Green solutions for treating groundwater polluted with nitrates, pesticides, antibiotics, and antibiotic resistance genes for drinking water production.

The present study evaluates for the first time the seasonal performance of an innovative green groundwater treatment. The pilot plant combines microalgae-bacteria treatment and a cork-wood biofilter to reduce nitrates, pesticides, antibiotics (ABs), and antibiotic resistance genes (ARGs) from groundwater. Groundwater had nitrate concentrations ranging from 220 to 410 mg/L, while ABs (sulfonamides and fluoroquinolones) and pesticides (triazines) were detected at concentrations ranging from a few ng/L to 150 ng/L. Only the gene targets sul1, tetM and the class 1 integron-integrase gene (intl1) were detected in the groundwater. The microalgae-biofilter treatment system effectively removed 15%-98% of nitrates, depending on the season, and consistently eliminated over 90% of ABs and pesticides year-round. Among the components of the treatment system, the microalgal system was the most effective at removing ABs and pesticides. However, the cork-wood biofilter showed superior performance in reducing the bacterial load in groundwater, achieving more than a 1-log reduction in the absolute abundance of genes such as sul1 and intl1. The accumulation of ABs and pesticides in microalgae biomass was minimal or undetectable (<20 ng/g of fresh weight). Overall, our results indicate that the microalgae-biofilter treatment plant is an effective solution for significantly reducing nitrates, antibiotics, and pesticides from groundwaters, while also producing a valuable biomass, and meeting drinking water standards during warmer months.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Victor Matamoros reports financial support was provided by European Union. Jessica Subirats Medina reports financial support was provided by Government of Catalonia Agency for Administration of University and Research Grants. Marc Vina reports financial support was provided by Government of Catalonia. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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