Biodegradation of tri-butyl phosphate by Trametes versicolor and its application in a trickle bed reactor under non-sterile conditions

Tri-butyl phosphate (TBP) is a widely used organophosphate flame retardant. However, it is also regarded as emerging contaminant due to its various toxic effects and poor removal by conventional wastewater treatment. In present study, we investigated the degradation of TBP (10 mg/L) by the white rot fungus Trametes versicolor in both laboratory conditions and a trickle bed reactor (TBR) under non-sterile conditions. The removal yield reached 98 % after 3 days, during which the intracellular enzymatic system cytochrome P450 was involved. Four transformation products (TPs) were identified, namely dibutyl 3-hydroxybutyl phosphate, dibutyl phosphate, butyl 3-hydroxybutyl phosphate and butyl dihydrogen phosphate, which allowed us to propose a degradation pathway where hydroxylation and hydrolysis made considerable contribution. TBP treatment in the TBR with T. versicolor immobilized on wood chips operating in sequential batch mode with 10 cycles of 3 days reached average removals higher than 93 %, demonstrating the potential for practical application. Despite similar removal rates in heat-killed and abiotic controls (89 % and 97 %, respectively), global mass balance analysis indicated 86 %, 64 %, and 86 % removal by degradation in the fungal, heat-killed, and abiotic controls, respectively. Analysis of the microbial assemblage in solid phase suggested that the established bacterial populations displayed a synergistic effect with immobilized fungus. This study is the first to report on TBP degradation by T. versicolor in a TBR under non-sterile conditions, suggesting that this method could be a viable option for large-scale environmental applications.