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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    Integrated pollution prevention and control for the municipal water cycle in a river basin context: validation of the three-step strategic approach
    Galvis Castaño, Alberto - \ 2019
    Wageningen University. Promotor(en): H.J. Gijzen, co-promotor(en): N.P. van der Steen. - Leiden : CRC Press/Balkema - ISBN 9780367375270 - 200

    The protection of water resources from deterioration in quality from pollution discharges has become one of the biggest challenge in sustainable water resources management in recent decades. In practice, most countries have adopted pollution control strategies and measures which are based on ‘end-of-pipe’ solutions, i.e. wastewater treatment plants and adjustments to the regulations, including taxes for wastewater discharges (Conventional Strategy). This approach involves very high costs, and it has in many cases has been a complete failure. The research described in this book contributes to the development of sustainable solutions for the previously outlined problem. It is based on the validation of the Three-Step Strategic Approach concept (3-SSA), which includes: 1) prevention or minimisation of waste production; 2) treatment aimed at recovery and reuse of waste components, and 3) polishing of remaining waste by stimulation of natural self-purification of receiving water body. The study on wastewater management in the Upper Cauca river basin (389 km), the second most important river in Colombia, shows overall positive effects of the 3-SSA, in comparison of Conventional Strategy. The Cost Benefit Analysis clearly favoured the 3-SSA, generating a major positive impact on the river water quality at lower cost compared to the Conventional Strategy.

    Procedures in child deaths in The Netherlands : a comparison with child death review
    Gijzen, Sandra ; Petter, Jessica ; Hoir, Monique L'; Boere-Boonekamp, Magda M. ; Need, Ariana - \ 2017
    Journal of Public Health = Zeitschrift für Gesundheitswissenschaften 25 (2017)4. - ISSN 0943-1853 - p. 357 - 370.
    Child death review - Child mortality - Implementation - Prevention
    Aim: Child Death Review (CDR) is a method in which every child death is systematically and multidisciplinary examined to (1) improve death statistics, (2) identify factors that give direction for prevention, (3) translate the results into possible interventions, and (4) support families. The aim of this study was to determine to what extent procedures of organizations involved in the (health) care for children in The Netherlands cover these four objectives of CDR. Subject and methods: Organizations in the Eastern part of The Netherlands and Dutch umbrella organizations involved in child (health) care were asked to provide their protocols, guidelines or other working agreements that describe their activities and responsibilities in case of a child’s death. Eighteen documents and nine interview reports were made available. For the analyses we used scorecards for each CDR objective. Results: The procedures of Perined, the National Cot Death Study Group, Dutch Cot Death Foundation and Child Protection Service cover the largest part of the objectives of CDR. Organizations pay most attention to the translation of results into possible interventions. Family support gets the least attention in protocols, guidelines and other working agreements. Conclusion: Dutch organizations separately cover parts of CDR. When the procedures of organizations are combined, all CDR objectives are covered in the response to only specific groups of child deaths, i.e., perinatal deaths, Sudden Unexpected Deaths in Infants and fatal child abuse cases. Further research into the conditions that are needed for an optimal implementation of CDR in The Netherlands is necessary. This research should also evaluate the recently implemented NODOK procedure (Further Examination of the Causes of death in Children), directed to investigate unexplained deaths in minors 0–18 years old.
    The Top 10 oomycete pathogens in molecular plant pathology
    Kamoun, S. ; Furzer, O. ; Jones, J.D.G. ; Judelson, H.S. ; Ali, G.S. ; Dalio, R.J.D. ; Roy, S.G. ; Schena, L. ; Zambounis, A. ; Panabières, F. ; Cahill, D. ; Ruocco, M. ; Figueiredo, A. ; Chen, X.R. ; Hulvey, J. ; Stam, R. ; Lamour, K. ; Gijzen, M. ; Tyler, B.M. ; Grünwald, N.J. ; Mukhtar, M.S. ; Tomé, D.F.A. ; Tör, M. ; Ackerveken, G. van den; McDowell, J. ; Daayf, F. ; Fry, W.E. ; Lindqvist-Kreuze, H. ; Meijer, H.J.G. ; Petre, B. ; Ristaino, J. ; Yoshida, K. ; Birch, P.R.J. ; Govers, F. - \ 2015
    Molecular Plant Pathology 16 (2015)4. - ISSN 1464-6722 - p. 413 - 434.
    grapevine downy mildew - irish potato famine - sudden oak death - blister rusts albuginaceae - eastern united-states - 3 clonal lineages - nb-lrr gene - phytophthora-infestans - plasmopara-viticola - arabidopsis-thaliana
    Oomycetes form a deep lineage of eukaryotic organisms that includes a large number of plant pathogens that threaten natural and managed ecosystems. We undertook a survey to query the community for their ranking of plant pathogenic oomycete species based on scientific and economic importance. In total, we received 263 votes from 62 scientists in 15 countries for a total of 33 species. The Top 10 species and their ranking are: (1) Phytophthora infestans; (2, tied) Hyaloperonospora arabidopsidis; (2, tied) Phytophthora ramorum; (4) Phytophthora sojae; (5) Phytophthora capsici; (6) Plasmopara viticola; (7) Phytophthora cinnamomi; (8, tied) Phytophthora parasitica; (8, tied) Pythium ultimum; and (10) Albugo candida. The article provides an introduction to these 10 taxa and a snapshot of current research. We hope that the list will serve as a benchmark for future trends in oomycete research.
    Dutch Caribbean Biodiversity Database
    Verweij, P.J.F.M. ; Hennekes, S.M. ; Meulebrouk, B. ; Gijzen, S.W.J.G.M. ; Dijkman, E.M. ; Meesters, H.W.G. ; Vermaas, T. - \ 2013
    WUR : WUR
    The Dutch Caribbean Biodiversity Database (DCBD) supplies a central repository for all biodiversity related research and monitoring data and information from the Dutch Caribbean. The goal of the DCBD is to guarantee long-term data access and availability, support nature management and facilitate international reporting obligations.
    Infrastructuur satellietdatabank
    Lokers, R.M. ; Gijzen, S.W.J.G.M. - \ 2013
    Wageningen : Alterra, Wageningen-UR - 4
    precisielandbouw - geografische informatiesystemen - satellietbeelden - satellietkarteringen - computer software - datacommunicatie - gegevens verzamelen - gegevensbeheer - precision agriculture - geographical information systems - satellite imagery - satellite surveys - computer software - data communication - data collection - data management
    Doelstelling is het ontwikkelen van een infrastructuur voor het ontsluiten van datasets afgeleid van de ruwe basisdata zoals beschikbaar is via de Nationale Satelliet databank. Ontsluiting vindt plaats volgens een Service Oriented Architecture (SOA) via de geëigende open standaarden en protocollen voor ontsluiting van ruimtelijke data, aansluitend op de principes en standaarden van OpenGIS en INSPIRE.
    The removal of faecal coliforms in waste stabilization pond systems and eutrophic lakes
    Ansa, E.D.O. - \ 2013
    Wageningen University. Promotor(en): H.J. Gijzen, co-promotor(en): H.J. Lubberding. - Leiden : CRC/Balkema - ISBN 9789461735362 - 114
    fecale coliformen - afvalwater - afvalwaterbehandeling - hergebruik van water - algen - stedelijk afvalwater - faecal coliforms - waste water - waste water treatment - water reuse - algae - municipal wastewater

