Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Continuous bioscorodite crystallization in CSTRs for arsenic removal and disposal
Gonzalez-Contreras, P.A. ; Weijma, J. ; Buisman, C.J.N. - \ 2012
Water Research 46 (2012)18. - ISSN 0043-1354 - p. 5883 - 5892.
ferrous iron oxidation - low ph - scorodite - precipitation - solubility - kinetics - batch
In CSTRs, ferrous iron was biologically oxidized followed by crystallization of scorodite (FeAsO4·2H2O) at pH 1.2 and 72 °C. The CSTRs were fed with 2.8 g L-1 arsenate and 2.4 g L-1 ferrous and operated at an HRT of 40 h, without seed addition or crystal recirculation. Both oxidation and crystallization were stable for periods up to 200 days. The arsenic removal efficiency was higher than 99% at feed Fe/As molar ratios between 1 and 2, resulting in effluents with 29 ± 18 mg As L-1. Arsenic removal decreased to 40% at feed Fe/As molar ratios between 2 and 5. Microorganisms were not affected by arsenic concentrations up to 2.8 g As5+ L-1. The bioscorodite solid yield was 3.2 g/g arsenic removed. Bioscorodite crystals precipitated as aggregates, causing scaling on the glass wall of the reactor. The observed morphology through SE microscopy of the precipitates appeared amorphous but XRD analysis confirmed that these were crystalline scorodite. Arsenic leaching of bioscorodite was 0.4 mg L-1 after 100 days under TCLP conditions, but when jarosite had been co-precipitated leaching was higher at 0.8 g L-1. The robustness of the continuous process, the high removal efficiency and the very low arsenic leaching rates from bioscorodite sludge make the process very suitable for arsenic removal and disposal.
Modeling lipid accumulation in oleaginous fungi in chemostatcultures. II: Validation of the chemostat model using yeast culturedata from literature
Meeuwse, P. ; Tramper, J. ; Rinzema, A. - \ 2011
Bioprocess and Biosystems Engineering 34 (2011)8. - ISSN 1615-7591 - p. 951 - 961.
stage continuous-culture - gamma-linolenic acid - rhodotorula-glutinis - apiotrichum-curvatum - candida-curvata - growth-rate - oxygen - batch
A model that predicts cell growth, lipid accumulation and substrate consumption of oleaginous fungi in chemostat cultures (Meeuwse et al. in Bioproc Biosyst Eng. doi: 10.1007/s00449-011-0545-8 , 2011) was validated using 12 published data sets for chemostat cultures of oleaginous yeasts and one published data set for a poly-hydroxyalkanoate accumulating bacterial species. The model could describe all data sets well with only minor modifications that do not affect the key assumptions, i.e. (1) oleaginous yeasts and fungi give the highest priority to C-source utilization for maintenance, second priority to growth and third priority to lipid accumulation, and (2) oleaginous yeasts and fungi have a growth rate independent maximum specific lipid production rate. The analysis of all data showed that the maximum specific lipid production rate is in most cases very close to the specific production rate of membrane and other functional lipids for cells growing at their maximum specific growth rate. The limiting factor suggested by Ykema et al. (in Biotechnol Bioeng 34:1268-1276, 1989), i.e. the maximum glucose uptake rate, did not give good predictions of the maximum lipid production rate
Enhanced Productivity of a Lutein-Enriched Novel Acidophile Microalga Grown on Urea
Casal, C. ; Cuaresma, M. ; Vega, J.M. ; Vilchez, C. - \ 2011
Marine Drugs 9 (2011)1. - ISSN 1660-3397 - p. 29 - 42.
spirulina-platensis - nitrogen-sources - macular disease - chlorella - nitrate - batch - cultivation - scenedesmus - ammonium - biomass
Coccomyxa acidophila is an extremophile eukaryotic microalga isolated from the Tinto River mining area in Huelva, Spain. Coccomyxa acidophila accumulates relevant amounts of b-carotene and lutein, well-known carotenoids with many biotechnological applications, especially in food and health-related industries. The acidic culture medium (pH <2.5) that prevents outdoor cultivation from non-desired microorganism growth is one of the main advantages of acidophile microalgae production. Conversely, acidophile microalgae growth rates are usually very low compared to common microalgae growth rates. In this work, we show that mixotrophic cultivation on urea efficiently enhances growth and productivity of an acidophile microalga up to typical values for common microalgae, therefore approaching acidophile algal production towards suitable conditions for feasible outdoor production. Algal productivity and potential for carotenoid accumulation were analyzed as a function of the nitrogen source supplied. Several nitrogen conditions were assayed: nitrogen starvation, nitrate and/or nitrite, ammonia and urea. Among them, urea clearly led to the best cell growth (~4 ´ 108 cells/mL at the end of log phase). Ammonium led to the maximum chlorophyll and carotenoid content per volume unit (220 mg·mL-1 and 35 mg·mL-1, respectively). Interestingly, no significant differences in growth rates were found in cultures grown on urea as C and N source, with respect to those cultures grown on nitrate and CO2 as nitrogen and carbon sources (control cultures). Lutein accumulated up to 3.55 mg·g-1 in the mixotrophic cultures grown on urea. In addition, algal growth in a shaded culture revealed the first evidence for an active xanthophylls cycle operative in acidophile microalgae
Effect of inoculum addition modes and leachate recirculation on anaerobic digestion of solid cattle manure in an accumulation system
El-Mashad, H.M. ; Loon, W.K.P. van; Zeeman, G. ; Bot, G.P.A. ; Lettinga, G. - \ 2006
Biosystems Engineering 95 (2006)2. - ISSN 1537-5110 - p. 245 - 254.
