Phytoremediation of olive mill wastewater with Vetiveria zizanioides (L.) Nash and Cyperus alternifolius L.

Abstract Olive Mill Wastewater (OMW) contains high concentrations of contaminants, including organic, nitrogen, and phenolic compounds that are extremely harmful to the environment and human health. The key purpose of this study was to remove total organic carbon (TOC), total nitrogen (TN), and phenolic compounds (TP) from OMW using floating wetland planted with Vetiveria zizanioides (L.) Nash (vetiver) and Cyperus alternifolius L. (umbrella palm) species. A total of eighteen floating wetlands were constructed. Twelve tanks were planted with vetiver and umbrella palm while another eighteen tanks were maintained as unplanted as controls. Experiments were conducted with wastewater volume of 56 L for 67 days using 5% (OMW-5) and 15% (OMW-15) treatments of OMW in a greenhouse. The highest TOC, TN, and TP removal efficiencies were found to be 95.3 ± 0.01, 82.7 ± 2.55, and 98.8 ± 0.07% in umbrella palm planted OMW-5, while the removal efficiencies were 84.9 ± 0.38, 92.7 ± 0.37, and 38.9 ± 1.97% in vetiver planted OMW-5. Similarly, the TOC, TN, and TP removal efficiencies in OMW-15 were 89.3 ± 0.28, 40.86 ± 1.73, and 96.8 ± 0.18% with umbrella palm and 89.1 ± 0.70, 23.7 ± 1.27, and 92.1 ± 0.41% with vetiver. The plants accumulated trace elements, especially in the roots, with the order of Fe > Mn > Cu > Zn > B > Pb > Cr > Ni > Co > Cd for umbrella palm. The umbrella palm shoot phenol content was found to be 2358 ± 201 and 1421 ± 198 mg/kg in OMW-5 and OMW-15, respectively. Overall, this study revealed that floating wetlands planted with vetiver and umbrella palm species have the potential to be used as a green treatment method to treat diluted high strength OMW.