    The reuse of domestic wastewater presents many challenges including the risk of pathogen infection; hence the removal of pathogens from domestic wastewater is very relevant. It is known that algae play a crucial role in the process of their removal by raising the pH and dissolved oxygen concentration which tend to be injurious to bacteria. It is however not known how algal disinfection ability is affected by biomass changes in sewage of varying strengths and whether algae contribute in sedimenting faecal coliforms (FC) from the water column through attachment to their surfaces. Experiments were conducted to investigate the importance of FC attachment to algae, the effect of varying concentration of algae in sewage of different strengths on FC removal and the effect of algae on FC removal in a tropical eutrophic lake. The effect of reducing algal densities in a pilot-scale hybrid algae-duckweed pond system on FC removal was also investigated with the aim of understanding the importance of FC attachment in such a treatment system in relation to pure algal and duckweed treatment lines. Algae helped in sedimenting FC to the bottom of reactors. It was shown by experimentation under laboratory conditions that in domestic wastewater treatment an optimum algal density exists at which maximum FC removal is achieved. Algae were also important in significantly reducing Escherichia coli contamination in a eutrophic lake through increased oxygenation and pH elevation. At algal density ≤0.08mgL-1 in the Weija Lake, decay rate of E. coli was directly proportional to the chlorophyll a concentration of the lake. The strength of domestic wastewater undergoing treatment may also affect the rate of decay of FC, particularly as algal concentration changes. In darkness, higher algal biomass (or chlorophyll a concentration) resulted in higher inactivation of FC although dissolved oxygen concentration and pH were low suggesting a role by another factor in the inactivation of FC. At algal densities ≥ 13.9mg L-1 higher removal of FC occurred in MSW (medium strength wastewater) compared with LSW (low strength wastewater) whether in light or in darkness. The highest rate of decay in LSW occurred at 3.2mgL-1 chlorophyll a concentration in light while that of the MSW occurred at 20.0mgL-1 in light. Addition of raw wastewater to an ongoing wastewater treatment process lowered the rate of FC removal for a wide range of algal densities (0.6 – 19.6mgL-1 chlorophyll a concentration), under light conditions. The hybrid pond system performed well in FC (4.3 log units) and Biochemical Oxygen Demand (BOD) (89%) removal and these parameters in addition to total phosphorus were not affected by seasonal changes. FC attachment to suspended matter was important only in the first two ponds of the duckweed, algal and hybrid pond systems. Little variation of FC decay with depth was observed. FC decay rates in the mornings were usually lower than in the afternoons in algal ponds but not in the duckweed ponds. High densities of macro-invertebrates belonging to the class Ostracoda were associated mainly with the surface and bottom of duckweed ponds and these were much higher than that of algal ponds at similar locations. FC numbers in duckweed ponds correlated strongly and positively with mean ostracod numbers in ponds. FC numbers also correlated well with Shannon-Wiener diversity index of macro-invertebrates in all the three pond systems. Integrating a hybrid pond system such as this for aquaculture would be a big boost economically and health-wise for communities in developing countries with warm tropical conditions.

