Browsing by Author "Goethals, Peter"

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An integrated mechanistic modeling of a facultative pond: parameter estimation and uncertainty analysis
(2019) Ho, Long; Alvarado Martínez, Andrés Omar; Larriva Vásquez, Josué Bernardo; Cássia Rocha, Pompeu; Goethals, Peter
Abstract Imitating natural lakes, pond treatment systems inherit a high complexity with interconnected web of biochemical reactions and complex hydraulic processes. As such, its simulation requires a large and integrated model, which has been a challenge for pond engineers. In this study, we develop an all-encompassing model to gain a quantitative and comprehensive understanding of the hydraulic, physicochemical and microbiological conversion processes in the most common pond, a facultative pond. Moreover, to deal with an evitable issue of large mechanistic models as overparameterization leading to poor identifiability, a systematic parameter estimation was implemented. The application of sensitivity analysis reveals the most influential parameters on pond performance. Particularly, physical parameters, such as vertical eddy diffusivity, water temperature, and maximum growth rate of heterotrophs induce the most changes of organic matters while microbial assimilation and ammonia volatilization appear to be main processes for nutrient removal. In contrast, the efficiency of phosphate precipitation and nutrient biological removal via polyphosphate accumulating organisms and denitrifying bacteria is limited. Identifiability problems are addressed mainly by the characterization of light dependence of algal growth, interaction between water temperature and its coefficient, and the growth of autotrophic bacteria while based on the determinant measures, the most important parameter subsets affecting model outputs are related to physical processes and algal activity. After the establishment of the influential and identifiable parameter subset, an automatic calibration with the data collected from Ucubamba pond system (Ecuador) demonstrates the effect of high-altitude climatic conditions on pond behaviors. An aerobic prevailing condition is observed as a result of high light intensity causing accelerated algal activities, hence, leading to the limitation of hydrolysis, anaerobic processes, and the growth of anoxic heterotrophs for denitrification. Furthermore, the output of uncertainty analysis indicates that a large avoidable uncertainty as a result of vast complexity of the applied model can be reduced greatly via a systematic approach for parameter estimation.
Implications of macroinvertebrate taxonomic resolution for freshwater assessments using functional traits: the Paute river basin (Ecuador) case
(2021) Sotomayor, Gonzalo; Goethals, Peter; Eurie Forio, Marie Anne; Vázquez Zambrano, Raúl Fernando; Hampel, Henrietta
Aim: This study aimed at investigating the taxonomic resolutions (TRs) of benthic macroinvertebrates for freshwater assessments in the scope of the functional trait approach (FTA). Location: Macroinvertebrate samples were collected in 22 locations within the Paute River Basin (PRB), Ecuador, over three years (2010, 2011 and 2012). Methods: Biological traits were allocated as scores to the macroinvertebrate data (at genus level) through fuzzy coding, using published data. The scores of each genus were used to derive scores for the corresponding family. These two sets of scores were standardized and compared, they were similar in 82% of the cases. Functional diversity (FD) was described by the rRao index, which showed no significant differences between coarse (family level) and fine (genus level) TRs. Cluster analyses using the K-means algorithm were performed to determine similarities between both rRao data sets. The WQ cluster number (K) was varied between 2 and 5 to determine a threshold K value (Kth), after which a WQ assessment differed as a function of the TR being used. Results: Kth was 3. Family-level identification in the framework of the FTA in the PRB was suitable in detecting changes of macroinvertebrate assemblages (until Kth = 3). Main conclusions: The proposed methodology could be implemented in other basins where decision-makers could decide whether the level of functional trait data similarity is sufficient for WQ management purposes and whether the defined Kth is acceptable. The reliability of the key methodological steps was assessed using performance statistics that have rarely been applied to ecological studies. Despite related research performed in other regions, the present study is the first South American attempt to investigate the effects of TR of benthic macroinvertebrates on freshwater bioassessments using functional traits
Improving water management education across the Latin America and caribbean region
(2019) Domínguez Granda, Luis Elvin; Hampel, Henrietta; Lam, Norris; Nolivos Alvarez, Indira Yadira; Reinstorf, Frido; Lyon, Steve W.; Ho, Long; Rodríguez Tejeda, Raymundo C.; Vázquez Zambrano, Raúl Fernando; Goethals, Peter; Schneider, Petra
Education can help secure inclusive and resilient development around water resources. However, it is difficult to provide the latest science to those managing water resources (both now and in the future). Collectively, we hypothesize that dissemination and promotion of scientific knowledge using students as central agents to transfer theoretical knowledge into practice is an efficient way to address this difficulty. In this study, we test this hypothesis in the Latin America and Caribbean (LAC) region as a representative case study region. First, we use a literature review to map a potential gap in research on education around water resources across the LAC region. We then review potential best practices to address this gap and to better translate water resources education techniques into the LAC region. Integral to these efforts is adopting students as agents for information transfer to help bridge the gap between the global state-of-the science and local water resources management. Our results highlight the need to establish a new standard of higher educational promoting exchange between countries as local populations are vulnerable to future shifts in climate at global scales and changes in land usage at regional scales. The new standard should include peer-to-peer mentoring achieved by jointly exchanging and training students and practitioners in water management techniques, increasing access to water data and pedagogic information across the region, and lowering administration roadblocks that prevent student exchange
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.
