Multi-component kinetics of activated sludge treatment of bleached kraft mill effluent.

This study investigated the discrepancies between the BOD removal rates measured during short term assays and those measured during continuous activated sludge treatment of bleached kraft mill effluent (BKME). A combination of batch tests and fed batch tests with oxygen uptake rate (OUR), chemical oxygen demand (COD), biochemical oxygen demand (BOD), and mixed liquor volatile suspended solids (MLVSS) measurements were used to characterize the degradation rates for the activated sludge treatment of BKME and to divide the soluble readily biodegradable substrate into two to five separate fractions based on biodegradation rates. The removal rates varied by over an order of magnitude between the most readily degradable substrates (1 x 10(-3) mg COD/mg MLVSS minute), and the more slowly degradable substrates (2 x 10(-5) mg COD/mg MLVSS minute). If the readily biodegradable fraction of BKME was modeled as one substrate, initial rate kinetic measurements from batch tests were heavily influenced by the fractions with the greatest degradation rates, while any remaining BOD in the treated effluent was predominantly from the slowly degradable fraction, giving inconsistent results. Taking the multi-component nature of the wastewater into account, batch test results can be used to predict fed-batch and continuous activated sludge reactor performance.

A sex difference on a novel spatial working memory task in humans.

Neurophysiological and behavioral evidence suggests that the prefrontal cortex (PFC) may be sexually differentiated in nonhuman primates. The present study examined whether there are sex differences in working memory in humans that might reflect sexual differentiation of human PFC. Male and female undergraduates were administered a novel multitrial spatial working memory task (SPWM) and a verbal working memory task. In three experiments, females committed significantly fewer working memory errors and took significantly less time to reach criterion than males on the SPWM task. The female advantage was not accounted for by differences in general intellectual ability, attention, perceptual speed, incidental memory, or speed of verbal access. In Study 3, a sex difference was also observed on a measure of verbal working memory. The findings suggest that some prefrontal functions may be sexually differentiated in humans.

A solid waste audit and directions for waste reduction at the University of British Columbia, Canada.

A novel design for a solid waste audit was developed and applied to the University of British Columbia, Canada, in 1998. This audit was designed to determine the characteristics of the residual solid waste generated by the campus and provide directions for waste reduction. The methodology was constructed to address complications in solid waste sampling, including spatial and temporal variation in waste, extrapolation from the study area, and study validation. Accounting for spatial effects decreased the variation in calculating total waste loads. Additionally, collecting information on user flow provided a means to decrease daily variation in solid waste and allow extrapolation over time and space. The total annual waste estimated from the experimental design was compared to documented values and was found to differ by -18%. The majority of this discrepancy was likely attributable to the unauthorised disposal of construction and demolition waste. Several options were proposed to address waste minimisation goals. These included: enhancing the current recycling program, source reduction of plastic materials, and/or diverting organic material to composting (maximum diversion: approximately 320, approximately 270, and approximately 1510 t yr(-1), respectively). The greatest diversion by weight would be accomplished through the diversion of organic material, as it was estimated to comprise 70% of the projected waste stream. The audit methodology designed is most appropriate for facilities/regions that have a separate collection system for seasonal wastes and have a means for tracking user flow.

Effect of oxygen delignification on the rate and extent of enzymatic hydrolysis of lignocellulosic material.

In this study, we examined the effect of oxygen delignification on the rate and extent of enzymatic hydrolysis (using commercial cellulase and beta-glucosidase) of a number of lignocellulosic substrates, including kraft pulp (model substrate), pulp mill primary clarifier sludge (PCS) and steam-exploded Douglas fir chips. Oxygen delignification removed up to 67% of the lignin from softwood pulp and improved the rate of, and yield from, hydrolysis by up to 111% and 174%, respectively. Glucose yield varied linearly with fractional lignin removal. Oxygen delignification of primary clarifier sludge improved hydrolysis yield by up to 90%. However steam-exploded Douglas fir was very resistant to hydrolysis at low enzyme loading, and oxygen delignification decreased hydrolysis rate and yield.

A beneficial effect of estrogen on working memory in postmenopausal women taking hormone replacement therapy.

Recent neurophysiological data suggest that the prefrontal cortex (PFC) may be susceptible to modulation by estrogen. In humans, the PFC mediates a number of cognitive processes that contribute to memory function, particularly working memory. The present study examined whether memory tasks that recruit PFC-dependent information processing might exhibit estrogen sensitivity in women. Performance on several memory tasks, including measures of working memory, was evaluated in three groups of postmenopausal women: (1) women who were tested when taking estrogen only (n = 38, M(age) = 55.1 years), (2) women who were tested when taking estrogen and a progestin concurrently (n = 23, M(age) = 55.9 years), and (3) women who were not taking hormone replacement therapy (n = 35, M(age) = 56.0 years). Estrogen users exhibited significantly better performance on a verbal task and on a spatial task, each with a prominent working memory component, but did not differ from nonusers on control tasks involving simple passive recall. These findings are consistent with the hypothesis that estrogen is active within PFC and is capable of influencing functions dependent on this region. The results of this study raise the possibility that estrogen may play a role in maintaining certain frontal lobe functions in women.

