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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    The use of Delft3D to simulate the deposition of cohesive and non-cohesive sediments in irrigation systems
    Theol, Shaimaa Abd Al Amear - \ 2020
    Wageningen University. Promotor(en): C.M.S. de Fraiture, co-promotor(en): F.X. Suryadi. - Leiden : CRC Press/Balkema - ISBN 9780367496913 - 146

    Sediment deposition threatens the performance of many irrigation systems. Because of the high impact on irrigation performance and crop production, many studies have been done on how to deal with sediment deposition. In this research, the Delft3D model, originally developed for hydro-morphologic modelling of rivers and estuaries, was adapted for the use in irrigation systems simulations and applied to different case studies. This research addresses two shortcomings of previous studies of sediments in irrigation systems. Firstly, while previous studies primarily used 1D models, this research uses a 2D/3D model. The use of 2D/3D models in irrigation systems is significant because the non-uniform flow around structures such as offtakes, weirs and gates, leads to asymmetric sedimentation patterns that are missed by 1D simulations. Secondly, whereas previous studies mostly considered non-cohesive sediments, this research simulates cohesive, non-cohesive and a mix of both sediment types. This is important for irrigation systems that draw water from natural rivers that carry a mix of cohesive and non-cohesive sediments. The findings of this research are important for irrigation system maintenance and gate operation. It is also essential for the development of canal operating plans that meet crop water requirements and at the same time minimizes sediment deposition by alternating gates.

    Integrated flood and drought mitigation measures and stategies : Case study: The Mun River Basin, Thailand
    Prabnakorn, Saowanit - \ 2020
    Wageningen University. Promotor(en): C.M.S. de Fraiture, co-promotor(en): F.X. Suryadi. - Leiden : CRC Press/Balkema - ISBN 9780367903787 - 158

    Floods and droughts are climate extremes that account for more than 80% of people affected by natural disasters worldwide. Both catastrophes co-exist in many river basins, for example, the Mun River Basin in Thailand, which is selected as the study area. Approximately 90% of rice cultivation here is rain-fed, and that results in the lowest yields in the country, making many farmers persist in poverty. This study aims to assess floods and droughts and their impacts on agriculture at the basin scale. For flooding, the hydrologic and hydraulic models were developed to produce the first completed flood hazard maps at the Mun River Basin. Droughts in the basin were determined by the proposed drought risk assessment scheme that combines all three key components (hazard, exposure, and vulnerability). Subsequently, the study attempts to tackle both floods and droughts simultaneously and sustainably by using integrated measures and strategies. If the problems caused by flood and drought climate extremes are solved, this will ensure adequate food availability and alleviate poverty in the basin. Furthermore, the study shows that a holistic approach to simultaneously solving both problems is efficient as most water will be utilized to benefit agriculture, the primary sector that feeds a growing population.

    Strategies to cope with risks of uncertain water supply in spate irrigation systems
    Bashir, Eiman Mohamed Fadul - \ 2020
    Wageningen University. Promotor(en): C.M.S. de Fraiture, co-promotor(en): I. Masih. - Leiden : CRC Press/Balkema - ISBN 9780367465827 - 132

    Flood based irrigation in particular spate irrigation relies on variable flood scenarios occurring every year. Management of spate flood for spate irrigation must cope with the variability and uncertainty of water supply. Coping with water supply risks is often the only way to harness the opportunities for a productive use of water in arid environment. Integrating and strengthening community responses into irrigation policies and improvement plans could ensure sustainable and productive spate irrigated systems that can achieve food security for the poor population. This research analyses and evaluates risks and coping strategies developed by farming communities in the Gash spate irrigation system in Sudan, Eastern Africa. The research has synthesized different coping strategies developed by farmers, water user associations and water managers to cope with low, high and untimely flood risks. The research provides different frameworks that can assist with the identification of risk sources, pathways and propagation as well as evaluation of locally developed strategies at field, secondary and intake systems. The findings of this study contribute to the scarce knowledge on spate irrigation systems and provide scientifically sound and evidence-based insights to aid informed policy and decision making to improve productivity and sustainability of the spate irrigation systems.

