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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A regional benthic fauna assessment method for the Southern North Sea using Margalef diversity and reference value modelling
Loon, Willem M.G.M. van; Walvoort, Dennis J.J. ; Hoey, Gert van; Vina-Herbon, Christina ; Blandon, Abigayil ; Pesch, Roland ; Schmitt, Petra ; Scholle, Jörg ; Heyer, Karin ; Lavaleye, Marc ; Phillips, Graham ; Duineveld, Gerard C.A. ; Blomqvist, Mats - \ 2018
Ecological Indicators 89 (2018). - ISSN 1470-160X - p. 667 - 679.
AMBI - Benthic assessment method - Fishing pressure - Index - ITI - Margalef diversity - Marine benthos - MMI - Model - MSFD - Multi-metric index - Organic enrichment - OSPAR - PIE - Reference value estimation - Sedimentation - Shannon index - SN - SNA - Species richness
The aims of this study are to develop an optimized method for regional benthic fauna assessment of the Southern North Sea which (a) is sensitive and precise (quantified as the slope and the R2 value of the pressure-impact relationships, respectively) for the anthropogenic pressures bottom fishing and organic enrichment, (b) is suitable for estimating and modelling reference values, (c) is transparent, (d) can be efficiently applied using dedicated software; and to apply this method to benthic data from the Southern North Sea. Margalef diversity appeared to be the best performing benthic index regarding these criteria, even better than several Multi-Metric Indices (MMIs) containing e.g. AMBI (AZTI Marine Biotic Index) and ITI (Infaunal Trophic Index). Therefore, this relatively simple and very practical index, including a new reference value estimation and modelling method, and BENMMI software were selected as a common OSPAR (Oslo Paris convention) method for the benthic fauna assessment of the Southern North Sea. This method was applied to benthic fauna data from the Southern North Sea collected during the period 2010–2015. The results in general show lower normalized Margalef values in coastal areas, and higher normalized Margalef values in deeper offshore areas. The following benthic indices were compared in this study: species richness, Margalef diversity, SNA index, Shannon index, PIE index, AMBI, ITI. For each assessment area, the least disturbed benthic dataset was selected as an adjacent 6 year period with, on average, the highest Margalef diversity values. For these datasets, the reference values were primarily set as the 99th percentile values of the respective indices. This procedure results in the highest stable reference values that are not outliers. In addition, a variable percentile method was developed, in which the percentile value is adjusted to the average bottom fishing pressure (according to data from the International Council for the Exploration of the Sea, ICES) in the period 2009–2013. The adjusted percentile values were set by expert judgement, at 75th (low fishing pressure), 95th (medium fishing pressure) and 99th (high fishing pressure) percentile. The estimated reference values for Margalef diversity correlate quite well with the median depth of the assessment areas using a sigmoid model (pseudo-R2 = 0.86). This relationship between depth and Margalef diversity was used to estimate reference values in case an assessment area had insufficient benthic data For testing the effects of bottom fishing pressure, normalized index values (NIV; index value divided by reference value) were used. The rationale for using NIVs is the assumption that, although a certain level of bottom fishing pressure will have a larger absolute effect on more biodiverse benthic communities in deeper waters than on more robust and less biodiverse coastal benthic communities, the relative effects (tested using NIVs) are comparable. A clear exponentially decreasing relationship (R2 = 0.26–0.27, p < 0.00001) was found between both bottom surface and subsurface fishing activity (penetration depth <2 cm and >2 cm, respectively) and normalized Margalef diversity values, with an asymptotic normalized Margalef value of 0.45 at a subsurface fishing activity >2.3 sweeps/year. This asymptotic value is predominantly found in coastal waters, and probably shows that the naturally more robust coastal benthic communities have been transformed into resilient benthic communities, which rapidly recover from increasing fishing pressure.
Application of the Benthic Ecosystem Quality Index 2 to benthos in Dutch transitional and coastal waters
Loon, W.M.G.M. van; Boon, A.R. ; Gittenberger, A. ; Walvoort, D.J.J. ; Lavaleye, M. ; Duineveld, G.C.A. ; Verschoor, A.J. - \ 2015
Journal of Sea Research 103 (2015). - ISSN 1385-1101 - p. 1 - 13.