Thermostability and irreversible activity loss of exoglucanase/xylanase Cex from Cellulomonas fimi.

The activity of the beta-1,4-glycanase Cex (EC 3.2.1.91) from Cellulomonas fimi is investigated in connection with its industrial application in cellulose hydrolysis and its potential use in cellosaccharide synthesis. Catalytic activity measurements as a function of temperature, complemented with differential scanning calorimetry (DSC) data, are used to characterize the thermostability of the protein and the influence of interdomain interactions. The data suggest that the enzyme is irreversibly deactivated in one of two possible ways: (1) through a low-temperature route characterized by first-order kinetics; or (2) through a high-temperature route characterized by an initial reversible step followed by an irreversible step. Melting temperatures (Tm) of Cex and p-33 (the isolated catalytic domain of Cex) as estimated by DSC are 64.2 and 64.0 degrees C, respectively, suggesting that the binding and catalytic domains of the protein fold independently. Kinetic parameters (Km, kcat, and kcat/Km) of Cex for the hydrolysis of p-nitrophenyl beta-D-cellobioside (pNPC) were determined at temperatures ranging from 15 to 80 degrees C. As demanded by reversible mass-action thermodynamics, the Tm of Cex in the presence of excess ligand as determined from activity-temperature data is ca. 66.55 degrees C, more than 2 degrees C higher than the Tm for Cex under ligand-free conditions. The effect of temperature on the rate constant has been determined using Arrhenius plots. Combined with irreversible deactivation half-life data and DSC data, the results are used to evaluate a model, based on a theory developed by Hei et al. (1993), for predicting the time-dependent activity and active-state stability of the protein under a range of potential operating conditions.

Comparison of industrial yeast strains for fermentation of spent sulphite pulping liquor fortified with wood hydrolysate.

Ethanol production from spent sulphite pulping liquor (SSL) was compared for four different yeasts. A second strain of S. cerevisiae as well as a 2-deoxyglucose-resistant strain formed through protoplast fusions between S. uvarum and S. diastaticus produced up to 27% more ethanol from SSL fortified with hydrolysis sugars than was produced by S. cerevisiae. The incremental improvement in ethanol yield appeared to vary with the degree of fortification, ranging from 5.8% for unfortified SSL, to 27% for the highest level of fortification tested. Decreasing fermentation rates were observed for SSL fortified with glucose, mannose and galactose, respectively. Sugar uptake rates in SSL fortified with glucose, galactose and mannose were 6.8, 2.8 and 2.0 g L-1 h-1, respectively. However, when these sugars were fermented along with a glucose cosubstrate, the rate at which the combined glucose/mannose medium was fermented was nearly identical to that of the glucose control.

Simultaneous saccharification and extractive fermentation of cellulosic substrates.

Alcohol fermentation has traditionally been carried out in aqueous environments because of the ready solubility of reactant (sugar) and product (ethanol). However, extraction of the product ethanol into a nonmiscible phase can result in kinetic benefits due to reduced inhibition of the fermentation reactions. In this study, we report the development of a novel simultaneous saccharification and extractive fermentation (SSEF) process. Ethanol productivity was increased by up to 65% over conventional (nonextractive) fed-batch simultaneous saccharification systems when calculated on the basis of aqueous phase volume. The amount of water required for SSEF reactions was dramatically reduced from that required for conventional SSF. In batch SSEF reactors with 2.5% aqueous phase, 50% conversion of 25% (aqueous phase concentration) Solka Floc could be achieved in 48 h using 2 FPU/g cellulase.

Effect of surfactant and particle size reduction on hydrolysis of deinking sludge and nonrecyclable newsprint.

Disposal of sludge from deinking mills represents a significant proportion of operating costs. Bioconversion of the cellulosic fraction of deinking sludge (DIS) to ethanol greatly reduces disposal costs while producing an environmentally friendly fuel. In this study, the cellulosic fraction of newsprint and deinking sludge was hydrolysed to produce fermentable sugars. For newsprint, a particle size of 1 to 1.5 mm provided optimal reaction rates in batch reactors over practical hydrolysis times, and reducing sugar concentrations as high as 35 g/L could be achieved using a fed-batch reactor configuration. For both newsprint and DIS, the hydrolysis rate increased nonlinearly with enzyme loading. Tween-80 only marginally improved sugar production but was able to release sugars from cellulosic substrates in the absence of lytic enzymes, in an amount proportional to the surfactant concentration and the substrate particle size. DIS was relatively recalcitrant to enzymatic hydrolysis, possibly due in part to inhibition by hydrophobic constituents. (c) 1995 John Wiley & Sons, Inc.

Effect of surfactants on cellulose hydrolysis.