    Effect of algal biofilm and operational conditions on nitrogen removal in wastewater stabilization ponds
    Babu, M. - \ 2011
    Wageningen University. Promotor(en): H.J. Gijzen, co-promotor(en): N.P. van der Steen; C.M. Hooijmans. - [S.l. : S.n. - ISBN 9780415669467 - 129
    afvalwaterbehandeling - bezinkingsvijvers - organische stikstofverbindingen - biofilms - algenculturen - ontwikkelingslanden - waste water treatment - stabilization ponds - organic nitrogen compounds - biofilms - algal cultures - developing countries
    Discharge of nutrient rich wastewater causes eutrophication of surface water; therefore wastewater treatment before discharge is required. Wastewater stabilization ponds are low cost technology used by developing countries but not effective in nitrogen removal due to low nitrifier biomass in the water column. Introduction of surface area for attachment of nitrifiers has therefore been proposed. This thesis reports the performance of pilot scale wastewater stabilization ponds fitted with baffles. The effect of baffles on nitrogen removal under tropical and two operational conditions was investigated. Under TKN/BOD ratio of 0.67, the baffled ponds performed better in nitrogen removal than the control pond. Total nitrogen mass balances showed that nitrification-denitrification, algal uptake and sedimentation were principle nitrogen removal mechanisms in biofilm waste stabilization ponds This study shows the potential of biofilms in improving nitrogen removal in wastewater stabilization ponds. The BOD and TSS concentrations were sufficiently low to permit for reuse in irrigation. If the objective is reuse and optimization of resources, the effluents from the ponds had sufficient nitrogen content for use in agriculture.
    TransForum: Innovatie van de kennisinfrastructuur in de Nederlandse landbouw
    Smeets, P.J.A.M. - \ 2009
    In: Agribusiness Clusters: Bouwstenen van de regionale biobased economy?. - Maastricht : Shaker Publishing - ISBN 9789042303539 - p. 83 - 96.
    landbouw - nederland - duurzaamheid (sustainability) - innovaties - biobased economy - kennisoverdracht - publiek-private samenwerking - duurzame ontwikkeling - cradle to cradle - agriculture - netherlands - sustainability - innovations - knowledge transfer - public-private cooperation - sustainable development
    Ten eerste wordt in dit hoofdstuk een aantal begrippen omtrent duurzaamheid uiteengezet. Ten tweede komt de Historie van de kennisinfrastructuur in de Nederlandse landbouw aan bod.Ten derde wordt dieper ingegaan op de werkwijze van TransForum en wordt een overzicht gegeven van projecten waarbij TransForum is betrokken en waarbij vernieuwende samenwerkingsverbanden zijn realiseerd. Het hoofdstuk wordt afgesloten met de praktijkervaringen die zijn opgedaan bij de praktijkprojecten waarbij TransForum is betrokken en de introductie van een extra P in het kader van people,planet en prosperity.
    Greenport Venlo: een gezamenlijke zoektocht naar duurzame regionale ontwikkeling
    Kranendonk, R.P. ; Kersten, P.H. ; Regeer, B.J. - \ 2009
    In: Agribusiness Clusters: Bouwstenen van de regionale biobased economy?. - Maastricht : Shaker Publishing - ISBN 9789042303539 - p. 65 - 82.
    regionale ontwikkeling - economische ontwikkeling - tuinbouw - duurzaamheid (sustainability) - innovaties - projectimplementatie - glastuinbouw - midden-limburg - biobased economy - regional development - economic development - horticulture - sustainability - innovations - project implementation - greenhouse horticulture - midden-limburg - biobased economy
    Vanuit het regionaal economisch perspectief is voor het Rijk een beperkt aantal locaties van belang waar de primaire productie, de handel en de distributie van tuinbouw zich ruimtelijk gebundeld hebben. Deze locaties zijn Greenports genaamd. Wat betreft Greenport Venlo, wordt aangetoond hoe nieuwe samenwerkingsverbanden een volstrekt nieuwe methode hanteren om innovatie en duurzame doelen na te streven bij regionale ontwikkeling. Dit wordt in een kader van veranderende inzichten over overheidssturing, nieuwe werkwijzen en nieuwe perspectieven geplaatst die deze veranderingen met zich meebrengen in termen van creativiteit, kennis en betekenis.
    Enhanced stabilisation of municipal solid waste in bioreactor landfills
    Valencia Vázquez, R. - \ 2008
    Wageningen University. Promotor(en): H.J. Gijzen, co-promotor(en): H.J. Lubberding. - [S.l.] : S.n. - ISBN 9789085049180 - 141
    bioreactoren - vaste afvalstoffen - huisvuilverwijdering - stortterreinen - septic tankafvalwater - bioreactors - solid wastes - municipal refuse disposal - landfills - septic tank effluent
    The increasing development and urbanization of the society has led to an increase per-capita production of municipal solid waste (MSW) materials. These MSW materials are of organic and inorganic nature that can be of rapidly, moderately and slowly biodegradable or inert characteristics. With regard to these waste streams a wide variety of treatments exist: reuse and recycling, composting, anaerobic digestion, incineration, and land disposal are the most common ones, pyrolysis and gasification are in use to a lesser extent or on a smaller scale. Regardless of the method chosen for treatment all these methods produce residues, which will be eventually disposed at open dumps or sanitary landfills. Sanitary landfills are engineered facilities that make use of barriers to isolate the waste from the biosphere in order to protect human health and the environment. However, these barriers will fail in the long-term allowing the intrusion of moisture into the waste mass, which will trigger restrained physical, chemical and biological processes causing pollution in the form of leachate and landfill gas. In order to minimise the negative impacts of landfilling of waste, researchers conducted experiments, which resulted today in the so-called bioreactor landfill approach. The bioreactor landfill is a system that is operationally influenced to promote synergy between the inherent microbial consortia, and is controlled to accelerate the sequential phases of waste stabilisation through the addition of liquids and/or air. These past investigations have allowed the determination of optimal ranges for the key process parameters and the implementation of alternative operational conditions, the so-called enhancement techniques. Two main perspectives can be identified: 1) the American perspective, which attempts to apply enhancement techniques in order to maximise landfill gas production; 2) the European perspective that focus on the achievement of the Final Storage Quality (FSQ) status of residues within a generation timeframe (30 years). The term FSQ suggests that the potential of a waste material to produce pollution is reduced to nearly zero in the long-term perspective, similar to the characteristics for inert waste laid in the Waste Acceptance Criteria (WAC) of the European Landfill Directive. Until now, the main technical problem faced by landfill operators is homogenous liquid addition and distribution (key enhancement technique) within the waste mass. The main objective of this thesis was to achieve a FSQ status of waste, through laboratory and pilot-scale experiments, that complies with the WAC of the Landfill Directive for Inert waste, which had been considered as the worstcase scenario due to the stringent criteria established. Therefore, this thesis focused on the interaction and modification of the factors controlling the waste stabilisation process in order to have a better understanding of the physical, chemical and biological processes occurring in a bioreactor landfill.

    Bench (1 L), laboratory (50 L) and pilot-scale (800 L) simulators were used to apply different combinations of enhancement techniques (shredding. buffer addition, septage addition, and forced air intrusion) in order to achieve FSQ of residues. In addition, coarse materials (as layers or homogenous mixtures) were used in order to improve the hydraulic conditions of the simulators. The results of these experiments revealed that it was possible to achieve biological stabilisation within 1 year, but not FSQ status. Achievement of FSQ status depends strongly on the initial solid waste composition. Nevertheless, the residues were close to comply with the WAC of the Landfill Directive for inert waste. Buffer and septage addition proved to have a positive impact on the waste stabilisation process, reducing the biogas production lag-phase. Additionally, the risks associated with septage disposal were practically eliminated as no faecal coliforms were detected after 1 year of operation. Also the use of coarse materials had a positive impact on the waste stabilisation process, especially as homogenous mixtures and layers to a lesser extent since they were prone to clogging. Nitrogen compounds, especially ammonium, have been identified as a main parameter that will jeopardise the achievement of FSQ status, hence the safe closure of landfill sites. Therefore, evolution and fate of nitrogen compounds were also investigated in this thesis. The experiments showed that about 40% of the total ammonium was released by physical processes within 24 hours; the other 60% was produced by biological degradation of proteins contained in the MSW. Anammox bacteria were found for the first time in bioreactor landfills and it was suspected to have an important contribution to the total removal of nitrogen from the system, beside other nitrogen removal processes. Nevertheless, it was not clear how or where the intermediate products (i.e. nitrite) necessary for Anammox metabolism were produced.

    The Landfill Degradation and Transport (LDAT) model was used to simulate the evolution of carbon and nitrogen compounds. The LDAT model was not suitable to represent accurately the processes occurring in the simulators mainly because the model operated at a fixed (20ºC) process temperature and the waste chemistry equations need to be improved. Other models found in literature could be more appropriate to describe these processes; however, it was noticed that these models lack a complete ionic balance which has great influence on the pH of the system. The experimental research emphasised the importance of increasing pH values to neutral pH values, which “triggered” most of the processes in the simulators. This thesis highlighted the need to focus future modelling efforts on the integration of this complete ionic balance and its influence on the development of neutral (even alkaline) pH levels.

