Analysing sludge balance in activated sludge systems with a novel mass transport model

• Published in: Water science and technology 2008-01, Vol.57 (9), p.1413-1419
• Main Authors: Patziger, M, Kainz, H, Hunze, M, Jozsa, J
• Format: Article
• Language: English
• Subjects: Activated sludge; Biological wastewater treatment; Biomass; bioreactors; Boundary conditions; calibration; Computational fluid dynamics; dynamic models; equipment performance; Investigations; Mass transport; model validation; Models, Theoretical; Reactors; Sea surface; Settling; Sewage - analysis; Sewage - chemistry; simulation models; Sludge; Sludge settling; Sludge thickening; Sludge volume index; Storms; Stormwater; Surface temperature; Thickening; Transport; Turbulence; Turbulent flow; Two dimensional models; Waste Disposal, Fluid - instrumentation; Waste Disposal, Fluid - methods; Wastewater; Wastewater treatment; Wastewater treatment plants; Water flow; Water Purification - instrumentation; Water Purification - methods; Water treatment plants
• ISSN: 0273-1223; 1996-9732
• DOI: 10.2166/wst.2008.221

In activated sludge systems the mechanically treated wastewater is biologically cleaned by biomass (activated sludge). The basic requirement of an efficient biological wastewater treatment is to have as a high biomass concentration in the biological reactor (BR) as possible. The activated sludge balance in activated sludge systems is controlled by the settling, thickening, scraper mechanism in the secondary settling tank (SST) and sludge returning. These processes aim at keeping maximum sludge mass in the BR and minimum sludge mass in the SST even in peak flow events (storm water flow). It can be, however, only reached by a high SST performance. The main physical processes and boundary conditions such as inhomogeneous turbulent flow, geometrical features of the SST, wastewater treatment plant (WWTP) load, return sludge flow, sludge volume index etc. all influence settling thickening and sludge returning. In the paper a novel mass transport model of an activated sludge system is presented which involves a 2-dimensional SST model coupled with a mixed reactor model of the biological reactor. It makes possible to investigate different sludge returning strategies and their influence on the sludge balance of the investigated activated sludge system, furthermore, the processes determining the flow and concentration patterns in the SST. The paper gives an overview on the first promising model results of a prevailing peak flow event investigation at the WWTP of Graz.