Application of activated sludge and biofilm sequencing batch reactor technology to treat reject water from sludge dewatering systems: a comparison

Side stream reactors to treat reject water from sludge dewatering facilitie s may be considered to be small treatment plants embedded in large ones. Co mbination of main stream and side stream treatment provides a number of adv antages. Of major importance is that tailored processes can be employed for the two waste streams very different in composition and concentration. Pil ot scale experiments were conducted to study the applicability, and to comp are the performance of two types of Sequencing Batch Reactor (SBR) systems, an activated sludge and a biofilm SBR. The reactors were operated to achie ve nitrification only. Subsequently, the effluent of the reactors is fed in to the anoxic zone of the main stream activated sludge plant to achieve den itrification. In general it can be stated that both, activated sludge and b iofilm SBR systems are applicable for treating reject water of high ammonia loading. Nitrogen removal efficiencies of more than 90% could be obtained with both systems, if complete nitrification without denitrification is to be achieved, pH control is necessary. However, the amount of sodium hydroxi de required for adjusting the pH during nitrification is significant. Foam development and accumulation caused major problems, especially during the e arly stage of start up. But the time proceeding, and by changing the type o f polyelectrolyte used in the sludge dewatering process foam problems could be kept under control.