    Reduction of low arsenic concentrations in drinking water to below 1 µg L−1 by adsorption onto granular iron (Hydr)oxides
    Jeworrek, A. ; Ahmad, A. ; Hofs, B. ; Mook, J. van; Wal, A. van der - \ 2019
    In: Environmental Arsenic in a ChangingWorld. - CRC Press/Balkema - ISBN 9781138486096 - p. 593 - 594.

    Arsenic in drinking water should be reduced as much as possible, because it is amongst carcinogenic substances. FerroSorp® Plus, Huijbergen and Spannenburg GIH could reduce As(V) levels in Ouddorp water below the desired 1 µg L−1. Particularly Huijbergen GIH had according to non-linear Freundlich modeling the higher KF value, translating into a potentially higher effective adsorption capacity. One of the characteristics that probably determines the success of a GIH is its physical properties. Since the effective adsorption capacity increases with higher initial As(V) concentrations, Huijbergen GIH is a promising adsorbent to reduce a wide range of arsenic concentrations from drinking water. Therefore, this affordable technology is not only reducing ultra-low arsenic concentrations to even lower concentrations in Ouddorp water but is also promising for developing countries that are seriously affected by high concentrations of arsenic in their drinking water.

    Waterbeheer en Voedselbossen
    Veraart, Jeroen ; Kruijt, Bart ; Sukkel, Wijnand ; Kruit, Jeroen ; Balkema, A. ; Rombouts, P. - \ 2019
    Lifecycle management and replacement strategies: Two of a kind?
    Zandvoort, M. ; Vlist, M.J. van der; Haitsma, R. ; Oosterveld, E. - \ 2019
    In: Life-Cycle Analysis and Assessment in Civil Engineering. - CRC Press/Balkema - ISBN 9781138626331 - p. 1507 - 1512.

    Due to the end of lifetime of infrastructure assets, water managers need to develop strategies for their replacement or demolishment. We outline four distinct reasons in which replacements differ from new assets and analyze which particular considerations about replacement can complement lifecycle management (LCM) practices. We conclude that these replacement considerations lead to additional technical design features for hydraulic structures and other assets. Complementing LCM with considerations about the new asset lifecycle after replacement informs planning approaches for developing adequate replacement strategies in the context of asset management.

    Effects of wetland conversion to farming on water quality and sediment and nutrient retention in a tropical catchment
    Uwimana, Abias - \ 2019
    Wageningen University. Promotor(en): K.A. Irvine, co-promotor(en): A.A. van Dam. - Leiden : CRC Press/Balkema - ISBN 9780367859732 - 131

    The study used a combination of landscape-scale synoptic surveys (catchment, reaches) and mesocosm surveys (experimental plots) to assess the impacts of conversion of natural valley-bottom wetlands to farming land on the water quality and retention of sediment and nutrients. The results showed that temperature, pH, electrical conductivity and dissolved oxygen concentration decreased, and total suspended solids (TSS) increased with storm water increase. Nitrogen (TN) and phosphorus (TP) accumulated in the catchment during the dry season and washed into the water courses during the early stages of the higher flows, with subsequent lower concentrations at the end of the rains due to dilution. Large proportions of the annual loads of TSS, TP and TN (93%, 60% and 67%, respectively) were transported during rainfall events that occurred in 115 days. Fishponds acted as temporal traps of TSS, TN and TP at the early stages of farming, and were a source of and TN and TP at the end of the farming period, in contrast to rice farming that generated sediments and nutrients early in the farming period and trapped them at the end of the farming season. Wetlands mostly acted as sinks but sometimes as a source of sediment and nutrients.

    The value of using hydrological datasets for water allocation decisions: earth observations, hydrological models, and seasonal forecasts
    Kaune Schmidt, Alexander José - \ 2019
    Wageningen University. Promotor(en): C.M.S. de Fraiture, co-promotor(en): M.G.F. Werner. - Leiden : CRC Press/Balkema - ISBN 9780367429553 - 166

    An increasing number of hydrological datasets from earth observations, hydrological models and seasonal forecasts have become available for water managers, consultants and the general public. These datasets are state-of-the-art products which are usually accessible online and may contribute to develop hydrological studies and support water resources management. However, the added value of these datasets has not been completely explored in decision-making processes. Research studies have assessed how well data can help in predicting climate, but there is a lack of knowledge on how well data can help in water allocation decisions. This work provides numerical tools, methods and results to evaluate the value of using hydrological datasets to support water allocation decisions at river basin and irrigation district scale. An integrated approach is used to predict climate, improve decisions and reduce negative impacts. Results show that investing in hydrological data with finer spatial and temporal resolution and longer periods of record improves water allocation decisions and reduces agricultural production loss in large irrigation schemes. Using river discharge data from hydrological models and global precipitation enhances irrigation area planning when little in-situ data is available. Moreover, using seasonal streamflow forecasts improves available water estimates resulting in better water allocation decisions. The framework was tested in Costa Rica, Colombia and Australia, but can be applied in any case study around the world.

