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.

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From first to last bite: Temporal dynamics of sensory and hedonic perceptions using a multiple-intake approach
Bommel, Roelien van; Stieger, Markus ; Boelee, Nicole ; Schlich, Pascal ; Jager, G. - \ 2019
Food Quality and Preference 78 (2019). - ISSN 0950-3293
Composite food - Multiple-intake assessment - Temporal Dominance of Sensations (TDS) - Temporal drivers of liking (TDL)

Sensory perceptions evolve over time. Evaluation of sensory and hedonic perceptions after one bite are common. However, single bite assessments do not represent normal eating behaviour as consumers eat food portions with multiple bites. We hypothesise that dynamics of sensations and hedonics not only evolve within a bite but also evolve over bites. This study aims to investigate the temporal dynamics of sensations and hedonic perceptions using multiple-intake assessment employing Temporal Dominance of Sensations (TDS) and Alternated Temporal Drivers of Liking (A-TDL). Seventy-six participants evaluated six yogurts with granola pieces varying in size, hardness and concentration. An attentional shift was observed from yogurt attributes (creamy and sour) in the beginning of each mouthful to granola attributes (sweet, wheat and sticky) at the end of each mouthful. Sticky sensations gradually increased in dominance duration from the first to the fifth mouthful for five of six yogurts demonstrating the built up of dominance of this attribute. Creamy, crunchy and sweet were observed to be positive drivers of liking, consequently increasing liking. Sour and sticky were negative drivers of liking, decreasing liking upon dominance of these attributes. We conclude that consumer's sensory perception of food products changes from bite to bite. Our findings indicate that multiple-intake evaluations of dynamic sensations provide additional information about food perception, such as the built up of sensations from bite to bite. These changes in sensations cannot be captured by single bite assessments.

Identifying barriers and levers of biodiversity mainstreaming in four cases of transnational governance of land and water
Karlsson-Vinkhuyzen, S.I.S.E. ; Boelee, E. ; Cools, J. ; Hoof, L.J.W. van; Hospes, O. ; Kok, M. ; Peerlings, J.H.M. ; Tatenhove, J.P.M. van; Termeer, C.J.A.M. ; Visseren-Hamakers, I.J. - \ 2018
Environmental Science & Policy 85 (2018). - ISSN 1462-9011 - p. 132 - 140.
Biodiversity - Mainstreaming - Integration - Values-based leadership - Governance - Certification - Economic sectors - Fisheries - Palm Oil - FDI - Land - Mangroves
Mainstreaming biodiversity into the governance of economic sectors such as agriculture, forestry and fisheries is required to reverse biodiversity loss and achieve globally adopted conservation targets. Governments have recognized
this but little progress has been made. This paper addresses the following research question: What are the barriers and levers for mainstreaming biodiversity into economic sectors that exert high pressure on biodiversity?
This question is approached through applying an analytical framework developed from literature on mainstreaming and Environmental Policy Integration as well as governance theory and practice to four cases in
agriculture, agro-forestry and fisheries covering multi-level and transnational governance contexts. Decisionmaking and governance in these cases look quite different compared to the kind of public policy machinery of governmental bureaucracies that much EPI literature has focused on. Our analysis demonstrates mainstreaming efforts in some of our cases at the degree of harmonization and even coordination among key actors. It further identifies a number of ‘additional’ barriers and levers that from an Environmental Policy Integration perspective would be considered as external factors out of reach for mainstreaming efforts. The results are pertinent for the evaluation of EPI performance because the governance perspective expands the borders of who can initiate, enable and sustain mainstreaming, what scope of regulatory norms they can use and the potentially useful resources for the process.
Overcoming water challenges through nature-based solutions
Boelee, Eline ; Janse, Jan ; Gal, Antoine Le; Kok, Marcel ; Alkemade, Rob ; Ligtvoet, Willem - \ 2017
Water Policy 19 (2017)5. - ISSN 1366-7017 - p. 820 - 836.
