Wastewater treatment improvement through an intelligent integrated supervisory system

This paper shows the result of years of work by a cooperative research group including chemical engineers, environmental scientists and computer scientists. This research has been focused on the development and implementation of new techniques for the optimisation of complex process management, mainly related to wastewater treatment plants (WWTP). The experience obtained indicates that the best approach is a Supervisory System that combines and integrates classical control of WWTP (automatic controller for maintaining a fixed dissolved oxygen level in the aeration tank, use of mathematical models to describe the process...) with the application of knowledge-based systems (mainly expert systems and case-based systems). The first part is an introduction to wastewater treatment processes and an explanation of the complexity of the management and control of such complex processes. The next section illustrates the architecture of the supervisory system and the work carried out to develop and build the expert system, the casebased system and the simulation model for implementation in a real plant (the Granollers WWTP). Finally, some results of the field validation phase of the Supervisory System when dealing with real situations in the plant are described.Aquest article mostra el resultat de la col·laboració portada a terme durant els darrers anys entre grups d'enginyeria química, enginyeria ambiental i intel·ligència artificial. El treball se centra en el desenvolupament de tècniques per a la millora i supervisió de processos complexos, especialment del tractament biològic d'aigües residuals. L'experiència demostra que la millor opció requereix desenvolupar un sistema supervisor que combini i integri tècniques de control clàssic (controlador automàtic del nivell d'oxigen dissolt en el reactor biològic, ús de models descriptius del procés, etc.) amb sistemes basats en el coneixement (concretament sistemes experts i sistemes basats en casos). El present article descriu la complexitat de la gestió del procés de tractament de les aigües residuals, l'arquitectura integrada que es proposa i el desenvolupament i la construcció de cadascun dels mòduls d'aquesta proposta per a la implementació real a l'estació depuradora d'aigües residuals de Granollers. Finalment, es detallen alguns resultats del procés de validació del seu funcionament enfront de situacions quotidianes de la planta

Desenvolupament d'un protocol per l'aplicació de sistemes basats en el coneixement a la gestió d'estacions depuradores d'aigües residuals urbanes

In this thesis, it is presented a research for the implementation of a supervisory system that integrates different technical to complement and improve the management of Waste Water Treatment Plants. The protocol proposed synthetizes the experiences for the last years in the development of the different technical in the following Waste Water Treatment Plants: Manresa and Saint Joan de Vilatorrada, Cassà de la Selva-Llagostera, Sils-Vidreres and GironaLa present tesi recull una proposta de protocol per a la implementació d’un sistema supervisor que integri diferents tècniques per complementar i millorar la gestió que actualment es porta a terme a les estacions depuradores d’aigües residuals. El protocol proposat sintetitza i destil·la les pròpies experiències dels darrers anys en el desenvolupament de les diferents tècniques per a les estacions depuradores de Manresa i Sant Joan de Vilatorrada, Cassà de la Selva-Llagostera, Sils-Vidreres i Giron

Application of a support system to the design of wastewater treatment plants

This paper presents a case study that explores the advantages that can be derived from the use of a design support system during the design of wastewater treatment plants (WWTP). With this objective in mind a simplified but plausible WWTP design case study has been generated with KBDS, a computer-based support system that maintains a historical record of the design process. The study shows how, by employing such a historical record, it is possible to: (1) rank different design proposals responding to a design problem; (2) study the influence of changing the weight of the arguments used in the selection of the most adequate proposal; (3) take advantage of keywords to assist the designer in the search of specific items within the historical records; (4) evaluate automatically thecompliance of alternative design proposals with respect to the design objectives; (5) verify the validity of previous decisions after the modification of the current constraints or specifications; (6) re-use the design records when upgrading an existing WWTP or when designing similar facilities; (7) generate documentation of the decision making process; and (8) associate a variety of documents as annotations to any component in the design history. The paper also shows one possible future role of design support systems as they outgrow their current reactive role as repositories of historical information and start to proactively support the generation of new knowledge during the design proces

