Thesis Summaries

ATINKPAHOUN Nelly Chrystelle Houéfa
PhD Université de Lorraine (Nancy, France) / Université d’Abomey-Calavi, Cotonou, Bénin – June 27, 2018

Relationship between the Variability of Urban Wastewater Pollution and the Geographical, Socio-economic and Cultural Contexts in Benin anf France

Untreated and / or inadequate treatment of wastewater is one of the main causes of water resource pollution. To remedy this it is important to establish functional sanitation infrastructure and optimize their performance. Improving control strategies is the main action of this optimization, and modeling is one of the challenges. To do this, the present work aims to provide specific knowledge on the variability of urban wastewater of Cotonou (Benin) and Grand Nancy (France) and to have experimental data to be used for short or medium term for the development of a generation model of virtual wastewater.
The work consisted in sampling for several months the urban wastewater at the entrance of WWTPs (« Vie-Nouvelle » city in Cotonou and Maxéville in Grand-Nancy) through hourly samples over 24 hours. In Cotonou, samples were also taken from the collectors. Simulation of wastewater variability is also done using a virtual wastewater generation model.
From this work, the following observations emerge:
– flows at Grand Nancy WWTP show a daily variability with three peaks respectively at around 10 am, 2 pm and 9 pm on weekdays and characterized on weekend days by a 2% decrease (Saturdays) and 9% (Sundays) with a delay of 2 hours in the appearance of the first peak of the day;
– Wastewater of Cotonou exhibits larger pollution than urban wastewater of Grand-Nancy although the population connected to the Cotonou WWTP (≈ 1,200 PE) is far lower than that of Grand-Nancy (≈ 275,000 PE);
– A higher electrical conductivity is recorded at Greater Nancy;
– The daily variability for all the parameters in the catchments is very pronounced, except for the pH which is simlar in the two geographical contexts ;

Avirtual wastewater generation model is taking into account the lifestyle of the Grand Nancy catchment basin. Simulations of flow and pollution showed variations similar to actual experimental variations. The development is on going to extend the model to heavy metals and apply it to other collection basins.

The model allows to bridge data gaps, giving higher frequencies to dynamic data, create various wastewater variability distubance scenarios in vituelles situation and make real situations predictions for improved performance of WWTP.

Language: French

Contact: marie-noelle.pons@univ-lorraine.fr

SAAGI Ramesh
PhD Lund University (IEA, Faculty of Engineering), Sweden – June 9, 2017

Benchmark Simulation Model for Integrated Urban Wastewater Systems: Model Development and Control Strategy Evaluation

The integrated urban wastewater system (UWS) consists of different sections that are interconnected. These include: i) catchment; ii) sewer network; iii) wastewater treatment plant (WWTP); and finally, iv) receiving water system. Traditionally, these sections are operated and evaluated individually. However, it is now well-established that all the sections of an UWS should be operated in a holistic manner in order to improve the receiving water quality.

The thesis aims at developing an integrated model library that can be used to simulate the dynamics of flow rate and pollutant loads in all the sections of an UWS on a single simulation platform. It is further aimed at defining a hypothetical UWS using the model library, so that future users can use the pre-defined layout to study multiple control strategies and structural modifications. In order to facilitate an objective evaluation of the results, criteria for evaluating river water quality as well as the sewer network and WWTP performance are described.

Firstly, the suitability of existing model libraries is assessed. The building blocks from the Dynamic Influent Pollutant Disturbance Scenario Generator (DIPDSG) are used as the starting point for the catchment and sewer network model library. Additional model blocks that are missing in the DIPDSG are developed. A modified version of the Benchmark Simulation Model No. 2 (BSM2) is used to simulate the WWTP. Model blocks for river water quality assessment are developed.

Using the model library, a hypothetical UWS for an urban catchment with 80 000 population equivalents and an area of 540 hectares is described. The UWS layout is used to develop and evaluate different control strategies (local/integrated) and structural modifications. The case studies indicate that: i) the presented model library and the layout can be used to develop various control strategies and evaluate their impact on river water quality; and ii) improving the performance of an individual section does not necessarily lead to better river water quality. It is expected that the model library will be widely used as an open-source software toolbox for benchmarking purposes, integrated modelling studies as well as for modelling the individual sections.

