Anaerobic digestion modeling: from one to several bacterial populations

Los sistemas de digestión anaeróbica son procesos complejos que desafortunadamente a menudo sufren de inestabilidad. A fin de diseñar, optimizar y operar eficientemente estos sistemas es necesario desarrollar estrategias apropiadas de control. Estas estrategias requieren, en general del desarrollo de modelos matemáticos. El proceso de digestión anaerobia comprende una red compleja de reacciones secuenciales y paralelas de naturaleza bioquímica y fisicoquímica. Generalmente, estas reacciones contienen un paso en particular, denominado reacción-limitante el cual siendo el más lento, limita la tasa de reacción del proceso global. Los primeros intentos del modelado de la digestión anaerobia condujeron a modelos que describen este paso limitante. Sin embargo, en una amplia gama de condiciones de funcionamiento, el paso limitante no siempre es el mismo. Este puede depender de las características de las aguas residuales, de la carga hidráulica, de la temperatura, etc. Es evidente que la "hipótesis del paso limitante" conduce a modelos simples y fácilmente utilizables. Sin embargo, estos modelos no describen muy bien el comportamiento del digestor, especialmente en condiciones transitorias de funcionamiento. Este trabajo revisa el estado del arte en modelización de la digestión anaerobia. Damos una breve descripción de los modelos clave de digestión anaerobia que se han desarrollado hasta el momento para describir sistemas con crecimiento de biomasa, incluyendo el modelo de digestión anaerobia No 1 (ADM1) de la Asociación Internacional del Agua (IWA) e identificamos las áreas que requieren esfuerzos futuros de investigación.Anaerobic digestion systems are complex processes that unfortunately often suffer from instability causing digester failure. In order to be able to design, optimizing and operate efficiently anaerobic digestion systems, appropriate control strategies need to be designed. Such strategies require, in general, the development of mathematical models. The anaerobic digestion process comprises a complex network of sequential and parallel reactions of biochemical and physicochemical nature. Usually, such reactions contain a particular step, the so called rate-limiting step which, being the slowest, limits the reaction rate of the overall process. The first attempts for modeling anaerobic digestion led to models describing only the limiting step. However, over a wide range of operating conditions, the limiting step is not always the same. It may depend on wastewater characteristics, hydraulic loading, temperature, etc. It is apparent that the "limiting step hypothesis" leads to simple and readily usable models. Such models, however, do not describe very well the digester behavior, especially under transient operating conditions. This work reviews the current state-of-the-art in anaerobic digestion modeling. We give a brief description of the key anaerobic digestion models that have been developed so far for describing biomass growth systems, including the International Water Association’s Anaerobic Digestion Model 1 (ADM1) and we identify the areas that require further research endeavors

Modelización de la digestión anaerobia: de una a varias poblaciones bacterianas

Anaerobic digestion systems are complex processes that unfortunately often suffer from instability causing digester failure. In order to be able to design, optimizing and operate efficiently anaerobic digestion systems, appropriate control strategies need to be designed. Such strategies require, in general, the development of mathematical models. The anaerobic digestion process comprises a complex network of sequential and parallel reactions of biochemical and physicochemical nature. Usually, such reactions contain a particular step, the so called rate-limiting step which, being the slowest, limits the reaction rate of the overall process. The first attempts for modeling anaerobic digestion led to models describing only the limiting step. However, over a wide range of operating conditions, the limiting step is not always the same. It may depend on wastewater characteristics, hydraulic loading, temperature, etc. It is apparent that the "limiting step hypothesis" leads to simple and readily usable models. Such models, however, do not describe very well the digester behavior, especially under transient operating conditions. This work reviews the current state-of-the-art in anaerobic digestion modeling. We give a brief description of the key anaerobic digestion models that have been developed so far for describing biomass growth systems, including the International Water Association’s Anaerobic Digestion Model 1 (ADM1) and we identify the areas that require further research endeavors.Los sistemas de digestión anaeróbica son procesos complejos que desafortunadamente a menudo sufren de inestabilidad. A fin de diseñar, optimizar y operar eficientemente estos sistemas es necesario desarrollar estrategias apropiadas de control. Estas estrategias requieren, en general del desarrollo de modelos matemáticos. El proceso de digestión anaerobia comprende una red compleja de reacciones secuenciales y paralelas de naturaleza bioquímica y fisicoquímica. Generalmente, estas reacciones contienen un paso en particular, denominado reacción-limitante el cual siendo el más lento, limita la tasa de reacción del proceso global. Los primeros intentos del modelado de la digestión anaerobia condujeron a modelos que describen este paso limitante. Sin embargo, en una amplia gama de condiciones de funcionamiento, el paso limitante no siempre es el mismo. Este puede depender de las características de las aguas residuales, de la carga hidráulica, de la temperatura, etc. Es evidente que la "hipótesis del paso limitante" conduce a modelos simples y fácilmente utilizables. Sin embargo, estos modelos no describen muy bien el comportamiento del digestor, especialmente en condiciones transitorias de funcionamiento. Este trabajo revisa el estado del arte en modelización de la digestión anaerobia. Damos una breve descripción de los modelos clave de digestión anaerobia que se han desarrollado hasta el momento para describir sistemas con crecimiento de biomasa, incluyendo el modelo de digestión anaerobia No 1 (ADM1) de la Asociación Internacional del Agua (IWA) e identificamos las áreas que requieren esfuerzos futuros de investigación

