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In this work, competition for two nitrogen resources (nitrate-, nitrite-nitrogen) between three hydrogen oxidizing denitrifying populations (Acidovorax sp. strain Ic3 (X 1), Paracoccus sp. strain Ic1 (X 2), and Acinetobacter sp. strain Ic2 (X 3)) was examined. The dynamics of three systems of microbial populations (system I: X 1 − X 3, system II: X 2 − X 3, and system III: X 1 − X 2 − X 3), grown in a chemostat, was studied using bifurcation analysis. The chemostat is the most common type of biological reactor used for the study of microbial growth under controlled conditions. The effect of the operating parameters (i.e., dilution rate and feed nitrate nitrogen concentration) on the long-term behavior of the systems showed that X 3 was the predominant population for a wide range of combinations of dilution rate and feed nitrate nitrogen concentration. Also, coexistence of two populations (X 2 X 3, X 1 X 3) was observed. The results of the bifurcation analysis were also used to determine the denitrification rate and the nitrite nitrogen accumulation for each of the three systems as a function of the dilution rate (up to 0.17h−1) and the feed nitrate nitrogen concentration (up to 300mg/L). The highest denitrification rate was achieved by system I (28mg/Lh). A comparison between the three systems showed that the nitrite nitrogen concentration in system I was less than the one in system III, while the two systems gave similar denitrification rates. The second system had the greatest accumulation of nitrites with the lowest denitrification rate. [Copyright &y& Elsevier]

Abstract: The growth kinetics of a bacterium of the strain Pseudomonas fluorescens, which is indigenous in soil, has been investigated in batch cultures and sand packs during biodegradation of phenol. Batch experiments were conducted at 25°C with four different initial concentrations of phenol for the estimation of the kinetic parameters. Phenol was found to inhibit microbial growth and so Andrews''s model was used to describe the growth rate. Growth kinetics in sand packs was studied in a series of eight virtually identical columns, which were operated simultaneously under the same conditions and in a continuous flow mode, with phenol as the sole carbon source. The idea of eight columns allowed monitoring of biomass growth as a function of time. Every 1 or 2 weeks, one column was drawn out of the system and was “sacrificed” to measure the developed biomass in the porous medium. The results indicated that growth of P. fluorescens in sand packs during biodegradation of phenol was an intensely dynamic phenomenon. Detachment of clusters of bacteria from the sand grains was found to be one of the main processes taking place in such a system, caused by a combination of low nutrient supply, oxygen availability and flow velocity. [Copyright &y& Elsevier]

Abstract: The progress of hydrogenotrophic denitrification in batch assays with a mixed culture was examined. The aim was to study the performance of the culture for hydrogenotrophic denitrification of drinking water at various NO3 − concentrations. The kinetics of the process were studied in batch experiments. The rates of the process were found to be inhibited at high nitrate concentrations. The nitrite concentration remained at very low values throughout the process but it still affected biomass growth. A kinetic model was developed and its kinetic parameters were determined from the batch experiments. The growth kinetics could be very well described by using expressions for double nutrient limitation (nitrate, nitrite) with inhibition from nitrate. The proposed model is capable of describing accurately enough cellular growth, nitrate and nitrite utilization and utilization rates under anoxic conditions in the presence of various concentrations of nitrate in the range of 7 to about 200mgN/l. [Copyright &y& Elsevier]

Ozone pretreatment studies of wastewater containing a specific azo dye -- Orange II -- were conducted in order to assess the kinetics of ozone oxidation and to evaluate the effect of ozonation on the biodegradability of the wastewater. Batch experiments were performed at different initial concentrations of the dye, showing that ozone is capable of a rapid disruption of the dye molecule. Moreover, the production of biodegradable compounds is apparent from the evolution of COD and BOD{sub}5{end} measurements. A mathematical model which describes the dye elimination, the COD and BOD{sub}5{end} variation, and the amount of ozone reacted has been developed. [ABSTRACT FROM AUTHOR]