Multivariate statistics based selection of a benthic macroinvertebrate index for assessing water quality in the Paute river basin (Ecuador)
(2020) Sotomayor Valarezo, Gonzalo Patricio; Hampel, Henrietta; Vázquez Zambrano, Raúl Fernando; Goethals, Peter
Elsevier Ltd Multivariate statistics -Soft Independent Modelling of Class Analogies (SIMCA), Principal Components Analysis (PCA), Multiple Regression (MR)- were used to search for key biotic and water quality (WQ) variables within a dataset/matrix collected over a five-year period in the Paute River Basin (Ecuador). Benthic macroinvertebrates and 27 descriptive physical, chemical, microbiological, hydrological and geomorphological variables were collected from 64 monitoring sites across the basin. Nine macroinvertebrate biotic indices were calculated. The SIMCA method was applied to find the most accurate biotic index that best discriminated among less polluted (C1), moderately polluted (C2) and highly polluted (C3) sites. A cross-validation scheme was applied to evaluate the performance of the modelling process. Within the PCA that was further refined using a Kruskal-Wallis test, the key WQ variables that mostly contributed to the macroinvertebrate-based WQ classification were identified. The results showed that the Elmidae-Plecoptera-Trichoptera (ElmPT) index was the most accurate biotic classifier. Riparian vegetation and streambed heterogeneity were the best predictors of the C1 class, while the concentration of faecal coliforms, pH, temperature and dissolved oxygen, best predicted the C3 class. The reduction of the field monitored parameters could help designing more cost-effective but equally accurate future WQ monitoring schemes in the basin.
Spatial and temporal variations of greenhouse gas emissions from a waste stabilization pond: effects of sludge distribution and accumulation
(2021) Ho, Long; Jerves Cobo, Ruben Fernando; Morales Matute, Oscar Patricio; Larriva Vasquez, Josue Bernardo; Arevalo Durazno, Maria Belen; Barthel, Matti; Six, Johan; Bode, Samuel; Boeckx, Pascal; Goethals, Peter
Due to regular influx of organic matter and nutrients, waste stabilization ponds (WSPs) can release considerable quantities of greenhouse gases (GHGs). To investigate the spatiotemporal variations of GHG emissions from WSPs with a focus on the effects of sludge accumulation and distribution, we conducted a bathymetry survey and two sampling campaigns in Ucubamba WSP (Cuenca, Ecuador). The results indicated that spatial variation of GHG emissions was strongly dependent on sludge distribution. Thick sludge layers in aerated ponds and facultative ponds caused substantial CO 2 and CH 4 emissions which accounted for 21.3% and 78.7% of the total emissions from the plant. Conversely, the prevalence of anoxic conditions stimulated the N 2 O consumption via complete denitrification leading to a net uptake from the atmosphere, i.e. up to 1.4 ±0.2 mg-N m −2 d −1 . Double emission rates of CO 2 were found in the facultative and maturation ponds during the day compared to night-time emissions, indicating the important role of algal respiration, while no diel variation of the CH 4 and N 2 O emissions was found. Despite the uptake of N 2 O, the total GHG emissions of the WSP was higher than constructed wetlands and conventional cen- tralized wastewater treatment facilities. Hence, it is recommended that sludge management with proper desludging regulation should be included as an important mitigation measure to reduce the carbon foot- print of pond treatment facilities.