waste - landfill - fermentation - temperature - degradation - biowaste - batch
The effect of both leachate recirculation (at 40 and 50 °C) and the mode of inoculum addition (at 50 °C) on the performance of a non-mixed accumulation (i.e. fed batch) system treating solid cattle wastes was investigated, using laboratory scale reactors at a filling time of 60 days. A relatively high methane production rate (MPR) and low stratification of intermediates occur with leachate recirculation. The leachate recirculation volume flow and methane production rate are smaller at 40 °C than at 50 °C: 0·31 and 0·7 l [CH4] l¿1 [reactor] day¿1, respectively. The increased MPR at higher temperature is at one hand caused by the increase of microbial activity, at the other hand by the lower viscosity causing the increased leachate recirculation volume. Dividing the inoculum in equal doses and distributing them with the feed positively affects the system behaviour as compared to adding the same inoculum amount at the reactor bottom at the start only. Without addition of inoculum a very poor system performance was observed. The average MPR was 0·2, 0·4 and 0·5 l [CH4] l¿1 [reactor] day¿1 for the reactor without inoculum, inoculum addition at the reactor bottom and inoculum addition in different equal doses, respectively.
Statistical evaluation of mathematical models for microbial growth
Lopez, S. ; Prieto, M. ; Dijkstra, J. ; Dhanoa, M.S. ; France, J. - \ 2004
International Journal of Food Microbiology 96 (2004)3. - ISSN 0168-1605 - p. 289 - 300.
predictive food microbiology - viable count data - bacterial-growth - nonlinear-regression - equation - curves - cultures - enough - batch - rates
The aim of this study was to evaluate the suitability of several mathematical functions for describing microbial growth curves. The nonlinear functions used were: three-phase linear, logistic, Gompertz, Von Bertalanffy, Richards, Morgan, Weibull, France and Baranyi. Two data sets were used, one comprising 21 growth curves of different bacterial and fungal species in which growth was expressed as optical density units, and one comprising 34 curves of colony forming units counted on plates of Yersinia enterocolitica grown under different conditions of pH, temperature and CO2 (time-constant conditions for each culture). For both sets, curves were selected to provide a wide variety of shapes with different growth rates and lag times. Statistical criteria used to evaluate model performance were analysis of residuals (residual distribution, bias factor and serial correlation) and goodness-of-fit (residual mean square, accuracy factor, extra residual variance F-test, and Akaike's information criterion). The models showing the best overall performance were the Baranyi, three-phase linear, Richards and Weibull models. The goodness-of-fit attained with other models can be considered acceptable, but not as good as that reached with the best four models. Overall, the Baranyi model showed the best behaviour for the growth curves studied according to a variety of criteria. The Richards model was the best-fitting optical density data, whereas the three-phase linear showed some limitations when fitting these curves, despite its consistent performance when fitting plate counts. Our results indicate that the common use of the Gompertz model to describe microbial growth should be reconsidered critically, as the Baranyi, three-phase linear, Richards and Weibull models showed a significantly superior ability to fit experimental data than the extensively used Gompertz
Modelling anaerobic biomass growth kinetics with a substrate threshold concentration
Ribes, J. ; Keesman, K.J. ; Spanjers, H. - \ 2004
Water Research 38 (2004)20. - ISSN 0043-1354 - p. 4502 - 4510.
geactiveerd slib - afvalwaterbehandeling - biomassa - substraten - kinetica - modellen - activated sludge - waste water treatment - biomass - substrates - kinetics - models - activated-sludge - waste-water - continuous-culture - methanol - batch
Abstract Many bacteria have been observed to stop growing below a certain substrate threshold concentration. In this study, a modification of the Monod kinetics expression has been proposed to take into account this substrate threshold concentration observed in bacterial growth. Besides the threshold concentration no additional parameters have been added to the kinetic expression and so, only the substrate threshold concentration and the half-saturation constant have to be estimated for model calibration purposes. Furthermore, for parameter estimation purposes, practical identifiability of this new function has been studied and the results have been satisfactory. The new model has been applied, as an example, to a simple anaerobic model to simulate the competition for hydrogen between sulphate reducers and methanogens in a thermophilic methanol-fed bioreactor. Oscillatory behaviour and mathematical instabilities have been avoided by using the proposed model. Parameter sensitivities have also been calculated along the simulation period in order to investigate the importance of hydrogen threshold concentration parameters.
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