INFLUENCE OF SLUDGE RECIRCULATION ON NUTRIENT REMOVAL IN SUBMERGED MEMBRANE BIOREACTORS

Membrane bioreactors (MBR) technology is a well-developed wastewater treatment process; however, the integrated operation between biological reactions and physical filtration has been poorly studied. Among other operational parameters, optimal control of sludge recirculation can enhance nitrogen and phosphorous removal processes, but the effects on sludge filterability is not clear. In this paper, different recirculation flow rates were tested to evaluate consequences on sludge filterability and nutrient removal in a MBR-UCT pilot plant treating real municipal wastewater. Three distinct sludge recirculation flows were studied during 10 weeks [external recirculation (from the membrane tank to the anoxic reactor), anoxic recirculation (from the aerobic to the anoxic reactor) and anaerobic recirculation (from the anoxic to the anaerobic reactor)]. The obtained results have shown that anaerobic recirculation affected nutrient removal in an inversely proportional way, whereas anoxic recirculation had a directly proportional effect. Referring sludge characteristics, filterability and capillarity suction time (CST) remained independent of sludge recirculation, whereas CST is proportional to transmembrane pressure (TMP), which seems to depend on external and anoxic sludge recirculation. ResumenLa tecnología de Biorreactores de Membrana (MBR) es un proceso de tratamiento de aguas residuales muy bien desarrollado; sin embargo, la operación integrada entre las reacciones biológicas y de filtración física ha sido poco estudiada. Entre otros parámetros de funcionamiento, el control óptimo de recirculación de lodos puede mejorar los procesos de eliminación de nitrógeno y fósforo, pero los efectos sobre la filtrabilidad de lodos no son claros. En este artículose ensayaron diferentes caudales de recirculación para evaluar las consecuencias de la filtrabilidad de lodos y la eliminación de nutrientes en una planta piloto real de tratamiento de aguas residuales municipales, MBR-UCT. Se estudiaron tres distintos flujos de recirculación de lodos durante 10 semanas [recirculación externa (desde el tanque de membrana al reactor anóxico), recirculación anóxica (desde el aeróbico al reactor anóxico) y de recirculación anaeróbica (del anóxico al reactor anaeróbico)]. Los resultados obtenidos han demostrado que la recirculación anaeróbica afectó la eliminación de nutrientes de una manera inversamente proporcional, mientras que la recirculación anóxica tuvo un efecto directamente proporcional. Haciendo referencia a las características del lodo, el tiempo de filtrabilidad y capilaridad de aspiración (CST) permanecieron independientes a la recirculación de lodos, mientras que el CST es proporcional a la presión transmembrana (TMP), que parece depender de la recirculación externa y anóxica de lodos. ResumoA tecnologia de bio-reatores de membrana (MBR) é um processo de tratamento de águas residuais muito bem desenvolvido; no entanto, a operação integrada entre as reações biológicas e filtração física tem sido pouco estudada. Entre outros parâmetros operacionais, o controle ótimo de recirculação de lamas pode melhorar os processos remoção de nitrogênio e de fósforo, mas os efeitos sobre a capacidade de filtração das lamas não são claras. Neste artigo foram testados diferentes fluxos de recirculação para avaliar as consequências da filtração de lamas e da remoção de nutrientes em uma usina piloto real de tratamento de águas residuais municipais, MBR-UCT. Foram estudados três fluxos diferentes de recirculação de lamas durante 10 semanas [recirculação exterior (a partir do tanque de membrana ao reator anóxico) recirculação anóxica (a partir de aeróbico ao reator anóxico) e de recirculação anaeróbica (do anóxico ao reator anaeróbico)]. Os resultados obtidos mostraram que a recirculação anaeróbica afetou a remoção de nutrientes de uma forma inversamente proporcional, enquanto que a recirculação anóxica teve um efeito diretamente proporcional. Fazendo referência as características das lamas, e o tempo de filtração e capilaridade de aspiração (CST) manteve-se independentes da recirculação das lamas, enquanto o CST é proporcional à pressão transmembranar (TMP), que parece depender de recirculação externa e anóxica das lamas.  Membrane bioreactors (MBR) technology is a well-developed wastewater treatment process; however, the integrated operation between biological reactions and physical filtration has been poorly studied. Among other operational parameters, optimal control of sludge recirculation can enhance nitrogen and phosphorous removal processes, but the effects on sludge filterability is not clear. In this paper, different recirculation flow rates were tested to evaluate consequences on sludge filterability and nutrient removal in a MBR-UCT pilot plant treating real municipal wastewater. Three distinct sludge recirculation flows were studied during 10 weeks [external recirculation (from the membrane tank to the anoxic reactor), anoxic recirculation (from the aerobic to the anoxic reactor) and anaerobic recirculation (from the anoxic to the anaerobic reactor)]. The obtained results have shown that anaerobic recirculation affected nutrient removal in an inversely proportional way, whereas anoxic recirculation had a directly proportional effect. Referring sludge characteristics, filterability and capillarity suction time (CST) remained independent of sludge recirculation, whereas CST is proportional to transmembrane pressure (TMP), which seems to depend on external and anoxic sludge recirculation. ResumenLa tecnología de Biorreactores de Membrana (MBR) es un proceso de tratamiento de aguas residuales muy bien desarrollado; sin embargo, la operación integrada entre las reacciones biológicas y de filtración física ha sido poco estudiada. Entre otros parámetros de funcionamiento, el control óptimo de recirculación de lodos puede mejorar los procesos de eliminación de nitrógeno y fósforo, pero los efectos sobre la filtrabilidad de lodos no son claros. En este artículose ensayaron diferentes caudales de recirculación para evaluar las consecuencias de la filtrabilidad de lodos y la eliminación de nutrientes en una planta piloto real de tratamiento de aguas residuales municipales, MBR-UCT. Se estudiaron tres distintos flujos de recirculación de lodos durante 10 semanas [recirculación externa (desde el tanque de membrana al reactor anóxico), recirculación anóxica (desde el aeróbico al reactor anóxico) y de recirculación anaeróbica (del anóxico al reactor anaeróbico)]. Los resultados obtenidos han demostrado que la recirculación anaeróbica afectó la eliminación de nutrientes de una manera inversamente proporcional, mientras que la recirculación anóxica tuvo un efecto directamente proporcional. Haciendo referencia a las características del lodo, el tiempo de filtrabilidad y capilaridad de aspiración (CST) permanecieron independientes a la recirculación de lodos, mientras que el CST es proporcional a la presión transmembrana (TMP), que parece depender de la recirculación externa y anóxica de lodos. ResumoA tecnologia de bio-reatores de membrana (MBR) é um processo de tratamento de águas residuais muito bem desenvolvido; no entanto, a operação integrada entre as reações biológicas e filtração física tem sido pouco estudada. Entre outros parâmetros operacionais, o controle ótimo de recirculação de lamas pode melhorar os processos remoção de nitrogênio e de fósforo, mas os efeitos sobre a capacidade de filtração das lamas não são claras. Neste artigo foram testados diferentes fluxos de recirculação para avaliar as consequências da filtração de lamas e da remoção de nutrientes em uma usina piloto real de tratamento de águas residuais municipais, MBR-UCT. Foram estudados três fluxos diferentes de recirculação de lamas durante 10 semanas [recirculação exterior (a partir do tanque de membrana ao reator anóxico) recirculação anóxica (a partir de aeróbico ao reator anóxico) e de recirculação anaeróbica (do anóxico ao reator anaeróbico)]. Os resultados obtidos mostraram que a recirculação anaeróbica afetou a remoção de nutrientes de uma forma inversamente proporcional, enquanto que a recirculação anóxica teve um efeito diretamente proporcional. Fazendo referência as características das lamas, e o tempo de filtração e capilaridade de aspiração (CST) manteve-se independentes da recirculação das lamas, enquanto o CST é proporcional à pressão transmembranar (TMP), que parece depender de recirculação externa e anóxica das lamas. 