Aquatic biodiversity - Ecosystems approach - Global model - IWRM - Mainstreaming biodiversity - Nature-based solutions - Pollution - Water challenges - Water management - Water shortage
Freshwater is a key resource and medium for various economic sectors and domestic purposes but its use is often at the expense of natural ecosystems. Water management must change to deal with urgent issues and protect aquatic ecosystems and their services, while addressing the demand for water from the competing claims for cities, agriculture, industry, energy and transport. In this paper key water challenges (shortage, pollution, aquatic ecosystems threatened) have been identified via global modelling. By the IMAGE-GLOBIO model chain a Trend scenario up to 2050 was modelled, as well as the potential of three 'pathways' aimed at halving average global biodiversity loss while also meeting the sustainable development goals. Biodiversity is then used as a guiding principle to address these challenges because water services depend on healthy and biodiverse ecosystems. Subsequently the potential of nature-based solutions is reviewed for four sub-sectors: cities, food production, hydropower, and flood protection, grouped under the three alternative pathways to meet key water challenges. Mainstreaming biodiversity into water policy requires integrated planning. Integrated Water Resource Management (IWRM) could provide an opportune starting point as a well recognised integrating framework for planning, to guide the actual implementation of nature-based solutions in sub-sectors.
Mainstreaming biodiversity where it matters most
Karlsson-Vinkhuyzen, S.I.S.E. ; Boelee, E. ; Cools, J. ; Visseren-Hamakers, I.J. ; Hoof, L.J.W. van; Hospes, O. ; Kok, M. ; Peerlings, J.H.M. ; Podvin, K.J. ; Tatenhove, J.P.M. van; Termeer, C.J.A.M. - \ 2014
Wageningen & Bilthoven : Wageningen University & PBL Netherlands Environmental Assessment Agency - ISBN 9789462573840 - 180
biodiversiteit - bosbouw - visserij - palmoliën - mangroves - wereld - biodiversity - forestry - fisheries - palm oils - world
This report presents the result of applying the framework in five cases in or on the cross roads between agriculture, forestry and fisheries where considerable pressure on biodiversity is exerted. The cases were selected based on several criteria with the aim that they together cover as broad span as possible of: Relevance for biodiversity (from having very clear impacts to much more uncertain impacts) Governance levels (including both local, national, global levels) Governance context (type of actors, type of norms etc.) Regions (continents and eco‐climatic zones)
How sectors can contribute to sustainable use and conservation of biodiversity
Kok, M. ; Alkemade, R. ; Bakkenes, M. ; Boelee, E. ; Christensen, V. ; Eerdt, M. van; Esch, S. van der; Janse, J. ; Karlsson-Vinkhuyzen, S.I.S.E. ; Kram, T. ; Lazarova, T. ; Linderhof, V.G.M. ; Lucas, P. ; Mandryk, M. ; Meijer, J. ; Oorschot, M. van; Teh, L. ; Hoof, L.J.W. van; Westhoek, H. ; Zagt, R. - \ 2014
The Hague : PBL (CBD technical series no. 79) - ISBN 9292255533 - 230
Balancing the organic load and light supply in symbiotic microalgal–bacterial biofilm reactors treating synthetic municipal wastewater
Boelee, N.C. ; Temmink, B.G. ; Janssen, M. ; Buisman, C.J.N. ; Wijffels, R.H. - \ 2014
Ecological Engineering 64 (2014). - ISSN 0925-8574 - p. 213 - 221.
afvalwaterbehandeling - biofilms - symbiose - algen - bacteriën - heterotrofe micro-organismen - fotosynthese - acetaten - stikstof - fosfor - nitrificatie - denitrificatie - biologische waterzuiveringsinstallaties - biobased economy - waste water treatment - biofilms - symbiosis - algae - bacteria - heterotrophic microorganisms - photosynthesis - acetates - nitrogen - phosphorus - nitrification - denitrification - biological water treatment plants - biobased economy - activated-sludge - nutrient removal - growth - phytoplankton - fluorescence - enhancement
Symbiotic microalgal–bacterial biofilms can be very attractive for municipal wastewater treatment. Microalgae remove nitrogen and phosphorus and simultaneously produce the oxygen that is required for the aerobic, heterotrophic degradation of organic pollutants. For the application of these biofilms in new wastewater treatment systems, the engineering aspects need to be investigated to obtain a balanced system where no additional oxygen is required. In this study symbiotic microalgal–bacterial biofilms were grown in flow cells with ammonium and phosphate, and with acetate as biodegradable organic pollutant at a hydraulic retention time of 4.5 h. The symbiotic biofilms removed acetate from 323 mg/L to 39 mg/L without an external oxygen or carbon dioxide supply at a removal rate of 43 g COD/m2/d. Ammonium and phosphate could not be completely removed, but removal rates of 3.2 g/m2/d and 0.41 g/m2/d were obtained, respectively. Further nitrogen removal may be obtained by nitrification and denitrification as the biofilm obtained a considerable heterotrophic denitrification capacity. The symbiotic relationship between microalgae and aerobic heterotrophs was proven by subsequently removing light and acetate. In both cases this resulted in the cessation of the symbiosis and in increasing effluent concentrations of both acetate and the nutrients ammonium and phosphate. Future research should investigate the dimensioning of an up-scaled symbiotic biofilm reactor, and the possibilities to obtain additional nitrogen and phosphorus removal under day–night cycles utilizing real wastewater.
