Browsing by Author "Nopens, Ingmar"

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A methodology to model environmental preferences of EPT taxa in the Machangara river basin (Ecuador)
(2017) Jerves Cobo, Rubén Fernando; Everaert, Gert; Iñiguez Vela, Xavier Patricio; Córdova Vela, Gonzalo Esteban; Díaz Granda, Catalina Monserrat; Cisneros Espinoza, Felipe Eduardo ; Nopens, Ingmar; Goethals, Peter L
Rivers have been frequently assessed based on the presence of the Ephemeroptera— Plecoptera—Trichoptera (EPT) taxa in order to determine the water quality status and develop conservation programs. This research evaluates the abiotic preferences of three families of the EPT taxa Baetidae, Leptoceridae and Perlidae in the Machangara River Basin located in the southern Andes of Ecuador. With this objective, using generalized linear models (GLMs), we analyzed the relation between the probability of occurrence of these pollution-sensitive macroinvertebrates families and physicochemical water quality conditions. The explanatory variables of the constructed GLMs differed substantially among the taxa, as did the preference range of the common predictors. In total, eight variables had a substantial influence on the outcomes of the three models. For choosing the best predictors of each studied taxa and for evaluation of the accuracy of its models, the Akaike information criterion (AIC) was used. The results indicated that the GLMs can be applied to predict either the presence or the absence of the invertebrate taxa and moreover, to clarify the relation to the environmental conditions of the stream. In this manner, these modeling tools can help to determine key variables for river restoration and protection management.
Biological impact assessment of sewage outfalls in the urbanized area of the Cuenca river basin (Ecuador) in two different seasons
(2018) Jerves Cobo, Rubén Fernando; Lock, Koen; Van Butsel, Jana; Pauta Calle, Gladys Guillermina; Cisneros Espinoza, Felipe Eduardo; Nopens, Ingmar; Goethals, Peter L
We evaluated the biological water quality in relation to chemicals discharged through sewage outfall during both dry and rainy season. The lowland area of the Cuenca River basin in the southern Andes of Ecuador, including the city of Cuenca, constituted the study area. To perform an integrated water quality assessment, data were collected of macroinvertebrates, physicochemical conditions and morphological characteristics in 43 sites in the Cuenca River and its tributaries. The Andean Biotic Index (ABI) and the Biological Monitoring Working Party adapted to Colombia (BMWP-Col) were used to evaluate the biological water quality. Both biological indexes were higher upstream than downstream from the city. Moreover, these indexes indicated better conditions during the rainy season than in the dry season, based on the presence of more sensitive families. The biological indexes related more to the oxygen saturation than to the five-day biological oxygen demand (BOD5), nutrients and chloride concentrations. The relationship between BOD5 and nutrient concentrations with the variation of both biological indexes was clearer in the dry season than in the rainy season. However, in some sites, these indexes were influenced more by morphological aspects than by pollutants. Both biological indexes showed similar patterns along the rivers, generally the BMWP-Col scored higher than the ABI index. The latter index was shown to be more suitable for the high Andes region. These results could be used to support the implementation of river restoration actions, such as determining priorities for splitting sewer and precipitation water transport systems and needs for improved wastewater treatment facilities in specific locations. © 2018 Elsevier GmbH
Biological water quality in tropical rivers during dry and rainy seasons: a model-based analysis
(2020) Jerves Cobo, Rubén Fernando; Eurie Forio, Marie Anne; Lock, Koen; Van Butsel, Jana; Pauta Calle, Gladys Guillermina; Cisneros Espinoza, Felipe Eduardo; Nopens, Ingmar; Goethals, Peter L
Recent studies on water quality in tropical rivers indicate substantial differences between seasons. However, investigations on the needs and added value of season-specific models are lacking. Thus, this paper aims to determine the accuracy and relevance of season-specific and season-overarching models to predict biological water quality. Additionally, we investigated the variation of prediction accuracy using sub-datasets from different parts of the Cuenca River basin. This study was accomplished in the rivers that pass through the urban and suburban areas of the city of Cuenca, which is located in the southern Andes of Ecuador. The Andean Biotic Index (ABI) was used as an indicator of biological water quality. Subsequently, models were developed to predict the ABI, with physicochemical and morphological variables as predictors, which were collected in 43 sites during both the dry and the rainy seasons. The predictions were obtained using three kinds of generalized linear models (GLMs): Gaussian, Gamma and Inverse Gaussian. The season-specific models were more accurate than the season-overarching models. Similarly, the predictions of the biological water quality in sites sampled in the urban area were more accurate than the forecasts performed in reference sites. The major variables predicting the ABI during the dry season were five-day biological oxygen demand (BOD5), ammonium and orthophosphate, while dissolved oxygen (DO), oxygen saturation (OS), nitrate, total solids proved to be important during the rainy season. The results of this research emphasize the importance of developing season-specific models and the implementation of different key actions for river restoration during both the dry and rainy seasons. The accuracy and the replication of these models could be improved and checked with more data taken from new sampling events. The modelling approach developed in this study can be applied to similar basins in the tropics and reveals that environmental investments need to count on monitoring strategies and data and analyses of the biological water quality variation in dry and rainy seasons, within the context of sustainable development.