Abstract: Rice hull hydrolysate was used as feedstock for microbial lipids production using the oleaginous fungus Mortierella isabellina. Kinetic experiments were conducted in C/N ratios 35, 44 and 57 and the oil accumulation into fungal biomass was 36%, 51.2% and 64.3%, respectively. A detailed mathematical model was used in order to describe the lipid accumulation process. This model was able to predict reducing sugar and nitrogen consumption, fat-free biomass synthesis and lipid accumulation. Neutral lipids constitute the predominant lipid fraction, while the major fatty acids were oleic, palmitic and linoleic acid. Fatty acids of long aliphatic chain were not detected, thus the microbial oil produced is a promising feedstock for biodiesel production. [Copyright &y& Elsevier]

Abstract: Several approaches of hydrogenotrophic denitrification of potable water as well as technical data and mathematical models that were developed for the process are reviewed. Most of the applications that were tested for hydrogenotrophic process achieved great efficiency, high denitrification rates, and operational simplicity. Moreover, this paper reviews the variety of reactor configurations that have been used for hydrogen gas generation and efficient hydrogen delivery. Microbial communities and species that participate in the denitrification process are also reported. The variation of nitrate concentration, pH, temperature, alkalinity, carbon and microbial acclimation was found to affect the denitrification rates. The main results regarding research progress on hydrogenotrophic denitrification are evaluated. Finally, the commonly used models and simulation approaches are discussed. [Copyright &y& Elsevier]

Abstract: A cluster of bench-scale packed-bed reactors was used to investigate nitrate removal from contaminated drinking water through hydrogenotrophic denitrification. A mixed culture originating from a wastewater treatment plant was used to inoculate four packed-bed reactors, with gravel as support media in different sizes (mean diameter 1.75, 2.41, 3.52 and 4.03 mm). We studied the effect of gravel size and operating mode (draw-fill or continuous) on filter performance. It was found that gravel size drastically affects the hydrogenotrophic denitrification rate, while draw-fill operation was more efficient for high nitrate nitrogen concentrations up to 200 mg/L. An increase of filter height increased drastically the retention time of the treated water and continuous operation became favourable for even higher nitrate nitrogen concentrations of 350 mg/L, where denitrification rates of about 6.5 g/Ld were achieved. The proposed procedure may prove to be an effective and economic method for nitrate removal from contaminated water resources. [Copyright &y& Elsevier]

The aim of this work was to study hydrogenotrophic denitrification in packed-bed reactors under draw-fill and continuous operation. Three bench-scale packed-bed reactors with gravel in different sizes (mean diameter 1.75, 2.41 and 4.03mm) as support media were used, in order to study the effect of particle size on reactors performance. The maximum denitrification rate achieved under draw-fill operation was 4.4gNO3 −-N/ld for the filter with gravel of 2.41mm. This gravel size was chosen to perform experiments under continuous operation. Feed NO3 −-N concentrations and hydraulic loadings (HL) ranged between 20–200mg/l and 5.7–22.8m3/m2 d, respectively. A comparison between the two operating modes showed that, for low HL the draw-fill operation achieved higher denitrification rates, while for high HL and intermediate feed concentrations (40–60mgNO3 −-N/l) the continuous operation achieved higher denitrification rates (4.67–5.65g/ld). Finally, experiments with three filters in series (with gravels of 4.03, 2.41 and 1.75mm mean diameter) were also performed under continuous operation. The maximum denitrification rate achieved was 6.2gNO3 −-N/ld for feed concentration of 340mg/l and HL of 11.5m3/m2 d. A model, which describes denitrification in packed-bed reactors, was also developed. The model predicts the concentration profiles of NO3 −-N along filter height, in draw-fill as well as in continuous operation, satisfactorily. [Copyright &y& Elsevier]

Abstract: The dynamics of a model of a free-living nitrogen-fixing population, grown in a chemostat together with a non-nitrogen-fixing bacterial population in competition for the available nutrients and a predator, was studied through bifurcation analysis. When the nitrogen-fixing population is slightly inhibited by ammonium nitrogen (NH3), then this population survives at steady state at low NH3 concentration for a wide range of dilution rate values. At high NH3 concentration the nitrogen-fixing population survives at high dilution rate values, while at lower dilution rate values survival of the nitrogen-fixing population is possible when both the competitive population and the predator are present. When inhibition of NH3 is high, the nitrogen-fixing population survives at steady state at low NH3 concentrations for a wide range of dilution rate values, while at high NH3 concentration the competitive prey stimulates the coexistence state of all populations. Therefore, under high NH3 concentration conditions the competitive population appears to be beneficial for the system and for the survival of the nitrogen-fixing prey. However, the presence of the competitive prey, in the regions where the nitrogen-fixing prey coexists with its predator at a stable state seems to have a negative effect on the nitrogen-fixing activity. [Copyright &y& Elsevier]

