Removal of nonionic surfactants from wastewater using a constructed wetland.

Removal of nonionic surfactants from municipal wastewater using a constructed wetland with a horizontal subsurface flow was studied in 2009 and 2010. Extraction spectrophotometry with 3',3″,5',5″-tetrabromophenolphthalein ethyl ester and KCl served to determine the analyte concentrations. Triton(®) X-100 was used as a standard to express the nonionic-surfactant concentrations. Anionic and cationic surfactants were shown not to interfere during the determination. Nonionic surfactants were degraded (to products undeterminable by the method) with a high average efficiency that reached 98.1% in 2009 and 99.1% in 2010, respectively. The average concentration of nonionic surfactants at the inflow was 0.978 mg/l, while it was close to the limit of quantification at the outflow (0.014 mg/l). A significant fraction of nonionic surfactants (38.7%) was already degraded during the pretreatment, and only 14.0% of the nonionic surfactants remained in the interstitial H(2) O taken in the vegetation bed at a distance of 1 m from the inflow zone at a 50-cm depth. Nonionic surfactants were degraded both under aerobic and anaerobic conditions.

Removal of anionic 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 processes of sulfur and manganese in a constructed wetland.

Constructed wetlands are very popular in terms of wastewater treatment today. Formation of redox potential gradients inside such a system strongly influences the wastewater-treatment efficiency. Individual oxidation forms of sulfur, and dissolved and precipitated manganese forms were determined in the vegetation bed of the constructed wetland. The aim of the speciation analysis was to contribute to the characterization of its redox properties. Sulfur was mostly oxidized at the inflow. The concentration of sulfates at the inflow varied from 25 to 55 mg/l, while concentration of sulfides was always lower than 6.0 mg/l and mostly even lower than 1.0 mg/l. However, sulfates were reduced during the pretreatment and the wastewater flow through the vegetation bed. The concentration of total manganese varied from 0.2 to 0.8 mg/l. Approximately 60% of Mn was precipitated at the inflow. The content of precipitated Mn forms declined to ca. 40-50% at the inflow zone, this content was almost constant across the vegetation bed to the outflow when water was sampled from 60-cm depth. However, the content of precipitated Mn forms increased to ca. 74% for samples from 20-cm depth. With respect to the aeration of the system, manganese can be precipitated as MnO2 in these samples.

The distribution of iron oxidation states in a constructed wetland as an indicator of its redox properties.

Wastewater-treatment processes taking place inside constructed wetlands are closely connected with chemical properties of these systems. The aeration of a wetland via the roots of the vegetation (and a subsequent formation of redox-potential gradients) strongly influences the wastewater treatment efficiency, and thus it represents one of the most important characteristics of the wetland. The concentration ratios of individual iron oxidation states (Fe(II) and Fe(III)) were determined as the indicator of the redox properties of the constructed wetland reed bed during this study. Interstitial water from the wetland was sampled eleven times throughout the year 2005. The spectrophotometric method using 1,10-phenanthroline was properly optimized (limits of detection and quantification, sensitivity, linear dynamic range, repeatability, and accuracy values were assessed) and applied for iron determination. Most of iron, ca. 98%, is reduced to the Fe(II) form in raw wastewater and water from the inflow zone of the constructed wetland, however, at the outflow and in the vegetation bed both iron oxidation states are usually detected. The presence of Fe(III) in the reed bed (ca. 10-30% for some samples) demonstrates the aeration of the wetland by the vegetation (Phragmites australis) resulting in a re-oxidation of Fe(II).