A rarely used hydroponic plant root mat filter (PRMF, of 6 m(2)) and a horizontal subsurface flow constructed wetland (HSSF CW, of 6 m(2)), operating in continuous flow and discontinuous outflow
flushing modes, were investigated for treating
sulfate-rich and organic
carbon-lean groundwater contaminated with
monochlorobenzene (MCB);
1,2-dichlorobenzene (1,2-DCB);
1,4-dichlorobenzene (1,4-DCB); and
2-chlorotoluene. Whereas the mean inflow loads ranged from 1 to 247 mg m(-2) days(-1), the range of mean inflow concentrations of the
chlorobenzenes recorded over a period of 7 months was within 0.04 and 8 mg L(-1). A hydraulic surface loading rate of 30 L m(-2) days(-1) was obtained in both systems. The mean load removal efficiencies were found to vary between 87 and 93 % in the PRMF after a flow path of 4 m, while the removal efficiencies were found to range between 46 and 70 % and 71 to 73 % in the HSSF CW operating in a continuous flow mode and a discontinuous outflow
flushing mode, respectively. Seasonal variations in the removal efficiencies were observed for all low-
chlorinated hydrocarbons both in the PRMF and the HSSF CW, whereby the highest removal efficiencies were reached during the summer months.
Sulfide formation occurred in the organic
carbon-lean groundwater particularly in summer, which is probably due to the plant-derived organic
carbon that fostered the microbial dissimilatory
sulfate reduction. Higher redox potential in water was observed in the PRMF. In conclusion, the PRMF could be an option for the treatment of water contaminated with compounds which in particular need oxic conditions for their microbial degradation, such as in the case of low-chlorinated benzenes.