Abstract: The kinetics of phenol biodegradation in draw-fill suspended and attached growth reactors by olive pulp bacteria were investigated. The Haldane equation was adopted in order to describe phenol biodegradation in the draw-fill suspended-growth flask reactors. Kinetic constants of the Haldane equation obtained from batch culture experiments with phenol concentration ranging from 13 to 280mgl−1, were μ max=0.054h−1, K S=19.23mgl−1, and K i=36.95mgl−1. However, in the draw-fill experiments at the packed-bed reactor, phenol inhibitory effects were minimized increasing the inhibitory constant value K i′ at 1571mgl−1. The model predicted phenol biodegradation in the packed-bed reactor adequately, for all initial phenol concentrations tested, apart from the highest phenol concentration of 1990mgl−1, where clogging problems and insufficient aeration in the filter prevailed. [Copyright &y& Elsevier]

Abstract: The survival of free-living nitrogen-fixing microbial populations in the natural ecosystem is crucial for the system maintenance and productivity due to the unique role of these organisms in the global biogeochemical cycle of nitrogen. The dynamics of a nitrogen-fixing microbial population grown at various conditions in a chemostat, together with a competitive (for the common resources) population, was studied through bifurcation analysis of a mathematical model of the system. When the carbon source is found in abundance in the feed, then the competition for this nutrient is low. High amounts of ammonium nitrogen (a substance that inhibits growth of the nitrogen-fixing population) are assimilated for the growth needs of both populations. Under these conditions the nitrogen-fixing population can survive (alone or together with its competitor) in a wide range of parameter values and operating conditions and in some cases nitrogenase synthesis occurs. When the inflow medium contains low carbon substrate concentrations, high competition occurs for this nutrient. In these conditions the nitrogen-fixing population can survive only if it has the competitive advantage over its competitor. However, if the inflow medium contains high ammonium concentrations, the nitrogen-fixing population is inhibited and loses its competitive advantage. Under these conditions, only nitrogen-fixing populations, which are able to establish amensalistic interactions can survive in the system. [Copyright &y& Elsevier]

Biological oxidation of organic dyes is important for textile industry wastewater treatment. The aim of this work was to assess the biodegradation kinetics of a specific azo-dye, p-aminoazobenzene. The degradation of p-aminoazoben-zene by Bacillus subtilis was examined through batch experiments in order to investigate the effect of p-aminoazo-benzene on the bacterial growth rate and elucidate the mechanism of dye degradation. The results proved that B. subtilis cometabolizes p-aminoazobenzene in the presence of glucose as carbon source, producing aniline and p-phenylenediamine as the nitrogen -- nitrogen double bond is broken. The azo-dye was found to act as an inhibitor to microbial growth. A mathematical model was developed that describes cellular growth, glucose utilization, p-aminoazobenzene degradation and product formation. [ABSTRACT FROM AUTHOR]

Aims Our main objective was to determine the neuropathological correlates of dementia in patients with Lewy body disease (LBD). Furthermore, we used data derived from clinical, neuropathological and genetic studies to investigate boundary issues between Dementia with Lewy bodies (DLB) and Parkinson's disease with (PDD) and without (PDND) dementia. Methods One hundred and twenty-one cases with a neuropathological diagnosis of LBD and clinical information on dementia status were included in the analysis (55 PDD, 17 DLB and 49 PDND). We carried out topographical and semi-quantitative assessment of Lewy bodies (LB), Aβ plaques and tau-positive neuropil threads (NT). The APOE genotype and MAPT haplotype status were also determined. Results The cortical LB (CLB) burden was the only independent predictor of dementia (OR: 4.12, P < 0.001). The total cortical Aβ plaque burden was an independent predictor of a shorter latency to dementia from onset of motor signs ( P = 0.001). DLB cases had a higher LB burden in the parietal and temporal cortex, compared to PDD. Carrying at least one APOE ϵ4 allele was associated with a higher cortical LB burden ( P = 0.02), particularly in the neocortical frontal, parietal and temporal regions. Conclusions High CLB burden is a key neuropathological substrate of dementia in LBD. Elevated cortical LB pathology and Aβ plaque deposition are both correlated with a faster progression to dementia. The higher CLB load in the temporal and parietal regions, which seems to be a distinguishing feature of DLB, may account for the shorter latency to dementia and could be mediated by the APOE ϵ4 allele. [ABSTRACT FROM AUTHOR]