INFLUENCE OF SLUDGE RECIRCULATION ON NUTRIENT REMOVAL IN SUBMERGED MEMBRANE BIOREACTORS

Membrane bioreactors (MBR) technology is a well-developed wastewater treatment process; however, the integrated operation between biological reactions and physical filtration has been poorly studied. Among other operational parameters, optimal control of sludge recirculation can enhance nitrogen and phosphorous removal processes, but the effects on sludge filterability is not clear. In this paper, different recirculation flow rates were tested to evaluate consequences on sludge filterability and nutrient removal in a MBR-UCT pilot plant treating real municipal wastewater. Three distinct sludge recirculation flows were studied during 10 weeks [external recirculation (from the membrane tank to the anoxic reactor), anoxic recirculation (from the aerobic to the anoxic reactor) and anaerobic recirculation (from the anoxic to the anaerobic reactor)]. The obtained results have shown that anaerobic recirculation affected nutrient removal in an inversely proportional way, whereas anoxic recirculation had a directly proportional effect. Referring sludge characteristics, filterability and capillarity suction time (CST) remained independent of sludge recirculation, whereas CST is proportional to transmembrane pressure (TMP), which seems to depend on external and anoxic sludge recirculation

Prediction of the bulking phenomenon in wastewater treatment plants

The control and prediction of wastewater treatment plants poses an important goal: to avoid breaking the environmental balance by always keeping the system in stable operating conditions. It is known that qualitative information — coming from microscopic examinations and subjective remarks — has a deep influence on the activated sludge process. In particular, on the total amount of effluent suspended solids, one of the measures of overall plant performance. The search for an input–output model of this variable and the prediction of sudden increases (bulking episodes) is thus a central concern to ensure the fulfillment of current discharge limitations. Unfortunately, the strong interrelationbetween variables, their heterogeneity and the very high amount of missing information makes the use of traditional techniques difficult, or even impossible. Through the combined use of several methods — rough set theory and artificial neural networks, mainly — reasonable prediction models are found, which also serve to show the different importance of variables and provide insight into the process dynamic

