BIOKINETIC BEHAVIOR AND SETTLING CHARACTERISTICS IN AN ACTIVATED-SLUDGE UNDER THE EFFECT OF TOXIC NI(II) INFLUENCES

The inhibitory effect of Ni upon a biological system of activated slud ge has been analyzed in two semicontinuous sequential reactors feeding synthetic wastewater. One of the reactors was used as control while i n the other given amounts of NiSO4 were added to the influent to achie ve a concentration of 30 ppm Ni(II). An analysis of the characteristic biokinetic parameters has been made and the correspondence with the o perating 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 accu mulation of undigested substrate on the flocs 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 ef fect upon the settling characteristics of the sludge must be also cons idered.