Wastewater treatment in a hybrid activated sludge baffled reactor

A novel hybrid activated sludge baffled reactor (HASBR), which contained both suspended and attached-growth biomass perfect mixing cells in series, was developed by installing standing and hanging baffles and introducing plastic brushes into a conventional activated sludge (CAS) reactor. It was used for the treatment of domestic wastewater. The effects on the operational performance of developing the suspended and attached-growth biomass and reactor configuration were investigated. The change of the flow regime from complete-mix to plug-flow, and the addition of plastic brushes as a support for biofilm, resulted in considerable improvements in the COD, nitrogen removal efficiency of domestic wastewater and sludge settling properties. In steady state, approximately 98+/-2% of the total COD and 98+/-2% of the ammonia of the influent were removed in the HASBR, when the influent wastewater concentration was 593+/-11 mg COD/L and 43+/-5 mg N/L, respectively, at a HRT of 10 h. These results were 93+/-3 and 6+/-3% for the CAS reactor, respectively. Approximately 90+/-7% of the total COD was removed in the HASBR, when the influent wastewater concentration was 654+/-16 mg COD/L at a 3h HRT, and in the organic loading rate (OLR) of 5.36kgCOD m(-3) day(-1). The result for the CAS reactor was 60+/-3%. Existing CAS plants can be upgraded by changing the reactor configuration and introducing biofilm support media into the aeration tank.     

New Raman spectrometer using a digital micromirror device and a photomultiplier tube detector for rapid on-line industrial analysis. Part I: description of the prototype and preliminary results

In this paper, a prototype of a new generation of Raman spectrometers, based on the use of a monochromator, a digital micromirror device as light modulator, and a photomultiplier tube as detector of the Raman light, is described. This spectrometer, containing no moving parts, is inexpensive, robust, and very precise. New in concept, this spectrometer makes it possible to record, in addition to classical Raman spectra, the intensity at several selected points of the spectrum and/or the total intensity in several selected intervals at the same time with great accuracy, thus giving new possibilities for analytical applications. Also, the work presented demonstrates the possibilities of this very simple prototype for rapid on-line industrial analysis, with an example of quantitative analysis of binary and ternary mixtures of xylene isomers. The precision obtained is satisfactory (errors of prediction approximately 3% in 5-6 seconds per sample).     

Going beyond the reflectance limit of cholesteric liquid crystals

Cholesteric liquid-crystalline states of matter are abundant in nature: atherosclerosis, arthropod cuticles, condensed phases of DNA, plant cell walls, human compact bone osteon, and chiral biopolymers. The self-organized helical structure produces unique optical properties. Light is reflected when the wavelength matches the pitch (twice periodicity); cholesteric liquid crystals are not only coloured filters, but also reflectors and polarizers. But, in theory, the reflectance is limited to 50% of the ambient (unpolarized) light because circularly polarized light of the same handedness as the helix is reflected. Here we give details of a cholesteric medium for which the reflectance limit is exceeded. Photopolymerizable monomers are introduced into a cholesteric medium exhibiting a thermally induced helicity inversion, and the blend is then cured with ultraviolet light when the helix is right-handed. Because of memory effects attributable to the polymer network, the reflectance exceeds 50% when measured at the temperature assigned for a cholesteric helix with the same pitch but a left-handed sense before the reaction. As cholesteric materials are used as tunable bandpass filters, reflectors or polarizers and temperature or pressure sensors, novel opportunities to modulate the reflection over the whole light flux range, instead of only 50%, are offered.     

Label-free microelectronic PCR quantification

We present a robust and simple method for direct, label-free PCR product quantification using an integrated microelectronic sensor. The field-effect sensor can sequentially detect the intrinsic charge of multiple unprocessed PCR products and does not require sample processing or additional reagents in the PCR mixture. The sensor measures nucleic acid concentration in the PCR relevant range and specifically detects the PCR products over reagents such as Taq polymerase and nucleotide monomers. The sensor can monitor the product concentration at various stages of PCR and can generate a readout that resembles that of a real-time fluorescent measurement using an intercalating dye but without its potential inhibition artifacts. The device is mass-produced using standard semiconductor processes, can be reused for months, and integrates all sensing components directly on-chip. As such, our approach establishes a foundation for the direct integration of PCR-based in vitro biotechnologies with microelectronics.     

