This research examined the influence of organic loading rate (OLR) and biosolids type on the performance of fermentative H2-producing membrane bioreactors (HPMBRs) with respect to H2 production and membrane fouling. Five OLRs ranging from 4.0 to 30 g COD L-1 d-1 were examined in a lab-scale HPMBR. The system performance with both suspended and granulated biosolids was also investigated. The H2 yield from the suspended biosolids HPMBR was not significantly influenced by OLR at OLRs ≤ 13 g COD L-1 d-1, appeared to be maximized at an OLR of 22 g COD L-1 d-1, and then decreased as the OLR was increased further. An optimum OLR that maximizes H2 yield may be near the OLR that causes reactor overload with respect to substrate utilization. Under the same operating conditions, the H2 yield from a suspended HPMBR was significantly higher than that from a granulated HPMBR. A higher H2 consumption rate and a higher concentration of bound extracellular polymeric substances from the granulated HPMBR may contribute 5–48% and 25–67% of the H2 production difference between the two systems, respectively. The experimental results accompanied with microscopic examination of fouled membrane surfaces indicated that biosolids deposition and colloidal adhesion were the two dominant membrane fouling mechanisms in the HPMBRs. Membrane fouling was characterized by two distinct stages: an initial stage with a relatively higher fouling rate and a second stage with a lower fouling rate. Membrane fouling rates and resistances were influenced by the properties of biosolids and colloids in the mixed liquor. The fouling rates increased with increased biomass concentration, but decreased as colloids became more negatively charged. The irreversible and irremovable fouling resistance increased with increased concentration of colloids, while the removable fouling resistance had no relationship with biomass concentration. Biosolids granulation may benefit membrane performance due to a lower colloidal concentration produced. The single cake filtration model was proper to simulate membrane performance in the initial fouling stage. Both cake filtration and combined cake-standard models provided good fits for the second fouling stage, whereas future study is required to improve model predictability for membrane fouling in this stage.

This research examined the influence of organic loading rate (OLR) and biosolids type on the performance of fermentative H2-producing membrane bioreactors (HPMBRs) with respect to H2 production and membrane fouling. Five OLRs ranging from 4.0 to 30 g COD L-1 d-1 were examined in a lab-scale HPMBR. The system performance with both suspended and granulated biosolids was also investigated. The H2 yield from the suspended biosolids HPMBR was not significantly influenced by OLR at OLRs ≤ 13 g COD L-1 d-1, appeared to be maximized at an OLR of 22 g COD L-1 d-1, and then decreased as the OLR was increased further. An optimum OLR that maximizes H2 yield may be near the OLR that causes reactor overload with respect to substrate utilization. Under the same operating conditions, the H2 yield from a suspended HPMBR was significantly higher than that from a granulated HPMBR. A higher H2 consumption rate and a higher concentration of bound extracellular polymeric substances from the granulated HPMBR may contribute 5–48% and 25–67% of the H2 production difference between the two systems, respectively. The experimental results accompanied with microscopic examination of fouled membrane surfaces indicated that biosolids deposition and colloidal adhesion were the two dominant membrane fouling mechanisms in the HPMBRs. Membrane fouling was characterized by two distinct stages: an initial stage with a relatively higher fouling rate and a second stage with a lower fouling rate. Membrane fouling rates and resistances were influenced by the properties of biosolids and colloids in the mixed liquor. The fouling rates increased with increased biomass concentration, but decreased as colloids became more negatively charged. The irreversible and irremovable fouling resistance increased with increased concentration of colloids, while the removable fouling resistance had no relationship with biomass concentration. Biosolids granulation may benefit membrane performance due to a lower colloidal concentration produced. The single cake filtration model was proper to simulate membrane performance in the initial fouling stage. Both cake filtration and combined cake-standard models provided good fits for the second fouling stage, whereas future study is required to improve model predictability for membrane fouling in this stage.

