Biochar and activated carbon act as promising amendments for promoting the microbial debromination of tetrabromobisphenol A

Abstract

The increasing occurrence of tetrabromobisphenol A (TBBPA) in the environment is raising questions about its potential environmental health impacts as it has been shown to cause various deleterious effects in humans. The fact that the highest concentrations of TBBPA have been reported in wastewater sludge is concerning as effluent discharge and biosolids land application are likely a route by which TBBPA can be further disbursed to the environment. Our objectives in this study were to evaluate the effect of biochar (BC) and activated carbon (AC) in promoting the biodegradation of TBBPA, and characterize the response of anaerobic sludge microbial communities following amendments. Both carbonaceous amendments were found to promote the reductive debromination of TBBPA. Nearly complete transformation of TBBPA to BPA was observed in the amended reactors ∼20 days earlier than in the control reactors. In particular, the transformation of diBBPA to monoBBPA, which appears to be the rate-limiting step, was accelerated in the presence of either amendment. Overall, microbial taxa responding to the amendments, i.e., 'sensitive responders', represented a small proportion of the community (i.e., 7.2%), and responded positively. However, although both amendments had a similar effect on TBBPA degradation, the taxonomic profile of the sensitive responders differed greatly from one amendment to the other. BC had a taxonomically broader and slightly more pronounced effect than AC. This work suggests that BC and AC show great potential to promote the biodegradation of TBBPA in anaerobic sludge, and their integration into wastewater treatment processes may be helpful for removing TBBPA and possibly other emerging hydrophobic contaminants.

Keywords: Activated carbon; Biochar; Flame-retardants; Reductive dehalogenation; TBBPA; Wastewater treatment.

Fig. 1

TBBPA degradation and formation of BPA in the biotic reactors. Concentration of TBBPA, BPA, and transformation by-products (i.e., 3,3′,5-triBBPA, 3,3′-diBBPA, 3-monoBBPA) in the control reactor, and reactors amended with biochar and activated carbon over time. Error bars represent standard deviation from the mean. TBBPA reductive debromination pathway is shown below the graphs. No loss of TBBPA was observed in the abiotic controls (See Fig. S4).

Fig. 2

Bray-Curtis matrix-based Principal Coordinate Analysis (PCoA) and Analysis of similarity (ANOSIM) results. The percentage of variation explained by the two axes is indicated on the graph. The table presents the results of the ANOSIM, with the null hypothesis (H₀) stating that the community composition does not differ between days or treatments. H₀ is rejected if p ≥ 0.05. The closer the R-value is to 1, the more difference between the groups tested in terms of community composition.

Fig. 3

Fold change in responding OTUs’ relative abundance between control and amended reactors for each post-amendment sampling date. Responders are defined as OTUs whose relative abundance significantly (p < 0.05) increases or decreases more than twice in the amended reactors relative to the control. Each black and white circle represents a responding OTU detected in the biochar - and activated carbon-amended reactors, respectively. Dash lines on each graph are visual references for a fold change of 5. Phylum-level taxonomic affiliation is indicated at the bottom, and the number of responding OTU in each taxonomic group is indicated between parentheses.

Fig. 4

Relative abundance of positive and negative responders in each reactor for each sampling day. Error bars represent the standard deviation from the mean. For each sampling day and category of responders, significant differences between treatments (t-test; p < 0.05), when found, are indicated by a different letter (upper case for the positive responders, and lower case for the negative responders). C: control; BC: biochar; AC: activated carbon.