Use of Granular Sludge to Increase the Capacity of Sequencing Batch Reactors

The sequencing batch reactor (SBR) installed at Pt Pirie WWTP in South Australia is hydraulically overloaded due to significant ground water infiltration into the sewer network and requires additional treatment capacity. Modifying the operational parameters of Pt Pirie’s SBRs to select for granular sludge (GS) could be a viable means of increasing capacity. Through the use of a pilot-scale SBR reactor, the aim of this study was to determine if GS can be developed and to identify the key operational parameters needed to maintain GS stability. Extensive pilot trials were conducted at two different WWTPs in South Australia which showed similar results. GS was readily established at both WWTPs where biomass settleability (as defined by the sludge volume index) improved by >90%. High removal of total nitrogen and BOD5 were also maintained. Pilot results also showed that GS could reduce the overall SBR cycle time by up to 1h thereby increasing the hydraulic capacity of Pt Pirie’s SBR by 24%, which would be an attractive, cost effective solution for a capacity upgrade. Our next step involves a full-scale trial, by modifying the operation of one existing SBR tanks. Information collected from the pilotand full-scale trials will determine whether the operational parameters of the existing SBRs can be modified to promote GS formation and if not, determine the capital costs associated with retrofitting and upgrading the SBR to operate with GS.