EXPERIENCES WITH SLUDGE SETTLEABILITY IN DIFFERENT PROCESS ALTERNATIVES FOR NUTRIENT REMOVAL

SVI and DSVI were measured three times at almost 100 Danish nutrient r emoval plants and the filamentous microorganisms were subsequently cha racterized in the laboratory. Information about the plant layout and t he operation was collected by means of a questionnaire. In general, th e sludge settleability index becomes worse by the introduction of nutr ient removal. Among nutrient removal plants the best settling characte ristics are found among plants with biological P removal and the poore st among the plants that perform simultaneous denitrification. When co mpared to iron products, aluminium products in some cases seem to redu ce the filament number and improve the settling characteristics in pla nts that apply simultaneous precipitation for P removal. Selectors may have a positive effect on the filament number but the effect may not be enough to prevent bulking. Copyright (C) 1996 IAWQ. Published by El sevier Science Ltd.