Language: English

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Contact: ulf.jeppsson[@]iea.lth.se

SOLON Kimberly
PhD Lund University (IEA, Faculty of Engineering), Sweden – May 19, 2017

Extending Wastewater Treatment Process Models for Phosphorus Removal and Recovery: A Framework for Plant-Wide Modelling of Phosphorus, Sulfur and Iron

As problems associated with shortage in resource supply arise, wastewater treatment plants turn to innovation to transform themselves into resource recovery facilities. Water groups worldwide recognize that wastewater treatment plants are no longer disposal facilities but rather sources of clean water, energy and nutrients.

One of the most important resources that can be recovered from wastewater treatment plants is phosphorus. Mathematical modelling can be utilised to analyse various operational strategies to recover phosphorus from the wastewater. However, incorporating phosphorus transformation processes in plant-wide models is complex. Firstly, the tri-valence of phosphates suggests non-ideality, which requires the use of a physico-chemical model to account for this non-ideality. Secondly, phosphorus has strong interlinks with sulfur and iron, which necessitates inclusion of their transformations in biological and physico-chemical models. Lastly, consolidating these into a plant-wide model aimed at describing phosphorus removal and/or recovery requires interfacing, modifications to the plant layout, addition of recovery unit processes and development of new control and operational strategies. The research work presented in this thesis addresses the aforementioned challenges.

A physico-chemical model is developed to take into account ion activity corrections, ion pairing effects, aqueous phase chemical equilibria, multiple mineral precipitation and gas stripping/adsorption. The model is then linked with standard approaches used in wastewater engineering, such as the Activated Sludge Model Nos. 1, 2d and 3 (ASM1, 2d, 3) and the Anaerobic Digestion Model No. 1 (ADM1). The extensions of the ASM2d and ADM1 with phosphorus, sulfur and iron-related conversions followed. And finally, the extended models and the physico-chemical model are consolidated into a plant-wide model provided by the Benchmark Simulation Model No. 2. The resulting model is used for simulation-based scenario analysis for finding ways to improve the operation of a wastewater treatment plant aimed at phosphorus removal and recovery.

Language: English

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Contact: ulf.jeppsson[@]iea.lth.se

Fernández-Arévalo Tamara
PhD University of Navarra (TECNUN) and Ceit-IK4, Spain – December 19, 2016

New heat transfer and operating cost models for the Plant-Wide simulations of full-scale WWTPs

The main objective of this thesis has been to develop and validate a systematic and rigorous procedure for constructing mathematical models describing both heat transfers and operating costs in Wastewater Treatment Plants (WWTPs).

In order to achieve this objective, the thesis presents a new modelling methodology for calculating the heat variations produced by biochemical, chemical and physico-chemical transformations in any unit. The methodology is based on the estimation of the heat of reaction of each phase (liquid, solid or gaseous) by the enthalpies of formation of model components, applying the Hess’s law. The detailed characterisation of the components that provides the Plant-Wide Modelling (PWM) methodology enables the estimation of the enthalpy of formation for each model component and makes possible a systematic and dynamic calculation of the heat released or absorbed by each transformation, guaranteeing heat energy continuity, in parallel with the mass continuity, at any point in the plant.

This methodology has been incorporated into a complete and generic heat transfer model for predicting the temperature of any phase present in the unit-processes.

Regarding the operating cost models, the thesis presents an extensive library of actuator models based on engineering equations. The engineering expressions adapted depend closely on the operational variables of the process (solids concentration, flowrates, enthalpy changes of reaction, etc.), allowing a more detailed and realistic estimate.

The heat transfer and operating costs models developed in this thesis, along with the physico-chemical model developed by Lizarralde et al. (2015), have been used to update the Ceit-IK4 PWM methodology to a new version of the methodology called Extended Plant-Wide Modelling (E-PWM).

The modelling methodology developed for calculating heat variations caused by transformations has been validated with experimental and theoretical data obtained in literature. After validation, a verification of the predictive capacity of the heat transfer model was carried out by simulating the behaviour of an Autothermal Thermophilic Aerobic Digester (ATAD). In order to test the usefulness and applicability of the overall heat transfer model, two case studies have been carried out. In the first study, the same ATAD reactor was simulated, and in the second case study a global reference plant (BSM2) was used.

In order to show the potential of the library, three WWTPs were compared from a techno-economic standpoint. The selected configurations were (1) a conventional WWTP based on a modified version of the Benchmark Simulation Model No. 2, (2) an upgraded or retrofitted WWTP, and (3) a new Wastewater Resource Recovery Facility (WRRF) concept denominated as C/N/P decoupling WWTP.