Nutrient Removal and Biomass Production in an Outdoor Pilot-Scale Phototrophic Biofilm Reactor for Effluent Polishing
Boelee, N.C. ; Janssen, M. ; Temmink, H. ; Shrestha, R. ; Buisman, C.J.N. ; Wijffels, R.H. - \ 2014
Applied Biochemistry and Biotechnology 172 (2014)1. - ISSN 0273-2289 - p. 405 - 422.
afvalwaterbehandeling - biofilms - algen - biologische waterzuiveringsinstallaties - fototropie - nitraten - fosfaten - waste water treatment - algae - biological water treatment plants - phototropism - nitrates - phosphates - waste-water treatment - rate algal pond - marine-phytoplankton - seasonal succession - phosphate-uptake - nitrogen uptake - nitrate uptake - phosphorus - growth - light
An innovative pilot-scale phototrophic biofilm reactor was evaluated over a 5-month period to determine its capacity to remove nitrogen and phosphorus from Dutch municipal wastewater effluents. The areal biomass production rate ranged between 2.7 and 4.5 g dry weight/m2/day. The areal nitrogen and phosphorus removal rates averaged 0.13 g N/m2/day and 0.023 g P/m2/day, which are low compared to removal rates achieved in laboratory biofilm reactors. Nutrient removal increased during the day, decreased with decreasing light intensity and no removal occurred during the night. Additional carbon dioxide supply was not requisite as the wastewater was comprised of enough inorganic carbon to sustain microalgal growth. The study was not conclusive for the limiting factor that caused the low nutrient removal rate, possibly the process was limited by light and temperature, in combination with pH increases above pH 9 during the daytime. This pilot-scale study demonstrated that the proposed phototrophic biofilm reactor is not a viable post-treatment of municipal wastewater effluents under Dutch climate conditions. However, the reactor performance may be improved when controlling the pH and the temperatures in the morning. With these adaptations, a phototrophic biofilm reactor could be feasible at lower latitudes with higher irradiance levels.
The effect of harvesting on biomass production and nutrient removal in phototrophic biofilm reactors for effluent polishing
Boelee, N.C. ; Janssen, M. ; Temmink, H. ; Taparaviciute, L. ; Khiewwijit, R. ; Janoska, A. ; Buisman, C.J.N. ; Wijffels, R.H. - \ 2014
Journal of Applied Phycology 26 (2014)3. - ISSN 0921-8971 - p. 1439 - 1452.
afvalwaterbehandeling - biofilms - dikte - dichtheid - algen - biologische waterzuiveringsinstallaties - fototropie - stikstof - fosfor - verwijdering - biobased economy - waste water treatment - biofilms - thickness - density - algae - biological water treatment plants - phototropism - nitrogen - phosphorus - removal - biobased economy - waste-water treatment - photosynthetic efficiency - chlorella-sorokiniana - microalgal biofilms - phosphorus removal - mass-transport - fresh-water - light - growth
An increasing number of wastewater treatment plants require post-treatment to remove residual nitrogen and phosphorus. This study investigated various harvesting regimes that would achieve consistent low effluent concentrations of nitrogen and phosphorus in a phototrophic biofilm reactor. Experiments were performed in a vertical biofilm reactor under continuous artificial lighting and employing artificial wastewater. Under similar conditions, experiments were performed in near-horizontal flow lanes with biofilms of variable thickness. It was possible to maintain low nitrogen and phosphorus concentrations in the effluent of the vertical biofilm reactor by regularly harvesting half of the biofilm. The average areal biomass production rate achieved a 7 g dry weight m-2 day-1 for all different harvesting frequencies tested (every 2, 4, or 7 days), corresponding to the different biofilm thicknesses. Apparently, the biomass productivity is similar for a wide range of biofilm thicknesses. The biofilm could not be maintained for more than 2 weeks as, after this period, it spontaneously detached from the carrier material. Contrary to the expectations, the biomass production doubled when the biofilm thickness was increased from 130 µm to 2 mm. This increased production was explained by the lower density and looser structure of the 2 mm biofilm. It was concluded that, concerning biomass production and labor requirement, the optimum harvesting frequency is once per week.
