Changes

[[Image:activated_carbon_bags.jpg|thumb|right|300px|Activated carbon bags for sale and use in water treatment systems. Photo: [http://www.alibaba.com/product-gs/246397546/activated_carbon_for_water_treatment.html Alibaba.com.]]]

Different types of activated carbon have different affinities for types of contaminants. The choice between PAC and GAC will depend upon the relative cost-effectiveness, frequency and dose required. PAC would generally be preferred in the case of seasonal or intermittent contamination or where low dosage rates are required. PAC is dosed as a slurry into the water and removed by subsequent treatment processes, together with the waterworks sludge. Its use is therefore restricted to surface water treatment works with existing filters. GAC in fixed-bed adsorbers is used much more efficiently than PAC dosed into the water, and the effective carbon use per water volume treated would be much lower than the dose of PAC required to achieve the same removal.