Biokinetic behavior and settling characteristics in an activated sludge under the effect of toxic Ni(II) influentes

The inhibitory effect of Ni upon a biological system of activated sludge has been analyzed in two semicontinuous sequential reactors feeding synthetic wastewater. One of the reactors was used as control while in the other given amounts of NiSO₄ were added to the influent to achieve a concentration of 30 ppm Ni(II). An analysis of the characteristic biokinetic parameters has been made and the correspondence with the operating conditions stated. A series of O₂ uptake tests were proposed and the results analyzed together with the specific rate of substrate removal (U) in order to explain the toxic influence of Ni(II). An accumulation of undigested substrate on the floes seems to explain certain aspects derived of the presence of Ni. The sludge residence time (SRT), within a certain range, can be used as a control operating variable to mitigate the inhibitory effect of Ni, since a somewhat contrary effect upon the settling characteristics of the sludge must be also considered.