Effects of plants and microorganisms in constructed wetlands for wastewater treatment.

http://dzumenvis.nic.in/microbes and metals interaction/pdf/metal uptake transport and release.pdf

Metal uptake, transport and release by wetland plants: implications for phytoremediation and restoration.

Accumulation properties of As, Cd, Cu, Pb and Zn by four wetland plant species growing on submerged mine tailings

The main contaminant removal processes occurring in subsurface-flow constructed wetlands treating wastewater are reviewed. Redox conditions prevailing in the wetlands are analyzed and linked to contaminant removal mechanisms. The removal of organic matter and its accumulation in the granular medium of the wetlands are evaluated with regard to particulate and dissolved components and clogging processes. The main biological processes linked to organic matter transformation—aerobic respiration, denitrification, acid fermentation, sulfate reduction, and methanogenesis—are reviewed separately. The processes of removal of surfactants, pesticides and herbicides, emergent contaminants, nutrients, heavy metals and faecal organisms are analyzed. Advances in wetland modeling are presented as a powerful tool for understanding multiple interactions occurring in subsurface-flow constructed wetlands during the removal of contaminants.

Contaminant Removal Processes in Subsurface-Flow Constructed Wetlands: A Review

High concentrations (20-75 pmol cm-3) of amorphous Fe(III) oxide were observed in unvegetated surface and Juncus eflusus rhizosphere sediments of a freshwater wetland in the southeastern United States. Incubation experiments demonstrated that microbial Fe(III) oxide reduction suppressed sulfate reduction and methanogenesis in surface scdimcnts and mediated 240% of depth-integrated (O-10 cm) unvegetated sediment carbon metabolism, compared to I 10% for sulfate reduction. In situ CO2 and CH, flux measurements verified that nonmethanogenic pathways accounted for - 50% of unvegetated sediment carbon metabolism. Lower (- 1 O-fold) rates of dark/anaerobic CH, flux from experimental vegetated cores relative to unvegetated controls suggested that methanogenesis was inhibited in the Juncus rhizosphere, in which active Fe(III) oxide reduction was indicated by the presence of low but readily detectable levels of dissolved and solid-phase Fe(II). Fe(III) oxide reduction accounted for 65% of total carbon metabolism in rhizosphere sediment incubations, compared to 22% for methanogenesis. In contrast, methanogenesis dominated carbon metabolism (72% of total) in experimental unvegetatcd sediment cores. The high Fe(III) oxide concentrations and reduction rates observed in unvegetated surface and Juncus rhizosphere sediments were perpetuated by rapid Fe(III) regeneration via oxidation of Fe(II) compounds coupled to 0, input from the overlying water and plant roots, respectively. The results indicate that Fe(III) oxide reduction could mediate a considerable amount of organic carbon oxidation and significantly suppress CH, production in freshwater wetlands situated within globally extensive iron-rich tropical and subtropical soil regimes.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1996.41.8.1733

Organic carbon oxidation and suppression of methane production by microbial Fe(III) oxide reduction in vegetated and unvegetated freshwater wetland sediments

Growth and trace metal absorption by Phragmites australis in wetlands constructed for landfill leachate treatment

Characterization of iron plaque stability on roots of wetland plants is of value in consideration of several wetland issues. Active and dormant roots of common reed [Phragmites australis (Cav.) Trin. ex Steudel] sampled from a constructed wetland were treated sequentially with 0.5 M MgCl 2 (salt extraction), HCl solution at pH 3, 2, 1.6, 0.6, 0.3, and 0 (acid extraction), and 0.385 M Na 2 S 2 O 4 (reductant extraction). Iron was measured with an orthophenanthrolene method. Results indicated that dormant roots contained 6, 890, 180, and 140 μg Fe g -1 fresh root weight in salt extractable, acid extractable, reductant extractable, and residual fractions, respectively, and active roots had a higher proportion of acid extractable Fe and lower proportions of reductant extractable and residual Fe than dormant roots. Following acid extraction, substantial Fe 2+ was detected. Ferric iron reduction after extraction was also found. The models of Fe extraction dynamics at different pH levels were fit to standard equations. According to the comparison of the constants in these models, the Fe release rate and potential for extraction in the acid solutions tended to increase as the pH decreased, but the effect on Fe extraction became saturated when pH approached zero. The oxidation state of Fe in root plaque was examined with Mossbauer spectroscopy after the roots were dried at 80°C in a regular oven and were powdered. The results indicated that the Fe(II) proportion is 33% in powdered dormant roots, and 27% in active roots. Based on these results, we suggest that the previously accepted concept of plaque composed entirely of Fe 3+ needs to be further examined.

Tiangen Wang

Papers

Growth and trace metal absorption by Phragmites australis in wetlands constructed for landfill leachate treatment

Oxidation States and Fractionation of Plaque Iron on Roots of Common Reeds