A review on anaerobic membrane bioreactors (AnMBRs) focused on modelling and control aspects

[EN] The use of anaerobic membrane bioreactor technology (AnMBR) is rapidly expanding. However, depending on the application, AnMBR design and operation is not fully mature, and needs further research to optimize process efficiency and enhance applicability. This paper reviews state-of-the-art of AnMBR focusing on modelling and control aspects. Quantitative environmental and economic evaluation has demonstrated substantial advantages in application of AnMBR to domestic wastewater treatment, but detailed modelling is less mature. While anaerobic process modelling is generally mature, more work is needed on integrated models which include coupling between membrane performance (including fouling) and the biological process. This should include microbial factors, which are important to generation of specific foulants such as soluble and particulate inert organics. Mature and well-established control tools, including better feedback control strategies are also required for both the process, and for fouling control.This work has been carried out under the umbrella of the Task Group on Membrane Bioreactor Modelling and Control of the International Water Association (IWA) (http://www.iwa-network.org/groups/membrane-bioreactor-modelling-and-control/). The authors also want to acknowledge the support from Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science & ICT (2017R1A2B4007804).Robles Martínez, Á.; Ruano García, MV.; Charfi, A.; Lesage, G.; Heran, M.; Harmand, J.; Seco Torrecillas, A.... (2018). A review on anaerobic membrane bioreactors (AnMBRs) focused on modelling and control aspects. Bioresource Technology. 270:612-626. https://doi.org/10.1016/j.biortech.2018.09.049S61262627

Probabilistic design and upgrade of wastewater treatment plants in the EU Water Framework directive context

The EU Water Framework Directive requires compliance with effluent and receiving water quality standards. This increased complexity implies that the evaluation of the impact of measures should be evaluated with adequate tools, both from the methodological point of view – by applying systems analysis investigations and modelling uncertainty assessment tools – and by making the developed methodology applicable in practice. Urban wastewater systems (UWWSs) are crucial components of river basins, since they usually contribute significantly to the pollution loads. They also have more flexibility in operation and management than other subsystems as agriculture. One part of this dissertation tries to answer the question “where” to improve the UWWS in a basin by means of systems analysis. A case study is tackled with the help of substance flow analysis (SFA) and of performance indicators. SFA allowed to identify the pressures on the receiving water. The indicators highlighted the critical structures in the basin. The spatial scale of the study was found to be of paramount importance. The other part of this dissertation deals with the question “how” to improve the UWWS, by proposing a systematic methodology to design correction measures, illustrated by the example of WWTP design and upgrade. The first step is the generation of influent time series to be fed to the WWTP models by means of a new phenomenological model of the draining catchment and sewer system. Ten different treatment process configurations were selected for the comparison. Further, eleven upgrade options were selected for evaluation, partly requiring real-time control (RTC) and partly the construction of additional treatment volume. For the immission-based evaluation, the integration of the WWTP model with a river model was made by means of the continuity-based interfacing method (CBIM). The propagation of the uncertainty on model parameters was performed with Monte Carlo simulations. Given the assumed boundary conditions, alternating systems show the best treatment cost-efficiency. RTC upgrades showed good potential for low-cost compliance, but with higher risk of limits exceedance. The immission-based evaluation revealed that considering the system from a holistic point of view can lead to substantial savings