Comparison of a deterministic and a data driven model to describe MBR fouling

Membrane bioreactors (MBRs) are a combination of activated sludge bioreactors and membrane filtration, enabling high quality effluent with a small footprint. However, they can be beset by fouling, which causes an increase in transmembrane pressure (TMP). Modelling and simulation of changes in TMP could be useful to describe fouling through the identification of the most relevant operating conditions. Using experimental data from a MBR pilot plant operated for 462days, two different models were developed: a deterministic model using activated sludge model n°2d (ASM2d) for the biological component and a resistance in-series model for the filtration component as well as a data-driven model based on multivariable regressions. Once validated, these models were used to describe membrane fouling (as changes in TMP over time) under different operating conditions. The deterministic model performed better at higher temperatures (>20°C), constant operating conditions (DO set-point, membrane air-flow, pH and ORP), and high mixed liquor suspended solids (>6.9gL-1) and flux changes. At low pH (<7) or periods with higher pH changes, the data-driven model was more accurate. Changes in the DO set-point of the aerobic reactor that affected the TMP were also better described by the data-driven model. By combining the use of both models, a better description of fouling can be achieved under different operating condition

Efficiently combining water reuse and desalination through forward osmosis - reverse osmosis (FO-RO) hybrids: a critical review

Forward osmosis (FO) is a promising membrane technology to combine seawater desalination and water reuse. More specifically, in a FO-reverse osmosis (RO) hybrid process, high quality water recovered from the wastewater stream is used to dilute seawater before RO treatment. As such, lower desalination energy needs and/or water augmentation can be obtained while delivering safe water for direct potable reuse thanks to the double dense membrane barrier protection. Typically, FO-RO hybrid can be a credible alternative to new desalination facilities or to implementation of stand-alone water reuse schemes. However, apart from the societal (public perception of water reuse for potable application) and water management challenges (proximity of wastewater and desalination plants), FO-RO hybrid has to overcome technical limitation such as low FO permeation flux to become economically attractive. Recent developments (i.e., improved FO membranes, use of pressure assisted osmosis, PAO) demonstrated significant improvement in water flux. However, flux improvement is associated with drawbacks, such as increased fouling behaviour, lower rejection of trace organic compounds (TrOCs) in PAO operation, and limitation in FO membrane mechanical resistance, which need to be better considered. To support successful implementation of FO-RO hybrid in the industry, further work is required regarding up-scaling to apprehend full-scale challenges in term of mass transfer limitation, pressure drop, fouling and cleaning strategies on a module scale. In addition, refined economics assessment is expected to integrate fouling and other maintenance costs/savings of the FO/PAO-RO hybrid systems, as well as cost savings from any treatment step avoided in the water recyclin

Selecting the most relevant variables for anaerobic digestion imbalances : Two case studies

In this study, a wrapper approach was applied to objectively select the most important variables related to two different anaerobic digestion imbalances, acidogenic states and foaming. This feature selection method, implemented in artificial neural networks (ANN), was performed using input and output data from a fully instrumented pilot plant (1 m 3 upflow fixed bed digester). Results for acidogenic states showed that pH, volatile fatty acids, and inflow rate were the most relevant variables. Results for foaming showed that inflow rate and total organic carbon were among the relevant variables, both of which were related to the feed loading of the digester. Because there is not a complete agreement on the causes of foaming, these results highlight the role of digester feeding patterns in the development of foamin

DAI-DEPUR: an integrated and distributed architecture for wastewater treatment plants supervision

The activated sludge process - the main biological technology usually applied towastewater treatment plants (WWTP) - directly depends on live beings (microorganisms), and therefore on unforeseen changes produced by them. It could be possible to get a good plant operation if the supervisory control system is able to react to the changes and deviations in the system and can take thenecessary actions to restore the system’s performance. These decisions are oftenbased both on physical, chemical, microbiological principles (suitable to bemodelled by conventional control algorithms) and on some knowledge (suitable to be modelled by knowledge-based systems). But one of the key problems in knowledge-based control systems design is the development of an architecture able to manage efficiently the different elements of the process (integrated architecture), to learn from previous cases (spec@c experimental knowledge) and to acquire the domain knowledge (general expert knowledge). These problems increase when the process belongs to an ill-structured domain and is composed of several complex operational units. Therefore, an integrated and distributed AIarchitecture seems to be a good choice. This paper proposes an integrated and distributed supervisory multi-level architecture for the supervision of WWTP, that overcomes some of the main troubles of classical control techniques and those of knowledge-based systems applied to real world system