Depuration of fungicide-contaminated effluents from fruit-packaging plants in a full-scale modular bioreactor inoculated with tailor-made microbial inocula

Effluents from fruit-packaging plants (FPPs) containing recalcitrant and toxic fungicides like fludioxonil and imazalil, pose a major environmental threat. This study evaluates a full-scale modular wastewater treatment system composed of an attached growth bioreactor, sedimentation tank, sand and activated carbon filters receiving effluents from a commercial FPP. The system was inoculated with a fludioxonil-degrading Ochrobactrum sp. bacterial strain and an imazalil-degrading Cladosporium herbarum fungal strain. Over two operational periods, removal efficiency was monitored in the outflow of the system components, and microbial succession was followed via amplicon sequencing. Fludioxonil levels were notably reduced in the bioreactor and further decreased by activated carbon filtration reaching final removal levels > 99 %. Imazalil partly dissipated in the bioreactor compartment (50 %) with activated carbon filtration further reducing imazalil levels (>90 %). Comparison between calculated pesticide exposure concentrations, derived in the context of effluent discharge scenarios, and ecotoxicity threshold values for surrogate aquatic and terrestrial organisms provided preliminary evidence that the release of treated effluents is not expected to be of concern for receiving ecosystems. Amplicon sequencing analysis showed (a) limited establishment of microbial inocula and (b) clear microbial succession patterns, common for bacterial and fungal communities which were mostly composed of microorganisms associated with cellulose, dyes and pesticide degradation. This study presents the first proof-of-concept study for full-scale treatment of wastewaters produced by FPPs.