Management of Water and Agroecosystems in Landscapes for Sustainable Food Security
Boelee, E. ; Scherr, S.J. ; Pert, P. ; Barron, J. ; Finlayson, M. ; Descheemaeker, K.K.E. ; Milder, J.C. ; Fleiner, R. ; Nguyen-Khoa, S. ; Barchiesi, S. ; Bunting, S.W. ; Tharme, R. ; Khaka, E. ; Coates, D. ; Solowey, E.M. ; Lloyd, G.J. ; Molden, D. ; Cook, S. - \ 2013
In: Managing water and agroecosystems for food security / Boelee, E., CABI - ISBN 9781780640884 - p. 156 - 170.
Increasing Water Productivity in Agriculture
Descheemaeker, K.K.E. ; Bunting, S.W. ; Bindraban, P.S. ; Muthuri, C. ; Molden, D. ; Beveridge, M. ; Brakel, M. van; Herrero, M. ; Clement, F. ; Boelee, E. ; Jarvis, D. - \ 2013
In: Managing water and agroecosystems for food security CABI - ISBN 9781780640884 - p. 104 - 123.
Microalgal biofilms for wastewater treatment
Boelee, N.C. - \ 2013
Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Hardy Temmink; Marcel Janssen. - [S.l. : S.n. - ISBN 9789461736666 - 213
algen - biofilms - afvalwaterbehandeling - bioproceskunde - milieutechnologie - algenteelt - mineralenopname - biomassa productie - biobased economy - algae - biofilms - waste water treatment - bioprocess engineering - environmental technology - algae culture - mineral uptake - biomass production - biobased economy
The objective of this thesis was to explore the possibilities of using microalgal biofilms for the treatment of municipal wastewater, with a focus on the post-treatment of municipal wastewater effluent. The potential of microalgal biofilms for wastewater treatment was first investigated using a scenario analysis. Then biofilms were grown on wastewater treatment plant effluent in horizontal flow cells under different nutrient loads to determine the maximum uptake capacity of the biofilms for NO3 and PO4. Subsequently, microalgal biofilms were grown in a vertical laboratory-scale biofilm reactor. The effect of harvesting and biofilm thickness on the biomass production and nutrient removal was investigated. The biofilm reactor was taken outdoors and a vertical pilot-scale biofilm reactor was evaluated as post-treatment of municipal wastewater in a pilot-study. Finally, symbiotic microalgal-bacterial biofilms were investigated for full treatment of (pre-settled) wastewater.
A physiologically based kinetic model for bacterial sulfide oxidation
Klok, J.B.M. ; Graaff, C.M. de; Bosch, P.L.F. van den; Boelee, N.C. ; Keesman, K.J. ; Janssen, A.J.H. - \ 2013
Water Research 47 (2013)2. - ISSN 0043-1354 - p. 483 - 492.
afvalwaterbehandeling - biotechnologie - zwavelwaterstof - oxidatie - ontzwaveling - alkalibacillus haloalkaliphilus - microbiële fysiologie - afvalwaterbehandelingsinstallaties - waste water treatment - biotechnology - hydrogen sulfide - oxidation - desulfurization - alkalibacillus haloalkaliphilus - microbial physiology - waste water treatment plants - sulfur-oxidizing bacteria - biologically produced sulfur - dissolved sodium sulfide - parameter-estimation - hydrogen-sulfide - soda lakes - bioreactors - thiosulfate - mechanisms - pathways
In the biotechnological process for hydrogen sulfide removal from gas streams, a variety of oxidation products can be formed. Under natron-alkaline conditions, sulfide is oxidized by haloalkaliphilic sulfide oxidizing bacteria via flavocytochrome c oxidoreductase. From previous studies, it was concluded that the oxidation-reduction state of cytochrome c is a direct measure for the bacterial end-product formation. Given this physiological feature, incorporation of the oxidation state of cytochrome c in a mathematical model for the bacterial oxidation kinetics will yield a physiologically based model structure. This paper presents a physiologically based model, describing the dynamic formation of the various end-products in the biodesulfurization process. It consists of three elements: 1) Michaelis–Menten kinetics combined with 2) a cytochrome c driven mechanism describing 3) the rate determining enzymes of the respiratory system of haloalkaliphilic sulfide oxidizing bacteria. The proposed model is successfully validated against independent data obtained from biological respiration tests and bench scale gas-lift reactor experiments. The results demonstrate that the model is a powerful tool to describe product formation for haloalkaliphilic biomass under dynamic conditions. The model predicts a maximum S0 formation of about 98 mol%. A future challenge is the optimization of this bioprocess by improving the dissolved oxygen control strategy and reactor design.
