Cuenca

Spatial and temporal variations of greenhouse gas emissions from a waste stabilization pond: Effects of sludge distribution and accumulation
April 2021
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.  It is recommended that sludge management with proper desludging regulation should be included as an important mitigation measure to reduce the carbon footprint of pond treatment facilities.

Analysis of the Behavior of Abstractions in Two Urban Micro-Basins of the City of Cuenca (Ecuador), through an Aggregate Model
March 2021
Several cities in developing countries are challenging the permanent process of urbanization. This generates a great disturbance on the hydrological response of the urbanized area during rainfall events, which can cause floods. Among the disturbances that urbanized basins may suffer, it is found that variations in rain losses (hydrological abstractions) can be estimated by the named volumetric runoff coefficient (CVOL) methodology. In the present study, this methodology is used in an attempt to estimate the hydrological abstraction of two nearby urbanized basins, with different degrees of impermeability, located in the city of Cuenca in Ecuador. The results demonstrate the importance of having higher pervious surfaces in urbanized areas because they lead to reduce negative impacts associated with increased stormwater runoff on impervious surfaces.

Effects of land use and water quality on greenhouse gas emissions from an urban river system
August 2020
​Rivers act as a natural source of greenhouse gases (GHGs) that can be released from the metabolisms of aquatic organisms. Anthropogenic activities can largely alter the chemical composition and microbial communities of rivers, consequently affecting their GHG emissions. To investigate these impacts, we assessed the emissions of CO2, CH4, and N2O from Cuenca urban river system (Ecuador). By using Prati and Oregon Indexes, a clear pattern was observed between water quality and GHG emissions in which the more polluted the sites were, the higher were their emissions. Furthermore, the results highlighted the impacts of land-use types on the river emissions via water contamination by sewage discharges and surface runoff.

Generalised Linear Models for Prediction of Dissolved Oxygen in a Waste Stabilisation Pond
July 2020
Pond modelling has become an interesting tool to improve and optimise the performance of waste stabilisation ponds (WSPs). This study aimed to investigate the key driving factors of dissolved oxygen variability in Ucubamba WSP (Ecuador), by applying and comparing numerous generalised linear models GLMs. Particularly, using different data partitioning and cross-validation strategies, we compared the predictive accuracy of 83 GLMs. The obtained results showed that chlorophyll a had a strong impact on the dissolved oxygen (DO) level near the water surface, while organic matter could be the most influential factor on the DO variability at the bottom of the pond.

Integrated ecological modelling for evidence-based determination of water management interventions in urbanized river basins: Case study in the Cuenca River basin (Ecuador)
March 2020
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 IEM was shown to be an essential tool to support decisions in the Cuenca River basin management.

Biological water quality in tropical rivers during dry and rainy seasons: A model-based analysis
January 2020
This paper aimed to determine the accuracy and relevance of season-specific and season-overarching models to predict biological water quality. Additionally, the variation of prediction accuracy using sub-datasets from different parts of the Cuenca River basin was investigated. The Andean Biotic Index (ABI) was used as an indicator of biological water quality. 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 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.

An integrated mechanistic modeling of a facultative pond: Parameter estimation and uncertainty analysis
March 2019
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, 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 was developed. Furthermore, to deal with an evitable issue of large mechanistic models as overparameterization leading to poor identifiability, a systematic parameter estimation was implemented.

 Exploring the influence of meteorological conditions on the performance of a waste stabilization pond at high altitude with structural equation modeling
August 2018
Algal photosynthesis plays a key role in the removal mechanisms of waste stabilization ponds (WSPs), which is indicated in the variations of three parameters, dissolved oxygen, pH, and chlorophyll a. These variations can be considerably affected by extreme climatic conditions at high altitude. To investigate these effects, three sampling campaigns were conducted in a high-altitude WSP in Cuenca (Ecuador). From the findings, the authors proposed insightful recommendations for future design, monitoring, and operation of high-altitude WSPs. Moreover, SEM to pond engineers as an effective tool for better simulation of such complex systems like WSPs was recommended.

Biological impact assessment of sewage outfalls in the urbanized area of the Cuenca River basin (Ecuador) in two different seasons
July 2018  
In this study, the biological water quality in relation to chemicals discharged through sewage outfall during both dry and rainy season was evaluated. The lowland area of the Cuenca River basin in the southern Andes of Ecuador, including the city of Cuenca, constituted the study area. The Andean Biotic Index (ABI) and the Biological Monitoring Working Party adapted to Colombia (BMWP-Col) were used to evaluate the biological water quality. The obtained 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.