CFD analysis of sludge accumulation and hydraulic performance of a waste stabilization pond
(2012) Alvarado Martínez, Andrés Omar; Sánchez Cordero, Esteban Remigio; Durazno, Galo; Vesvikar, Mehul; Nopens, Ingmar
Sludge management in waste stabilization ponds (WSPs) is essential for safeguarding the system performance. Sludge accumulation patterns in WSPs are strongly influenced by the pond hydrodynamics. CFD modeling was applied to study the relation between velocity profiles and sludge deposition during 10 years of operation of the Ucubamba WSP in Cuenca (Ecuador). One tracer experiment was performed and three sludge accumulation scenarios based on bathymetric surveys were simulated. A residence time distribution (RTD) analysis illustrated the decrease of residence times due to sludge deposition. Sludge accumulation rates were calculated. The influence of flow pattern on the sludge deposition was studied, enabling better planning of future pond operation and desludging. © IWA Publishing 2012.
Development of an automated tracer testing system for UASB laboratory-scale reactors
(2021) Cisneros Ramos, Juan Fernando; Nopens, Ingmar; Pinos Vélez, Verónica Patricia; Peláez Samaniego, Manuel Raúl; Alvarado Martínez, Andrés Omar
Residence time distribution (RTD) curves play an essential role in the hydraulic characterization of reactors. Current approaches for obtaining RTD curves in laboratory-scale reactors are time-consuming and subject to large errors. Thus, automated systems to obtain RTD curves in laboratory-scale reactors are of great interest for reducing experimental errors due to human interaction, minimizing experimentation costs, and continuously obtaining experimental data. An automated system for obtaining RTD curves in laboratory-scale reactors was designed, built, and tested in this work. During the tests conducted in a cylindrical upflow anaerobic sludge blanket (UASB) reactor, the system worked properly using the stimulus–response pulse technique with sodium chloride as a tracer. Four main factors were found to affect the representativeness of the RTD curves: flow stabilization time, test water conductivity, temperature, and surface tension. A discussion on these factors and the corresponding solutions is presented. The RTD curves of the UASB reactor are left-skewed with a typical tank reactor’s flow shape with channeling and dead zones. A transitory flow behavior was evidenced in the reactor, which indicates the influence of internal turbulent flow structures. The system proposed herein is expected to help study the hydraulics of reactors using laboratory-scale models more efficiently
Hydraulic assessment of waste stabilization ponds: comparison of computational fluid dynamics simulations against tracer data
(Universidad de Cuenca, 2011-07) Alvarado, Andrés; Vedantam, Sreepriya; Durazno, Galo; Nopens, Ingmar; DIUC; Universidad de Cuenca; Dirección de Investigación de la Universidad de Cuenca
The overall performance of a wastewater treatment plant is in addition to the effectiveness of the biokinetic processes controlled by the flow dynamics. A wide used technique to characterize the water flow dynamics is the use of tracers. At full-scale tracer experiments in wastewater treatment plants provide insufficient information to completely grasp the flow dynamics. Additionally results are often biased by uncontrolled external factors. As alternative, computational fluid dynamic (CFD) models for performance analysis of existing and the design of new wastewater treatment plants have been increasingly used over the last decade. The paper presents the results of a tracer experiment against the output of a CFD model with application to a 7 ha large maturation pond. The tracer study was conducted with the fluorescence dye Rhodamine WT using the stimulus response technique. The three dimensional CFD model was built considering a variable density distribution of spatial grids based on the specific characteristics of the system. For the unsteady flow simulations the turbulence model k- was adopted. Residence time distribution (RTD) generated by both approaches were compared and showed fairly good agreement. The velocity and turbulence profiles of the CFD model were compared with experimental data confirming, although the high computational demand, the robustness of the used CFD model.
