Cost-effectiveness of in situ treatment of multiple contaminant mixtures in groundwater by means of sequenced units of zero valent iron and granular activated carbon

This modelling study reveals that the sequential use of zero valent iron (ZVI) and granular activated carbon (GAC) can potentially be used for in situ treatment of groundwater with multiple contaminant mixtures, but crucial design rules should be followed, since the performance of the combined system depends on the interplay of both reactor units. As an example a mixture of aliphatic chlorinated hydrocarbons (PCE, TCE, and cis-DCE) and one aromatic chlorinated hydrocarbon (monochlorobenzene) is considered. The results show that the concentrations of less sorbing compounds such as cis-DCE have to be reduced in the ZVI reactor far beyond the desired maximum contaminant level in order to restrict concentration build-ups in the GAC reactor, which occur due to competitive sorption with contaminants withheld in the GAC. Results from reactor modelling studies are used to economically analyse feasible reactor designs. Cost-optimal ZVI-GAC combinations are derived by a general approach based on unit cost ratios.