Finally, the thesis concludes with a presentation of three case studies conducted in full-scale wastewater treatment plants, in order to show the usefulness of adapted and flexible model libraries for optimising real full-scale WWTPs, as is the case of the PWM library. This final chapter analyse in detail the aeration system of La Cartuja WWTP (Zaragoza, Spain), performs a comprehensive cost analysis in Galindo WWTP (Bilbao, Spain), and carries out an economic study to analyse the different ways to manage the phosphorus in Palma 1 WWTP (Palma de Mallorca, Spain).

Language: English

Contact: tfernandez [@] ceit.es

Arnell Magnus
PhD Lund University (IEA, Faculty of Engineering), Sweden – December, 2016

Performance Assessment of Wastewater Treatment Plants Multi-Objective Analysis Using Plant-Wide Models

As the knowledge about anthropogenic impacts of climate change has grown, the awareness of the contributions from treatment of wastewater has widened the scope for wastewater treatment plants (WWTPs). Not only shall ever stricter effluent constraints be met, but also energy efficiency be increased, greenhouse gases mitigated and resources recovered. All under a constant pressure on costs. The main objective of this research has been to develop a plant-wide modelling tool to evaluate the performance of operational strategies for multiple objectives at the plant and for off-site environmental impact.

The plant-wide model platform Benchmark Simulation Model no. 2 (BSM2) has been modified to improve the evaluation of energy efficiency and include greenhouse gas emissions. Furthermore, the plant-wide process model has been coupled to a life cycle analysis (LCA) model for evaluation of global environmental impact. For energy evaluation, a dynamic aeration system model has been adapted and implemented. The aeration model includes oxygen transfer efficiency, dynamic pressure in the distribution system and non-linear behaviour of blower performance. To allow for modelling of energy recovery via anaerobic co-digestion the digestion model of BSM2 was updated with a flexible co-digestion model allowing for dynamic co-substrate feeds. A feasible procedure for substrate characterisation was proposed. Emissions of the greenhouse gases CO2, CH4 and N2O were considered. The bioprocess model in BSM2 was updated with two-step nitrification, four-step denitrification and nitrifier denitrification to capture N2O production. Fugitive emissions of the three gases were included from digestion, cogeneration and sludge storage. The models were tested in case studies for the three areas of development: aeration, co-digestion and greenhouse gas production. They failed to reject the hypothesis that dynamic process models are required to assess the highly variable operations of wastewater treatment plants. All parts were combined in a case study of the Käppala WWTP in Lidingö, Sweden, for comparison of operational strategies and evaluation of stricter effluent constraints. The averaged model outputs were exported to an LCA model to include off-site production of input goods and impact of discharged residues and wastes. The results reveal trade-offs between water quality, energy efficiency, greenhouse gas emissions and abiotic depletion of elemental and fossil resources.

The developed tool is generally applicable for WWTPs and the simulation results from this type of combined models create a good basis for decision support.

Language: English

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Contact: ulf.jeppsson[@]iea.lth.se

Randrianarimanana Jean Jacques
PhD Université de Nantes, France – June 21, 2016

Experimental study of the spatial representativeness of velocity and particular pollutants in wastewater system

The good management of wastewater systems is essential to meet the technical, environmental and regulatory. It requires better understanding of the pollutant loads discharged to the event and annual scales, to improve the operation and management of networks to ultimately minimize untreated emissions. This thesis aims to study the influence of a singularity, namely a confluence, on the spatial and temporal representativeness of velocity and solid upstream and downstream of the main branch, to improve understanding the dynamics of pollutants in wastewater systems. For this, combined studies on continuous monitoring of the flow and quality parameters of wastewater with the study of repartition of velocity and concentrations. It has been shown that the contribution of the side branch has an influence on the hydraulic and the spatial distribution of both upstream and downstream velocity and concentrations. Sampling of velocity on dry weather showed the presence of the maximum velocity below the free surface. For solids, it has been noted vertical gradients of concentrations indicating the presence of the dense layer at the bottom or at the water-sediment interface. The pH ranges of conductivity and turbidity and flow concentrations of various pollutants parameters (SS, COD, major cations and anions) were determined. It has been shown the effect of the variability of the flow velocity on the growth of biofilm in sewer networks.

Language: French

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Contact: marie-noelle.pons [@] univ-lorraine.fr, frederique.larrarte [@]ifsttar.fr

Zhang Yuhai
PhD Université de Lorraine, Nancy, France – Dec 17, 2014

Natural purification: from river to constructed wetland

The present PhD work was carried out within the project EPEC (Epuration en Eau Courante) funded by an ANR program, ECOTECH, in order to meet the requirements of Water Framework Directive for small streams, in particular in rural areas where domestic wastewater could be directly discharged by reason of lack of sewerage network and contribute to water quality degradation. Two study directions have been taken: i) the first aimed to study natural purification in stream systems and find out the way to improve water quality, and 2) the second concerned the reduction of the impact of wastewater treatment plants (WWTP) discharge to receiving water bodies by installation of a free-surface constructed wetland between them.

