Effect of silica-core gold-shell nanoparticles on the kinetics of biohydrogen production and pollutant hydrogenation via organic acid photofermentation over enhanced near-infrared illumination.

A biological photoinduced fermentation process provides an alternative to traditional hydrogen productions. In this study, biohydrogen production was investigated at near IR region coupled to a near-field enhancement by silica-core gold-shell nanoparticles (NPs) over a range of acetate concentrations (5-40 mM) and light intensities (11-160 W/m2). The kinetic data were modeled using modified Monod equations containing light intensity effects. The yields of H2 and CO2 produced per acetate were determined as 2.31 mol-H2/mol-Ac and 0.83 mol-CO2/mol-Ac and increased to 4.38 mmol-H2/mmol-Ma and 2.62 mmol-CO2/mmol-Ma when malate was used. Maximum increases in H2 and CO2 productions by 115% and 113% were observed by adding NPs without affecting the bacterial growth rates (6.1-8.2 mg-DCM/L/hour) while the highest hydrogen production rate was determined as 0.81 mmol/L/hour. Model simulations showed that the energy conversion efficiency increased with NPs concentration but decreased with the intensity. Complete hydrogenation application was demonstrated with toxic 2-chlorobiphenyl using Pd catalysts.

Selenium removal by activated alumina in batch and continuous-flow reactors.

Selenium removal by activated alumina (AA) in batch and continuous-flow reactors was investigated in this study. The adsorption kinetics fitted pseudo-first as well as pseudo-second order models with equilibrium time for Se(VI) and Se(IV) adsorption of 8 and 12 hr, respectively. A significant higher adsorption capacity for Se(IV) than Se(VI) was observed in isothermal adsorption experiments. The adsorption isotherms of Se(VI) and Se(IV) agreed well with both Langmuir and Freundlich adsorption models. The results also showed that Se(VI) adsorption was adversely affected by NaHCO3 concentrations, while Se(IV) adsorption was not due to the selectivity of activated alumina for anions. In the continuous-flow reactor packed with AA and inoculated with Shigella fergusonii strain TB42616 under a hydraulic detention time of 3 days, approximately 74% and 70% Se(VI) were removed after 40 days at influent concentrations of 10 and 50 mg/L, respectively. Effluent concentrations of Se(IV) from the bioreactor were insignificant due to the combination of bioactivities and adsorption. The AA-packed bioreactor is promising in both Se(VI) and Se(IV) removal as better removal efficiency may be accomplished by increasing the liquid retention time. PRACTITIONER POINTS: The adsorption capacity for Se(IV) of activated alumina was significantly higher than that for Se(VI). Se(VI) adsorption was inhibited by NaHCO3 , while Se(IV) adsorption was not. Se(IV) formed by biological Se(VI) reduction was adsorbed by activated alumina in continuous-flow reactors. Both Se(VI) and Se(IV) were significantly removed by activated alumina-packed continuous-flow reactors.

Selenium reduction by a defined co-culture of Shigella fergusonii strain TB42616 and Pantoea vagans strain EWB32213-2.

Selenium reduction was evaluated with pure batch cultures of Shigella fergusonii strain TB42616 (TB) and Pantoea vagans strain EWB32213-2 (EWB), respectively. A two-stage process, from Se(VI) to Se(IV) and then from Se(IV) to Se(0), was observed. The second stage of reduction, from Se(IV) to Se(0), was observed as the rate-limiting step resulting in accumulation of the more toxic Se(IV). In order to facilitate Se(VI) reduction and reduce Se(IV) accumulation, the Se(VI)-reducing strain TB was co-cultured with a Se(IV)-reducing strain EWB. Although Se(VI) reduction rate was not affected, Se(IV) reduction was significantly enhanced with low Se(IV) accumulation in the defined co-culture. Effects of culture composition as well as nitrate and arsenate on Se(VI) reduction were also investigated. A co-culture composition of 10:1 (EWB:TB) ratio was observed to achieve the best total selenium reduction. In addition, nitrate at 50 mg/L was observed to inhibit Se(IV) reduction but not Se(VI) reduction, while arsenate at 200 mg/L exhibited slight inhibition on both Se(VI) and Se(IV) reduction.