Short-term effects of additives on sludge sedimentation characteristics

The effect of different concentrations of additives on the settling propert ies of two types of activated sludge were evaluated by means of a Settlomet er. In addition to the evaluation of the immediate positive effect of the a dditive, a method consisting of consecutive cycles of resuspension and eval uation of the settling properties, is proposed to study the stability of th e beneficial effect of the additive. First, a sludge from industrial origin was supplemented with talc and with a polymer. Subsequently, a sludge from domestic origin was tested. Both additives were successful in improving th e sedimentation characteristics of the sludges. The effect of talc was stab le over a period of at least 14 h. However, the positive effect of the poly mer was transient because after 4 h the beneficial effect disappeared. The experimental results from the talc addition were analysed by means of a phy sical model. The latter revealed that the observed increase of the initial settling velocity is smaller than but close to the increase related to the specific weight of the floc. (C) 1998 Elsevier Science Ltd. All rights rese rved.