Open AccessRedox Dynamics of Arsenic Species in the Root‐Near Environment of Juncus effusus Investigated in a Macro‐Gradient‐Free Rooted Gravel Bed Reactor
Author(s) -
Rahman K. Z.,
Wiessner A.,
Kuschk P.,
Mattusch J.,
Offelder A.,
Kästner M.,
Müller R. A.
Publication year - 2008
Publication title -
engineering in life sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.547
H-Index - 57
eISSN - 1618-2863
pISSN - 1618-0240
DOI - 10.1002/elsc.200800093
Subject(s) - rhizosphere , juncus , chemistry , wastewater , constructed wetland , redox , anoxic waters , environmental chemistry , scirpus , sulfate , environmental engineering , adsorption , precipitation , wetland , environmental science , inorganic chemistry , ecology , geology , biology , bacteria , organic chemistry , paleontology , physics , meteorology
In the framework of investigating the dynamics of As species within the planted soil beds of treatment wetlands, the redox dynamics of As species particularly in the root‐near environment of the rhizosphere were investigated. For this purpose, long‐term experiments were carried out using a specially designed macro‐gradient‐free rooted gravel bed reactor, planted with Juncus effusus to treat an artificial wastewater containing As (200 μg As/L). The exceptional quality of the biofilm processes at the helophyte root‐surfaces in treatment wetlands were of special importance in this investigation. The results showed that under C‐deficient conditions, a highly efficient As immobilization (> 85 %), obviously due to adsorption and/or co‐precipitation, was attained. The addition of organic carbon immediately caused an elevated As concentration and enrichment of As(III) (nearly 80 % of total As) in the reactor. Increasing the SO 4 2– concentration in the artificial wastewater inflow facilitated a high As immobilization (> 82 %) under sulfate reducing condition. In principle, a highly efficient microbial dissimilatory sulfate reduction contributed to S 2– formation and a greater As immobilization (most likely as As 2 S 3 ) under C surplus and reducing conditions. Significant differences in As immobilization were observed by varying the inflow of the SO 4 2– concentration (0.2, 5, 10, 25 S/L) under C surplus conditions. More As(III) precipitates (15 % less in the outflow) when the inflow of the SO 4 2– concentration was decreased from 25 mg S/L to 10 mg S/L. Immobilized As showed greater instability by releasing As(V) (up to 85 % of total As) due to changes in the dynamic redox conditions inside the reactor. Re‐oxidation of reduced sulfur into other S species (e.g. S 0 , SO 4 2– ) due to plant‐root mediated O 2 release probably caused an oxidative dissolution of already precipitated insoluble As (e.g. As 2 S 3 ) and as a consequent As remobilization. The findings of this study highlighted the significance of SO 4 2– in relation to organic C supply in planted soil beds treating As‐contaminated wastewater under constructed wetland conditions.