    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.

    Estimating combined loads of diffuse and point-source pollutants into the Borkena River, Ethiopia
    Belachew, Eskinder Zinabu - \ 2019
    Wageningen University. Promotor(en): K.A. Irvine, co-promotor(en): P. Kelderman; J. van der Kwast. - Leiden : CRC Press/Balkema - ISBN 9780367253455 - 150

    Estimating the relative contribution of heavy metals and nutrients loads from diffuse and point sources and various hydrological pathways is a major research challenge in catchment hydrology. Understanding of the transfer, loads and concentration of these loads in basins is useful in designing and implementing policies for the managements of surface waters. In sub-Saharan countries, few studies have been done to estimate heavy metals and nutrients transfers in catchments. It is usually difficult to obtain hydrological and hydro-chemical data even for smaller catchments. This Thesis presents the estimates of loads of heavy metals and nutrients from industry and land use into two rivers that flow through an industrializing catchment, additionally presents the selection and application of a model to estimate TN and TP loads in the Kombolcha catchments. The study of the transfer contaminants from diffuse and point sources illustrates management, capacity and policy needs for the monitoring of rivers in Ethiopia, and with relevance for other sub-Saharan countries.

    The study was done in the semi-arid catchments of Kombolcha city, which sits within an urban and peri-urban setting in north-central Ethiopia. The Leyole and Worka rivers drain the catchments, and receive industrial effluents from several factories in the surrounding area and wash-off from the surrounding catchment. The rivers flow into the larger Borkena River. The goal of this research was to monitor and quantify sources and transfer of heavy metals (Cr, Cu, Zn and Pb) and nutrients ((NH4 +NH3)–N, NO3–N, TN, PO4–P, TP) into the Leyole and Worka rivers, and evaluate their management/control in a data-poor catchment. The apportionments of the total nitrogen and phosphorus loads from diffuse and point sources were investigated. The work is placed in a policy context through a review of relevant policy within Ethiopia and at the wider perspective of sub-Saharan Africa.

    The first set of measurements was on industrial effluent samples collected from discharge from five factories. In total, 40 effluent samples were taken in both 2013 and 2014. The second set of measurements were on waters and sediments. In total, 120 water samples were collected from the rivers in the wet season of two monitoring years of 2013 and 2014. River bed sediment samples, in total 18 samples, were taken at six stations on three occasions in the wet seasons the two monitoring years. In order to estimate the dilution capacities of the Leyole and Worka rivers, daily flow depths of the river water were recorded twice a day during the sampling campaigns of 2013 and 2014. Stage‐discharge rating curves were used to estimate the flows of both the Leyole and Worka Rivers. The heavy metals concentrations were measured using Inductively Coupled Plasma Mass Spectrometry.

    The median concentrations of Cr from tannery effluents and Zn from steel processing effluents were 26,600 and 155,750 µg/L, respectively, much exceeding emission guidelines. Concentrations of Cr were high in the Leyole river water (median: 2660 µg/L) and sediments (maximum: 740 mg/kg), Cu in the river water was highest at the midstream part of the Leyole river (median: 63µg/L), but a maximum content of 417 mg/kg was found in upstream sediments. Concentrations of Zn were highest in the upstream part of the Leyole river water (median 521µg/L) and sediments (maximum: 36,600 mg/kg). Pb concentration was low in both rivers, but, relatively higher content (maximum: 3,640 mg/kg) found in the sediments in the upstream of the Leyole river. Chromium showed similar patterns of enhanced concentrations in the downstream part of the Leyole River. Except for Pb, the concentrations of all heavy metals surpassed the guidelines for aquatic life, human water supply, and irrigation and livestock water supply. All of the heavy metals exceeded guidelines for sediment quality for aquatic organisms.