Hydrodynamic evaluation of five influent distribution systems in a cylindrical UASB reactor using CFD simulations
(2021) Cisneros Ramos, Juan Fernando; Cobos Cobos, Fabiola Estefania; Peláez Samaniego, Manuel Raúl; Nopens, Ingmar; Alvarado Martínez, Andrés Omar
UASB reactors are a promising option for environmentally friendly wastewater treatment due to their reduced carbon footprint and their capacity to treat a variety of wastewater strengths, among other recognized advantages over alternative wastewater treatment systems. The Influent Distribution System (IDS) is a critical structure for generating granules in a UASB reactor since it provides the required flow hydrodynamics for their formation. Thus, the objective of this study was to evaluate and compare the efficiency of five IDS configurations to generate ideal granulation conditions using Computational Fluid Dynamics (CFD) simulations. The IDS configurations were as follows: (C1) single radial inflow, (C2) upward axial inflow, (C3) downward distributed axial inflow, and two novel configurations in the form of (C4) double opposite radial inflow and (C5) downward tangential inflow. The hydrodynamic response of configuration C1 was validated in a physical model with dynamic Froude similitude. The granulation measurement was velocity-based in the reactor reaction zone using steady-state CFD simulations. The novel IDS configuration C4 was the one that resulted in the highest granulation volume, with up to 45.5% of the potential granulation volume of the UASB reactor, in contrast to the IDS C2 that obtained the lowest granulation with only 10.8%. Results confirm that the IDS directly impacts the hydrodynamics of the reactor and that model-based design can be used to ascertain IDS configurations that better promote granulation in UASB reactors
Integrated ecological modelling for evidence-based determination of water management interventions in urbanized river basins: case study in the Cuenca river basin (Ecuador)
(2020) Jerves Cobo, Rubén Fernando; Benedetti, Lorenzo; Amerlinck, Youri; Lock, Koen; De Mulder, Chaim P.; Van Butsel, Jana; Cisneros Espinoza, Felipe Eduardo; Goethals, Peter; Nopens, Ingmar
The growth of urbanization worldwide has contributed to the deterioration of the ecological status of water bodies. Efforts at improving the ecological status have been made either in isolated form or by means of integrated measures by stakeholders, but in many cases, these measures have not been evaluated to determine their benefit. In this study, we implemented a scenario analysis to restore the ecological water quality in the Cuenca River and its tributaries, which are located in the southern Andes of Ecuador. For this analysis, an integrated ecological model (IEM) was developed. The IEMlinked an urban wastewater system (IUWS) model, which gave satisfactory results in its calibration and validation processes, with ecological models. The IUWS is a mechanistic model that incorporated the river water quality model, a wastewater treatment plant (WWTP) with activated sludge technology, and discharges from the sewage system. The ecological status of the waterways was evaluated with the Andean Biotic Index (ABI), which was predicted using generalized linear models (GLMs). The GLMs were calculated with physicochemical results from the IUWS model. Four scenarios that would enhance the current ecological water quality were analyzed. In these scenarios, the inclusion of a new WWTP with carbon, and with carbon and nitrogen removal as well as the addition of retention tanks before the discharges of combined sewer overflows (CSOs) were assessed. The new WWTP with carbon and nitrogen removal would bring about a better restoration of the ecological water quality due to better nitrogen removal. The retention tanks would help to enhance the ecological status of the rivers during rainy seasons. The integrated model implemented in this study was shown to be an essential tool to support decisions in the Cuenca River basin management.
