Spiking trials of MIB and geosmin into the GAC filters were
first undertaken in August 2005, a month after the GAC filters
had been commissioned. MIB and geosmin, at concentrations
between 50 and 200 ng/L, were dosed into each GAC filter. Five
samples were taken over 3 days. Whilst there was some
variation in the inlet concentrations over this period, no MIB
and geosmin was detected in the outlet of any of the GAC
filters. This was despite significant differences in DOC
concentrations in water entering the GAC filters between the
streams with and without MIEX treatment. Source water for
GAC 1 and 2 had DOC concentrations of 2.7 mg/L and 2 mg/L
respectively, whilst source water for GAC 4 and 5 had DOC
concentrations of 4 mg/L and 2 mg/L respectively. It appears
that when using virgin GAC and 20 min EBCT, the large
amount of adsorption capacity available compensates for any
difference in competition for adsorption sites caused by
different DOC concentrations.