Nonionic surfactant greatly enhances the reductive debromination of polybrominated diphenyl ethers by nanoscale zero-valent iron: mechanism and kinetics.

Nanoscale zero-valent iron (nZVI) has been considered as an effective agent for reductive debromination of polybrominated diphenyl ethers (PBDEs). But the high lipophilicity of PBDEs will hinder their debromination owing to the inefficient contact of PBDEs with nZVI. In this study, different ionic forms of surfactants were investigated aiming to promote PBDE debromination, and the beneficial effects of surfactant were found to be: nonionic polyethylene glycol octylphenol ether (Triton X-100, TX)>cationic cetylpyridinium chloride (CPC)>anionic sodium dodecyl benzenesulfonate (SDDBS). Except for with SDDBS, the promotion effect for PBDE debromination was positively related to the surfactant concentrations until a critical micelle concentration (CMC). The debromination process of octa-BDE and its intermediates could be described as a consecutive reaction. The corresponding rate constants (k) for the debromination of parent octa-BDE (including nona- to hepta-BDEs), the intermediates hexa-, penta-, and tetra-BDEs are 1.24 × 10(-1) h(-1), 8.97 × 10(-2) h(-1), 6.50 × 10(-2) h(-1) and 2.37 × 10(-3) h(-1), respectively.

[Reductive debromination of polybrominated diphenyl ethers in aquifier by nano zero-valent iron: debromination kinetics and pathway].

Nano-zerovalent iron (nZVI) approach is effective in the debromination of polybrominated biphenyl ethers (PBDEs). The kinetics and degradation pathway are the key issues to understand the PBDEs degradation mechanisms. In this study, nZVI, synthesized through liquid phase reduction method, coupled with Triton X-100, could completely debrominate the highly brominated congeners of a commercial octa-BDEs mixture within 46 h. The debromination of octa-BDEs could be described by means of pseudo-first-order kinetics with the reaction constant (k) of 0.106 h(-1). In case of lacking the PBDE standards, an effective approach has been developed to determine the unknown PBDE congeners using the quantitative-structure retention relationship (QSRR) model. The retention time of all 39 PBDE congeners in a standard mixture was firstly analyzed with gas chromatography coupled with an electron capture detector (GC-ECD), and the relative retention time (RRT) for each standard was obtained after normalizing the RT by the average RT of BDE47 and BDE183. Then a QSRR model was developed by fitting the RRT of each PBDE congener and its specific RRT index. The debromination products of octa-BDEs were identified using this QSRR model and the degradation pathway of octa-BDEs was elucidated. The results showed that in the stepwise reductive debromination process of PBDEs by nZVI, meta-debromin was facile to be degraded.

Enhancement of hydrogen production in a single chamber microbial electrolysis cell through anode arrangement optimization.

Reducing the inner resistances is crucial for the enhancement of hydrogen generation in microbial electrolysis cells (MECs). This study demonstrates that the optimization of the anode arrangement is an effective strategy to reduce the system resistances. By changing the normal MEC configuration into a stacking mode, namely separately placing the contacted anodes from one side to both sides of cathode in parallel, the solution, biofilm and polarization resistances of MECs were greatly reduced, which was also confirmed with electrochemical impedance spectroscopy analysis. After the anode arrangement optimization, the current and hydrogen production rate (HPR) of MEC could be enhanced by 72% and 118%, reaching 621.3±20.6 A/m3 and 5.56 m3/m3 d respectively, under 0.8 V applied voltage. A maximum current density of 1355 A/m3 with a HPR of 10.88 m3/m3 d can be achieved with 1.5 V applied voltage.