Benthic invertebrates - BEQI2 - Dutch transitional and coastal waters - Multi-metric index - Water framework directive

The Benthic Ecosystem Quality Index 2 (BEQI2) is the Dutch multi-metric index (MMI) for assessing the status and trend of benthic invertebrates in transitional and coastal waters for the Water Framework Directive (WFD). It contains the same indicators, i.e. species richness, Shannon index and AMBI, as in the multivariate m-AMBI. The latter MMI has been adopted by several European countries in the context of WFD implementation. In contrast to m-AMBI, the BEQI2 calculation procedure has been strongly simplified and consists of two steps, i.e. the separate indicator values are normalized using their long-term reference values resulting in three Ecological Quality Ratios (EQRs), which are subsequently averaged to give one BEQI2 value. Using this method only small numbers of samples need to be analysed by Dutch benthos laboratories annually, without the necessity to co-analyse a larger historical dataset. BEQI2 EQR values appeared to correlate quantitatively very well with m-AMBI EQR values. In addition, a data pooling procedure has been added to the BEQI2 tool which enables the pooling of small core samples (0.01-0.025m2) into larger standardized data pools of 0.1m2 in order to meet the data requirements of the AMBI indicator and to obtain comparable reference values. Furthermore, the BEQI2 tool automatically and efficiently converts species synonym names into standardized species names. The BEQI2 tool has been applied to all Dutch benthos data monitored by Rijkswaterstaat in the period of 1991-2010 in the transitional and coastal waters and salt lakes and these results are reported here for the first time. Reference values for species richness and Shannon index (99 percentile values) and AMBI reference values (1 percentile values) were estimated for all water body-ecotopes and are discussed. BEQI2 results for all these water bodies are discussed in view of natural and human pressures. The pressure sensitivity of the BEQI2 for sewage and dredging/dumping, via the state variables oxygen and suspended matter respectively, was demonstrated.

Extending potential flow modelling of flat-sheet geometries as applied in membrane-based systems
Dirkse, M.H. ; Loon, W.K.P. van; Stigter, J.D. ; Post, J.W. ; Veerman, J. ; Bot, G.P.A. - \ 2008
Journal of Membrane Science 325 (2008)2. - ISSN 0376-7388 - p. 537 - 545.
reverse electrodialysis - mass-transport - power - energy
Abstract The efficiency of chemical reactors can be analysed using the residence time distribution. This research focusses on flat-sheet geometries applied in membrane-based systems. The residence time distribution depends mainly on the 2D velocity field, parallel to the membrane. The velocity average over the transversal direction is calculated using potential flow theory. A combination of real and virtual sources and sinks are used to model the internal inlets and outlets. Furthermore, a novel method is presented to calculate the residence time distribution. By ignoring diffusion and dispersion, every streamline is modelled to have a fixed residence time, which can be calculated with a simple quadrature based on a coordinate transformation. The model predicts the impact of the two-dimensional geometry on the residence time distribution, but it is demonstrated that large zones of nearly stagnant flow have only a limited impact on the residence time distribution. The new model can predict the travelling time from the inlet to each interior location, providing a better tool to analyse spatially distributed chemical reactions. The models agreed highly with pressure measurements (R2 = 0.94¿0.98) and they agreed well with tracer experiments for the residence time (R2 = 0.73¿0.99).
Modelling of natural-convection driven heat exchangers
Dirkse, M.H. ; Loon, W.K.P. van; Stigter, J.D. ; Bot, G.P.A. - \ 2007
In: Agricontrol 2007 Proceedings of the 2nd IFAC Intern. Conf. on Modeling and Design of Control Systems in Agriculture, Osijek, Croatia, 3 - 5 September, 2007. - Osijek : IFAC - p. 47 - 52.
Abstract: A lumped model is developed for shell-and-tube heat exchangers driven by natural convection, which is based on a one-dimensional approximation. The heat flux is driven by the logarithmic mean temperature difference. The volumetric air flow rate is driven by the buoyant force. Based on the Boussinesq aproximation, this force is characterised by an analytic expression of the inflow and outflow temperatures. The lumped model is finished by relating the buoyant force to the friction force via the drag coefficient. The model was calibrated and validated based on Computational Fluid Dynamics calculations and physical measurements.
Site influence on wind induced pressure distribution on a dairy house
Loon, W.K.P. van; Ooster, A. van 't; Dekker, E. - \ 2007
In: Agricontrol 2007 Proceedings of the 2nd IFAC Intern. Conf. on Modeling and Design of Control Systems in Agriculture, Osijek, Croatia, 3 - 5 September, 2007. - Osijek : - p. 83 - 89.