O mercado de biorreatores com membranas (BRMs) têm exibido alto crescimento. Contudo, o fouling diminui o desempenho desses sistemas drasticamente. A aeração promove a mitigação do fouling, mas possui alto custo operacional (de até 70% do total da demanda energética) e é utilizada de forma otimizada apenas 10% das vezes, gerando a necessidade de estudos sobre a hidrodinâmica em BRMs. Ferramentas de dinâmica de fluidos computacional (CFD) são úteis para esse tipo de análise. Um dos primeiros passos para encontrar uma solução apropriada em simulações numéricas é propor uma modelagem correta. Dentre os fenômenos a serem modelados, os efeitos da turbulência são provavelmente um dos mais importantes; porém, nenhum artigo que comparasse predições com base na escolha de modelo de turbulência para simulações de sistemas BRM foi encontrado. Dessa forma, o objetivo desse trabalho foi verificar a importância da escolha do modelo de turbulência para simulações de biorreatores com membranas através de CFD. Para isso, as predições obtidas de velocidade local próxima às superfícies das membranas e de tensão cisalhante nessas superfícies para duas taxas de aeração, 5 e 15 m³/h, empregando dois modelos de turbulência, k-ϵ com funções de parede para alto (aR) e para baixo número de Reynolds (bR) e k-ω SST (Shear Stress Transport) com funções de parede automáticas, na análise de um sistema BRM foram comparadas entre si e com dados experimentais e simulados disponíveis na literatura. Os perfis temporais da velocidade e da tensão cisalhante exibiram alta variabilidade no período das oscilações em certos pontos, exigindo um longo tempo de escoamento para a convergência das variáveis locais. Identificou-se a necessidade de outorgar maior importância à definição do intervalo de tempo de coleta de dados experimentais, de modo a adquirir médias representativas do perfil dinâmico das variáveis e destes perfis serem também analisados para comparações mais definitivas entre resultados de simulações e medições experimentais. As diferenças, entre as medições experimentais da literatura e predições, obtidas pelas simulações deste trabalho foram, no geral, de ordem similar ou menores que as obtidas pelas simulações na literatura. Além disso, maior atenção deve ser dada à escolha da estratégia de modelagem de turbulência, visto que houve alta sensibilidade das predições, que variaram em até 21,6% dependendo dessa escolha. / Membrane bioreactors (MBR) market has been showing high growth rates over recent years. However, membrane fouling drastically reduces MBR overall performance. Aeration promotes fouling mitigation, but at a high operational cost (up to 70% of the MBR energy demand) and it is optimally employed only in 10% of the cases. This created the need of studies focused on MBR hydrodynamic. Computational fluid dynamics (CFD) is a useful tool for hydrodynamic analysis. One of the first steps in finding a proper solution for numerical simulation is proposing a correct modelling. Among the phenomena to be modelled for MBR simulations, turbulence effects are probably one of the most important; nevertheless, no paper comparing the predictions based on the turbulence model choice for MBR simulations was found. In sight of that, this work aimed to verify the relevance of the choice of turbulence model for MBR simulations through CFD. Predictions of local velocities near membranes surfaces and of local shear stress on those surfaces, for two aeration rates (5 and 15 m³/h), employing k-ϵ with wall functions for high (aR) and low (bR) Reynolds number and k-ω SST with automatic wall functions, on the analysis of a MRB system, were compared between each other and with experimental and simulated data available in the literature. The velocity and shear stress temporal profiles showed oscillations with highly variable periods in some points, which required a long process real time to verify the local variables convergence. It was identified the need to give more importance to the definition of the time interval for experimental data collection in order to acquire reliable temporal means; also, one must properly analyze the temporal profiles for more definitive comparisons between predictions and experimental measurements. The differences, between experimental data and predictions, obtained through this work simulations were, in general, of similar order or smaller than the ones reported in the literature. Besides, more attention must be given to the turbulence modelling choices, since the predictions obtained here were highly sensitive to those choices, showing differences up to 21,6% among them.