Scenario Analysis of Nutrient Removal from Municipal Wastewater by Microalgal Biofilms
Boelee, N.C. ; Temmink, H. ; Janssen, M. ; Buisman, C.J.N. ; Wijffels, R.H. - \ 2012
Water 4 (2012)2. - ISSN 2073-4441 - p. 460 - 473.
afvalwaterbehandeling - biofilms - algen - biologische waterzuiveringsinstallaties - vergelijkend onderzoek - volgorden - haalbaarheidsstudies - heterotrofe micro-organismen - stikstof - fosfor - verwijdering - biomassa productie - biobased economy - waste water treatment - algae - biological water treatment plants - comparative research - sequences - feasibility studies - heterotrophic microorganisms - nitrogen - phosphorus - removal - biomass production - marine-phytoplankton - chemical-composition - chlorella-vulgaris - nitrate uptake - algal biofilm - growth - photobioreactor - photosynthesis
Microalgae can be used for the treatment of municipal wastewater. The application of microalgal biofilms in wastewater treatment systems seems attractive, being able to remove nitrogen, phosphorus and COD from wastewater at a short hydraulic retention time. This study therefore investigates the area requirement, achieved effluent concentrations and biomass production of a hypothetical large-scale microalgal biofilm system treating municipal wastewater. Three scenarios were defined: using microalgal biofilms: (1) as a post-treatment; (2) as a second stage of wastewater treatment, after a first stage in which COD is removed by activated sludge; and (3) in a symbiotic microalgal/heterotrophic system. The analysis showed that in the Netherlands, the area requirements for these three scenarios range from 0.32 to 2.1 m2 per person equivalent. Moreover, it was found that it was not possible to simultaneously remove all nitrogen and phosphorus from the wastewater, because of the nitrogen:phosphorus ratio in the wastewater. Phosphorus was limiting in the post-treatment scenario, while nitrogen was limiting in the two other scenarios. Furthermore, a substantial amount of microalgal biomass was produced, ranging from 13 to 59 g per person equivalent per day. These findings show that microalgal biofilm systems hold large potential as seasonal wastewater treatment systems and that it is worthwhile to investigate these systems further
An ecosystem services approach to water and food security
Boelee, E. ; Chiramba, T. ; Khaka, E. ; Andreini, M. ; Atapattu, S. ; Barchiesi, S. ; Baron, J. ; Beveridge, M. ; Bindraban, P. - \ 2011
Colombo : UNEP (Job number: DEP/1371/NA ) - ISBN 9789280731521 - 66
ecosysteemdiensten - voedselzekerheid - waterzekerheid - ecosystem services - food security - water security
Ecosystems for water and food security
Boelee, E. ; Atapattu, S. ; Barron, J. ; Bindraban, P. ; Bunting, S.W. ; Coates, D. ; Descheemaeker, K.K.E. ; Eriyagama, N. ; Finlayson, M. ; Gordon, L. - \ 2011
Colombo : UNEP (Job Number: DEPI/1392/NA ) - ISBN 9789280731705 - 194
ecosysteemdiensten - voedselzekerheid - waterzekerheid - ecosystem services - food security - water security
Nitrogen and phosphorus removal from municipal wastewater effluent using microalgal biofilms
Boelee, N.C. ; Temmink, H. ; Janssen, M.G.J. ; Buisman, C.J.N. ; Wijffels, R.H. - \ 2011
Water Research 45 (2011)18. - ISSN 0043-1354 - p. 5925 - 5933.