Integrated mechanistic and data-driven modeling for risk assessment of greenhouse gas production in an urbanized river system
(2021) Ho, Long; Jerves Cobo, Ruben Fernando; Forio, Marie Anne Eurie; Mouton, Ans; Nopens, Ingmar; Goethals, Peter
Surrounded by intense anthropogenic activities, urban polluted rivers have increasingly been reported as a significant source of greenhouse gases (GHGs). However, unlike pollution and climate change, no integrated urban water models have investigated the GHG production in urban rivers due to system complexity. In this study, we proposed a novel integrated framework of mechanistic and data-driven models to qualitatively assess the risks of GHG accumulation in an urban river system in different water management interventions. Particularly, the mechanistic model delivered elaborated insights into river states in four intervention scenarios in which the installation of a new wastewater treatment plant using two different technologies, together with new sewage systems and additional retention tanks, were assessed during dry and rainy seasons. From the insights, we applied fuzzy rule-based models as a decision support tool to predict the GHG accumulation risks and identify their driving factors in the scenarios. The obtained results indicated the important role of new discharge connection and additional storage capacity in decreasing pollutant concentrations, consequently, reducing the risks. Moreover, among the major variables explaining the GHG accumulation in the rivers, DO level was considerably affected by the reaeration capacity of the rivers that was strongly dependent on river slope and flow. Furthermore, river water quality emerged as the most critical variable explaining the pCO2 and N2O accumulation that implied that the more polluted and anaerobic the sites were, the higher were their GHG accumulation. Given its simplicity and transparency, the proposed modeling framework can be applied to other river basins as a decision support tool in setting up integrated urban water management plans.
Integrated water system modelling to support water management in the Cuenca Basin
(Ghent University, 2020-01-17) Jerves Cobo, Rubén Fernando; Goethals, Peter; Nopens, Ingmar
In this chapter is evaluated the biological water quality in relation to chemicals discharged through sewage outfall during doth dry and rainy season. The lowland area of the Cuenca River basin in the southern Andes of Ecuador, including the city of Cuenca, constituted the study area. To perform an integrated water quality assessment, date were collected of macroinvertebrates, physicochemical conditions and morphological characteristics in 43 sites in the Cuenca River and its tributaries. The Andean Biotic Index (ABI) and the Biological Monitoring Working Party adapted to Colombia (BMWP-Col) were used to evaluate the biological water quality. Both biological indexes were higher upstream than downstream form the city. Moreover. These indexes indicated better conditions during the rainy season than in the dry season, based on the presence of more sensitive families. The biological indexes related more to the oxygen saturation than to the five-day biological oxygen demand (BOD5), nutrients and chloride concentrations. The relationship between BOD5 and nutrient concentrations with the variation of both biological indexes was clearer in the dry season than in the rainy season. However, in some sites, these indexes were influenced more by morphological aspects than by pollutants. Both biological indexes shoed similar patterns along the rivers, generally the BMWP-Col scored higher than the ABI index. The later index was shown to be more suitable for the high Andes region as an indicator of water quality. These results could be used to monitor the implementation of river restoration actions, such as determining priorities for splitting sewer and precipitation water transport systems and needs for improved wastewater treatment facilities in specific locations.
Integrating hydraulic, physicochemical and ecological models to assess the effectiveness of water quality management strategies for the river Cuenca in Ecuador
(2013-04-10) Holguin Gonzalez, Javier E.; Boets, Pieter; Alvarado, Andrés; Cisneros, Felipe; Carrasco, María C.; Wyseure, Guido; Nopens, Ingmar; Goethals, Peter L. M.