A preocupação com a qualidade das águas está intensificando estudos com tecnologias avançadas para tratamento de efluentes. Uma tecnologia promissora no Brasil é a de biorreatores à membrana (MBR), pois há a possibilidade de trabalhar com altas taxas de aplicação e ainda pode obter um efluente tratado passível de reuso. Assim, o presente trabalho teve por objetivo estudar um MBR com módulo de membranas externo. Para tanto, foram estipulados os parâmetros operacionais em ensaios preliminares, tais como compactação da membrana, permeabilidade hidráulica e permeabilidade ao lodo ativado. Desta forma, efetuou-se a montagem do MBR, o qual foi inicialmente alimentado com um efluente sintético e posteriormente com efluente de curtume coletado pós-tratamento convencional. Operando com efluente sintético, obteve-se redução superior a 95% para DQO e turbidez. Com efluente de curtume pós-tratamento, obteve-se eficiência de 46%, 88%, 16%, 67% e 48% para DQO, DBO5, NTK, P-Total e cromo, respectivamente. Ademais, após 15 dias de operação, o sistema estabilizou com fluxo permeado elevado: 43 L/m².h. / The preoccupation with the quality of water resources is intensifying studies about advanced technologies for wastewater treatment. A promising technology in Brazil is the membrane bioreactors (MBR), due its capacity to operate with high application rates and may also obtains a treated effluent able to reuse. Thus, this work aimed to study a MBR with external membrane module. Firstly, it has been determined operational parameters by preliminary studies, namely: membrane compactation, hydraulic permeability and permeability to activated sludge. After that, the MBR was setting. Then, it was initially fed a synthetic wastewater and, then, with tannery wastewater collected after conventional treatment. Operating with synthetic wastewater, it was obtained a reduction of more than 95% for COD and turbidity. The operation with tannery wastewater post treatment resulted in efficiency of 46%, 88%, 16%, 67% and 48% for COD, BOD5, TKN, Total-P and chromium, respectively. Moreover, after 15 days of operation, the system has stabilized with high permeate flux: 43 L/m².h.

O mercado de biorreatores com membranas (BRMs) têm exibido alto crescimento. Contudo, o fouling diminui o desempenho desses sistemas drasticamente. A aeração promove a mitigação do fouling, mas possui alto custo operacional (de até 70% do total da demanda energética) e é utilizada de forma otimizada apenas 10% das vezes, gerando a necessidade de estudos sobre a hidrodinâmica em BRMs. Ferramentas de dinâmica de fluidos computacional (CFD) são úteis para esse tipo de análise. Um dos primeiros passos para encontrar uma solução apropriada em simulações numéricas é propor uma modelagem correta. Dentre os fenômenos a serem modelados, os efeitos da turbulência são provavelmente um dos mais importantes; porém, nenhum artigo que comparasse predições com base na escolha de modelo de turbulência para simulações de sistemas BRM foi encontrado. Dessa forma, o objetivo desse trabalho foi verificar a importância da escolha do modelo de turbulência para simulações de biorreatores com membranas através de CFD. Para isso, as predições obtidas de velocidade local próxima às superfícies das membranas e de tensão cisalhante nessas superfícies para duas taxas de aeração, 5 e 15 m³/h, empregando dois modelos de turbulência, k-ϵ com funções de parede para alto (aR) e para baixo número de Reynolds (bR) e k-ω SST (Shear Stress Transport) com funções de parede automáticas, na análise de um sistema BRM foram comparadas entre si e com dados experimentais e simulados disponíveis na literatura. Os perfis temporais da velocidade e da tensão cisalhante exibiram alta variabilidade no período das oscilações em certos pontos, exigindo um longo tempo de escoamento para a convergência das variáveis locais. Identificou-se a necessidade de outorgar maior importância à definição do intervalo de tempo de coleta de dados experimentais, de modo a adquirir médias representativas do perfil dinâmico das variáveis e destes perfis serem também analisados para comparações mais definitivas entre resultados de simulações e medições experimentais. As diferenças, entre as medições experimentais da literatura e predições, obtidas pelas simulações deste trabalho foram, no geral, de ordem similar ou menores que as obtidas pelas simulações na literatura. Além disso, maior atenção deve ser dada à escolha da estratégia de modelagem de