    In conclusion, this research reduced our current gaps-in-knowledge and offered feasible technical alternatives to control and steer the processes occurring in a bioreactor landfill aiming to achieve FSQ status of residues
    The use and fate of pesticides in vegetable-based agroecosystems in Ghana
    Ntow, W.J. - \ 2008
    Wageningen University. Promotor(en): H.J. Gijzen, co-promotor(en): P. Kelderman. - [S.l.] : S.n. - ISBN 9789085048367 - 111
    pesticiden - endosulfan - lekkage - oppervlakkige afvoer - beroepsgevaren - choline esterase - ghana - acetylcholine esterase - milieuafbraak - agro-ecosystemen - persistente organische verontreinigende stoffen - bioaccumulatie - pesticides - endosulfan - leakage - runoff - occupational hazards - cholinesterase - ghana - acetylcholinesterase - environmental degradation - agroecosystems - persistent organic pollutants - bioaccumulation
    The use of a wide range of chemicals to destroy pests and weeds is an important aspect of agricultural practice in Ghana, contributing to increased crop yield and reduced post-harvest losses. Notwithstanding the beneficial effects of pesticides, their adverse effects on environmental quality and human health constitute a major issue that gives rise to concerns at local, regional and national scales. The situation is particularly worrying in view of the lack of reliable data on the long-term consequences of exposure to pesticides. Ntow’s thesis reports on current knowledge on pesticides use in vegetable farming in Ghana and establishes the fate of pesticides in situ in tropical vegetable-based agroecosystems, as well as their environmental and public health impacts on selected population groups. Thus, water, waterbed sediment and vegetable crops (viz. tomato, cabbage, pepper, onion and eggplant) were checked for residues of the pesticides monitored on the farmers’ fields. Data on persistent pesticide residues in farmers’ breast milk and blood serum indicated the presence of DDTs, dieldrin, HCB, and HCHs; this especially raises concerns for children’s health. The thesis concludes that successful actions to reduce negative impacts of pesticides require sustained, low cost, and well-targeted training interventions.
    Interaction between digestion conditions and sludge physical characteristics and behaviour for anaerobically digested primary sludge
    Mahmoud, N. ; Zeeman, G. ; Gijzen, H. ; Lettinga, G. - \ 2006
    Biochemical Engineering Journal 28 (2006)2. - ISSN 1369-703X - p. 196 - 200.
    activated-sludge - extracellular polymer - de-waterability - retention time - particle-size - dewaterability - biopolymers - sewage
    The interaction between digestion conditions and the sludge physical characteristics and behaviour was investigated for anaerobically digested primary sludge in completely stirred tank reactors (CSTRs). The CSTRs were operated to maintain sludge retention times (SRTs) of 10, 15, 20 and 30 days and temperatures of 25 and 35 degrees C. The change of the floe size as a result of digestion was examined using wet sieve analysis (0.100, 0.125, 0.200, 0.500 and 1.000 mm). The results reveal a substantial reduction in all floc sizes with improving digestion conditions. Digestion leads to the transfer of bigger flocs into smaller ones, which has a remarkable effect on the sludge physical behaviour. The majority of the raw and digested floes are smaller than 0.100 mm. The dewatering results showed the existence of an optimal SRT for dewaterability at 20 and 15 days for the reactors operated at 25 and 35 degrees C, respectively. The dewaterability of sludge digested at less favourable conditions, viz. 10 days at 25 degrees C deteriorates due to increase of small floes generated from destruction of larger flocs. The digested sludge settling results showed a slight worsening but insignificant trend with increasing the SRT.
    Phytophthora genomics: the plant destroyers' genome decoded
    Govers, F. ; Gijzen, M. - \ 2006
    Molecular Plant-Microbe Interactions 19 (2006)12. - ISSN 0894-0282 - p. 1295 - 1301.
    pathogen phytophthora - oomycete pathogen - saprolegnia-parasitica - microsatellite markers - expressed sequences - downy mildew - infestans - sojae - avirulence - ramorum
    The year 2004 was an exciting one for the Phytophthora research community. The United States Department of Energy Joint Genome Institute (JGI) completed the draft genome sequence of two Phytophthora species, Phytophthora sojae and Phytophthora ramorum. In August of that year over 50 people gathered at JGI in Walnut Creek, California, for an annotation jamboree and searched for the secrets and surprises that the two genomes have in petto. This culminated in a paper in Science in September of this year describing the highlights of the sequencing project and emphasizing the power of having the genome sequences of two closely related organisms. This MPMI Focus issue on Phytophthora genomics contains a number of more specialized manuscripts centered on gene annotation and genome organization, and complemented with manuscripts that rely on genomics resources
    Pathogen removal mechanisms in macrophyte and algal waste stabilization ponds
    Awuah, E. - \ 2006
    Wageningen University. Promotor(en): H.J. Gijzen, co-promotor(en): H.J. Lubberding. - [S.l.] : S.n. - ISBN 9789085045007 - 147
    algen - plassen - afval - pathogenen - verwijdering - afvalwaterbehandeling - protozoa - bacteriën - bezinkingsvijvers - algae - ponds - wastes - pathogens - removal - waste water treatment - protozoa - bacteria - stabilization ponds
    Waste stabilization ponds are recognized as the solution to domestic wastewater treatment in developing countries. The use of such natural systems is considered to be very important. This is because it is cheap, easy to construct and they do not require high skilled labour. In the developing countries the objectives for wastewater treatment should put emphasis on pathogen removal since most diseases and deaths in these areas are caused by poor sanitation. The efficiency in the removal of pathogens in algal waste stabilization ponds has been found to be very good. The global awareness on resource depletion calls for the use of macrophytes to recover nutrients from wastewater and also to act as an incentive to wastewater treatment. However, the pathogen removal efficiencies of macrophyte-based stabilization ponds are not well known. An understanding of the mechanism involved could be used to improve on the technology and maximize the benefits through effective operation and maintenance practices
    Phytophthora genome sequences uncover evolutionary origins and mechanisms of pathogenesis
    Tyler, B.M. ; Tripathy, S. ; Zhang, X. ; Dehal, P. ; Jiang, R.H.Y. ; Aerts, A. ; Arredondo, F.D. ; Baxter, L. ; Bensasson, D. ; Beynon, J.L. ; Chapman, J. ; Damasceno, C.M.B. ; Dorrance, A.E. ; Dou, D. ; Dickerman, A.W. ; Dubchak, I.L. ; Garbelotto, M. ; Gijzen, M. ; Gordon, S.G. ; Govers, F. ; Grunwald, N.J. ; Huang, W. ; Ivors, K.L. ; Jones, R.W. ; Kamoun, S. ; Krampis, K. ; Lamour, K.H. ; Lee, M.K. ; McDonald, W.H. ; Medina, M. ; Meijer, H.J.G. ; Nordberg, E.K. ; Maclean, D.J. ; Ospina-Giraldo, M.D. ; Morris, P.F. ; Phuntumart, V. ; Putnam, N.H. ; Rash, S. ; Rose, J.K.C. ; Sakihama, Y. ; Salamov, A.A. ; Savidor, A. ; Scheuring, C.F. ; Smith, B.M. ; Sobral, B.W.S. ; Terry, A. ; Torto-Alalibo, T.A. ; Win, J. ; Xu, Z. ; Zhang, H. ; Grigoriev, I.V. ; Rokhsar, D.S. ; Boore, J.L. - \ 2006
    Science 313 (2006)5791. - ISSN 0036-8075 - p. 1261 - 1266.
    effector proteins - downy mildew - resistance - arabidopsis - avirulence - genes - locus - sojae - expression - virulence
    Draft genome sequences have been determined for the soybean pathogen Phytophthora sojae and the sudden oak death pathogen Phytophthora ramorum. Oömycetes such as these Phytophthora species share the kingdom Stramenopila with photosynthetic algae such as diatoms, and the presence of many Phytophthora genes of probable phototroph origin supports a photosynthetic ancestry for the stramenopiles. Comparison of the two species' genomes reveals a rapid expansion and diversification of many protein families associated with plant infection such as hydrolases, ABC transporters, protein toxins, proteinase inhibitors, and, in particular, a superfamily of 700 proteins with similarity to known oömycete avirulence genes
    Beschrijving module OSmanSoil : een eenvoudig bodemmodel voor de beschrijving van waterbeweging, convectief stikstoftransport, water- en stikstofopname, denitrificatie, nitrificatie en mineralisatie
    Heinen, M. - \ 2005
    Wageningen : Alterra (Alterra-rapport 1261)
    bodem - modellen - transportprocessen - beweging in de bodem - bodemwaterbeweging - stikstof - denitrificatie - nitrificatie - bodemtemperatuur - soil - models - transport processes - movement in soil - soil water movement - nitrogen - denitrification - nitrification - soil temperature
    In het onderzoek naar organisch stofmanagement in biologische kasteelt (bijvoorbeeld Marcelis et al., 2003) is tot nu toe gebruik gemaakt van een gekoppeld bodem-plant model, bestaande uit FUSSIM2 (Heinen and de Willigen, 1998; 2001) en INTKAM (Gijzen, 1994). Omdat de rekentijd van dit gekoppelde model relatief groot is, kon dit niet worden toegepast in het te ontwikkelen adviesmodel voor organische bemesting. Daarom is besloten om een eenvoudig bodemmodel op te zetten, welke ongekoppeld met het plantmodel kan functioneren. In dit rapport wordt kort de theorie en gebruikershandleiding van het eenvoudige bodemmodel beschreven
    Effect of operational variables on nitrogen transformations in duckweed stabilization ponds
    Caicedo Bejarano, J.R. - \ 2005
    Wageningen University. Promotor(en): H.J. Gijzen, co-promotor(en): N.P. van der Steen. - [S.l.] : S.n. - ISBN 9789085041627 - 163
    spirodela polyrhiza - stikstof - stikstofbalans - nitrificatie - anaërobe behandeling - algen - bezinkingsvijvers - spirodela polyrhiza - nitrogen - nitrogen balance - nitrification - anaerobic treatment - algae - stabilization ponds
    There is a diversity of conventional technologies available for removal of pollutants from wastewater. Most of these technologies are aerobic alternatives with high construction cost and high energy consumption and require skilled personal for operation and maintenance. As a consequence, only countries with a high gross national product (GNP) can afford these options. Where these technologies were introduced in developing countries, in most cases these could not be operated sustainably, leading to loss of investments and continued water resource contamination. Extensive investments in wastewater treatment plants world-wide during the last decades have greatly reduced the organic loading of receiving water bodies in high GNP countries. Only recently, many of these plants were appropriated to remove nitrogen and phosphorus. The increasing use of chemical fertilizer may cause high levels of eutrophication in water bodies, which may induce algae blooms resulting in strong fluctuations in oxygen concentration. Oxygen depletion causes fish kill as well as odor problems.

