Fertilizer-drawn forward osmosis as a solution to improve the quality of wastewater treatment plant effluents used for agricultural irrigation

This study assesses the effectiveness of a forward osmosis (FO) pilot plant (max. Flow rate 0.36 m3/h) to improve the quality of a wastewater treatment plant (WWTP) effluent and its use for irrigating lettuce in greenhouse conditions. FO treated WWTP-effluent had nutrient levels comparable to well-water (control), except for ammonia and phosphates -which were recovered from the effluent- and potassium, which was added as fertilizer. FO also removed >95 % of organic pollutants from WWTP effluent. In addition, the toxicity associated with the WWTP effluent was reduced after FO treatment, reaching eleutheroembryo toxicity-biomarker levels similar to those found in well water. Finally, FO reduced the bacterial load of WWTP effluent, and significantly reduced its levels of ARGs. Lettuces irrigated with the three water sources did not show differences in terms of agronomic parameters, ARG and pathogen levels, and only some patterns were observed on plant metabolomics or transcriptomics. However, the potential accumulation of pollutants in the soil over time could amplify the impact of using WWTP effluent in crops compared to the use of FO-treated WWTP effluent. [Display omitted] •Forward osmosis removed contaminants and toxicity from WWTP effluent•Forward osmosis delivered fertilizer and retained nutrients from WWTP effluent•Irrigation after forward osmosis reduced pathogen and ARGs addition to soil•Irrigation with forward osmosis water did not affect lettuce productivity•Water composition induced minor shifts in the metabolomics and transcriptomics of lettuces