Jan Šíma

Removal of Nonionic Surfactants from Wastewater Using a Constructed Wetland

Removal of anionic surfactants from municipal wastewater using a constructed wetland with a horizontal subsurface flow was studied in 2007 and 2008. Extraction spectrophotometry with methylene blue served to determine the analyte concentrations in individual samples. The anionic surfactant‐removal efficiency depended on actual conditions, mostly the treated water flow intensity, its temperature, and a redox‐potential gradient in the longitudinal profile of the wetland bed. It increased with decreasing inflow and increasing temperature. The average efficiency was 83.7% in 2007 and 81.7% in 2008; however, values higher than 85% were often determined during the summer period. On the other hand, the efficiencies were usually lower than 80% in winter, especially in periods with intensive precipitation and inflows. The average concentration of anionic surfactants in water taken at the outflow was lower than 0.65 mg/l (expressed as sodium dodecyl sulfate). The most significant fraction of anionic surfactants (almost 50%) was degraded at the beginning (1 m from the inflow zone) of the wetland bed. The rhizosphere aeration via the vegetation roots strongly supported the anionic‐surfactant removal.

Redox properties of a constructed wetland: theoretical and practical aspects.

Constructed wetlands represent a progressive approach to the wastewater treatment. A fundamental prerequisite of the efficient water quality improvement is the presence of redox potential gradients (connected with the aeration of the system) inside the vegetation bed. Redox properties of a constructed wetland were tested in three longitudinal transects crossing the vegetation bed from the inflow zone to the outflow using diverse indicators (e.g., Fe(III)/Fe(II), SO(2-)(4)/S(2-)). Approximately 10-25% of iron was reoxidized in samples taken 10 m from the inflow zone in 2006. Redox processes of iron in artificial (constructed wetland) and natural (peat bog) ecosystems were compared. The peat bog was characterized with higher percentages of Fe(II) (usually ca. 90-100%). Thus, the aeration of the peat land was lower in comparison with the constructed wetland. The constructed wetland efficiently reduced sulfates (average concentrations of 44.7 and 11.2 mg/l at the inflow and the outflow, resp., in 2007). Organics, expressed as COD(Cr) and BOD(5), and NH+(4) were removed with efficiencies of 86.4, 92.2, and 60.4%, respectively. However, total phosphorus (redox processes play a negligible role in this case) was removed only with 39.6% efficiency. Redox properties of the wetland did not significantly depend on the heterogeneity of the treated wastewater flow.

Removal of Selected Metals from Wastewater Using a Constructed Wetland

Removal of selected metals from municipal wastewater using a constructed wetland with a horizontal subsurface flow was studied. The objective of the work was to determine the efficiency of Cu, Zn, Ni, Co, Sr, Li, and Rb removal, and to describe the main removal mechanisms. The highest removal efficiencies were attained for zinc and copper (89.8 and 81.5%, respectively). It is apparently due to the precipitation of insoluble sulfides (ZnS, CuS) in the vegetation bed where the sulfate reduction takes place. Significantly lower removal efficiencies (43.9, 27.7, and 21.5%) were observed for Li, Sr, and Rb, respectively. Rather, low removal efficiencies were also attained for Ni and Co (39.8 and 20.9%). However, the concentrations of these metals in treated water were significantly lower compared to Cu and Zn (e.g., 2.8 ± 0.5 and 1.7 ± 0.3 μg/l for Ni at the inflow and outflow from the wetland compared to 27.6 ± 12.0 and 5.1 ± 4.7 μg/l obtained for Cu, respectively). The main perspective of the constructed wetland is the removal of toxic heavy metals forming insoluble compounds depositing in the wetland bed. Metal uptake occurs preferentially in wetland sediments and is closely associated with the chemism of sulfur and iron.

A comparison of fluorescein and deuterated water as tracers for determination of constructed wetland retention time

AbstractRetention time of treated water in a horizontal subsurface flow constructed wetland was determined in the non-vegetative period using fluorescein and deuterium oxide. Fluorescein served as one of the most frequent tracers detectable at extremely low concentrations by fluorimetry; however, deuterated water (concentrations of deuterium measured by IRMS and expressed as δ (‰) against VSMOW) was used to precisely simulate the treated water flow movement. Tracer retention time (TRT) of fluorescein was 194 h while deuterated water TRT was 192 h. TRT and nominal hydraulic retention time (nHRT, 190 h) were nearly exactly equal. The tracer behavior of deuterated water was almost ideal. On the other hand, the fluorescein movement through the system was slightly influenced by the interaction with the vegetation bed (sorption causing the tailing of tracer-response curves). Nevertheless, both tracers can be successfully used and provide similar results. Retention time is a very important characteristic of a constructed wetland. It is closely connected with the efficiency of the contaminant removal from treated water. It has to be determined correctly when wetland operation parameters are optimized. The choice of the suitable and reliable tracer is always necessary. Fluorescein takes preference with respect to its simple and inexpensive determination.

The Long-Term Study of the Surfactant Degradation in a Constructed Wetland

Abstract A horizontal subsurface flow constructed wetland was studied with respect to its capability to remove surface active compounds from municipal wastewater. The long-term aspect (five years) of the study is emphasized. The degradation efficiency reached 82.3 and 98.5% in the case of anionic and nonionic surfactants, respectively. All data were processed using multivariate statistical analysis. The removal efficiency of anionic surfactants depended mainly on the flow rate of the influx (multiple R2 of 0.300). A significant effect of redox potential was observed in the case of nonionic surfactants (multiple R2 of 0.812). No systematic decrease of the surfactant degradation efficiency was observed. The constructed wetland can serve as a suitable natural alternative to clean the wastewater generated by small communities.

The effect of macrophytes on retention times in a constructed wetland for wastewater treatment

Retention times of treated water in a constructed wetland (CW) with horizontal subsurface flow were determined both in the vegetative and non-vegetative periods of 2005. Tracer experiments were performed using fluorescein, an organic compound detectable at extremely low concentrations. Nominal and tracer retention times were determined and compared. Winter tracer retention time (TRT 194 h) and nominal retention time (nHRT 190 h) were nearly exactly equal, while summer TRT (335 h) was approximately twofold higher than nHRT (158 h). Residence time distribution function (RTD) was used to compare retention times obtained for the vegetative and non-vegetative periods. The obtained results document a significant influence of dense common reed vegetation on retention characteristics of the studied system. Common reed can convert a significant volume of water from liquid to gas via evapotranspiration (ET) and thus prolong water retention times in the system. This is very important both technically and ecologically. Longer retention times mean a longer time for microbiological decay of wastewater. Water converted from liquid to gas causes cooling of the microclimate, which is very important, especially in intensively cultivated areas with a lack of water.