Remediation of sediment and water contaminated by copper in small-scaled constructed wetlands: effect of bioaugmentation and phytoextraction

AbstractThe use of plants and microorganisms to mitigate sedimentcontaminatedbycopperwasstudiedinmicrocosms that mimicthe functioning of a stormwater basin (SWB) connected tovineyard watershed. The impact of phytoremediation and bio-augmentation with siderophore-producing bacteria on the fateof Cu was studied in two contrasted (batch vs. semi-continu-ous) hydraulic regimes. The fate of copper was characterisedfollowing its discharge at the outlet of the microcosms, its porewater concentration in the sediment, the assessment of itsbioaccessible fraction in the rhizosphere and the measurementof its content in plant tissues. Physico-chemical (pH, redoxpotential) and biological parameters (total heterotrophic bacte-ria) were also monitored. As expected, the results showed aclear impact of the hydraulic regime on the redox potential andthus on the pore water concentration of Cu. Copper in porewater was also dependent on the frequency of Cu-pollutedwaterdischarges.Repeatedbioaugmentationincreasedthetotalheterotrophic microflora as well as the Cu bioaccessibility inthe rhizosphere and increased the amount of Cu extracted byPhragmitesaustralis byafactorof~2.Sugarbeetpulp,usedasafiltertoavoidcopperflushing,retained20%ofoutcomingCuand led to an overall retention of Cu higher than 94 % whenarranged at the outlet of microcosms. Bioaugmentation clearlyimprovedthephytoextractionrateofCuinasmall-scaledSWBdesigned to mimic the functioning of a full-size SWB connect-ed to vineyard watershed.Highlights- Cu phytoextraction in constructed wetlands much dependsonthehydraulicregimeandonthefrequencyofCu-pollutedwater discharges- Cu phytoextraction increases with time and plant density- Cu bioaccessibility can be increased by bioaugmentationwith siderophore-producing bacteriaKeywords Bioaccessibility .Copper .Phytoremediation .Phragmitesaustralis .Siderophore-producingbacteriaAbbreviations3,4-DCA 3,4-DichloroanilineANOVA Analysis of varianceBI Batch-inoculatedBNI Batch-non-inoculatedCEC Cation exchange capacity