afvalwaterbehandeling - biofilms - anaërobe afbraak - modellen - waste water treatment - biofilms - anaerobic digestion - models - nutrient removal - photosystem-ii - phytoplankton - growth - bioavailability - photosynthesis - plants - algae - ph
Microalgal biofilms have so far received little attention as post-treatment for municipal wastewater treatment plants, with the result that the removal capacity of microalgal biofilms in post-treatment systems is unknown. This study investigates the capacity of microalgal biofilms as a post-treatment step for the effluent of municipal wastewater treatment plants. Microalgal biofilms were grown in flow cells with different nutrient loads under continuous lighting of 230 µmol/m(2)/s (PAR photons, 400-700 nm). It was found that the maximum uptake capacity of the microalgal biofilm was reached at loading rates of 1.0 g/m(2)/day nitrogen and 0.13 g/m(2)/day phosphorus. These maximum uptake capacities were the highest loads at which the target effluent values of 2.2 mg/L nitrogen and 0.15 mg/L phosphorus were still achieved. Microalgal biomass analysis revealed an increasing nitrogen and phosphorus content with increasing loading rates until the maximum uptake capacities. The internal nitrogen to phosphorus ratio decreased from 23:1 to 11:1 when increasing the loading rate. This combination of findings demonstrates that microalgal biofilms can be used for removing both nitrogen and phosphorus from municipal wastewater effluent
Can Irrigation Water Management Be Used as a Tool for Malaria Mosquito Control? The Case of the Office du Niger in Mali
Klinkenberg, E. ; Huibers, F.P. ; Takken, W. ; Toure, Y.T. - \ 2002
In: Malaria in Irrigated Agriculture : ICID 18th International Congress on Irrigation and Drainage, Montreal, 2002 / E. Boelee, F. Konradsen and W. van der Hoek. - Colombo : International Water Management Institute, 2002. (Working Paper ; 47). - SIMA document 2 - p. 49 - 49.
Irrigation ecology of schistosomiasis : environmental control options in Morocco
Boelee, E. - \ 2000
Agricultural University. Promotor(en): R.A. Feddes; B.M.A.J. Gryseels; F.P. Huibers. - S.l. : S.n. - ISBN 9789058081438 - 199
irrigatie - schistosomiase - schistosoma - humane ziekten - milieubeheersing - irrigatiesystemen - ziekteoverdracht - ecologie - marokko - irrigation - schistosomiasis - schistosoma - human diseases - environmental control - irrigation systems - disease transmission - ecology - morocco

The concept of irrigation ecology is introduced to study the transmission and the control of urinary schistosomiasis in Moroccan irrigation systems. By distinguishing a biological, a human and an irrigation environment, crucial interactions are identified in the overlap of these three environments. In the semi-arid Haouz plain in Central Morocco, schistosomiasis was introduced after the construction of the Tessaout Amont irrigation system in the early 1970s. The typical design of this canal irrigation system, with elevated semi-circular conduits as secondary and tertiary canals, is based on upstream control and the water is distributed in rotation. Inverted siphons, consisting of two square boxes connected by an underground pipe, have been constructed to convey the water under roads or tracks. The boxes contain stagnant water and provide excellent breeding sites for Bulinus truncatus , the intermediate snail host of schistosomiasis.

A cross-sectional survey showed that especially inverted siphons on tertiary canals harbour high densities of B.truncatus . A length profile study along one secondary canal and four of its tertiaries showed that conditions near the tail end of canals, especially in the downstream siphon boxes, are most favourable to the intermediate snail host. The transmission of schistosomiasis in Tessaout Amont is concentrated at these siphons as, in the absence of other sources, water from the boxes is used for all kinds of agricultural and domestic purposes, inducing frequent water contact.

Three environmental control options have been studied. Regular emptying and cleaning of siphon boxes had a limited effect on densities of Bulinus truncatus snails and eggs. Creating a dark environment by covering siphon boxes with iron plates proved to be much more effective in reducing B.truncatus populations. Some of the covers were equipped with moveable lids to leave the water accessible to the villagers. The third control option concerned measures to increase the water flow velocity in siphons. Combining flow velocities with the duration of the flow results in a mean annual flow velocity. According to literature, above a critical value of 0.042 m/s, no B.truncatus snails are to be found in siphon boxes. In siphons with a lower mean annual flow velocity, this critical value can be obtained by reducing the inner dimensions of the siphon boxes, thus increasing the water flow velocity. However, in experiments with such smaller siphon boxes, the siphons were quickly repopulated with B.truncatus . Better results might be achieved by redefining the critical value. However, the small diameter siphons generate higher energy losses. Consequently, such siphons can only be applied in a layout where access to the fields is guaranteed through simple bridges over the drains, which significantly reduces the number of required siphons.

Domestic water use in Morocco's Tessaout Amont irrigation system
Boelee, E. ; Laamrani, H. ; Khallaayoune, K. ; Watts, S. - \ 1999
Waterlines 18 (1999)1. - ISSN 0262-8104 - p. 21 - 23.
Detection of urinary schistosomiasis in a low prevalence region.
Tiemersma, E.W. ; Hafid, S. ; Boelee, E. ; Khallaayoune, K. ; Gryseels, B. - \ 1997
Transactions of the Royal Society of Tropical Medicine and Hygiene 91 (1997). - ISSN 0035-9203 - p. 285 - 286.
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