Tetrabromobisphenol A (TBBPA) biodegradation in acidogenic systems: One step further on where and who

The occurrence of brominated flame retardants such as Tetrabromobisphenol A (TBBPA) in water bodies poses a serious threat to aquatic ecosystems. Degradation of TBBPA in wastewater has successfully been demonstrated to occur through anaerobic digestion (AD), although the involved microorganisms and the conditions favouring the conversion remains unclear. In this study, it was observed that bioconversion of TBBPA did not occur during the hydrolytic stage of the AD, but during the strictly fermentative stage. Bioconversion occurred in hydrolytic-acidogenic as well as in strictly acidogenic continuous bioreactors. This indicates that the microorganisms that degrade TBBPA benefit from the electron flux taking place during glycolysis and further transformations into short-chain fatty acids. The degradation kinetics of TBBPA was inversely proportional to the complexity of the wastewater as the apparent kinetics constants were 2.11, 1.86, and 0.52 h-1·gVSS-1 for glucose, starch, and domestic sewage as carbon source, respectively. Additionally, the micropollutant loading rate relative to the overall organic loading rate is of major importance during the investigation of cometabolic transformations. The long-term exposure to TBBPA at environmentally realistic concentrations did not cause any major changes in the microbiome composition. Multivariate statistical analysis of the evolvement of the microbiome throughout the incubation suggested that Enterobacter spp. and Clostridium spp. are the key players in TBBPA degradation. Finally, a batch enrichment was conducted, which showed that concentrations of 0.5 mg·L-1 or higher are detrimental to Clostridium spp., even though these organisms are putative TBBPA degraders. The Clostridium genus was outcompeted by the Enterobacter and Klebsiella genera, hereby highlighting the effect of unrealistic concentrations frequently used in culture-dependent studies on the microbial community composition.