Standardization of activated sludge for biodegradation tests

Activated sludges are an inoculum source commonly used in biodegradation studies, as wastewater treatment facilities constitute an entry point to the environment for many chemicals. In this paper, the main issues relating to the use of activated sludge in biodegradability tests are presented. Special attention is also devoted to discussing the factors affecting both the activity of the microbial communities and the test results. After a short survey of the state of the art of microbiology of activated sludge, the paper focuses on the methods used to reduce the variations in the diversity, quality and quantity of these communities. Finally, use of surrogates as reference materials in biodegradability tests is discussed

Changes in tolerance to herbicide toxicity throughout development stages of phototrophic biofilms

Ecotoxicological experiments have been performed in laboratory-scale microcosms to investigate thesensitivity of phototrophic biofilm communities to the alachlor herbicide, in relation to the stages ofphototrophic biofilm maturation (age of the phototrophic biofilms) and physical structure (intact biofilmversus recolonization). The phototrophic biofilms were initially cultivated on artificial supports in aprototype rotating annular bioreactor (RAB) with Taylor–Couette type flow under constant operatingconditions. Biofilms were collected after 1.6 and 4.4 weeks of culture providing biofilms with differentmaturation levels, and then exposed to nominal initial alachlor concentration of 10 ug L−1in either intactor recolonized biofilms for 15 days in microcosms (mean time-weighted average concentration – TWACof 5.52 ± 0.74 ug L−1).At the end of the exposure period, alachlor effects were monitored by a combination of biomass descrip-tors (ash-free dry mass – AFDM, chlorophyll a), structural molecular fingerprinting (T-RFLP), carbonutilization spectra (Biolog) and diatom species composition. We found significant effects that in terms ofAFDM, alachlor inhibited growth of the intact phototrophic biofilms. No effect of alachlor was observedon diatom composition or functional and structural properties of the bacterial community regardless ofwhether they were intact or recolonized. The intact three-dimensional structure of the biofilm did notappear to confer protection from the effects of alachlor. Bacterial community structure and biomass levelof 4.4 weeks – intact phototrophic biofilms were significantly influenced by the biofilm maturation pro-cesses rather than alachlor exposure. The diatom communities which were largely composed of mobileand colonizer life-form populations were not affected by alachlor.This study showed that the effect of alachlor (at initial concentration of 10 ug L−1or mean TWAC of5.52 ± 0.74 ug L−1) is mainly limited to biomass reduction without apparent changes in the ecologicalsuccession trajectories of bacterial and diatom communities and suggested that carbon utilization spec-tra of the biofilm are not damaged resulting. These results confirmed the importance of consideringthe influence of maturation processes or community age when investigating herbicide effects. This isparticularly important with regard to the use of phototrophic biofilms as bio-indicators

X-ray diffraction as a tool for the determination of the structure of double-walled carbon nanotube batches

The average structure of double-walled carbon nanotube DWCNT samples can be determined by x-ray diffraction XRD. We present a formalism that allows XRD patterns of DWCNTs to be simulated and we give researchers the tools needed to perform these calculations themselves. Simulations of XRD patterns within this formalism are compared to experimental data obtained on two different DWCNT samples, produced by chemical vapor deposition or by peapod conversion i.e., high-temperature peapod annealing. For each sample, we are able to determine structural aspects such as the number of walls, the diameter distribution of inner and outer tubes, the intertube spacing, and the bundled structure

A photosynthetic rotating annular bioreactor (Taylor–Couette type flow) for phototrophic biofilm cultures

In their natural environment, the structure and functioning of microbial communities from river phototrophic biofilms are driven by biotic and abiotic factors. An understanding of the mechanisms that mediate the community structure, its dynamics and the biological succession processes during phototrophic biofilm development can be gained using laboratory-scale systems operating with controlled parameters. For this purpose, we present the design and description of a new prototype of a rotating annular bioreactor (RAB) (TayloreCouette type flow, liquid working volume of 5.04 L) specifically adapted for the cultivation and investigation of phototrophic biofilms. The innovation lies in the presence of a modular source of light inside of the system, with the biofilm colonization and development taking place on the stationary outer cylinder (onto 32 removable polyethylene plates). The biofilm cultures were investigated under controlled turbulent flowing conditions and nutrients were provided using a synthetic medium (tap water supplemented with nitrate, phosphate and silica) to favour the biofilm growth. The hydrodynamic features of the water flow were characterized using a tracer method, showing behaviour corresponding to a completely mixed reactor. Shear stress forces on the surface of plates were also quantified by computer simulations and correlated with the rotational speed of the inner cylinder. Two phototrophic biofilm development experiments were performed for periods of 6.7 and 7 weeks with different inoculation procedures and illumination intensities. For both experiments, biofilm biomasses exhibited linear growth kinetics and produced 4.2 and 2.4 mg cm-2 of ash-free dry matter. Algal and bacterial community structures were assessed by microscopy and T-RFLP, respectively, and the two experiments were different but revealed similar temporal dynamics. Our study confirmed the performance and multipurpose nature of such an innovative photosynthetic bioreactor for phototrophic biofilm investigations

Ab initio lattice dynamics simulations and inelastic neutron scattering spectra for studying phonons in BaFe2As2: Effect of structural phase transition, structural relaxation and magnetic ordering

We have performed extensive ab initio calculations to investigate phonon dynamics and their possible role in superconductivity in BaFe2As2 and related systems. The calculations are compared to inelastic neutron scattering data that offer improved resolution over published data [Mittal et al., PRB 78 104514 (2008)], in particular at low frequencies. Effects of structural phase transition and full/partial structural relaxation, with and without magnetic ordering, on the calculated vibrational density of states are reported. Phonons are best reproduced using either the relaxed magnetic structures or the experimental cell. Several phonon branches are affected by the subtle structural changes associated with the transition from the tetragonal to the orthorhombic phase. Effects of phonon induced distortions on the electronic and spin structure have been investigated. It is found that for some vibrational modes, there is a significant change of the electronic distribution and spin populations around the Fermi level. A peak at 20 meV in the experimental data falls into the pseudo-gap region of the calculation. This was also the case reported in our recent work combined with an empirical parametric calculation [Mittal et al., PRB 78 104514 (2008)]. The combined evidence for the coupling of electronic and spin degrees of freedom with phonons is relevant to the current interest in superconductivity in BaFe2As2 and related systems

Haydeeite: a spin-1/2 kagome ferromagnet

The mineral haydeeite, alpha-MgCu3(OD)6Cl2, is a S=1/2 kagome ferromagnet that displays long-range magnetic order below TC=4.2 K with a strongly reduced moment. Our inelastic neutron scattering data show clear spin-wave excitations that are well described by a Heisenberg Hamiltonian with ferromagnetic nearest-neighbor exchange J1=-38 K and antiferromagnetic exchange Jd=+11 K across the hexagons of the kagome lattice. These values place haydeeite very close to the quantum phase transition between ferromagnetic order and non-coplanar twelve-sublattice cuboc2 antiferromagnetic order. Diffuse dynamic short-range ferromagnetic correlations observed above TC persist well into the ferromagnetically ordered phase with a behavior distinct from critical scattering