Treatment of a sulfate-rich groundwater contaminated with perchloroethene in a hydroponic plant root mat filter and a horizontal subsurface flow constructed wetland at pilot-scale.

A hydroponic plant root mat filter (HPRMF) was compared over 7months with a horizontal subsurface flow constructed wetland (HSSF CW) regarding the removal of perchloroethene (PCE) (about 2 mg L(-1)) from a sulfate- (850 mg L(-1)) and ammonia-rich (50 mg L(-1)) groundwater with a low TOC content. At a mean area specific inflow PCE load of 56 mg m(-2)d(-1), after 4m from inlet, the mean PCE removal during summer time reached 97% in the HPRMF and almost 100% in the HSSF CW. Within the first 2m in the HSSF CW metabolites like dichloroethenes, vinyl chloride and ethene accumulated, their concentrations decreased further along the flow path. Moreover, the tidal operation (a 7-d cycle) in the HSSFCW decreased the accumulation of PCE metabolites within the first 1m of the bed. The carcinogenic degradation metabolite vinyl chloride was not detected in the HPRMF. The smaller accumulation of the degradation metabolites in the HPRMF correlated with its higher redox potential. It can be concluded from this study that HPRMF appears an interesting alternative for special water treatment tasks and that tidal operation will show some positive effects on the removal of the accumulated PCE metabolites in HSSF CW.

Comparative evaluation of pilot scale horizontal subsurface-flow constructed wetlands and plant root mats for treating groundwater contaminated with benzene and MTBE.

In order to evaluate technology options for the treatment of groundwater contaminated with benzene and MTBE in constructed wetlands (CWs), a scarcely applied plant root mat system and two horizontal subsurface-flow (HSSF) CWs were investigated. The inflow load of benzene and MTBE were 188-522 and 31-90 mg d(-1)m(-2), respectively. Higher removal efficiencies were obtained during summer in all systems. The benzene removal efficiencies were 0-33%, 24-100% and 22-100% in the unplanted HSSF-CW, planted HSSF-CW and the plant root mat, respectively; the MTBE removal efficiencies amounted to 0-33%, 16-93% and 8-93% in the unplanted HSSF-CW, planted HSSF-CW and the plant root mat, respectively. The volatilisation rates in the plant root mat amounted to 7.24 and 2.32 mg d(-1)m(-2) for benzene and MTBE, which is equivalent to 3.0% and 15.2% of the total removal. The volatilisation rates in the HSSF-CW reached 2.59 and 1.07 mg d(-1)m(-2), corresponding to 1.1% and 6.1% of the total removal of benzene and MTBE, respectively. The results indicate that plant root mats are an interesting option for the treatment of waters polluted with benzene and MTBE under moderate temperatures conditions.