Abstract: Numerical CFD experiments were performed on dairy cow house ¿Ossekampen¿ of Wageningen University to investigate the influences of surrounding buildings and wind direction on pressure distribution on the building envelope and on wind induced ventilation rate. A qualitative verification of air flow patterns was performed with smoke experiments. East of the cow house some adjacent buildings were present. With east wind, a clear wind `shadow¿ was found as a projection of the two buildings NE of the cow house. This shadow shifts with the wind direction.
Understanding heat transfer in 2D channel flows including recirculation
Dirkse, M.H. ; Loon, W.K.P. van; Stigter, J.D. ; Bot, G.P.A. - \ 2007
International Journal of Thermal Sciences 46 (2007)7. - ISSN 1290-0729 - p. 682 - 691.
comprehensive approach - cfd simulations - verification - validation - convection
Inviscid, irrotational two-dimensional flows can be modelled using the Schwarz¿Christoffel integral. Although bounded flows including boundary layer separation and recirculation are not irrotational, a model is presented that uses the Schwarz¿Christoffel integral to model these flows. The model separates the flow domain in the main flow area, where irrotational flow is assumed, and recirculation areas, which are modelled as monopolar vortices. The model has unknown parameters, which are geometric characteristics of the velocity field. The method is demonstrated on a channel with alternating baffles. Many variations of this system were modelled using CFD modelling, and the flow was a typical combination of main flow and recirculation. The CFD results were used as reference to calibrate the parameters of the Schwarz¿Christoffel model. Many parameters appeared to be constant, and calibrating only three variable parameters yielded about 22% error for most velocity fields. After this, heat transfer was added to the CFD models, and the heat flux was analysed using the three variable parameters representing the velocity field. This way, a new model is found for the heat flux from a wall bounding a vortex, which has an error of 7%. Finally, we have calibrated the parameters using a limited number of given velocity vectors, demonstrating that the parameters can be calibrated against a real set of measurements.
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.
Measuring thermal conductivity in freezing and thawing soil using the soil temperature response to heating
Overduin, P. ; Kane, D.L. ; Loon, W.K.P. van - \ 2006
Cold Regions Science and Technology 45 (2006)1. - ISSN 0165-232X - p. 8 - 22.
frozen soils - active-layer - probe - model
The thermal conductivity of the thin seasonally freezing and thawing soil layer in permafrost landscapes exerts considerable control over the sensitivity of the permafrost to energy and mass exchanges at the surface. At the same time, the thermal conductivity is sensitive to the state of the soil, varying, for example, by up to two orders of magnitude with varying water contents. In situ measurement techniques perturb the soil thermally and are affected by changes in soil composition, for example through variations in thermal contact resistance between sensor and soil. The design of a sensor for measuring the temperature of the soil rather than the axial heating wire temperature has consequences for the modeling of heat flow. We introduce an approximation of heat flow from a heated cylinder with thermal contact resistance between the cylinder and the surrounding medium. This approximation is compared to the standard line source approximation, and both are applied to data measured over a one-year period in northern Alaska. Comparisons of thermal conductivity values determined numerically using the line source solution, line source approximation and the analytical form of the heated cylinder model fall within 10% of accepted values, except for measurements made in pure ice, for which all methods of calculation under-predicted the thermal conductivity. Field data collected from a complete freeze¿thaw cycle in silty clay show a seasonally bimodal apparent thermal conductivity, with a sharp transition between frozen and thawed values during thaw, but a three-month transition period during freezing. The use of soil composition data to account for changes in heat flow due to the effect of latent heat during phase change results in a relationship between soil thermal conductivity and temperature.
A computational fluid dynamics model for designing heat exchangers based on natural convection
Dirkse, M.H. ; Loon, W.K.P. van; Walle, T. van der; Speetjens, S.L. ; Bot, G.P.A. - \ 2006
Biosystems Engineering 94 (2006)3. - ISSN 1537-5110 - p. 443 - 452.
finite-volume method - greenhouses
A computational fluid dynamics model was created for the design of a natural convection shell-and-tube heat exchanger with baffles. The flow regime proved to be turbulent and this was modelled using the k¿¿ turbulence model. The features of the complex geometry were simplified considerably resulting in an almost two-dimensional mesh with only 30 000 mesh cells. The effect of black-body radiation was investigated. The modelling results were validated experimentally and a model neglecting the effect of radiation turned out to be sufficiently accurate, reducing calculation times with a factor 60. Different meshes were used to check that the solution did not depend on the mesh chosen. The measurements indicated that the cross-flow caused by the baffles improved the heat-flux dramatically. The heat exchanger in this case study was intended to be used in an experimental greenhouse. The usefulness of the heat exchanger model was demonstrated by applying it to relevant variations of the experimental arrangements. The model calculations resulted in many recommendations on the dimensions and the operation of the heat exchanger.