    The situation in countries with a low GNP is worse than in the developed world. The unequal expansion of water supply coverage compared to the expansion in wastewater and sanitation services leads to increased contamination of surface and ground waters. The general trend is to use conventional WWT systems for big cities, but for medium and small sized cities non-conventional systems are often considered. Therefore, there is an urgent need to develop and improve low cost technologies for wastewater treatment that are within the economic and technological capabilities of developing countries. In countries like Colombia it is very common that the regulation controls mainly the removals of organic matter and suspended solids. Other parameters like nitrogen, phosphorus, pathogens, micro-contaminants are also crucial and need to be addressed. This makes a response via conventional technologies very expensive, and for developing regions in fact unachievable. It would be ideal if new technologies can provide besides the removal of organic matter and solids, resource recovery like the generation of biogas (energy production) or high quality biomass (animal fodder). At the moment, no technological packages appear to be readily available.

    Experience has shown that no single technology can offer an optimum treatment for the different components to be treated in wastewater or to recover them as valuable resources. Therefore an adequate combination of different technologies in an integrated system could convert a wastewater treatment into an attractive sustainable system. For example UASB reactor and duckweed ponds are relatively low cost technologies and their combination offers several advantages. Firstly, anaerobic treatment will reduce considerably the organic matter in the wastewater and convert it into methane, which can be used as a source of renewable energy. Secondly, the effluents of anaerobic treatment could be post-treated to meet discharge standards in duckweed ponds for nutrient recovery in the form of high quality biomass.At this point three valuable products can be listed: biogas for use as an energy source, biomass that can be used for aquaculture or animal feed and treated effluent that can be re-used in irrigation. A system that generates such by-products increases the feasibility and sustainability of pollution control programs. Furthermore, the products may help to address the increasing need for food production in the world. 

    The development of duckweed pond technology has been concentrated on the study of the processes occurring within the ponds, with respect to organic matter, nitrogen, phosphorus and pathogen removal and the corresponding mechanisms. Further research is needed in order to have a good control of effluent nitrogen levels. There are still important questions to be answer like how to maximize nitrogen recovery via duckweed production, how to get good effluent levels depending on effluent reuse. If the effluent is going to be used in crop irrigation, to reduce nitrogen effluent concentration to 15-20 mg l -1 will be enough. If the effluent is going to be discharge in surface waters the nitrogen level would have to be reduced as much as possible. Therefore it is important to study how the design and combination of technologies could generate the required nitrogen effluent levels. The present work was focus on the study of the effect of different operational variables, like the effect of anaerobic pre-treatment, the combination of algae and duckweed ponds, the effect of pond depth on nitrogen transformation and removals.

    The effect of anaerobic pre-treatment on environmental and physicochemical characteristics of duckweed stabilization ponds was studied in Chapter 2 .The environmental and physicochemical conditions affect both plant growth and microbiological treatment processes in the system. Two series of continuous-flow pilot plants, composed of seven ponds in series each, were operated side by side. One system received artificial sewage with anaerobic pre-treatment, while the other system received the same wastewater without anaerobic pretreatment. pH, temperature, dissolved oxygen, alkalinity, conductivity, biochemical oxygen demand, total and ammonium nitrogen, nitrites and nitrates, and phosphorus were monitored under steady state conditions. It was found that pH levels were very stable in both systems with and without anaerobic pretreatment. Vertical temperature gradients were present during daytime but not as strong as they may occur in conventional stabilization ponds. Oxygen levels were significantly higher in the duckweed system with anaerobic pretreatment, especially in the top layer. (up to 2 mg O 2 l -1 ) than in the system without pretreatment (up to 1.2 mg O 2 l -1 ). Nevertheless, aeration rates were low in both systems. Both systems were efficient in removing organic matter. The system without pretreatment obtained 98% of BOD 5 removal in pond 4, so 12 days of retention time will be sufficient to reach high organic matter removal. The system with pretreatment obtained also 98% BOD 5 removal (92% in UASB reactor). In this case the duckweed ponds will serve as a polishing step for remaining organic matter. Nutrient removals were 37-48% for nitrogen and 45-50 % for phosphorus in the lines with and without pretreatment respectively.

