Structural investigation of catalyst deactivation of Pt/SDB for catalytic oxidation of VOC-containing wastewater

The stability of styrene-divinyl benzene copolymer (SDB)-supported Pt (Pt/SDB) catalysts for destruction of volatile-organic-compound (VOC) in wastewater was examined. The test reaction was wet oxidation of water-containing aliphatic alcohol and formaldehyde at 140 degrees C and 90 psig for 40 h. The catalytic performance tests indicated that activity of the Pt/SDB catalysts could be maintained for VOC concentration of 3 wt.%, whereas the catalysts deactivated rapidly for 10 wt.% VOC containing wastewater. In order to investigate the nature of catalyst deactivation, extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge (XANES) spectroscopy were used to characterize the fresh and used catalysts. After the reaction, there is no oxidation of Pt clusters observed in EXAFS and XANES spectroscopy suggesting that the oxidation reaction takes places via the adsorbed oxygen. The spectroscopy results further indicated that deactivation of the catalysts were mainly caused by the increase of Pd particle size. After the reaction, the Pt-Pt coordination number has no significant change for the 3 wt.% wastewater whereas increase from 5.6 to 6.2 for 10 wt.% wastewater. Combined with the fact that the catalysts fractured during the reactions, we suggested that Pt agglomeration was mainly caused by thermal migration of the metal clusters.     

Development of a simple and sensitive method for the characterization of odorous waste gas emissions by means of solid-phase microextraction (SPME) and GC-MS/olfactometry

A solid-phase microextraction (SPME) method has been developed for the extraction of odorous compounds from waste gas. The enriched compounds were characterized by gas chromatography-mass spectrometry (GC-MS) and gas chromatography followed by simultaneous flame ionization detection and olfactometry (GC-FID/O). Five different SPME fiber coatings were tested, and the carboxen/polydimethylsiloxane (CAR/PDMS) fiber showed the highest ability to extract odorous compounds from the waste gas. Furthermore, parameters such as exposure time, desorption temperature, and desorption time have been optimized. The SPME method was successfully used to characterize an odorous waste gas from a fat refinery prior to and after waste gas treatment in order to describe the treatment efficiency of the used laboratory scale plant which consisted of a bioscrubber/biofilter combination and an activated carbon adsorber. The developed method is a valuable approach to provide detailed information of waste gas composition and complements existing methods for the determination of odors. However, caution should be exercised if CAR/PDMS fibers are used for the quantification of odorous compounds in multi-component matrices like waste gas emissions since the relative affinity of each analyte was shown to differ according to the total amount of analytes present in the sample.     

Immobilisation of heavy metal in cement-based solidification/stabilisation: a review

Heavy metal-bearing waste usually needs solidification/stabilization (s/s) prior to landfill to lower the leaching rate. Cement is the most adaptable binder currently available for the immobilisation of heavy metals. The selection of cements and operating parameters depends upon an understanding of chemistry of the system. This paper discusses interactions of heavy metals and cement phases in the solidification/stabilisation process. It provides a clarification of heavy metal effects on cement hydration. According to the decomposition rate of minerals, heavy metals accelerate the hydration of tricalcium silicate (C3S) and Portland cement, although they retard the precipitation of portlandite due to the reduction of pH resulted from hydrolyses of heavy metal ions. The chemical mechanism relevant to the accelerating effect of heavy metals is considered to be H+ attacks on cement phases and the precipitation of calcium heavy metal double hydroxides, which consumes calcium ions and then promotes the decomposition of C3S. In this work, molecular models of calcium silicate hydrate gel are presented based on the examination of 29Si solid-state magic angle spinning/nuclear magnetic resonance (MAS/NMR). This paper also reviews immobilisation mechanisms of heavy metals in hydrated cement matrices, focusing on the sorption, precipitation and chemical incorporation of cement hydration products. It is concluded that further research on the phase development during cement hydration in the presence of heavy metals and thermodynamic modelling is needed to improve effectiveness of cement-based s/s and extend this waste management technique.     

Transcervical chorionic villus biopsy with a brush

A brush delivered to the biopsy site by a metal introducer and cannula set was tested as an alternative implement for transcervical collection of chorionic villi. This implement was easy to use and readily identified by ultrasound. With only one attempt at sampling, the overall collection rate for 83 patients was 65 per cent. With practice 84 per cent successful collection was achieved. Gestations between 8 and 11 weeks was the best time for collection of chorionic villi. A single sampling can produce adequate material (15 mg wet weight) suitable for diagnostic purposes. No gestation sac was perforated but some slight bleeding followed the procedure. Appreciable success following a single sampling attempt coupled with the low complication rate suggests that this technique may have clinical application and deserves further investigation.     

The post-Bhopal and post-9/11 transformations in chemical emergency prevention and response policy in the United States

The United States' approach to incident prevention and response to hazardous chemical facilities has undergone two major transformations in the last 20 years. The first was triggered by the Bhopal tragedy in 1984, which led to major changes within the US chemical industry and a series of Federal laws and regulations intended to prevent major chemical accidents. A more recent transformation is currently underway in the wake of the 9/11 attacks on New York and Washington. It involves the advent of various security-related requirements affecting many of the same facilities covered under the existing accident prevention rules. This paper provides an overview of these transformations and their impacts.     

Discovery of Components Acting as the Obstacles in the Detection of Enteric Viruses from Berries

Food and Environmental Virology - This study investigated the obstacles in detecting enteric viruses from berry fruits, which are on the one hand often associated with outbreaks of viral enteric...