the reactors to maintain aerobic conditions (>2mg/l). pH levels were maintained between 7.0 and 7.2 by addition of acid or base. The reactor temperature was at 28Different amounts of sodium acetate (0gl, 3g/l, 6g/l, 8g/ l) were added. Various parameters within the reactors such as, optical density of the mixture, suspended solid concentration, inorganic and organic nitrogen concentrations were measured during bacteria production. Resulting yields, VSS and Kjeldahl nitrogen production were increasing depending on carbon supplementation level (Table 1). Using a factor 6.25 to convert Kjeldahl nitrogen to crude protein, a maximum production of 112g protein per kg feed can be obtained (6.25*17.9g KjD-N). It can be concluded, that bacterial biomass yields are dependent on carbon supplementation level. The maximum crude protein production for the highest tested supplementation level was 112g protein/kg feed. Such production by bacteria can increase systems protein production, meaning + bacteria, by 50%.
|Publication status||Published - 2005|