    The main form of nitrogen in anaerobic effluent is ammonium. This is the preferred nitrogen source for duckweed, but at high levels it may become inhibitory to the plant. Renewal fed batch experiments at laboratory scale were performed (Chapter 3 ) to assess the effect of total ammonia (NH 3 + NH 4+ ) nitrogen and pH on the growth rate of the duckweed Spirodela polyrrhiza. The experiments were performed at different total ammonia nitrogen concentrations, different pH ranges and in three different growth media. The inhibition of duckweed growth by ammonium was found to be due to a combined effect of ammonium ions (NH 4+ ) and ammonia (NH 3 ), the relative importance of each one depending on pH.

    The effect of anaerobic pre-treatment on the performance of a duckweed stabilization pond system was assessed in a pilot plant located in the Ginebra Research Station-Colombia (Chapter 4). The pilot plant consisted of two lines of seven duckweed ponds in series. One line received de-gritted domestic wastewater and the other received effluent of a 250 m 3 Up-flow Anaerobic Sludge Blanket (UASB) reactor, treating the same wastewater. Both lines were operated at a total hydraulic retention time of 21 days.The systems were monitored for temperature, pH, oxygen, biochemical oxygen demand, chemical oxygen demand, total suspended solids, total phosphorus, biomass production, and different forms of nitrogen. No effect of anaerobic pretreatment was observed on pH and temperature in the two systems. Oxygen concentrations were higher in the system with UASB reactor. Although both systems complied with the Colombian regulation for BOD removal (> 85%)pretreatment with UASB reactor may contribute to the reduction of area requirement for the stabilization ponds. Effluent quality in terms of total suspended solids was excellent, i.e. 9 ± 2 and 4 ± 1 mg l -1 in the system with and without pre-treatment, respectively. Total nitrogen removals were 63 % and 68% and phosphorus removals were 24% and 29% in the system with and without pre-treatment, respectively. The differences between the two systems were found not to be significant. Duckweed biomass production was in the range of 54-90 g m -2 -d -1 (fresh weight) in the system with pre-treatment and 36-84 g m -2 -d -1 in the system without pre-treatment. Total biomass productions were significantly different at 92% level of confidence. Protein content was 35.1% and 36.6% for the system with and without pre-treatment, respectively.Nitrogen removal is nowadays one of the most important effluent treatment objectives because of the serious pollution problems it causes to the environment. How nitrogen is transformed and removed in duckweed ponds was studied and nitrogen balances were established (Chapter 5). The experimental system was the same as in the previous chapter. Ammonia volatilization was found to be not an important removal mechanism in duckweed ponds (less than 1%). Removal by sedimentation was also low at 2.1% and 4.7% for the systems with and without anaerobic pre-treatment, respectively. Instead, denitrification was found to be the most important removal mechanism (42% and 48%), followed by duckweed biomass up-take (15.6% and 15.1%). Average nitrogen biomass up-take rates were 199 mg N m -2 d -1 and 193 mg N m -2 d -1 for the system with and without pre-treatment, respectively. Nitrification rates were in the range of112 - 1190 mg N m -2d -1 and 58-1123 mg N m -2 d -1 for the system with and without anaerobic pretreatment respectively. Denitrification rates were in the range of 112 - 937 mg N m -2 d -1 and 59 - 1039 mg N m -2 d -1 for the system with and without pre-treatment respectively. The configuration of the system, in particular the down and up flow pattern seemed to have an important stimulating effect on denitrification rates, probably by causing alternative exposure of the pond water to aerobic and anoxic conditions.Although the potential of duckweed ponds for removing carbonaceous and suspended material from wastewater has been demonstrated, the system could be further optimized for nitrogen removal. The effect of introducing algae-ponds (aerobic zones) into a series of duckweed stabilization ponds on nitrification and denitrification (Chapter 6 ) was studied in two consecutive phases. During the first phase, the seven ponds of the pilot plant were fully covered with duckweed (Spirodela polyrrhiza). Before the start of the second phase, the duckweed cover was removed from ponds 1 and 3, with a view to allow algae growth in the 'open' ponds. The feed of the duckweed pond system consisted of the effluent of a real scale UASB reactor, which treated domestic wastewater from Ginebra-Colombia. The system was operated with a continuous flow to produce a hydraulic retention time (HRT) of 3 days per pond and a total HRT of 21 days. Effluent total nitrogen was significantly different in the two phases, with 13.8± 2.9 mg TN l -1 (63 % removal) and 3.7±1.5 mg TN l -1 (90%) for first and second phase, respectively.Denitrification was the most important removal mechanism during both phases, and amounted to 43.5 % and 76.2 % of influent nitrogen, in first and second phase, respectively. Ammonia volatilization and sedimentation were insignificant processes for nitrogen removal in both phases. Nitrification played an important role in nitrogen transformations in the duckweed systems and it was favored by the introduction of aerobic zones in ponds 1 and 3. Denitrification also played a key role in nitrogen transformations and removal. Despite the presence of oxygen in the water column, denitrification occurred, probably due to the anaerobic microenvironment of system biofilms. Higher nitrogen removal might be obtained in duckweed pond systems through the introduction of aerobic zones in early stages of the system. Where effluents cannot be reused for crop irrigation, strict nitrogen effluent criteria can be met using hybrid duckweed-algal ponds at considerably shorter hydraulic retention time compared to fully duckweed covered systems.

