Sequence Batch Reactors – past, present and future
Smyth, M. – Aqua Enviro
(free)
A sequencing batch reactor (SBR) is a variant of the activated sludge process: a suspended growth, variable-volume, wastewater treatment technology. SBRs were wisely adopted by the UK Water Industry in the mid to late 1990’s and into the early 2000’s (AMP 2 & AMP 3). However during this period it became apparent that some SBRs were prone high suspended solids losses during the decant phase of the cycle and on occasions the sludge blanket itself. Often this was a result of filamentous bulking, in particular caused by Microthrix parvicella. The process therefore failed to consistently deliver a compliant final effluent and as a result SBRs fell out of favour, and in some cases were even replaced in AMPs 3 & 4 with conventional activated sludge processes. In the past 5 years there has been an increase in the uptake of SBRs and they look set to be the choice of technology for organic waste digestion plants treating dewatering liquor. In addition 2014 will see the completion of the £200million upgrade to Liverpool WwTW with 16 basins on 2 levels.
This papers looks to:
- review the causes of the problems witnessed in the 1990’s which included: filamentous bulking and foaming); poor sludge age control, resulting in partial or unintentional nitrification; inadequate blower capacity and shortened cycle times in high flow conditions.
- evaluate how these factors have been accounted for in present day designs,
- consider whether design modifications will result in a trouble free future for SBRs.
