Biohydrogen production from wheat straw hydrolysate using Caldicellulosiruptor saccharolyticus followed by biogas production in a two-step uncoupled process

A two-step, un-coupled process producing hydrogen (H₂) from wheat straw using Caldicellulosiruptor saccharolyticus in a ‘Continuously stirred tank reactor’ (CSTR) followed by anaerobic digestion of its effluent to produce methane (CH₄) was investigated. C. saccharolyticus was able to convert wheat straw hydrolysate to hydrogen at maximum production rate of approximately 5.2 L H₂/L/Day. The organic compounds in the effluent collected from the CSTR were successfully converted to CH₄ through anaerobic digestion performed in an ‘Up-flow anaerobic sludge bioreactor’ (UASB) reactor at a maximum production rate of 2.6 L CH₄/L/day. The maximum energy output of the process (10.9 kJ/g of straw) was about 57% of the total energy, and 67% of the energy contributed by the sugar fraction, contained in the wheat straw. Sparging the hydrogenogenic CSTR with the flue gas of the UASB reactor ((60% v/v) CH₄ and (40% v/v) CO₂) decreased the H₂ production rate by 44%, which was due to the significant presence of CO₂. The presence of CH₄ alone, like N₂, was indifferent to growth and H₂ production by C. saccharolyticus. Hence, sparging with upgraded CH₄ would guarantee successful hydrogen production from lignocellulosic biomass prior to anaerobic digestion and thus, reasonably high conversion efficiency can be achieved.     

THE DISCRETE MAXIMUM PRINCIPLE IN FINITE-ELEMENT THERMAL RADIATION ANALYSIS

Under certain conditions, usually intense surface heat transfer associated with radiation, finite-element solutions display anomalous behaviors. These behaviors have been traced to the violation of a discrete maximum principle. Here, necessary and sufficient conditions for satisfaction of the discrete maximum principle are discussed. Special elements that satisfy a discrete maximum principle for a wider range of parameters, thereby improving the accuracy of the solution, are introduced into standard finite-element formulations for the heat conduction equation. The improved performance of these elements is then demonstrated by means of a few examples.     

Preservation of hermaphrodite and female papaya fruits (Carica papaya L?., Cv Sunrise, Solo group) by freezing: physical, physico-chemical and sensorial aspects

 The physical, physico-chemical and sensorial changes that occur during the freezing and frozen storage of hermaphrodite and female papaya slices (Carica papaya L., cv Sunrise, Solo group) were studied. Samples were evaluated by panellists throughout a 1-year period of storage at –24°C; the panellists described the fruit in terms of physico-chemical measurements of texture (firnmess and total pectins content), colour [L, a _L , b _L , peroxidase (POD) and polyphenoloxidase (PPO) activities] and flavour/taste [soluble solids content, pH, tritatable acidity and quality index (^oBrix/acidity)], and ranked them in order of preference. Desserts prepared from frozen slices of hermaphrodite and female papaya fruits mixed with orange, lemon and sugar were also evaluated. The freezing process itself did not result in significant changes in the more commonly assessed quality parameters of texture, colour and flavour/taste. However, during storage at –24°C, changes in sensorial characteristics occurred that became more evident as storage continued (≤ 9 months). Nevertheless, these quality changes can be masked by using these papaya slices as an ingredient in fruit products, with frozen female papaya slices being especially suitable for this purpose. Received: 1 August 1997 / Revised version: 14 November 1997     

Biocompatibility of multi-walled carbon nanotubes grown on titanium and silicon surfaces

Cell adhesion and cell viability of aligned multi-walled carbon nanotube (MWCNT) films were verified using Fibroblast L929 mouse cells. The MWCNTs were produced by a microwave plasma chemical vapor deposition (2.45 GHz) on silicon (Si), with a nickel catalyst, and titanium (Ti), with an iron catalyst. MTT assay and cellular adhesion were used for biocompatibility tests (ISO 10993-5). The results show very high cell viability and many layers of cells adhered on the surface formed by the nanotube tips at films grown on silicon surfaces. The MWCNT grown on Ti surfaces presented lower cell viability and a reduced number of cells on the surface formed by the nanotube tips. The different behavior is most probably related to excess iron contamination present in the case of titanium substrate, while nickel catalyst is probably enclosed by the nanotubes.     

Development of fireside waterwall corrosion correlations using pilot-scale test furnace

Fireside waterwall wastage in a pulverized coal-fired boiler was investigated and the relevant rate correlations were developed for three corrosion mechanisms: gas-phase attack by reduced sulfur species, chlorine-based attack, and unoxidized fuel deposition. Rate correlations were based on the published data and the experiments at a pilot-scale test furnace. The parameters of the correlations include local flue gas composition, flue gas temperature, metal surface temperature, deposition, deposit characteristics, and heat flux. Validation work performed using the same furnace and the different operating conditions provided good agreement between predictions and measurements. The correlations in conjunction with computational fluid dynamics simulation are expected to provide a predictive tool that can optimize the furnace operating conditions to reduce fireside waterwall wastage.     

Effects of freezing and canning of papaya slices on their carotenoid composition

An HPLC study of the carotenoid composition of fresh, frozen and canned papaya fruit slices was done. There were no qualitative differences between the carotenoid patterns of fresh and frozen papaya fruit slices (cultivar Sunrise). The major carotenoids found in papaya extracts were lycopene and carotenol fatty acid esters of-cryptoxanthin and-cryptoxanthin-5, 6-epoxide. Other xanthophylls detected were-crypto-xanthin,trans-zeaxanthin and cryptoflavin. It was possible to determine the quantitative losses of carotenoids in papaya slices as a result of the freezing process and frozen storage, since samples of these fruits were available before processing. The pigment pattern of the canned product showed lycopene as being a major pigment. Thermal treatment induced the degradation of carotenol fatty acid esters of xanthophylls. The freezing and canning processing of papaya slices led to significant decreases in the total carotenoids quantified by HPLC, with frozen female slices and canned samples showing lower amounts of pigments. Hunter colour values of frozen slices were similar to those of fresh papaya fruit slices.     

Use of needle track detection to quantify the displacement of stranded seeds following prostate brachytherapy

We aim to compute the movement of permanent stranded implant brachytherapy radioactive sources (seeds) in the prostate from the planned seed distribution to the intraoperative fluoroscopic distribution, and then to the postimplant computed tomography (CT) distribution. We present a novel approach to matching the seeds in these distributions to the plan by grouping the seeds into needle tracks. First, we identify the implantation axis using a sample consensus algorithm. Then, we use a network flow algorithm to group seeds into their needle tracks. Finally, we match the needles from the three stages using both their transverse plane location and the number of seeds per needle. We validated our approach on eight clinical prostate brachytherapy cases, having a total of 871 brachytherapy seeds distributed in 193 needles. For the intraoperative and postimplant data, 99.31% and 99.41% of the seeds were correctly assigned, respectively. For both the preplan to fluoroscopic and fluoroscopic to CT registrations, 100% of the needles were correctly matched. We show that there is an average intraoperative seed displacement of 4.94±2.42 mm and a further 2.97±1.81 mm of postimplant movement. This information reveals several directional trends and can be used for quality control, treatment planning, and intraoperative dosimetry that fuses ultrasound and fluoroscopy.