Influence of Pre-Ozonation and Media Type on Biological Activated Carbon (BAC) Performance
Annual Conference
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Activated Carbon has long been used as a potable water filtration media for the removal of Dissolved Organic Carbon (DOC) that would otherwise lead to chlorine decay, regrowth in distribution networks and elevated THM levels.
Australia and New Zealand have widely adopted Biological Granular Activated Carbon (BAC) filtration for the selective removal of that fraction of the DOC that most contributes to chlorine decay - Bio-Degradable Dissolved Organic Carbon (BDOC).
In the BAC process, DOC is converted to biomass by naturally occurring biology that colonise the surface of GAC, excess biomass being eliminated during backwash. This strategy for GAC use avoids requirement for regeneration or replacement, typical bed life is 15 years.
Ozonation is a complimentary step to BAC filtration by converting some of the DOC into BDOC thus greatly enhancing total DOC reduction.
Previous studies show that during cooler water periods, biological activity of BAC filters decreases. This, if not effectively managed, can lead to breakthrough of DOC and BDOC in the BAC filtered water.
This pilot plant study looks at the effect of activated carbon type on BAC performance, by comparing two different steam activated, coal based carbons (the most common type of BAC in Australia and New Zealand) during winter months.
Previous studies show that the presence of ozone prior to the BAC filters significantly influences the character of the carbon both biologically and physically. This study followed previous work and looked at the influence of pre-ozonation on the BAC filtered water quality, in particular the ability of the carbon filters to reduce DOC and manganese both in the presence and absence of ozone.
Biological diversity of the BAC pilot columns was examined (through DNA profiling and SEM) to determine the impact of different activated carbon media, the presence and absence of ozonation, and water temperature.