Sulfate removal from industrial wastewater in a hydroponic system planted with Bidens pilosa L

Sulfate-reducing bacteria and macrophytes play an essential role in sulfate degradation in constructed wetlands. This study provides an evaluation of sulfate removal in a hydropond planted with B. pilosa. Two hydroponds, the experimental (planted with B. pilosa) and reference sections (unplanted) were tested for their ability to remove sulfate from industrial wastewater. Wastewater containing the concentrations of sulfate (mean = 705 mg/l) was run in both systems. The samples were collected at 24 h' intervals and were analysed for pH, dissolved oxygen, temperature, chemical oxygen demand (COD) and sulfate. After 288 h, the final concentration of sulfate was 169 mg/l (mean value), representing 76% removal in the planted section and was 309 mg/l (mean value), representing 56% in the reference section. The removal in the planted section was found to be within the acceptable limits (<250 mg/l) as per the South Africa's Department of Water and Sanitation. Temperature had a moderate negative correlation on sulfate removal in both the planted (r = -0.38) and reference sections (r = - 0.42). COD also had a very strong negative correlation in both sections (r = -0.97 in the reference and - 0.94 in the plated). The dissolved oxygen indicated a weak positive correlation in both sections (r = 0.29 in the planted and 0.37 in the reference), while the pH had a strong positive correlation on both the sections (r = 0.79 in the reference and 0.80 in the planted section). More sulfate removals by macrophytes were due to conducive temperatures and microbial activities in the system created by macrophytes. Based on the findings, the hydropond planted with B. pilosa has a potential to remove sulfate from wastewater, thus could be used as an alternative technology of sulfate removal from sulfate contaminated wastewater.