Improving the settling properties of activated sludge by gradually decreasing the settling time

Sadrzadeh F., Dulekgurgen E.

DESALINATION AND WATER TREATMENT, vol.52, pp.2465-2471, 2014 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 52
  • Publication Date: 2014
  • Doi Number: 10.1080/19443994.2013.795874
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.2465-2471
  • Keywords: Hydraulic selection pressure, Sequencing batch reactor, Settling properties, Settling time, Sludge volume index, SEQUENCING BATCH REACTORS, GRANULAR SLUDGE
  • Istanbul Technical University Affiliated: Yes


The study aims at evaluating the impact of gradually decreasing the settling time on settling properties of activated sludge removing organic matter. For that, a lab-scale sequencing batch reactor (SBR), fed with soluble starch and acetate, was seeded with floccular biomass. As the selected strategy to washout slowly settling flocks and retain biomass with improved settling capacity, settling time (T-s) was decreased gradually from 45 to 30, 15, 5 and 1min. Long-term monitoring showed that each time the T-s was decreased to the next lower level, there was biomass washout. Yet high amount of biomass (10g MLVSS/L) with improved settling properties (sludge volume index16mL/g) and high chemical oxygen demand (COD) removal performance (97%) was maintained with a T-s as low as 5min. Further decreasing T-s to 1min did not impose any negative effect. Biomass maintenance, settling properties, and COD removal performance of the system were comparable with those of aerobic granular biomass. Yet, minimum settling velocities corresponding to 5 and 1min settling times applied at the last two phases of operation (0.4 and 2.0cm/min) were lower than those reported for granular biomass systems, hence the biomass remained floccular but the system had an exceptionally good settling capacity and COD removal efficiency.