The effect of surfactants on the heterogeneous enzymatic hydrolysis of Sigmacell 100 cellulose and of steam-exploded wood was studied. Certain biosurfactants (sophorolipid, rhamnolipid, bacitracin) and Tween 80 increased the rate of hydrolysis of Sigmacell 100, as measured by the amount of reducing sugar produced, by as much as seven times. The hydrolysis of steam-exploded wood was increased by 67% in the presence of sophorolipid. At the same time, sophorolipid was found to decrease the amount of enzyme adsorbed onto the cellulose at equilibrium. Sophorolipid had the greatest effect on cellulose hydrolysis when it was present from the beginning of the experiment and when the enzyme/cellulose ratio was low.

Oxidation of benzyl alcohol by whole cells of Pichia pastoris and by alcohol oxidase in aqueous and nonaqueous reaction media.

The low substrate specificity of alcohol oxidase from Pichia pastoris makes this enzyme system of potential biotechnological interest. Whole cells of Pichia pastoris are able to oxidize benzyl alcohol to benzaldehyde in aqueous reaction media. The low water solubility of the reactant and product of this bioconversion, combined with the ability of both to strongly inhibit the reaction, favor the use of nonaqueous reaction fluids. Purified alcohol oxidase was shown to function in a number of 2-phase reaction systems of varied aqueous to organic phase ratios (0.01-0.05 v/v). The apparent V(max) and K(m) were 5.26 g/Lh and 7.41 g/L respectively, for the oxidation of benzyl alcohol to benzaldehyde in hexane containing 3% aqueous phase. The volume of the aqueous phase had a strong effect on the reaction, with an aqueous: organic ratio of 3-5% found to be optimum. The enzyme could be firmly immobilized on DEAE-Biogel (Biorad) to enhance stability and biocatalyst recovery.

Comparison of free and immobilized Pichia pastoris cells for conversion of ethanol to acetaldehyde.

Free and immobilized cells of Pichia pastoris were used to convert ethanol to acetaldehyde in small-scale batch reactors. Immobilized cells were less active than free cells (V(max) free = 7.81 g/L h, V(max) immobilized = 3.17 g/L h) due to a number of factors including end product inhibition and diffusional limitations. Immobilized cells were more resistant to heat denaturation both in the presence and absence of ethanol. Immobilized cells retained more of their activity during repeated batch cycles than did free cells.

Use of surface-immobilized Trichoderma in batch and fed-batch fermentations.

Needle-punch polyester was shown to be an effective support material for the immobilization of Trichoderma reesei Rut C30. When used as a resident inoculum for a batch process, the immobilized Trichoderma was very stable and resulted in a reduced rate of biomass generation in the bulk liquid phase as compared to cultures inoculated with free mycelium. Fed-batch fermentations with the immobilized Trichoderma produced ca. 80% of the activity of those using free cells; however, the activity was more stable and the crude enzyme broth produced had a greatly reduced biomass concentration.

Production and application of methylotrophic yeast Pichia pastoris.

Pichia pastoris is a methylotrophic yeast that makes use bf the enzyme alcohol oxidase to catalyze the first step of the dissimilatory pathway that enables it to grow on methanol. Because of its stability and low substrate specificity, alcohol oxidase is of considerable interest for a range of biotechnological processes. Various feeding regimes were evaluated in an effort to increase the biomass concentration and productivity that could be achieved from fermentations using this organism. Through continuous or semicontinuous feeding, biomass concentrations were increased 10-fold over those achieved in batch fermentations. In subsequent trials, nongrowing whole cells were applied successfully to convert ethanol to acetaldehyde. Quantitative conversions of 20-g/L solutions of ethanol have been achieved in 2 h, and acetaldehyde concentrations of up to 35 g/L have been achieved using extended reaction times of 5 h. The conversion reaction was limited by end product inhibition and by acetaldehyde holdup within the yeast cells.

Effect of Colloidal Materials on Cellulase Production by Trichoderma reesei Rut-C30.

The addition of positively charged colloidal materials to the growth medium markedly increased the concentration of cellulase enzymes produced by Trichoderma reesei Rut-C30. Filter paper activities of up to 4 and 13 IU/ml have been achieved by the addition of colloidal materials, using 3% lactose and 3% cellulose, respectively, as a substrate. The particles exert their effect by binding soluble sugars and slowing their uptake by the organism.

Enhanced Production of Surfactin from Bacillus subtilis by Continuous Product Removal and Metal Cation Additions.

The lipopeptide, surfactin, is produced by Bacillus subtilis. A study has been made on large-scale production of this surfactant. A good yield was obtained from a glucose substrate fermentation by continuously removing the product by foam fractionation. The surfactin could be easily recovered from the collapsed foam by acid precipitation. The yield was also improved by the addition of either iron or manganese salts. Hydrocarbon addition to the medium, which normally increases biosurfactant production, completely inhibited surfactin production by B. subtilis.