Simulation of oxygen regime of tree substrates
Balakina, J.N. ; Makarova, O.V. ; Bondarenko, V. ; Koudstaal, L.J. ; Ros, E.J. ; Koolen, A.J. ; Loon, W.K.P. van - \ 2005
Urban Forestry and Urban Greening 4 (2005)1. - ISSN 1618-8667 - p. 23 - 35.
The oxygen regime of urban tree-growing sites may be sub-optimal for tree growth and the related ornamental value of trees. Problems may especially occur in situations where the substrate is covered by pavement and/or where the water table is very shallow. The stability (oxygen consumption rate) of the organic components of the substrate (peat, green waste compost, etc.) and the design of the growing site also play an important role. The oxygen regime of a number of designs (wide strip of substrate; narrow strip; wide strip with multiple aeration pipes; narrow strip with one aeration pipe) was simulated for a range of substrates with the computer program ¿Matlab, pde toolbox¿. The program computed equilibrium distributions of oxygen in the substrates from gas diffusion coefficients of the different parts of the growing site constructions and from the specific oxygen consumption rate of the substrate. The simulation results were compared with measurements on an experimental substrate strip. The simulation results clearly showed the importance of organic matter stability and growing site design. On wide strips the presence of aeration pipes may be very advantageous, or even necessary.
Rheological properties of dairy cattle manure
El-Mashad, H.M. ; Loon, W.K.P. van; Zeeman, G. ; Bot, G.P.A. ; Lettinga, G. - \ 2005
Bioresource Technology 96 (2005)5. - ISSN 0960-8524 - p. 531 - 535.
waste slurries - anaerobic-digestion - model
Rheological properties are important for the design and modelling of handling and treating fluids. In the present study, the viscosity of liquid manure (about 10% total solids) was measured at different shear rates (2.38¿238 s¿1). The effect of temperature on the viscosity at different shear rates was also studied. The results showed that manure has non-Newtonian flow properties, because the viscosity strongly depended on the applied shear rate. The results showed also that manure behaves like real plastic materials. The power-law model of the shear stress and the rate of shear showed that the magnitude of the consistency coefficient decreased while increasing the temperature, with high values of the determination coefficient. Moreover, the results showed that the Arrhenius-type model fitted the temperature effect on manure viscosity very well (R2 at least 0.95) with calculated activation energy of 17.0 ± 0.3 kJ mol¿1
A dispersion based model for anaerobic digestion of solid cattle waste in a stratified thermophillic accumulation system
El-Mashad, H.M. ; Loon, W.K.P. van; Zeeman, G. ; Bot, G.P.A. ; Lettinga, G. - \ 2005
Water Science and Technology 52 (2005)1-2. - ISSN 0273-1223 - p. 195 - 202.
water treatment - simulation - state
A dynamic model has been developed to describe the anaerobic digestion of solid cattle waste in an accumulation system (AC), To calibrate the model an experiment was carried out at a lab-scale AC at 50 degrees C. The predicted methane production shows a very good agreement (i.e. R-2 = 0.998) with the experimental data. However less agreement is evident for the intermediates. After model validation the model was applied to study the effect of different aspect ratios on the system performance. An optimum aspect ratio of 2-3 could be determined.
Sorption isotherms, GAB parameters and isosteric heat of sorption
Quirijns, E.J. ; Boxtel, A.J.B. van; Loon, W.K.P. van; Straten, G. van - \ 2005
Journal of the Science of Food and Agriculture 85 (2005)11. - ISSN 0022-5142 - p. 1805 - 1814.
