Antipyrine removal by TiO2 photocatalysis based on spinning disc reactor technology.

The photo-degradation of the emerging contaminant antipyrine (AP) was studied and optimized in a novel photocatalytic spinning disc reactor (SDR). A heterogeneous process (UV/H2O2/TiO2) was used. TiO2 was immobilized on the surface of a glass disc using a sol-gel method. A factorial design of experiments followed by a Neural Networks fitting allowed the optimal conditions to be determined for treating 50 mg/L of AP. Under these conditions (pH = 4; [H2O2]0 = 1500 mg/L; disc speed = 500 rpm; flowrate = 25 mL/s), AP was completely degraded in 120 min and regeneration of the disc allowed 10 cycles with no loss in efficiency. The value of the apparent volumetric rate constant was found to be 6.9·10-4 s-1 with no apparent mass transfer limitation. Based on the main intermediates identified, a mechanism is proposed for antipyrine photodegradation: Firstly, cleavage of the NN bond of penta-heterocycle leads to the formation of two aromatic acids and N-phenylpropanamide. An attack to the CN bond in the latter compound produces benzenamine. Finally, the phenyl ring of the aromatic intermediates are opened and molecular organic acids are formed.

Heterogeneous lollipop-like V2O5/ZnO array: a promising composite nanostructure for visible light photocatalysis.

ZnO/V(2)O(5) core-shell nanostructures have been prepared by a two-step synthesis route through combined hydrothermal growth and magnetron sputtering. After annealing under oxygen ambience, a ZnO/V(2)O(5) heterogeneous lollipop-like nanoarray formed. The microstructure and crystal orientation of those nanolollipops were investigated by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), which show single crystal structure. The optical properties were characterized by UV-vis spectroscopy and showed quite different absorption curves for the as-deposited and annealed samples. The ZnO/V(2)O(5) nanolollipops demonstrated excellent photocatalytic activity in terms of decomposing 2,6-dichlorophenol (2,6-DCP) under visible light, indicating their promising potential as catalysts for industrial wastewater and soil pollution treatments.

Evidence of species succession during chlorobenzene biodegradation.

We have previously reported the disappearance of a specific strain degrading chlorobenzene from a functionally stable bioreactor. In the present work, we investigated this species succession and isolated a new dominant strain, identified as Pandoraea pnomenusa sp. strain MCB032. A specific 16S rRNA-targeted oligonucleotide probe was designed and validated to identify strain MCB032 using fluorescence in situ hybridisation (FISH). The results confirmed the presence of strain MCB032 in samples collected over time, and showed that it was primarily located within the biofilm. Denaturing gradient gel electrophoresis (DGGE) provided evidence that the species succession occurred early in the operating period. The application of these biomolecular tools highlighted the remarkable stability of this new strain during the 15 months of reactor operation. The succession was attributed to the competitive kinetic behaviour of strain MCB032, which exhibited faster growth (micro(max) = 0.34 h(-1)) and higher substrate affinity (K(s) = 0.35 mg L(-1)) than strain JS150. Finally, this study contributed to the characterisation of the recently established Pandoraea genus, an emerging group in the biodegradation field.

Strain stability in biological systems treating recalcitrant organic compounds.

The availability of molecular probing technology in recent years has facilitated investigation of microbial community composition during bio-treatment of organic wastes. Particularly, it has allowed the study of microbial culture stability and correlation between stability and treatment performance. However, most studies to date have only addressed mixed cultures and there is limited information regarding single strain stability. Here we have investigated the microbial community dynamics in two bioreactors, each inoculated with a pure bacterial strain capable of degrading a recalcitrant substrate, namely Xanthobacter aut. GJ10 degrading 1,2-dichloroethane (DCE) and Burkholderia sp. JS150 degrading monochlorobenzene (MCB). Universal and strain specific 16S rRNA oligonucleotide probes were designed and used to follow strain stability. The bioreactor fed with DCE was functionally stable and the percentage of GJ10 cells in the community remained high (around 95% of total cells) throughout, even after introduction of foreign microorganisms. The bioreactor fed with MCB was also functionally stable, but in contrast to the DCE bioreactor, probing results revealed the disappearance of strain JS150 from the bioreactor within a week. The difference in behavior between the two systems is attributed to the specific pathway required to degrade DCE.

Overcoming oxygen limitations in membrane-attached biofilms--investigation of flux and diffusivity in an anoxic biofilm.

The possibility of overcoming oxygen limitations in membrane-attached biofilms has been investigated by using nitrate as an electron acceptor instead of oxygen in an extractive membrane bioreactor (EMB) degrading toluene. The effect of nitrate concentration on toluene flux, the effective diffusivity in the biofilm and the biofilm activity has been investigated. A counter-diffusion-reaction model is also presented, describing the pollutant flux versus biofilm thickness. The toluene flux decreased with increasing biofilm thickness under excess nitrate concentrations, similar to the experiment with low nitrate. Mathematical modelling indicated that this was either due to decreasing activity, and/or different diffusivities in the biofilm. The effective diffusivity was investigated by using an inert tracer molecule. It remained constant for biofilm thicknesses up to 1.8mm, with a value twice that in water. The biofilm activity was investigated by inactivating a mature biofilm using sodium azide. The toluene flux remained the same before and after the addition of sodium azide, suggesting that the activity in the biofilm is very low. We conclude that the decreasing toluene flux with increasing biofilm thickness is due to the diffusional resistance of the inactive biofilm.

The anoxic extractive membrane bioreactor.

The extractive membrane bioreactor (EMB) employs a dense silicone rubber membrane to selectively extract hydrophobic organic compounds from industrial wastewaters into a bioreactor in order to biodegrade them. The major drawback of the EMB is excess biofilm growth on the membrane, which limits mass transfer and creates oxygen limitations. In this work, nitrate has been used as an electron acceptor instead of oxygen. Due to the high solubility of nitrate in water, it is hypothesised that nitrate penetrates the whole biofilm, preventing the formation of inactive zones of bacteria. Four experiments have been performed with toluene as a model substrate under anoxic conditions. The effect of nitrate concentrations on the biofilm and on the toluene flux have been investigated. In addition, the production of soluble microbial products (SMPs), and bacterial hydrophobicity were studied. Under high nitrate concentrations, the performance of the anoxic EMB was stable and no biofilm was formed. The bacteria metabolised toluene, and the toluene flux remained approximately constant. Conversely, at low nitrate concentration, a decrease in pollutant flux concomitant with biofilm growth was observed. The production of SMPs increased under limiting nitrate concentrations, but the hydrophobicity of the suspended bacteria remained constant. However, the bacterial hydrophobicity of the attached cells was significantly greater than that of the suspended cells.