    Regarding nutrients, emissions from a brewery and a meat processing unit were rich in nutrients, with median concentrations of TN of 21,00–44,000 µg/L and TP of 20,000 – 58,000 µg/L. These had an average apportionment of 10% and 13%, respectively, of the total nutrient loads. In the waters, higher TN concentrations were found from sub‐catchments with largest agricultural land use, whereas highest TP was associated with sub‐catchments with hilly landscapes and forest lands. Both the TN and TP concentrations exceeded standards for aquatic life protection, irrigation, and livestock water supply. Using specific criteria to assess model suitability resulted in the use of PLOAD. The model relies on estimates of nutrient loads from point sources such as industries and export coefficients of land use, calibrated using measured TN and TP loads from the catchments. The model was calibrated and its performance was increased, reducing the sum of errors by 89 % and 5 % for the TN and TP loads, respectively. The results were validated using independent field data.

    The findings of the research shows high loads of heavy metals and nutrients in rivers of the industrializing regions of Kombolcha, identified gaps in estimating heavy metals and nutrient pollution and in policy implementation. Recommended future research and policy development to address a number of key gaps in water quality protection measures include control of point and diffuse loads of heavy metals and nutrients from sources, and improvement in land managements and monitoring and regulation.

    Editors’ foreword
    Zhu, Yong Guan ; Guo, Huaming ; Bhattacharya, Prosun ; Bundschuh, Jochen ; Ahmad, Arslan ; Naidu, Ravi - \ 2018
    In: Environmental Arsenic in a ChangingWorld. - Beijing : CRC Press/Balkema (Environmental Arsenic in a ChangingWorld - 7th International Congress and Exhibition Arsenic in the Environment, 2018 ) - ISBN 9781138486096 - p. xlv - xlvi.
    Editors’ foreword
    Zhu, Yong Guan ; Guo, Huaming ; Bhattacharya, Prosun ; Bundschuh, Jochen ; Ahmad, Arslan ; Naidu, Ravi - \ 2018
    In: Environmental Arsenic in a Changing World. - CRC Press/Balkema - ISBN 9781138486096 - p. xlv - xlvi.
    Arsenic removal to <1 µg l−1 by coprecipitation with in-situ generated Fe(III) precipitates with and without advanced pre-oxidation
    Ahmad, A. ; Mook, J. van; Schaaf, B. ; Wal, A. van der - \ 2018
    In: Environmental Arsenic in a ChangingWorld - 7th International Congress and Exhibition Arsenic in the Environment, 2018. - CRC Press/Balkema (Environmental Arsenic in a ChangingWorld - 7th International Congress and Exhibition Arsenic in the Environment, 2018 ) - ISBN 9781138486096 - p. 591 - 592.

    The aim of this study is to investigate removal of low As concentrations from groundwater at a Drinking Water Treatment Plant (DWTP) in The Netherlands in order to achieve <1 µg L−1 As in produced drinking water. Two iron based emerging technologies, both relying on in-situ generated Fe(III) precipitates for As adsorption, were investigated. These include: 1) Advanced Oxidation-Coprecipitation-Filtration (AOCF) and 2) Coprecipitation prior to ultrafiltration (C-UF). We show that most of the As removal occurs in the top half of a Rapid Sand Filter (RSF) bed. In this part we also observe the conversion of As(III) into As(V). The mechanism of As(III) oxidation to As(V) in the RSF is still not understood, however we hypothesize that either the manganese oxides or the biological activity in the filter bed may be responsible for this conversion. In agreement with this observation, we also notice that drinking water only contains As(V) and that the levels of As(III) are negligible. The experiments have shown that both AOCF and C-UF are promising emerging technologies to reduce arsenic levels to below 1 µg L−1 which is the agreed target in The Netherlands between the Dutch water companies.

    Integrating arsenic in water safety planning in the Netherlands
    Wens, P. van der; Ahmad, A. - \ 2018
    In: Environmental Arsenic in a ChangingWorld - 7th International Congress and Exhibition Arsenic in the Environment, 2018. - CRC Press/Balkema (Environmental Arsenic in a ChangingWorld - 7th International Congress and Exhibition Arsenic in the Environment, 2018 ) - ISBN 9781138486096 - p. 618 - 619.