    The effect of pond depth on nitrogen removal in duckweed stabilization ponds was studied in Chapter 7. The pilot plant consisted of two lines with seven duckweed ponds in series, with different depths and fed with effluent of a laboratory scale UASB reactor. Three experimental conditions were studied: DSP1 with pond depth 0.7 m and HRT= 21 days, DSP2 with pond depth 0.4 m and HRT = 12 days, and DSP3 with pond depth 0.4 m and HRT = 21 days. The systems were monitored for pH, temperature and oxygen profiles, organic matter removal (BOD 5 ), nitrogen transformations, biomass production and biomass nitrogen content. Average total nitrogen removal rates were 598 mg N m -2 d -1 for DSP 1, 589 mg N m -2 d -1 for DSP 2 and 482 mg N m -2 d -1 for DSP 3. In spite of the lower nitrogen removal rate in DSP 3, it had higher removal efficiency (44 %, 43 % and 62 % for DSP 1, 2 and 3 respectively) due to the lower surface loading rate in this system. This shows that using the percentage of removal as a parameter for comparison should be done with care and the operational parameters of the compared systems should be taken into account. Denitrification was the most important nitrogen removal mechanism for the three DSPs. Nitrogen removal via biomass production was the second most important removal mechanism for the three experiments. Pond depth does not seem to determine nitrification or denitrification. Nitrification seems to be related to surface organic loading rate, while denitrification was related to BOD availability. The comparison between two pond systems with different depth, but operated at the same hydraulic surface loading rate (DSP 1 and 2) showed similar nitrogen removals in the shallower system as in the deeper system. This suggests that duckweed pond system could be designed with shallow depth without affecting surface loading and nitrogen removal efficiency. Nitrogen removal appeared to be governed by surface loading rate rather than by hydraulic retention time.

    Most of the research so far has been performed at laboratory or pilot scale. In the process of technology-development it is important to test findings at full scale. In Chapter 8 , the performance of a full scale duckweed pond was compared with a full scale algae pond treating effluent of a UASB reactor operated under similar conditions of climate, configuration, wastewater composition and loading rate. The real scale experimental system was composed of two continuous flow channels. One operated as an algae pond and the other as a duckweed pond ( Spirodela polyrrhiza and Lemna minor . ) . The volume of each channel was 225 m 3 , an average surface area of 322 m 2 , L/W ratio= 13.1 and depth of 0.7 m. The wastewater flow was 19.7 m 3 d -1 , for each system and the theoretical hydraulic retention time was 11.5 days. The ponds were monitored for the following parameters: Organic matter (BOD 5 ), total suspended solids (TSS), ammonium nitrogen (NH 4+ -N), total Kjeldahl nitrogen (TKN), nitrite nitrogen (NO 2 -N), nitrate nitrogen (NO 3 -N), total phosphorous (TP) and faecal coliform (FC). The duckweed pond developed different environmental conditions in terms of pH, temperature and oxygen, compared to the algae pond. The duckweed pond was more efficient in removing organic matter and the algae pond was more efficient in nitrogen removal. Denitrification accounted for most of the nitrogen removal in the algae and duckweed ponds. The second most important mechanism for nitrogen removal was ammonia volatilization for the algae pond and plant up-take for the duckweed pond. In the design of duckweed pond systems special attention should be paid to the reactor configuration and flow pattern in order to obtain good contact between water column and the duckweed cover and to reduce hydraulic problems.

    Practical applications.

    Wastewater treatment can be converted into an attractive, feasible and sustainable alternative by combining anaerobic pretreatment, duckweed ponds, and algae ponds. The integrated system UASB reactor, algae pond and duckweed pond offers the possibility to remove the various unwanted component in wastewater and to recover part of the valuable material present in the wastewater in the form of biomass or biogas The effluents may be suitable for discharge or for irrigation depending on the removal efficiencies of the system. The design and operation of this integrated system may have two different approaches. Firstly, one could optimize nitrogen recovery by duckweed uptake and effluent irrigation. Secondly, one could maximize nitrogen removal in order to protect the receiving water resources. 

    If the objective of the treatment is recovery of nitrogen then the stimulation of duckweed incorporation and the reduction of effluent nitrogen to a suitable range for irrigation would be the best option. The configuration of an efficient anaerobic pre-treatment followed by a series of ponds completely covered with duckweed would be recommendable. Influent ammonium nitrogen concentration below 50 mg l -1 and pH below 8 would be desirable to avoid biomass growth inhibition. The comparison between two pond systems with different depths and the same hydraulic surface loading rate showed similar nitrogen removals in the shallower system as in the deeper system. This means that duckweed pond system could be designed with the shallower depth without affecting nitrogen removal efficiency. Shallow ponds are easier to build, to operate and to maintain and in the case of duckweed covered ponds, they can be regarded as a crop production system.

    If the objective of the treatment is nitrogen removal due to disposal regulations, a strategy to enhance denitrification should be adopted. Higher nitrogen removals may be obtained in duckweed pond systems through the introduction of aerobic zones in early stages of the system, which allows a considerable reduction of the hydraulic retention time. Strict nitrogen effluent criteria can therefore be met at relatively short hydraulic retention times. The configuration of the system, in particular the down and up flow pattern seems to have an important positive effect on denitrification rates. Compartmentalization of the treatment system improves the pond performance. In the design of pond systems special attention should be paid to the reactor configuration and hydraulic flow pattern, good contact water-biomass and to avoidance of short circuiting and dead zones. In the process of technology development the following studies are envisaged and recommended for further research: Future studies should be focused on shallow ponds with the views to enhance nitrogen removal via its recovery in the form of duckweed biomass. Shallow ponds will also reduce construction cost of the treatment systems.