Three study scales were investigated within two rural streams of Lorraine, Brénon and St-Oger. At stream scale, characterization of water quality along its course allowed us to distinguish some segments where occurred naturel purification processes. The second study scale was on relevant stream sections presenting interesting hydromorphologic features. These sections were located at the downstream of urban areas and present a succession of rectified and naturel segments. The response of naturel sections to domestic pollutants was different for the two streams. The Brénon section length of about 6 km was efficient for organic matter, ammonium nitrogen and nitrates removal. Concerning the St-Oger stream, the pollutants were less influenced in the natural section long of only 0.5 km. The last study scale focused on the hyporheic zone where system function depends on hydromorphologic features of the stream, composition of streambed, especially its porosity, and hydrologic conditions which depends on climate. According to analysis on hyporheic waters sampled at -30 and -50 cm for Brénon and -20 and -30 cm for St-Oger, four functional zones were distinguished in relation with dissolved oxygen availability and possible water exchange between hyporheic zone and surface water: (1) aerobic zones at high hyporheic exchange showing contribution to organic matter degradation and oxidation of ammonium nitrogen; (2) Anoxic zones with less hyporheic exchange characterized by fast dissolved oxygen depletion by aerobic microbial metabolism and reduction of nitrates; (3) Anoxic zones with low hyporheic exchange characterized by accumulation of salts in deep layers and reduction of nitrates and sulfates and (4) “closed” zones characterized by clogged spaces or very low hydraulic conductivity. These functions could be partially reproduced in laboratory within a porous bed reactor simulating an hyporheic zone.

Free-surface wetlands are spaces constructed between the discharge point of the WWTP and the receiving watercourse, here small streams in rural areas, with the aim to finish the waste water treatment. The wetlands had shown high capacity to remove nitrates and phosphates in summer periods. However a production of dissolved organic carbon was noticed and results from plant decomposition (reed, duckweed, algae, etc.). Algae contributed to high oxygen production through photosynthesis in spring. This production progressively decreased with the proliferation of duckweed on the water surface. Two biological tests on sediment’s potentiality for denitrification and methane production were carried out at laboratory scale in order to corroborate the field observations.

Language: French & English

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Contact: nouceiba.adouani [@] univ-lorraine.fr

Bouarab Amine
PhD Université de Lorraine, Nancy, France – July 22, 2014

On-line treatment of stormwater in a dense urban area

An online urban storm-water treatment system has been studied in this work. This system is able to treat the runoff from a highly impervious watershed (Boudonville) in Greater Nancy (North-East of France). It has a capacity of 7000 cubic meters. Some storage tanks are existing in the watershed. The treated water is discharged into the Meurthe River, while the sludge is treated in the Greater Nancy wastewater treatment plant in Maxéville.

The strategy adopted in this work allowed for the consideration of the treatment system from several angles:

  • first of all, the system is analyzed through its elementary components (sand removal unit, reagents injection and reactors for flocculation-coagulation and clarifiers): this has been done by observing the variations in water quality at the different treatment levels with online instrumentation. This has been completed with an offline characterization.
  • the flocculation-coagulation section, which was not yet operational during our work, was studied in the laboratory by jar tests. The water to be treated was sampled from the Boudonville watershed to be close to the conditions that should be observed in the Charles Keller treatment system.
  • finally the stormwater treatment was simulated as part of a full storm-water management system (watershed-Charles Keller treatment system-wastewater treatment plant). Different scenarios, which provided realistic situations, were tested. The Benchmarking Simulation Model 2 was used to model the behavior of the wastewater treatment plant and to test the effect of Charles Keller Basin on the receiving bodies.

The results that were obtained showed in the one hand the complexity of using such a treatment system in real-life conditions, especially with a coagulation / flocculation part to it, which has some conceptual issues. The presence of the huge channel (850 m3) also complicates the process by storing pollution between rain events and releasing it at the beginning of each new rain event event. Keeping the basin full of water in order to protect the concrete is also a issue for the process.

However, simulations have shown the potential value of such work for the minimization of the impact of storm water discharges on the environment and for the limitation of the number of non-standard discharges.

Language: French

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Contact: marie-noelle.pons [@] univ-lorraine.fr