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

Effluents from fruit-packaging plants (FPPs) are major environmental threat due to their high load of recalcitrant and toxic fungicides like fludioxonil, imazalil and thiabendazole. These effluents should be treated on site according to the European Commission, still no treatment systems are in place. We previously demonstrated the efficiency of a lab-scale attached growth bioreactor for the treatment of such effluents. Here we assess the efficacy of 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 operated for three successive periods receiving fludioxonil, imazalil and thiabendazole-containing effluents during which the bioreactor was inoculated with fludioxonil-, imazalil and thiabendazole-degrading microorganisms respectively. The removal efficiency of the system was monitored in the outflow of each of the system components, and microbial succession was also followed via amplicon sequencing. Fludioxonil was effectively removed in the bioreactor compartment and activated carbon filtration further contributed to its removal to levels below 0.1 mg L-1. Imazalil was partially removed in the bioreactor compartment (ca. 50%) with sand filtration and particularly activated carbon filtration significantly reducing imazalil levels (100-120 mg L-1 to < 0.1 mg L-1). Thiabendazole was removed in the bioreactor compartment (>75%), and further reduction (<0.1 mg L-1) occurring upon activated carbon filtration. Amplicon sequencing analysis showed (a) limited establishment of microbial inocula, (b) clear microbial succession patterns for both bacterial and fungal communities. Our results suggest that the modular full-scale bioreactor tested could be a valuable solution for reducing the environmental footprint of fruit-packaging plants.