Advances in Water Treatment and Enviromental Management

188 WATER TREATMENTDISCUSSIONThe results clearly demonstrate that silicalite is capable of adsorbing chloroformfrom aqueous solution over a broad concentration range and research currently inprogress indicates that all THMs can be adsorbed in this way. Initial experimentswith dibromochloromethane, CHCBr 2 , indicate that the brominated THMs are morestrongly adsorbed than chloroform. For example, for a liquid phase concentrationTable 1 THM solubilities in water at 25°CaLange (ed), 1985, pp214, 650bExperimental dataof 60 mg - 1 the adsorbed phase concentrations are 0.072 and 0.10 g g- 1 forchloroform and dibromochloromethane, respectively. This result is consistentwith other studies using carbon (Faust et al, 1987, p214), and the generalprinciple that the lower the solubility of a compound (see Table 1) the greater itsextent of adsorption. This is because the bonding between a compound and thewater in which it is dissolved must be broken before adsorption can occur.Hence the lower the solubility, the weaker the bond, and the greater the extentof adsorption.An important factor in the potential use of silicalite rather than carbon in waterpurification is its ease of regeneration. However, it is important that this benefit isnot outweighed by a significantly lower capacity, or other detrimental effects,compared to carbon.Table 2 gives a comparison of Freundlich isotherm constants for the adsorptionof chloroform from water onto silicalite and GAG. Whilst it is difficult to attributeprecise physical significance to the parameters, K F gives an indication of adsorptioncapacity, whilst is a measure of rate of change of adsorption with concentration.As shown, the constants are very similar indicating little difference in the adsorptive