MODEL DEVELOPMENT AND SYSTEM OPTIMIZATION TO MINIMIZE GREENHOUSE GAS EMISSIONS FROM WASTEWATER TREATMENT PLANTS

As greenhouse gas emissions (GHG) reduction has drawn considerable attention, various methods have been established to estimate greenhouse gas emissions from wastewater treatment plants (WWTPs). In order to establish a design and operational strategy for GHG mitigation, accurate estimates are essential. However, the existing approaches (e.g. the IPCC protocol and national greenhouse gas inventories) do not cover emissions from all sources in WWTPs and are not sufficient to predict facility-level emissions. The ultimate goal of this research was to improve the quantification of GHG emissions from WWTPs. This was accomplished by creating a new mathematical model based on an existing activated sludge model. The first part of the research proposed a stepwise methodology using elemental balances in order to derive stoichiometry for state variables used in a mass balance based whole-plant wastewater treatment plant model. The two main advantages of the elemental balance method are the inclusion of carbon dioxide (CO2) into the existing model with no mass loss and ease of tracking elemental pathways. The second part of the research developed an integrated model that includes (1) a direct emission model for onsite emissions from treatment processes and (2) an indirect emission model for offsite emissions caused by plant operation. A sensitivity analysis of the proposed model was conducted to identify key input parameters. An uncertainty analysis was also carried out using a Monte Carlo simulation, which provided an estimate of the potential variability in GHG estimations. Finally, in the third part, the research identified an optimal operational strategy that resulted in minimizing operating costs and GHG emission, while simultaneously treating the wastewater at better levels. To do this, an integrated performance index (IPI) was proposed to combine the three criteria. The IPI was then incorporated into an optimization algorithm. The results obtained in this research demonstrated that the variation of GHG emissions is significant across the range of practical operational conditions. With system optimization, however, WWTPs have the potential to reduce GHG emissions without raising operating costs or reducing effluent quality. Further research should include a mechanistic examination of processes that produce methane (CH4) in the wastewater treatment stream and nitrous oxide (N2O) in the sludge treatment stream

Sustainable Design of Wastewater Treatment Systems: Evaluations of Operational Flexibility and Phototrophs for Resource Recovery.

The overarching goal of this dissertation is to advance the sustainability of wastewater systems. Although concepts surrounding sustainable wastewater infrastructure have advanced in recent years, a defined methodology to develop designs and elucidate trade-offs across dimensions of sustainability (social, economic, environmental, functional), space (local, regional, global), and time (present, future) does not exist. In particular, social barriers have not been sufficiently addressed and there is a lack of integration in quantitative assessments of economic, environmental, and functional sustainability. This limitation not only impacts the industry’s ability to develop more sustainable designs and evaluate configuration alternatives, but it also inhibits the comparative evaluation of traditional with emerging technologies in wastewater management (e.g., the use of phototrophic microorganisms for energy recovery). In order to address social factors, we have developed a planning and design process for wastewater treatment systems that is centered on a process of continuous stakeholder participation and that is enhanced through communication tools and lessons learned from the social sciences literature. To provide stakeholders with the a broader set of information in the context of WWTP design, we have also integrated state of the art tools to assess the performance, cost, and life cycle environmental impacts of WWTP designs. Although these tools have been developed independent of one another in the literature, their integration creates opportunities to elucidate tensions and synergistic relationships among goals for sustainability. Ultimately, this methodology and the case study used for its demonstration offer insight into broader themes of WWTP sustainability, improve designs in multiple dimensions, and provide a framework to evaluate emerging technologies in wastewater management. Finally, we have developed a phototrophic process model to predict the performance of phototrophic microorganisms as an energy recovery technology. Through these efforts, this dissertation advances the sustainability of wastewater treatment systems by facilitating sustainable design and decision-making in the context of WWTP design and operation.Ph.D.Environmental EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91603/1/jsguest_1.pd

Processing of East African Highland Green Bananas: Waste Generation and Characterization as a Potential Feedstock for Biogas Production in Uganda