moisture sorption - water sorption - desorption isotherms - dehydrated foods - temperature - equation - thermodynamics - adsorption - products - starch
The diffusion-sorption drying model has been developed as a physics-based way to model the decreasing drying rate at low moisture contents. This new model is founded on the existence of different classes of water: free and bound water. The transition between these classes and the corresponding thermodynamics form distinct components of the drying model. This paper shows that the characteristics of the different classes of water and of the transition between them can be deduced from the GAB sorption isotherm. The parameters in the GAB sorption isotherm support the theory of localised sorption, establishing the existence of different classes of water. Moreover, the sorption mechanism retrieved from the GAB parameters is in accordance with the sorption mechanism, which is obtained from the moisture dependence of the net isosteric heat of sorption. This holds for experimental sorption data of corn and starch as well as for literature data on five vegetables and four fortified cassava products. An extremum in the net isosteric heat of sorption coincides with the transition between bound and free water, and the partition moisture content corresponds with the monolayer value derived from the GAB equation. This confirms that the GAB monolayer value can be chosen as model boundary between bound and free water. Moreover, it reveals that this method can be developed into a technique to estimate the bound water content in foods.
A simple model for obstructed two-dimensional turbulent channel flow
Dirkse, M.H. ; Loon, W.K.P. van; Stigter, J.D. - \ 2005
We have investigated obstructed two-dimensional turbulent channel flow. The objective is to provide a simple building block for design models and to gain physical insight in this type of flow. We have designed a simple model with some unknown parameters to be calibrated against a CFD model. The model divides the domain between an area of main flow and recirculation areas. The model approximates these areas by polygonal shapes. The locations of the vertices of these polygons are the parameters in the model. This way, we can evaluate the simple model using the Schwarz-Christoffel integral. As a consequence, the model can be evaluated much more quickly than CFD models. The main flow is modeled to be irrotational. The recirculation area behind the obstacle is modeled as a stretched monopolar vortex and this requires 4 extra parameters. The other areas of separated flow are simply modeled to be stationary. By calibrating the simple model we have demonstrated that this physical description works reasonably well. Using only 9 parameters, the simple model reaches an error of 22\\% of the inflow velocity.
An improved experimental and regression methodology for sorption isotherms
Quirijns, E.J. ; Boxtel, A.J.B. van; Loon, W.K.P. van; Straten, G. van - \ 2005
Journal of the Science of Food and Agriculture 85 (2005)2. - ISSN 0022-5142 - p. 175 - 185.
equilibrium moisture-content - water activity - 3 temperatures - desorption - equations - products - fruit - foods - seeds - fufu
Sorption isotherms of corn and starch cylinders with immobilised catalase are experimentally determined at different temperatures for use in drying models in optimal control studies. This application of the sorption isotherm requires an accurate prediction of the sorption data at different temperatures for the low water activity range. The GAB equation is used for the prediction of the sorption isotherms. Two major problems are encountered by employing standard procedures, ie prediction of sorption at aw <0.11 and sensitivity of the GAB parameters to the applied data range. An improved methodology is developed, consisting of extending the standard experimental procedure with additional data points in the low water activity range and changing the criterion in the regression procedure in the sum of squares, which is weighed by the variance of the experimental data. The new methodology leads to accurate, consistent and physically relevant parameters of the GAB equation, which are independent of the applied data range in the regression analysis and which result in accurate predictions of the sorption behaviour at low water activity. The sorption data at different temperatures at low water activity can be predicted in the best way with parameters obtained after direct regression based on weighed SSQ.
Effect of temperature and temperature fluctuation on thermophilic anaerobic digestion of cattle manure
Mashad, H. El; Zeeman, G. ; Loon, W.K.P. van; Bot, G.P.A. ; Lettinga, G. - \ 2004
Bioresource Technology 95 (2004)2. - ISSN 0960-8524 - p. 191 - 201.
methane production - biogas plants - ammonia - waste - inhibition - retention - toxicity - nitrogen - state
The influence of temperature, 50 and 60 °C, at hydraulic retention times (HRTs) of 20 and 10 days, on the performance of anaerobic digestion of cow manure has been investigated in completely stirred tank reactors (CSTRs). Furthermore, the effect of both daily downward and daily upward temperature fluctuations has been studied. In the daily downward temperature fluctuation regime the temperatures of each reactor was reduced by 10 °C for 10 h while in the daily upward fluctuation regime the temperature of each reactor was increased 10 °C for 5 h. The results show that the methane production rate at 60 °C is lower than that at 50 °C at all experimental conditions of imposed HRT except when downward temperature fluctuations were applied at an HRT of 10 days. It also was found that the free ammonia concentration not only affects the acetate-utilising bacteria but also the hydrolysis and acidification process. The upward temperature fluctuation affects the maximum specific methanogenesis activity more severely as compared to imposed downward temperature fluctuations. The results clearly reveal the possibility of using available solar energy at daytime to heat up the reactor(s) without the need of heat storage during nights, especially at an operational temperature of 50 °C and at a 20 days HRT, and without the jeopardising of the overheating.
