Agricultural wastewater treatment by Trametes versicolor immobilized on wood in a rotating drum bioreactor

Abstract

The deterioration of water quality by persistent organic pollutants (POPs) is a global concern. Even at low concentrations, these compounds pose a significant toxicological risk to the ecosystem and human health. Among POPs, pesticides are still indispensable in addressing multiple challenges worldwide, but most of them fail to interact with the target pest and are disseminated in water and other environmental compartments, potentially triggering detrimental effects on numerous organisms. Responding to this concern, the scientific community is currently investigating different technologies to remove pesticides from water resources. Among other alternatives, fungal treatment by white rot fungi (WRF) has become an attractive strategy because these organisms present a powerful enzyme system capable of degrading a wide range of POPs, including pesticides, and is considered an environmentally friendly and low-cost approach. The present thesis aims to develop a fungal bioreactor using Trametes versicolor immobilized on wood chips to remove pesticides from agricultural wastewater (AW) in a long-term treatment under non-sterile conditions. First of all, a rotating drum bioreactor (RDB) was set up to treat AW spiked with diuron, as a model pollutant, using T. versicolor immobilized on pine wood chips. Although good results were obtained in terms of pesticide removals, T. versicolor was progressively detached from the wood surface. Subsequently, another bioremediation study was conducted using T. versicolor immobilized on holm oak wood chips to remove two model pesticides (diuron and bentazon) in a column reactor. Sorption played a predominant role in the removal of both pesticides, which motivated a comprehensive sorption study. The pesticide-contaminated wood was subsequently treated by T. versicolor in a solid biopile-like system. Secondly, AW spiked with diuron and bentazon was treated by T. versicolor immobilized on holm oak wood chips in the RDB for 225 days, optimizing some operational parameters to achieve the consolidation of the fungal biomass in the reactor and promising removal performances. Additionally, a cross-sectional study was conducted to shed light on some key questions about fungal bioremediation, including the effect of limiting dissolved oxygen level on contaminant degradation, growth kinetics on wood, and organic matter removal by T. versicolor. Based on gained experiences and knowledge, the RDB was applied to treat agricultural rinse wastewater (RW), comparing its performance with that obtained by both a well-established fungal bioreactor (fluidized bed bioreactor) and a consolidated physical-chemical technology (ozonation). In this regard, the RDB proved to be the best option between the two fungal reactors, whereas the comparative study between the fungal and the ozonation treatments showed that each technology had its own advantages and achieved better results depending on the studied parameter. Furthermore, a treatment train consisting of a first stage of fungal bioremediation followed by ozonation was performed, in which the advantages of each process were synergistically combined to offer greater flexibility in the relationship between effluent quality and operating costs. Therefore, this study expands the knowledge on fungal treatment of pesticides and proposes a viable and promising solution to a real agricultural contamination issue.