A Closer Look on Spatiotemporal Variations of Dissolved Oxygen in Waste Stabilization Ponds Using Mixed Models
February 2018
Dissolved oxygen is an essential controlling factor in the performance of facultative and maturation ponds since both take many advantages of algal photosynthetic oxygenation. The rate of this photosynthesis strongly depends on the time during the day and the location in a pond system, whose roles have been overlooked in previous guidelines of pond operation and maintenance (O&M). To elucidate these influences, in this study, a linear mixed effect model (LMM) was built on the data collected from three intensive sampling campaigns in a waste stabilization pond in Cuenca, Ecuador. As a mixed model showed high predictive performance, i.e., high goodness-of-fit (R2 of 0.94), low values of mean absolute error, this advanced statistical technique as an effective tool for dealing with high autocorrelation of data in pond systems is recommended.

Análisis espacial-temporal de procesos relacionados con concentraciones de oxígeno disuelto en lagunas de maduración
December 2017
El artículo presenta un análisis de la variabilidad de concentraciones de oxígeno disuelto en el tiempo y espacio en las lagunas de maduración de la Planta de Tratamiento de Aguas Residuales de Ucubamba (Cuenca, Ecuador), en función de diferentes parámetros físicos, químicos, biológicos y meteorológicos. Se utilizó un enfoque estadístico mediante modelos de efectos mixtos para evaluar la variabilidad de las concentraciones de oxígeno disuelto en forma espacial y temporal en cada laguna y analizar la influencia de los factores meteorológicos, químicos y biológicos, sobre las concentraciones de oxígeno disuelto.

Algal community analysis in a waste stabilisation pond
December 2014
​In the present paper the spatial distribution of the algal community in a waste stabilisation pond in Cuenca (Ecuador) was studied. The study concluded that the distribution was associated with the BOD concentration of the system. The results of this research are valuable for a better understanding of the algae-based processes in waste stabilisation ponds.

CFD study to determine the optimal configuration of aerators in a full-scale waste stabilization pond
September 2013
Aerated lagoons (ALs) are important variants of the pond wastewater treatment technology that have not received much attention in the literature. In this work, the energy expenditure of the aerators was studied by means of a scenario analysis. 3D CFD models (one phase and multiphase) of a 3 ha FAL in a waste stabilization pond system in Cuenca (Ecuador) were built for different configurations of aerators. This analysis showed that the aeration scheme with all 10 aerators switched on produced a similar hydraulic behaviour compared to using only 6 or 8 aerators. 

Integrating hydraulic, physicochemical and ecological models to assess the effectiveness of water quality management strategies for the River Cuenca in Ecuador
April 2013
​A generic framework for decision support in water management that can be applied to any river basin based on an integrated modelling approach was developed. This approach integrates a mechanistic hydraulic and physicochemical water quality model with aquatic ecological models. The 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. The results indicated 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. 

A compartmental model to describe hydraulics in a full-scale waste stabilization pond
February 2012
The advancement of experimental and computational resources has facilitated the use of computational fluid dynamics (CFD) models as a predictive tool for mixing behaviour in full-scale waste stabilization pond systems. However, in view of combining hydraulic behaviour with a biokinetic process model, the computational load is still too high for practical use. This contribution presented a method that uses a validated CFD model with tracer experiments as a platform for the development of a simpler compartmental model (CM) to describe the hydraulics in a full-scale maturation pond (7 ha) of a waste stabilization ponds complex in Cuenca (Ecuador).

Biokinetic modeling of a WSP in combination with a rigorous, yet simple mixing model
January 2011
This research presented the first results obtained with a combined rigorous hydraulic-biokinetic model of the large scale Ucubamba Waste Stabilization Pond System (WSP) in Cuenca, Ecuador. A Compartmental Model (CM) approach for modelling the pond’s hydrodynamics is compared with tanks-in-series approach for both the RTD analysis and when coupled to ASM3 model extended for algal biomass processes. It was concluded that a proper hydrodynamic model is required when modelling biokinetics in large WSPs for reliable results and useful for decision support.