Minimum-phase-function-based processing in frequency-domain optical coherence tomography systems

We present a simple processing technique that uses the concept of minimum-phase functions to improve frequency-domain optical coherence tomography systems. Our approach removes the autocorrelation noise and therefore increases both the accessible depth range and the recovery accuracy. To our knowledge, this is the first time that the concept of minimum-phase functions has been applied to improve optical coherence tomography.     

Bayesian decision threshold, detection limit and confidence limits in ionising-radiation measurement

Based on Bayesian statistics and the Bayesian theory of measurement uncertainty, characteristic limits such as the decision threshold, detection limit and limits of a confidence interval can be calculated taking into account all sources of uncertainty. This approach consists of the complete evaluation of a measurement according to the ISO Guide to the Expression of Uncertainty in Measurement (GUM) and the successive determination of the characteristic limits by using the standard uncertainty obtained from the evaluation. This procedure is elaborated here for several particular models of evaluation. It is, however, so general that it allows for a large variety of applications to similar measurements. It is proposed for the revision of those parts of DIN 25482 and ISO 11929 that are still based on conventional statistics and, therefore, do not allow to take completely into account all the components of measurement uncertainty in the calculation of the characteristic limits.     

Effects of the surface boundary on the determination of the optical properties of a turbid medium with time-resolved reflectance

Solutions of the time-dependent diffusion equation were developed to take into account the depth of the source and the detector inside a semi-infinite medium. These solutions permitted an evaluation of optical properties at different depths below the surface by fitting time-resolved data. Measurements were performed on liquid optical phantoms with optical fibers for delivering and collecting light. A time-correlated single-photon-counting chain was used for electronic detection. The determination of optical properties underlines the continuity between the surface model and the infinite model and shows the depth at which the derived solutions can be applied.     

Laser-induced breakdown spectroscopy of high-pressure bulk aqueous solutions

Laser-induced breakdown spectroscopy (LIBS) is presented for detection of several Group I and II elements (e.g., Na, Ca, Li, and K), as well as Mn and CaOH, in bulk aqueous solution at pressures exceeding 2.76 x 10(7) Pa (276 bar). Preliminary investigations reveal only minor pressure effects on the emission intensity and line width for all elements examined. These effects are found to depend on detector timing and laser pulse energy. The results of these investigations have implications for potential applications of LIBS for in situ multi-elemental detection in deep-ocean environments.     

Synthesis and enzymatic degradation of epichlorohydrin cross-linked pectins

The water solubility of pectin was successfully decreased by cross-linking with increasing amounts of epichlorohydrin in the reaction media. The initial molar ratios of epichlorohydrin/ galacturonic acid monomer in the reaction mixtures were 0, 0.37, 0.56, 0.74, 1.00, 1.47, and 2.44. The resulting epichlorohydrin cross-linked pectins were thus referred to as C-LP0, C-LP37, C-LP56, C-LP75, C-LP100, C-LP150, and C-LP250, respectively. Methoxylation degrees ranged from 60.5 ± 0.9% to 68.0 ± 0.6%, and the effective cross-linking degrees, determined by quantification of the hydroxyl anions consumed during the reaction, were 0, 17.8, 26.0, 38.3, 46.5, 53.5, and 58.7%, respectively. After incubating the different cross-linked pectins (0.5% w/v) in 25 mL of 0.05 M acetate-phosphate buffer (pH 4.5), containing 50 µL of Pectinex® Ultra SP-L (pectinolytic enzymes), between 60 and 80% of the pectin osidic bounds were broken in less than 1 hr. Moreover, increasing the cross-linking degree only resulted in a weak slowing on the enzymatic degradation velocity.     

Molecular junctions based on aromatic coupling

If individual molecules are to be used as building blocks for electronic devices, it will be essential to understand charge transport at the level of single molecules. Most existing experiments rely on the synthesis of functional rod-like molecules with chemical linker groups at both ends to provide strong, covalent anchoring to the source and drain contacts. This approach has proved very successful, providing quantitative measures of single-molecule conductance, and demonstrating rectification and switching at the single-molecule level. However, the influence of intermolecular interactions on the formation and operation of molecular junctions has been overlooked. Here we report the use of oligo-phenylene ethynylene molecules as a model system, and establish that molecular junctions can still form when one of the chemical linker groups is displaced or even fully removed. Our results demonstrate that aromatic pi-pi coupling between adjacent molecules is efficient enough to allow for the controlled formation of molecular bridges between nearby electrodes.