    The Dutch drinking water sector complies with the most restrictive guidelines in the world and has a long-standing history of striving for excellence in water quality standards. The Dutch Association of Drinking Water Companies (Vewin) concluded in 2015 to lower the standard on arsenic in drinking water to 1 µg L−1. Following the new recommendation Brabant Water, a major water supply company in The Netherlands developed its masterplan on arsenic reduction by analysing the presence of arsenic in the systems from source to tap. Several measures were put in place to integrate arsenic into water safety planning in order to manage the risks. The underlying cost-benefit study and its implication on water safety planning at Brabant Water is discussed in this presentation.

    Visual MINTEQ simulation for prediction of the adsorption of arsenic on ferrihydrite
    Irunde, R. ; Bhattacharya, P. ; Ijumulana, J. ; Ligate, F.J. ; Ahmad, A. ; Mtalo, F. ; Mtamba, J. - \ 2018
    In: Environmental Arsenic in a ChangingWorld - 7th International Congress and Exhibition Arsenic in the Environment, 2018. - CRC Press/Balkema (Environmental Arsenic in a ChangingWorld - 7th International Congress and Exhibition Arsenic in the Environment, 2018 ) - ISBN 9781138486096 - p. 435 - 436.

    The surface of ferrihydrite adsorbs arsenic (As) effectively. In this investigation, the As laced water samples collected from Geita and Mara regions within the Lake Victoria Basin (LVB) under DAFWAT project were simulated onVisual MINTEQ 3.1 software to determine the amount of ferrihydrite required to adsorb a given amount of As from water. Model simulations show that As concentration of ≤1 mM can be completely adsorbed by 4 g L−1 ferrihydrite. Previous studies show that the lower pH 4 to 4.5 influences adsorption, while it decreases as pH increases as well as when As concentration increases. The increase of adsorbent dose to 4 g L−1 has shown to improve As(V) adsorption on pH 5 to 8 at 100%. The amount of adsorbent can now be used for laboratory adsorption experiments by using iron-based materials or commercial ferrihydrite.

    Modeling arsenic removal by co-precipitation under variable redox conditions
    Korevaar, M.W. ; Vries, D. ; Ahmad, A. - \ 2018
    In: Environmental Arsenic in a ChangingWorld - 7th International Congress and Exhibition Arsenic in the Environment, 2018. - CRC Press/Balkema (Environmental Arsenic in a ChangingWorld - 7th International Congress and Exhibition Arsenic in the Environment, 2018 ) - ISBN 9781138486096 - p. 432 - 434.

    Drinking water companies in the Netherlands are actively investigating routes to reduce arsenic (As) to <1 µg L−1 in drinking water. Co-precipitation of As with iron during groundwater treatment is a promising method. When As(III) is present in raw water, permanganate (MnO4) can be dosed to oxidize As(III) to As(V) in order to improve As removal efficiency. The dosages of MnO4 and Fe(III) to achieve <1 µg L−1 As in the treatment effluents depend on the composition of raw water. The coprecipitation of As(III) and As(V) with ferrihydrite under variable raw water composition and redox environments, controlled by oxygen (O2) or MnO4 is modeled in this study by the generalized double layer model, and redox equilibrium reactions. Results show that the pH of the treatment process is critical to determine the As removal efficiency. At pH = 8 the highest As removal is obtained, followed by pH = 6 while pH = 7 gives the least removal. HCO3, PO4 and H4 SO4 hamper the adsorption of As(V). In future work, the model outcome will be assessed by experiments. Furthermore, the model will be extended with oxidation kinetics in case oxidation (by e.g. oxygen) occurs at a slower rate than the (mean) residence time of the water in the process.