turbulência, visto que houve alta sensibilidade das predições, que variaram em até 21,6% dependendo dessa escolha. / Membrane bioreactors (MBR) market has been showing high growth rates over recent years. However, membrane fouling drastically reduces MBR overall performance. Aeration promotes fouling mitigation, but at a high operational cost (up to 70% of the MBR energy demand) and it is optimally employed only in 10% of the cases. This created the need of studies focused on MBR hydrodynamic. Computational fluid dynamics (CFD) is a useful tool for hydrodynamic analysis. One of the first steps in finding a proper solution for numerical simulation is proposing a correct modelling. Among the phenomena to be modelled for MBR simulations, turbulence effects are probably one of the most important; nevertheless, no paper comparing the predictions based on the turbulence model choice for MBR simulations was found. In sight of that, this work aimed to verify the relevance of the choice of turbulence model for MBR simulations through CFD. Predictions of local velocities near membranes surfaces and of local shear stress on those surfaces, for two aeration rates (5 and 15 m³/h), employing k-ϵ with wall functions for high (aR) and low (bR) Reynolds number and k-ω SST with automatic wall functions, on the analysis of a MRB system, were compared between each other and with experimental and simulated data available in the literature. The velocity and shear stress temporal profiles showed oscillations with highly variable periods in some points, which required a long process real time to verify the local variables convergence. It was identified the need to give more importance to the definition of the time interval for experimental data collection in order to acquire reliable temporal means; also, one must properly analyze the temporal profiles for more definitive comparisons between predictions and experimental measurements. The differences, between experimental data and predictions, obtained through this work simulations were, in general, of similar order or smaller than the ones reported in the literature. Besides, more attention must be given to the turbulence modelling choices, since the predictions obtained here were highly sensitive to those choices, showing differences up to 21,6% among them.

A preocupação com a qualidade das águas está intensificando estudos com tecnologias avançadas para tratamento de efluentes. Uma tecnologia promissora no Brasil é a de biorreatores à membrana (MBR), pois há a possibilidade de trabalhar com altas taxas de aplicação e ainda pode obter um efluente tratado passível de reuso. Assim, o presente trabalho teve por objetivo estudar um MBR com módulo de membranas externo. Para tanto, foram estipulados os parâmetros operacionais em ensaios preliminares, tais como compactação da membrana, permeabilidade hidráulica e permeabilidade ao lodo ativado. Desta forma, efetuou-se a montagem do MBR, o qual foi inicialmente alimentado com um efluente sintético e posteriormente com efluente de curtume coletado pós-tratamento convencional. Operando com efluente sintético, obteve-se redução superior a 95% para DQO e turbidez. Com efluente de curtume pós-tratamento, obteve-se eficiência de 46%, 88%, 16%, 67% e 48% para DQO, DBO5, NTK, P-Total e cromo, respectivamente. Ademais, após 15 dias de operação, o sistema estabilizou com fluxo permeado elevado: 43 L/m².h. / The preoccupation with the quality of water resources is intensifying studies about advanced technologies for wastewater treatment. A promising technology in Brazil is the membrane bioreactors (MBR), due its capacity to operate with high application rates and may also obtains a treated effluent able to reuse. Thus, this work aimed to study a MBR with external membrane module. Firstly, it has been determined operational parameters by preliminary studies, namely: membrane compactation, hydraulic permeability and permeability to activated sludge. After that, the MBR was setting. Then, it was initially fed a synthetic wastewater and, then, with tannery wastewater collected after conventional treatment. Operating with synthetic wastewater, it was obtained a reduction of more than 95% for COD and turbidity. The operation with tannery wastewater post treatment resulted in efficiency of 46%, 88%, 16%, 67% and 48% for COD, BOD5, TKN, Total-P and chromium, respectively. Moreover, after 15 days of operation, the system has stabilized with high permeate flux: 43 L/m².h.