Abstract: An oleaginous fungus, Mortierella isabellina, able to transform efficiently sugar to storage lipid, was used as a model microorganism which develops a biofilm structure during the semi-solid fermentation process for the production of biodiesel from sweet sorghum. A mathematical model was developed to describe the fungal oil production in M. isabellina biofilm. The model describes diffusion and consumption of sugars and nitrogen of sweet sorghum and single cell oil production in a biofilm, which grows according to the kinetics of double-substrate limitation (sugars and nitrogen) with sugar inhibition. Experimental data from a previous experimental study were used to determine the kinetic parameters of the model. Maximum biofilm thickness and the percentage of lipid inside the biofilm were estimated using the model at 1892μm and 15%, respectively. The proposed mathematical model could prove a useful tool for designing semi-solid fermentation processes. [Copyright &y& Elsevier]

Abstract: A semi-solid fermentation process for the production of biodiesel from sweet sorghum is introduced. The microorganism used is the oleaginous fungus Mortierella isabellina, which is able to transform efficiently sugar to storage lipid. Kinetic experiments were performed at various water content percentages. The fungus consumed simultaneously sugars and nitrogen contained in sorghum and after nitrogen depletion the biomass growth was completed and oil accumulation began. Water content of 92% presented the highest oil efficiency of 11g/100g dry weight of substrate. The semi-solid process is shown to have certain advantages compared to liquid cultures or solid-state fermentation and gives oil of high quality. [Copyright &y& Elsevier]

Abstract: The strategy of alternative prey (switching), regulated by a catabolic repression control-like (CRCL) mode, in which the desirable prey acts as repressor on the predator''s attack on the alternative prey, was studied in a two-prey–one-predator chemostat system. In this system, alternative prey has to survive predation and competition for nutrients from the desirable prey. Therefore, when the alternative prey has no competitive advantage for the common substrate over the desirable prey, its survival depends on the protection offered by the desirable prey via CRCL. In this case, CRCL allows the coexistence of both desirable and alternative prey and predator populations. However, when the alternative prey has the competitive advantage over the desirable prey, CRCL negatively affects both the state of survival of the desirable prey and the coexistence state. [Copyright &y& Elsevier]

Biodegradation in porous media is studied with carefully controlled and well-characterized experiments in model porous media constructed of etched glass. Porous media of this type allow visual observation of the phenomena that take place at pore scale. An aqueous solution of five organic pollutants (toluene, phenol, o-cresol, naphthalene and 1,2,3-trimethylbenzene) was used as a model NAPL (representing creosote). The bacteria used were Pseudomonas fluorescens, which are indigenous (even predominant) in many contaminated soils. The maximum aqueous concentrations of the specific organic substances, below which biodegradation becomes possible, were determined as a function of temperature from toxicity experiments. Visualization experiments were made under various flow velocities and organic loadings to study the morphology and thickness of the biofilm as a function of the pore size and the distance from the entrance, and the efficiency of biodegradation. The efficiency of biodegradation decreased as the aqueous concentration of NAPL at the inlet increased and/or as the flow velocity increased. The thickness of biofilm decreased as the distance from the inlet increased and/or the pore diameter decreased. A quasi-steady-state theoretical model of biodegradation was used to calculate the values of the mesoscopic biochemical rates and to predict the profile of NAPL concentration in the porous medium and the thickness of biofilm in pores. The agreement between experimental data and model predictions is quite satisfactory. [Copyright &y& Elsevier]