During the past decades, the development and use of ecological models to predict the presence or absence of macroinvertebrates as water quality indicators for decision support in river management has gained a lot of interest. However, these models rarely integrate hydromorphological, physicochemical, and biological components in the submodels. We developed a generic framework for decision support in water management that can be applied to any river basin based on an integrated modelling approach. This approach integrates a mechanistic hydraulic and physicochemical water quality model with aquatic ecological models. Two types of ecological models were developed, habitat suitability models to predict the occurrence of macroinvertebrates and ecological assessment models to predict a biotic index score. Our main purpose was to assess the effectiveness of different wastewater treatment/disposal strategies considering receiving water's ecological aspects and to determine water quality requirements. This paper presents the testing and validation of this integrated framework on a case study of a mountain river (River Cuenca) in the Andes of Ecuador. Three wastewater management scenarios were tested. The different scenarios indicated that the foreseen investments in sanitation infrastructure will lead to modest improvements of the ecological water quality. This improvement (i.e. increase of the biotic index) was only identified in 6 of the 21 monitoring stations considered in the River Cuenca and its tributaries. Therefore, it is necessary to control the impact of the industrial wastewaters discharges and the diffuse pollution at the upper catchment of the tributaries to achieve a good ecological status. With these results, we proved that integrated models, like the one presented here, have an added value for decision support in water management by coupling ecological water quality to a set of hydraulic and chemical water quality measures based on a water quality model. In order to improve these models, it is necessary to change the river monitoring strategy towards collection of data which include simultaneous measurements of physicochemical, hydromorphological and biological data.
Model based analysis of the growth kinetics of microalgal species residing in a waste stabilization pond
(2017) Decostere, Bjorge; Alvarado Martínez, Andrés Omar; Sanchez Merchan, Esteban Andres; Pauta Calle, Gladys Guillermina; Rousseau, Diederik; Nopens, Ingmar; Van hulle, Stijn W.h
BACKGROUND: In this study the growth kinetics of Chlorella and Scenedesmus, isolated from a Waste Stabilization Pond were investigated under different conditions of light intensity and temperature. Experimental data were collected by means of a combined respirometric and titrimetric set-up and used to extend a mathematical model. RESULTS: The experimental results illustrated the interdependent relationship of light intensity and temperature, which had a significant influence on the microalgal growth. Consequently, a previously developed model was extended with a mathematical function that describes this relationship. The maximum specific growth rate and oxygen mass transfer coefficient were considered for model calibration. The optimized parameter values for Chlorella were μmax = 0.56 ± 0.0008 d−1 and KLa = 10.02 ± 0.02 d−1. For Scenedesmus, the optimized parameter values were μmax = 0.19 ± 0.0004 and KL a = 7.71 ± 0.004 d−1. The model with optimized parameter settings described the dissolved oxygen production (derived from the respirometric data) and the related proton consumption (derived from the titrimetric data) reasonably well for both microalgal species. The threshold value for Theil's Inequality Coefficient of 0.3 was never exceeded. In addition, model validation for both species was performed indicating good correspondence between model prediction and experimental values. CONCLUSIONS: Based on the experimental observations, a previously developed mathematical model was extended with a function that describes the interaction between light intensity and temperature. After model calibration a difference in maximum specific growth rate between the two microalgal species was observed. This might be explained by differences in cell metabolism. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry
Model-based analysis of the potential of macroinvertebrates as indicators for microbial pathogens in rivers
(2018) Jerves Cobo, Rubén Fernando; Van Echelpoel, Wout; Cisneros Espinoza, Felipe Eduardo; Nopens, Ingmar; Goethals, Peter L
The quality of water prior to its use for drinking, farming or recreational purposes must comply with several physicochemical and microbiological standards to safeguard society and the environment. In order to satisfy these standards, expensive analyses and highly trained personnel in laboratories are required. Whereas macroinvertebrates have been used as ecological indicators to review the health of aquatic ecosystems. In this research, the relationship between microbial pathogens and macrobenthic invertebrate taxa was examined in the Machangara River located in the southern Andes of Ecuador, in which 33 sites, according to their land use, were chosen to collect physicochemical, microbiological and biological parameters. Decision tree models (DTMs) were used to generate rules that link the presence and abundance of some benthic families to microbial pathogen standards. The aforementioned DTMs provide an indirect, approximate, and quick way of checking the fulfillment of Ecuadorian regulations for water use related to microbial pathogens. The models built and optimized with the WEKA package, were evaluated based on both statistical and ecological criteria to make them as clear and simple as possible. As a result, two different and reliable models were obtained, which could be used as proxy indicators in a preliminary assessment of pollution of microbial pathogens in rivers. The DTMs can be easily applied by staffwith minimal training in the identification of the sensitive taxa selected by the models. The presence of selected macroinvertebrate taxa in conjunction with the decision trees can be used as a screening tool to evaluate sites that require additional follow up analyses to confirm whether microbial water quality standards are met. © 2018 by the authors.