    Photo-Activated Sludge: a novel algal-bacterial biotreatment for nitrogen removal from wastewater
    Rada Ariza, Angélica - \ 2018
    Wageningen University. Promotor(en): P.N.L. Lens, co-promotor(en): P. van der Steen; C.M. Lopez Vazquez. - Leiden : CRC Press/Balkema - ISBN 9780367178864 - 324

    Nitrogen rich wastewaters (10-400 mg N L-1) are usually produced by municipal, industrial and agricultural wastes, such as effluents from anaerobic treatments. These represent a risk to the environment due to the high nutrient concentrations (nitrogen and phosphorous), which can cause eutrophication of water bodies, deteriorating the quality of the ecosystems. As a solution, the potential nitrogen removal capacity of a novel bio-treatment system, namely the Photo-Activated Sludge (PAS), which is composed of microalgae and bacteria consortia, is presented in this thesis. This novel bio-treatment is based on the symbiosis between microalgae, nitrifiers and heterotrophic bacteria (microalgal-bacterial consortia). Experimental work using photobioreactors for the cultivation of microalgae and bacteria under sequencing batch conditions showed that microalgal-bacterial consortia can remove ammonium 50% faster than solely microalgal consortia. The increase in ammonium removal rates was due to the action of nitrifying bacteria, supplied with oxygen produced by algae. Nitrification was the main ammonium removal mechanism within the microalgal-bacterial biomass, followed by algal uptake and nutrient requirements for bacterial growth. Carbon oxidation and denitrification were the main removal mechanisms for organic carbon. Hence, the role of algae within the microalgal-bacterial system is to provide oxygen to support the aerobic processes. The microalgal-bacterial system offers the possibility of reducing the hydraulic retention time, which can decrease the large area requirements often demanded by algal systems.

    Sediments in the Tema Harbour (Ghana): chemical pollution and sedimentation rates
    Botwe, Benjamin Osei - \ 2018
    Wageningen University. Promotor(en): P.N.L. Lens, co-promotor(en): E. Nyarko. - Leiden : CRC Press/Balkema - ISBN 9781138323513 - 270

    The Tema Harbour in Ghana has been in operation for nearly six decades and is subject to large influxes of sediments and sediment pollution due to the intense human activities in the harbour area. This thesis assessed sediment pollution in the Tema Harbour by using the standard 10-day Corophium volutator and 28-day Hediste diversicolor whole-sediment toxicity bioassays as well as chemical contaminant (DDTs, HCHs, PAHs and metal - Cd, Pb, Cr, Ni, Cu, Zn and As) data. The bioassay results showed significant C. volutator and H. diversicolor mortalities, indicating that the Tema Harbour sediments are polluted and toxic. Biota-sediment accumulation factors further revealed a high potential for bioaccumulation of the sediment-associated metals, which can have adverse implications for the food chain. Thus, the Tema Harbour sediments are unsuitable for disposal at sea without remediation.

    The thesis further investigated sediment accumulation rates in the Tema Harbour by the combined analyses of sediment trap and sediment core data. The sediment cores exhibited variable bulk density profiles, indicating highly dynamic and non-steady sedimentation conditions. 7Be-derived gross-estimates of very recent sediment accumulation rates using the constant flux-constant sedimentation (CF-CS) model were in the range of 2.5-9.0 g.cm-2.y-1. These values were much lower than the estimated average settling fluxes from the sediment trap data (15.2-53.8 g.cm-2.y-1), indicating sediment resuspension plays an important role in the sedimentation process. Conventional 210Pb sediment dating models did not allow any estimation of SARs in the Tema Harbour. The 210Pb-based TERESA model, on the other hand, proved to be a good tool for quantifying sediment accumulation rates in the Tema Harbour with time-averaged values in the range of 1.4-3.0 g.cm-2.y-1 and sediment accretion rates of 1.7-3 cm.y-1.

    In conclusion, this study has shown that the Tema Harbour has been severely affected by anthropogenic activities, resulting in pollution of the sediments, especially those from the Fishing Harbour and the Canoe Basin. Moreover, the sediment accretion rates in the harbour may pose moderate problems for sustainable use of the harbour. There is, therefore, a need to improve sediment and environmental management in the Tema Harbour and regulate the disposal of the dredged material originating from this tropical coastal harbour.

    Treatment of petroleum refinery wastewater with constructed wetlands
    Mustapha, Hassana Ibrahim - \ 2018
    Wageningen University. Promotor(en): P.N.L. Lens, co-promotor(en): J.J.A. Bruggen. - Leiden : CRC Press/Balkema - ISBN 9781138324398 - 277

    The use of constructed wetlands (CWs) for polishing of petroleum refinery wastewater in Nigeria was evaluated. Secondary treated petroleum refinery wastewater from a refinery (Kaduna, Nigeria) was characterized with different types of organic and inorganic pollutants (Chapter 3). Vertical subsurface flow (VSSF) CWs planted with locally available macrophytes (Cyperus alternifolius and Cynodon dactylon) were designed and built for polishing of secondary treated refinery wastewater in terms of organic matter, nutrients and suspended solids removal (Chapter 4). The tertiary treated refinery wastewater did, however, not meet effluent discharged compliance limits in terms of total suspended solids (TSS), biochemical oxygen demand (BOD5), chemical oxygen demand (COD) and ammonium-N (NH4+-N) removal.

