SLUDGE STORAGE FOR COUNTERING NITROGEN SHOCK LEADS AND TOXICITY INCIDENTS

Spare nitrification capacity is usually needed for a nitrifying activa ted sludge plant to counter nitrogen shock loads and/or toxicity incid ents. The traditional way to provide this Capacity is to apply a sludg e retention time which is much longer than what needed to obtain a sta ble nitrification, resulting in over designed plants. Another approach , which is investigated in this paper, is to store the spare biomass i n a separate sludge storage tank and return it to the main stream proc ess when a shock nitrogen load or a toxicity incident occurs. Model ba sed analysis reveals the unique feature of the scheme: different parti culate components in the sludge have a different retention time, and m ore specifically, active biomass stays longer in the plant than inert solids. This results in that a plant with a storage tank can have the same amount of active biomass as a traditional plant but less sludge, opening the potential of reducing the volume of the plant. analysis sh ows that a plant with a sludge storage tank can be about twenty percen t smaller than a traditional plant that has the same treatment capabil ity. Analysis is verified by simulation studies. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.