Performance and population analysis of a non-sterile trickle bed reactor inoculated with Caldicellulosiruptor saccharolyticus, a thermophilic hydrogen producer.

Non-axenic operation of a 400 L trickle bed reactor inoculated with the thermophile Caldicellulosiruptor saccharolyticus, yielded 2.8 mol H2/mol hexose converted. The reactor was fed with a complex medium with sucrose as the main substrate, continuously flushed with nitrogen gas, and operated at 73 degrees C. The volumetric productivity was 22 mmol H2/(L filterbed h). Acetic acid and lactic acid were the main by-products in the liquid phase. Production of lactic acid occurred when hydrogen partial pressure was elevated above 2% and during suboptimal fermentation conditions that also resulted in the presence of mono- and disaccharides in the effluent. Methane production was negligible. The microbial community was analyzed at two different time points during operation. Initially, other species related to members of the genera Thermoanaerobacterium and Caldicellulosiruptor were present in the reactor. However, these were out-competed by C. saccharolyticus during a period when sucrose was completely used and no saccharides were discharged with the effluent. In general, the use of pure cultures in non-sterile industrial applications is known to be less useful because of contamination. However, our results show that the applied fermentation conditions resulted in a culture of a single dominant organism with excellent hydrogen production characteristics.

The implications of integrated assessment and modelling studies for the future remediation of chromite ore processing residue disposal sites.

Chromite ore processing residue (COPR) waste from a former chromium chemical works (1830-1968) is still contaminating groundwater in Glasgow, Scotland, with carcinogenic hexavalent chromium, Cr(VI). An integrated analytical, experimental and modelling approach has identified and accounted for mineral phases and processes responsible for the retention and release of Cr(VI) under prevailing field conditions. Both the nature of mineral phase retention and the buffered high pH of the sites, however, militate against direct remediative treatment of the source material, for example by the application of generic methods (e.g. FeSO4) that have been successfully employed elsewhere for the reduction of Cr(VI) to Cr(III) in other matrices. The interception and treatment of groundwater to remove Cr(VI) and the capping of sites to reduce human exposure to airborne Cr(VI)-contaminated dust may well be more realistic and effective, at least in the short to medium term.

Role of quantitative mineralogical analysis in the investigation of sites contaminated by chromite ore processing residue.

A range of techniques, normally associated with mineralogical studies of soils and sediments, has been used to characterise the solid materials found on sites contaminated with chromite ore processing residue (COPR). The results show that a wide range of minerals are present, many of which are found extensively in high-temperature synthetic systems such as cements and clinkers and their low temperature hydration products. Thus, the minerals in COPR can be divided into three main categories: unreacted feedstock ore (chromite); high temperature phases produced during chromium extraction (brownmillerite, periclase and larnite); and finally, minerals formed under ambient weathering conditions on the disposal sites (brucite, calcite, aragonite, ettringite, hydrocalumite, hydrogarnet). Apart from chromite, chromium occurs in brownmillerite, ettringite, hydrocalumite and hydrogarnet. Detailed study of the chemistry and stoichiometry of chromium-bearing phases in conjunction with phase abundance provides a quantitative description of the solid state speciation of Cr(III) and Cr(VI) in and amongst these minerals and in the COPR as a whole. Of the total chromium present in the samples most, approximately 60-70% is present as Cr(III) in chromite, whilst brownmillerite also represents a significant reservoir of Cr(III) which is approximately 15% of the total. The remaining chromium, between 20 and 25%, is present as Cr(VI) and resides mainly in hydrogarnet, and to a slightly lesser extent in hydrocalumite. In the latter, it is present principally in an exchangeable anionic form. Chromium (VI) is also present in ettringite, but quantitatively ettringite is a much less important reservoir of Cr(VI), accounting for approximately 3% of total chromium in one sample, but less than 1% in the other two. This description provides insight into the processes likely to control the retention and release of Cr(VI) from COPR-contaminated sites. Such information is of particular value in chemical modelling of the system, in risk assessment and in the development of methods of informed remediation.