    Typha latifolia planted-VSSF CWs could, however, treat TSS, BOD5, COD and NH4+-N in the petroleum refinery wastewater to below World Health Organization and Federal Environmental Protection Agency (Nigeria) effluent discharge limits of 30 mg/L for TSS, 10 mg/L for BOD5, 40 mg/L for COD and 0.2 mg/L for NH4+-N (Chapter 5). T. latifolia-planted VSSF CW achieved higher removal efficiencies for all parameters measured in comparison to C. alternifolius and C. dactylon planted-VSSF CWs. In addition, the T. latifolia-planted VSSF CW had the best heavy metal removal performance, followed by the C. alternifolius-planted VSSF CW and then the C. dactylon-planted VSSF CW (Chapter 6). The accumulation of the heavy metals in the plants accounted for only a rather small fraction (0.09 - 16 %) of the overall heavy metal removal by the wetlands. Coupling a horizontal subsurface flow (HSSF) CW to the VSSF CW (hybrid CW) further improved effluent quality with an overall BOD5 and PO43--P removal efficiency of, respectively, 94% and 78% (Chapter 5).

    Diesel contaminated wastewater was treated in the hybrid CWs spiked with three different nutrient concentrations. Numerical experiments were performed to investigate the biodegradation of the diesel compounds in the synthetic contaminated wastewater by the duplex-CWs using constructed wetland 2D. The VF CWs had a higher removal efficiency than the HFF CWs and the hybrid CW showed higher removal efficiencies in the days with nutrient application than the days without nutrient application (Chapter 8).

    This study showed that VSSF CWs planted with T. latifolia, C. alternifolius and C. dactylon can be used for the removal of suspended solids, organic contaminants and heavy metals from secondary refinery wastewater under tropical climate conditions. Especially T. latifolia-planted hybrid CWs are viable alternatives for the treatment of secondary refinery wastewater to below standards of the World Health Organization and Federal Environmental Protection Agency (Nigeria) under the prevailing climatic conditions in Nigeria.

    Lactic acid fermentation of human excreta for agricultural application
    Andreev, Nadejda - \ 2017
    Wageningen University. Promotor(en): P.N.L. Lens, co-promotor(en): B. Boincean; M. Ronteltap. - Leiden : CRC Press/Balkema - ISBN 9781138049895 - 207
    lactic acid - manure fermentation - fermentation - fertilizers - human faeces - biochar - composting - melkzuur - mestvergisting - fermentatie - kunstmeststoffen - mensenfeces - biochar - compostering

    Human excreta is a valuable fertilizer for improving soil quality and crop productivity, with a potential to replace or complement the mineral fertilizers. The main challenges related to human excreta regarding agricultural applications are microbial contamination risks, loss of nutrients, and odor issues. Fertilization by lacto-fermented faeces supplemented by biochar has benefits such as improved soil bulk density, nitrate and potassium concentrations as well as the yield and yield components of corn, compared to untreated, simple stored faeces, urine, cattle manure, and unfertilized controls. Even though the mineral fertilizer produced corn with significantly higher height and leaf length, it did not add significantly higher yields than lacto-fermented faeces supplemented by biochar. A faeces treatment process by combined lacto-fermentation with thermophilic composting and biochar supplementation had better reduction of coliforms, Escherichia coli, Enterococcus faecalis and Clostridium perfringens, and higher germination of radish and growth of tomatoes than combined lacto-fermentation with vermicomposting. Urine lacto-fermentation contributed to a pH reduction below 4, a decrease in the ammonium concentration and odor strength, as well as an increase in the germination rates compared to untreated stored urine. The results of this study provide important information that can set the basis for scaling up a sustainable technology for the treatment of source separated human excreta while improving its potential for resource recovery.

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