    Alternative uses of treated effluent and produced biomass should be investigated.In the case of effluent reuse on irrigation, the reduction of nitrogen concentrations in the treatment system to 15-25 mg l -1 will be enough. The use of vegetable biomass as a food complement on the diet of fish and pork is an alternative that has been preliminary explored in the area of research. Further studies are necessary to determine its feasibility.For safe discharge of effluent to open water bodies, effluent nitrogen concentration should be low. In this case nitrogen removal processes may be influence by affecting growth conditions of nitrifiers/dentrifiers like oxygen levels or availability of area for bacterial attachment. It is important to performed studies in order to find the best combination of duckweed and algae ponds for nitrogen removal. The introduction of baffles on the treatment channels will increase the availability of area for biomass growth and will improved the hydraulic characteristics of the treatment systems. The appropriated number and distribution of baffles should be investigated. Recycling of final aerobic effluent to the UASB reactor or to the entrance of the duckweed pond could be an interesting option to stimulate denitrification. Pathogen removal will be affected by the use of low pond depths, the presence of aerobic zones and compartmentalization in the treatment system. These effects should be researched in order to optimizedalso the removal of pathogenic microorganisms.
    Anaerobic sewage treatment in a one-stage UASB reactor and a combined UASB Digester system
    Mahmoud, N.A. ; Zeeman, G. ; Gijzen, H.J. ; Lettinga, G. - \ 2004
    Water Research 38 (2004)9. - ISSN 0043-1354 - p. 2348 - 2358.
    domestic sewage - waste-water - de-waterability - low-temperature - sludge - wastewaters - particles
    The treatment of sewage at 15°C was investigated in a one-stage upflow anaerobic sludge blanket (UASB) reactor and a UASB-Digester system. The latter consists of a UASB reactor complemented with a digester for mutual sewage treatment and sludge stabilisation. The UASB reactor was operated at a hydraulic retention time of 6 h and a controlled temperature of 15°C, the average sewage temperature during wintertime of some Middle East countries. The digester was operated at 35°C. The UASB-Digester system provided significantly (significance level 5%) higher COD removal efficiencies than the one-stage UASB reactor. The achieved removal efficiencies in the UASB-Digester system and the one-stage UASB reactor for total, suspended, colloidal and dissolved COD were 66%, 87%, 44% and 30%, and 44%, 73%, 3% and 5% for both systems, respectively. The stability values of the wasted sludge from the one-stage UASB reactor and the UASB-Digester system were, respectively, 0.47 and 0.36 g CH4-COD/g COD. Therefore, the anaerobic sewage treatment at low temperature in a UASB-Digester system is promising
    Options for wastewater management in Harare, Zimbabwe
    Nhapi, I. - \ 2004
    Wageningen University. Promotor(en): H.J. Gijzen, co-promotor(en): M.A. Siebel. - S.l. : Balkema - ISBN 9789085040446 - 179
    afvalwater - waterbeheer - afvalwaterbehandeling - stedelijke gebieden - zimbabwe - waste water - water management - waste water treatment - urban areas - zimbabwe
    The capital city of Zimbabwe, has adopted an urban water cycle that is geared towards high level service provision. Water supply and sewerage/sanitation coverage amounts to over 98%, which makes Harare with the highest coverage. The city's high volume of water abstraction from its main water resource, Chivero, however, can no longer be sustained. The lake has been seriously polluted by large volumes of (partially) treated effluents from wastewater treatment plants in Harare and the neighbouring town of Chitungwiza. It also receives pollution from agricultural, solid waste, industrial, and natural sources. Most of the wastewater treatment plants in the lake's catchment are overloaded and they experience frequent breakdowns. This situation has been worsened by repeated years of drought, resulting in the accumulation of nitrogen and phosphorous in the lake. The negative impacts of this have been reflected in periodic fish kills, proliferation of algae and water hyacinth, and the reduction in biological diversity. Other related problems are difficulties in potable water treatment and clogging of irrigation pipes.There is now an urgent need to control pollution loads and to remove contaminants that haveaccumulatedin LakeChivero over many years. A great deal could be achieved through rational management of the urban water system and the associated nutrient cycle. This should be based on an integrated approach that includes reduction of water consumption, and the wise use of water through pollution prevention/reduction measures. On the water supply side, available options include reduction of water losses (now at ± 30%), water-saving installations (in households, commerce, and industry), direct reuse ( e.g ., greywater), and alternative water resources ( e.g. , rainwater harvesting and groundwater). On the wastewater side, options available include onsite, decentralised and centralised treatment plus reuse.The general objectives of this research were to assess the contribution of wastewater from Harare to the nitrogen and phosphorous inflows into Lake Chivero and, based on this assessment, to formulate feasible sanitary engineering solutions to the problem of excessive nutrient inflows into the lake. The research specifically targeted nutrients because these are the major problem parameters. BOD is largely taken care of via current wastewater treatment and river self-purification processes. The general strategy was to intervene at various levels; i.e. , property, decentralised and centralised levels, with various options aimed at reducing water use and limiting wastewater production and reusing or recycling water and nutrients. This strategy would reduce nitrogen and phosphorous flows to the lake, whilst increasing water availability.An extensive water quality and quantity monitoring study in the Chivero catchment was carried out from June 2000 to December 2001 to assess the current situation in terms of water use, treatment and reuse levels, and flow balances. In addition, current contributions of wastewater discharges to nutrient flows in the rivers and Chivero were assessed. Intervention strategies were developed based on an approach, referred to as the " 3-Step Strategic Approach " to wastewater management. The steps include: 1) pollution prevention/reduction at source, 2) treatment in the direction of reuse, and 3) disposal with stimulation of self-purification capacity of the receiving water body. The three steps should be considered in this chronological order. Options considered include source control by the users (residents, industries, etc) using various strategies such as greywater separation and reuse, implementation of toilets with urine separation, and other ecological methods of wastewater management. Other possible options are invoking better behaviour through fees and information, and user responsibility through education, legislative changes and stricter controls over industry. Options for boosting the self-purification capacity of water bodies include introducing wetlands into the river system via natural overflow, land irrigation, reducing retention time in the lake, etc. Flexible and differential solutions were developed for each landuse category (commercial, industrial and residential).The results of this study confirmed that wastewater plays a major role in the pollution of Chivero. Wastewater contributed over 50% of the annual water flows in the major inflow rivers of Marimba and Mukuvisi. Water quality was found to be an urgent problem that requires immediate action whilst water scarcity was considered a medium-term problem. The river water quality for points upstream and downstream of wastewater discharge points were far above the 0.03 mg/l TP required for avoiding excessive plant growth in rivers. The lake nutrient concentrations were 2.01.3 mg/l TN and 0.6 ±3 mg/l TP ( standard deviation), reflecting a hypertrophic status. Nearly 70% of the annual phosphorus inflows were retained within the lake, which had a hydraulic retention time of 1.6 ±1.1 years based on rainfall years 1981/2 to 2000/1. However, for the monitoring period, the hydraulic retention time reduced to 0.4 years due to the heavy rains received in that period. Besides the need to substantially reduce nutrient inflows in Lake Chivero, adequate water inflows are also essential for the flushing out of nutrients from the lake, especially phosphorus. The continued accumulation of phosphorus in the lake sediments leads to an internal phosphorus cycle, further complicating remedial measures. The effective reduction of nutrient inflows into Lake Chivero hinges on solutions related to wastewater management. It is in this context that the "3-Step Strategic Approach" was applied, focusing on wastewater treatment and reuse options at onsite, decentralised, and centralised levels. An aggregation of these options led to the development of short-term, medium-term, and long-term solutions. It was estimated that significant improvements in the lake water quality (to about 0.4 mg/l TN and 0.07 mg/l TP in the medium-term) could be achieved by applying the measures suggested in this dissertation. In addition, the treatment of part of the effluent to tertiary standard and subsequent discharge into Lake Chivero could also reduce the lake hydraulic retention time to below 0.5 years, thereby enhancing the flushing out of nutrients. It was concluded that both water quality and quantity problems in the Chivero catchment could be significantly reduced via improvements in wastewater management in combination with the control of other point and non-point sources of pollution.
    Nutrients valorisation via duckweed-based wastewater treatment and aquaculture
    El-Shafai, S.A.A.M. - \ 2004
    Wageningen University. Promotor(en): H.J. Gijzen; F. El-Gohary, co-promotor(en): Johan Verreth; P. van der Steen. - [S.l.] : Balkema - ISBN 9789058089564 - 174
    afvalwaterbehandeling - aquacultuur - lemna - voedingsstoffen - egypte - waste water treatment - aquaculture - lemna - nutrients - egypt
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