Improved removal of pesticides in biological granular activated carbon filters by pre-oxidation of natural organic matter

Two drinking water pilot plants were in operation for up to 600 days to assess the influence of pre-oxidation on the removal of natural organic matter (NOM), easily assimilable organic carbon (AOC) and pesticides during (biological) granular activated carbon ((B)GAC) filtration. Pre-oxidation resulted in an increase in AOC concentrations. BGAC filters following the pre-oxidation removed up to 70% of the produced AOC. However, in none of the BGAC filters were AOC concentrations reduced to the concentrations before pre-oxidation. The increased biodegradation of NOM was confirmed by the increased removal of dissolved organic carbon (DOC) in the steady-state situation. The increased biodegradation of NOM was assumed to be one of the main reasons that BGAC filters were more effective in DOC removal than the GAC filters. For seven pesticides it was demonstrated that, at a desired mixed effluent water quality of 0.1 × 10⁻³ g m⁻³, the maximum throughput of the BGAC filter was 1.5–3.2 times larger than the maximum throughput of the GAC filter. It was assumed that pre-oxidation reduced NOM adsorption, pore blocking and pre-loading, resulting in more effective pesticide removal.