Experiment and modelling of parameters influencing natural wind drying of willow chunks
Gigler, J.K. ; Loon, W.K.P. van; Sonneveld, C. - \ 2004
Biomass and Bioenergy 26 (2004)6. - ISSN 0961-9534 - p. 507 - 514.
energy - stems - chips
The objective of this study was to investigate the parameters that govern the drying process of willow chunks. Indicative chunk drying trials were conducted to assess the potential of natural wind drying. Supportive model simulations were conducted to gain insight into the influence of different process parameters (particle size, pile depth) on drying. Natural wind drying experiments showed that willow chunks could be dried from 50% (wet basis) to around 10% within 5 months. Internal heating in the pile did not occur and dry matter losses were reasonably low (3.5-5%). The drying time of willow chunks depended on drying air conditions, particle size and pile dimensions (depth). The particle size of chunks should be large enough to create a low airflow resistance in the pile, but small enough to avoid that internal diffusion of moisture limits the drying process.
Design of A solar Thermophilic Anaerobic Reactor for Small Farms
Mashad, H. El; Loon, W.K.P. van; Zeeman, G. ; Bot, G.P.A. ; Lettinga, G. - \ 2004
Biosystems Engineering 87 (2004)3. - ISSN 1537-5110 - p. 345 - 353.
energy - digestion - simulation - system - waste - temperature - manure
A 10 m(3) completely stirred tank reactor has been designed for anaerobic treatment of liquid cow manure under thermophilic conditions (50degreesC), using a solar heating system mounted on the reactor roof. Simulation models for two systems have been developed. The first system consists of loose components and in the second system the components are integrated. Each of the two systems includes a heat recovery unit to heat the influent by extracting heat from the effluent. The integrated system includes an extra chamber for the pumps and the heat recovery unit, which are in the same insulating cover as the reactor and the solar collector. The control system is based on simple on/off strategy. An auxiliary heater, operated with the produced biogas, can be used during cold months. The measured and calculated design parameters are presented. The simulation results show that the temperature fluctuation of the reactor during the night is less than VC, which is too small to harm the microbial activity. The results show that an annual net thermal energy production and overall annual energy efficiency of 100 and 95%, respectively, could be obtained from the integrated system. (C) 2003 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd.
Reuse potential of agricultural wastes in semi-arid regions: Egypt as a case study
Mashad, H. El; Loon, W.K.P. van; Zeeman, G. ; Bot, G.P.A. ; Lettinga, G. - \ 2003
Reviews in Environmental Science & Bio-technology 2 (2003)1. - ISSN 1569-1705 - p. 53 - 66.
Agricultural wastes represent an important source of bio-energy and valuable products. In Egypt, 18% of the agricultural wastes is used directly as fertiliser. Another 30% is used as animal food. The remainder is burnt directly on the fields or is used for heating in the small villages, using low efficiency burners. These wastes can be used more efficiently as a source of energy and as organic fertiliser. The anaerobic bioconversion of these materials will result in a net energy production. The utilisation of agricultural wastes for the production of energy and compost, combined with using solar energy will save fossil fuel, improve health conditions and the general life quality in the villages.
Anaerobic digestion of solid animal waste in an accumulation system at mesophilic and thermophilic conditions, start up
Mashad, H. El; Zeeman, G. ; Loon, W.K.P. van; Bot, G.P.A. ; Lettinga, G. - \ 2003
Water Science and Technology 48 (2003)4. - ISSN 0273-1223 - p. 217 - 220.
The anaerobic digestion of solid animal wastes has been studied in an accumulation system (AC) at a filling time of 60 days followed by about 50 days batch digestion at 40 and 50degreesC. Poor mixing conditions during anaerobic digestion of solid wastes promote stratification of the substrate and intermediate products along the reactor height. The effect of layers stratification has also been followed in the AC system. The results showed a pronounced stratification of both CODdis and VFA concentrations along the AC system height. The temperature had a minor effect on the methane yield. The results also showed that methanogenesis was rate limiting in the AC system while the hydrolysis was the rate-limiting step during batch digestion.
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