Phytoremediation of untreated wastewater using wetland plants: implications for water quality improvement and sustainable lettuce production

Wastewater reuse in agriculture enhances nutrient availability, potentially increasing the risk of heavy-metal contamination. Phytoremediation using wetland plants such as Phragmites australis and Typha latifolia provides a sustainable approach to treating contaminated water. This study evaluated the effects of irrigation with untreated wastewater (UWW) and phytoremediation-treated water (PTW) on soil properties, elemental composition, and the growth, yield, and biochemical traits of lettuce plants. The constructed wetland system significantly improved water quality, reducing key parameters such as BOD5, COD, nutrients, suspended solids, and heavy metals, and lowering the Irrigation Water Quality Index (IWQI) from 119 (poor) to 53 (moderate), confirming a marked improvement in irrigation suitability. UWW irrigation increased soil fertility and enhanced plant growth due to its high nutrient content but it also elevated concentrations of potentially toxic elements (Cu, Pb, Cd, and Cr) and salinity levels. PTW significantly reduced contaminant loads while maintaining adequate nutrient availability. Lettuce irrigated with UWW showed increased biomass and pigment content, but also higher oxidative stress indicators. Conversely, PTW-treated plants exhibited improved root dry matter, higher ascorbic acid content, and a more balanced elemental profile. Overall, PTW reduced contamination risks, improved soil quality, and produced safer lettuce than irrigation with untreated wastewater.