Enhancing the removal of arsenic, boron and heavy metals in subsurface flow constructed wetlands using different supporting media

The presence of arsenic and heavy metals in drinking water sources poses a serious health risk due to chronic toxicological effects. Constructed wetlands have the potential to remove arsenic and heavy metals, but little is known about pollutant removal efficiency and reliability of wetlands for this task. This lab-scale study investigated the use of vertical subsurface flow constructed wetlands for removing arsenic, boron, copper, zinc, iron and manganese from synthetic wastewater. Gravel, limestone, zeolite and cocopeat were employed as wetland media. Conventional gravel media only showed limited capability in removing arsenic, iron, copper and zinc; and it showed virtually no capability in removing manganese and boron. In contrast, alternative wetland media: cocopeat, zeolite and limestone, demonstrated significant efficiencies – in terms of percentage removal and mass rate per m3 of wetland volume – for removing arsenic, iron, manganese, copper and zinc; their ability to remove boron, in terms of mass removal rate, was also higher than that of the gravel media. The overall results demonstrated the potential of using vertical flow wetlands to remove arsenic and metals from contaminated water, having cocopeat, zeolite or limestone as supporting media

The effect of substrate media on the removal of arsenic, boron and iron from an acidic wastewater in planted column reactors

Acidic wastewaters, such as occur in acid mine drainage, typically contain heavy metals and metalloids that pose a serious threat to receiving waters, due to their high toxicity. In this study, vertical flow wetland columns, using a range of filter media, were investigated for their potential to provide an effective onsite treatment for acidic wastewaters with a pH value of 2.0 ± 0.1. The effectiveness of four types of wetland media: gravel, cocopeat, zeolite and limestone, was studied for the removal of arsenic, boron and iron, under an average hydraulic loading of 0.073 m3/m2d. On average, limestone wetland columns gave the highest removal percentage for arsenic (99%) and iron (98%), followed by zeolite columns (92% removal for arsenic and 86% for iron). Although gravel columns were able to remove 43% of dissolved arsenic (from average input of 3.0 ± 0.1 mg/L), they were not able to remove iron simultaneously. In contrast, wetland columns with cocopeat media only showed modest capacity for arsenic removal (9%), but greater capacity for removing iron (46%), and cocopeat was the only wetland media that demonstrated potential to remove boron. Overall, the results indicated that the most effective mechanism of arsenic removal in vertical flow wetlands is coprecipitation with iron, which can be enhanced by using alkaline wetland media to increase the pH of the wastewater. Combinations of media appear worthy of examination in order to optimise the efficacy and sustainability of heavy metal removal

The influence of media type on removal of arsenic, iron and boron from acidic wastewater in horizontal flow wetland microcosms planted with Phragmites australis

In this study, horizontal flow wetland microcosms were used to test the effectiveness of two media types: (1) zeolite and (2) a series of limestone and cocopeat in the removal of arsenic (As), boron (B) and iron (Fe) from contaminated acidic waters such as those associated with mine waste. The wetlands were operated under a hydraulic loading of 30. mm/d, to treat acidic water with As. = 2.3. mg/L, Fe. = 97.3. mg/L and B. = 30.8. mg/L at pH 2. ±. 0.2. Both media were highly effective in the removal of As and Fe. The zeolite wetlands removed 99.9%, 96.1% and 12% of As, Fe and B respectively, whereas the removal efficiencies of the limestone/cocopeat wetlands were 99.8%, 87.3% and 17%. The contribution of plant uptake to As, Fe and B removal in both wetland types was almost negligible (<3% in all cases). The results confirm the key role of the wetland media in fostering specific removal processes. These processes include As co-precipitation with Fe due to pH adjustment provided by limestone, and As and Fe removal facilitated by the cation exchange capacity of the zeolite. Limestone/cocopeat wetlands may offer a more suitable treatment, given the neutral pH achieved and the slightly higher B removal, but zeolite wetlands are able to achieve lower concentrations of Fe, despite the acidic water in the treated effluent.</p