STABILITY AND VARIATION IN SLUDGE PROPERTIES IN 2 PARALLEL SYSTEMS FOR ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL OPERATED WITH AND WITHOUT NITROGEN REMOVAL

In order to introduce nitrogen removal, many conventional activated sl udge systems in Sweden have been transformed into low-loaded systems d uring the 1990's. Occasionally these systems have been combined with e nhanced biological phosphorus removal (EBPR). Increased problems of sl udge loss from secondary clarifiers have aroused new interest in the p roperties of activated sludge. The aim of this study was to investigat e the longterm variation and stability of sludge properties in two par allel EBPR systems, operating on the same wastewater. One of the syste ms was designed as a conventional system, and the other as a low-loade d system with nitrogen removal, The study was performed at the Sjolund a plant in Malmo: during a two-year period, in a pilot plant which has been in operation since 1986. The diluted sludge volume index (DSVI) was found to be about 150 ml/g in both systems. The highest values wer e recorded during the winter season. The variation in the DSVI was muc h greater in the conventional system than in the low-loaded system, Th e dominating filamentous bacteria in the conventional system were Type 021N and Thiothrix, and in the low loaded system Type 0041/0675 and T ype 0092. The EBPR operation induced large amounts of poly-P-containin g flocs in both systems, Although it was not possible to determine to what extent the poly-P-containing flocs affected the sludge properties in this study, it was clearly demonstrated that EBPR operation may no t always provide conditions which lead to superior sludge properties. Copyright (C) 1996 IAWQ.