A coupled UV photolysis-biodegradation process for the treatment of decabrominated diphenyl ethers in an aerobic novel bioslurry reactor.

The commercial flame retardant is an emerging contaminant (EC) commonly found in soils and sediments. A coupled UV-photolysis-biodegradation process was used to decompose decabromodiphenyl ether (BDE-209) in clay slurries. A novel bioslurry bioreactor (NBB) was employed in which BDE-209 degradation was maximized by the simultaneous application of LED UVA irradiation and biodegradation by a mixed bacterial culture. The rate of BDE-209 degradation decreased in the order: coupled UV photolysis-biodegradation (1.31 × 10-2 day-1) > UV photolysis alone (1.10 × 10-2 day-1) > biodegradation alone (1.00 × 10-2 day-1). Degradation intermediates detected included hydroxylated polybrominated diphenylethers, partially debrominated PBDE congeners and polybrominated dibenzofuran. The UV-resistant bacterial strains isolated that could utilize BDE-209 as a sole carbon source included Stenotrophomonas sp., Pseudomonas sp., and Microbacterium sp. These strains encoded important functional genes such as dioxygenase and reductive dehalogenases. Continuous UV irradiation during the NBB process affected various biochemical oxidative reactions during PBDEs biodegradation. Simultaneous photolysis and biodegradation in the NBB system described reduces operational time, energy, expense, and maintenance-demands required for the remediation of BDE-209 when compared to sequential UV-biodegradation process or to biodegradation alone.

Characterization of a Sequential UV Photolysis-Biodegradation Process for Treatment of Decabrominated Diphenyl Ethers in Sorbent/Water Systems.

Decabrominated diphenyl ether (BDE-209) is a primary component of the brominated flame retardants used in a variety of industrial and domestic applications. BDE-209 bioaccumulates in aquatic organisms and has been identified as an emerging contaminant that threatens human and ecosystem health. Sequential photolysis-microbial biodegradation processes were utilized here to treat BDE-209 in clay- or soil-water slurries. The removal efficiency of BDE-209 in the clay-water slurries was high; i.e., 96.5%, while that in the soil-water slurries was minimal. In the clay-water slurries the first order rate constants for the UV photolysis and biodegradation of BDE-209 were 0.017 1/day and 0.026 1/day, respectively. UV wavelength and intensity strongly influenced the BDE-209 photolysis and the subsequent biodegradation of photolytic products. Facultative chemotrophic bacteria, including Acidovorax spp., Pseudomonas spp., Novosphingobium spp. and Sphingomonas spp., were the dominant members of the bacterial community (about 71%) at the beginning of the biodegradation; many of these organisms have previously been shown to biodegrade BDE-209 and other polybrominated diphenyl ether (PBDE) congeners. The Achromobacter sp. that were isolated (NH-2; NH-4; NH-6) were especially effective during the BDE-209 degradation. These results indicated the effectiveness of the sequential UV photolysis and biodegradation for treating certain BDE-209-contaminated solids; e.g., clays; in bioreactors containing such solids as aqueous slurries. Achieving a similar treatment effectiveness for more heterogeneous solids containing natural organic matter, e.g., surface solids, appears to be significantly more difficult. Further investigations are needed in order to understand the great difference between the clay-water or soil-water slurries.

TCDD administered on activated carbon eliminates bioavailability and subsequent shifts to a key murine gut commensal.

Activated carbon (AC) is an increasingly attractive remediation alternative for the sequestration of dioxins at contaminated sites globally. However, the potential for AC to reduce the bioavailability of dioxins in mammals and the residing gut microbiota has received less attention. This question was partially answered in a recent study examining 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced hallmark toxic responses in mice administered with TCDD sequestered by AC or freely available in corn oil by oral gavage. Results from that study support the use of AC to significantly reduce the bioavailability of TCDD to the host. Herein, we examined the bioavailability of TCDD sequestered to AC on a key murine gut commensal and the influence of AC on the community structure of the gut microbiota. The analysis included qPCR to quantify the expression of segmented filamentous bacteria (SFB) in the mouse ileum, which has responded to TCDD-induced host toxicity in previous studies and community structure via sequencing the 16S ribosomal RNA (rRNA) gene. The expression of SFB 16S rRNA gene and functional genes significantly increased with TCDD administered with corn oil vehicle. Such a response was absent when TCDD was sequestered by AC. In addition, AC appeared to have a minimal influence on murine gut community structure and diversity, affecting only the relative abundance of Lactobacillaceae and two other groups. Results of this study further support the remedial use of AC for eliminating bioavailability of TCDD to host and subsequent influence on the gut microbiome.

Sequestration of 2,3,7,8-tetrachlorodibenzo-p-dioxin by activated carbon eliminates bioavailability and the suppression of immune function in mice.

The effectiveness of activated carbon in reducing the bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was examined from the context of using in situ sorbent amendments to remediate soils/sediments contaminated with polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs). This technology has gained rapid acceptance based on observations that activated carbon amendments predictably lower PCDD/F concentrations in water and bioaccumulation by simple aquatic organisms and earthworms; it has been assumed that bioavailability to mammals is similarly reduced, although this has been disproven for other sorbent materials. In the present study TCDD was absorbed to a microporous activated carbon (TCDD-AC) using the incipient wetness method. An aqueous suspension of TCDD-AC and an equivalent dosage of TCDD in corn oil were administered by oral gavage to B6C3F1 mice. The relative bioavailability of TCDD-AC was determined by quantifying and comparing the hepatic induction of cyp1A1 (messenger ribonucleic acid) and suppression of the immunoglobulin M antibody-forming cell immune response by the 2 forms of TCDD. A concentration-dependent response was observed for both assays when TCDD in corn oil was administered to mice. However, when equivalent masses of TCDD were administered as TCDD-AC, no induction of cyp1A1 or suppression of the immunoglobulin M antibody-forming cell response was observed. The absence of these 2 sensitive aryl hydrocarbon receptor-mediated responses in mice provides the first direct evidence that activated carbon can sequester TCDD in a form that eliminates its bioavailability to mammals. These results support the premise that activated carbon can be used to reduce the bioeffective dose of TCDD delivered to mammals and that activated carbon amendments may provide a low-cost alternative to traditional remediation technologies. Environ Toxicol Chem 2017;36:2671-2678. © 2017 SETAC.

Degradation of organic dyes via bismuth silver oxide initiated direct oxidation coupled with sodium bismuthate based visible light photocatalysis.

Organic dye degradation was achieved via direct oxidation by bismuth silver oxide coupled with visible light photocatalysis by sodium bismuthate. Crystal violet dye decomposition by each reagent proceeded via two distinct pathways, each involving different active oxygen species. A comparison of each treatment method alone and in combination demonstrated that using the combined methods in sequence achieved a higher degree of degradation, and especially mineralization, than that obtained using either method alone. In the combined process direct oxidation acts as a pretreatment to rapidly bleach the dye solution which substantially facilitates subsequent visible light photocatalytic processes. The integrated sequential direct oxidation and visible light photocatalysis are complementary manifesting a > 100% increase in TOC removal, compared to either isolated method. The combined process is proposed as a novel and effective technology based on one primary material, sodium bismuthate, for treating wastewaters contaminated by high concentrations of organic dyes.