Uganda is the second largest global producer of bananas and the industry generates different waste residues both at production and processing levels. This study aimed at assessing the state of banana processing, waste generation and its characterization for evaluation as feedstock for biogas production. The study was undertaken through a reconnaissance visit to western Uganda, one of the most banana producing regions. The information was collected following standard qualitative methods and laboratory analysis. Results revealed that processing of banana fruits mainly involved manual peeling of fruits to generate fresh pulp and large quantities of banana waste. The waste contained more than 80 % moisture content and volatile solids. It also had higher carbon content than total nitrogen that translated into a high C:N ratio of 41:1. The lignocellulose content comprised cellulose 21.16 %, hemicelluloses 10.46 % and lignin 11.31 %. The Biochemical Methane Potential (BMP) test showed a methane yield of 0.436 m3 CH4/KgVS which was higher than 0.340 m3 CH4/KgVS for grass. The highest methane production of 79.9 ml CH4/gVS/day was recorded at a retention time of 24 days. These results showed that banana waste was a favorable feedstock for biogas production through anaerobic digestion. Appropriate pre-treatment of lignocellulose would be required to enhance feedstock digestibility to improve biogas yield. The study concluded that utilization of banana waste via anaerobic digestion to produce biogas was the most economically viable option to alleviate the industry’s energy scarcity

Measurement of composition of organic constituents of municipal wastewater for plant-wide modelling

Includes bibliographical references.Historically wastewater treatment unit operation models have been developed in isolation. Attempts have been made at creating common platform models, which would allow modellers to speak a common language when researching wastewater treatment modelling. However, few attempts have been made at integrating different models into a plant-wide WWTP simulation model. Increasing pressure towards the optimisation of water treatment systems have prompted investigation into integrated WWTP modelling. The use of different state variables in WWTP unit operation models has meant that modelling incompatibilities exist in the theoretical coupling of certain models. Attempts made towards the development of integrated WWTP models have experienced difficulties due to a number of factors. State variables required in one model may be non-existent in other models, the definition of state variables may be different between different unit process models and compounds that are considered constant in a unit process model may be a state-variable in another unit process model Thus the difficulties in coupling different unit process models are mainly due to differences in state variable meaning and occurrence in different unit process models. Recent approaches towards the development of plant-wide WWTP simulation models have included the continuity based interfacing method (CBIM) of Vanrolleghem et al. (2005) and Volcke et al. (2006), the 'supermodel approach' of Jones &Tákacs (2004 cited in Grau et al 2007) and Seco et al. (2004 cited in Grau et al 2007) , the transformation based approach of Grau et al. (2007) and the mass balances based plant-wide WWTP model approach of Ekama et al. (2006 a,b), Sötemann et al. (2006) and Wentzel et al. (2006). The use of compounds in their elemental composition forms, viz. C, H, O, N, P and charge content, as part of a method to transform incompatible unit process state variables into compatible forms is a general theme in integrated modelling approaches. The elemental compositions of readily biodegradable (RB), slowly biodegradable (SB), unbiodegradable soluble (US) and unbiodegradable particulate (UP) organic compounds are often unknown. Little practical investigation into their determination for the purpose of integrated WWTP modelling has been performed. This project was therefore focussed on the determination of wastewater compound elemental compositions, with the inclusion of carbon data, for integrated WWTP modelling purposes. The aims of this project were therefore two fold, viz. an investigation into current whole WWTP integration model approaches and the performance evaluation of a simple batch test method for the determination of organic compound elemental compositions over a standard WWTP incorporating primary settling, an AS reactor as well as primary sludge and WAS anaerobic digestion. A simple anaerobic batch test approach towards determining wastewater organics total, biodegradable and unbiodegradable as well as soluble and particulate fraction elemental compound compositions was investigated. This approach was evaluated according to the fulfilment of three research objectives, viz. (1) the fractionation of raw wastewater, PS and WAS organics into biodegradable and unbiodegradable soluble and particulate components, (2) the fractionation of raw wastewater concentrations (C,N,COD,VS) into settlable and colloidal particulate organic material, (3) the determination of the organic compositions of the form CxHyOzNa for the above wastewater and sludge fractions. Research performed by Wentzel et al. (2006) and Ekama et al (2006 b) have supported the notion that organic material termed unbiodegradable from an activated sludge standpoint remain unbiodegradable under anaerobic digestion processes. Thus, the use of an anaerobic batch test method for determination of unbiodegradable organic compositions over a plant-wide WWTP was considered to be valid