A preocupação com a qualidade das águas está intensificando estudos com tecnologias avançadas para tratamento de efluentes. Uma tecnologia promissora no Brasil é a de biorreatores à membrana (MBR), pois há a possibilidade de trabalhar com altas taxas de aplicação e ainda pode obter um efluente tratado passível de reuso. Assim, o presente trabalho teve por objetivo estudar um MBR com módulo de membranas externo. Para tanto, foram estipulados os parâmetros operacionais em ensaios preliminares, tais como compactação da membrana, permeabilidade hidráulica e permeabilidade ao lodo ativado. Desta forma, efetuou-se a montagem do MBR, o qual foi inicialmente alimentado com um efluente sintético e posteriormente com efluente de curtume coletado pós-tratamento convencional. Operando com efluente sintético, obteve-se redução superior a 95% para DQO e turbidez. Com efluente de curtume pós-tratamento, obteve-se eficiência de 46%, 88%, 16%, 67% e 48% para DQO, DBO5, NTK, P-Total e cromo, respectivamente. Ademais, após 15 dias de operação, o sistema estabilizou com fluxo permeado elevado: 43 L/m².h. / The preoccupation with the quality of water resources is intensifying studies about advanced technologies for wastewater treatment. A promising technology in Brazil is the membrane bioreactors (MBR), due its capacity to operate with high application rates and may also obtains a treated effluent able to reuse. Thus, this work aimed to study a MBR with external membrane module. Firstly, it has been determined operational parameters by preliminary studies, namely: membrane compactation, hydraulic permeability and permeability to activated sludge. After that, the MBR was setting. Then, it was initially fed a synthetic wastewater and, then, with tannery wastewater collected after conventional treatment. Operating with synthetic wastewater, it was obtained a reduction of more than 95% for COD and turbidity. The operation with tannery wastewater post treatment resulted in efficiency of 46%, 88%, 16%, 67% and 48% for COD, BOD5, TKN, Total-P and chromium, respectively. Moreover, after 15 days of operation, the system has stabilized with high permeate flux: 43 L/m².h.

For decades, mainstream domestic wastewater treatment has relied on activated sludge processes to remove organic matter, and on biological nutrient removal systems like the A2/O process to remove nutrients. Recently, membrane filtration was also added to the realm of possible technologies for domestic wastewater treatment, with aerobic membrane bioreactors (MBRs) becoming increasingly popular, especially for decentralized, and small to medium scale applications. However, the aerobic activated sludge and MBR processes, which are often combined with biological nutrient removal processes, have high energy costs associated with supplying oxygen to the process, and end up converting the organic matter into CO2 and high amounts of microbial biomass, instead of more useful byproducts. In order to remedy the aforementioned shortcomings of the aerobic processes, anaerobic wastewater treatment has been a focus of research, with anaerobic baffled reactors (ABRs) and anaerobic membrane bioreactors (AnMBRs) having shown promise for achieving acceptable organic matter removal performance, along with potential to be energy neutral or positive through biogas production. In addition, phototrophic technologies, such as algal photobioreactors, have recently been shown to be able to remove nutrients from waste streams, while at the same time having the potential to be used as feedstock to produce biofuels. In this dissertation, a novel concentrically-baffled reactor (CBR) was designed that has the potential to reduce heat loss by transfering more of the heat between reactor zones than traditional baffled reactor designs, which will increase energy efficiency for heated systems. A prototype CBR was operated abiotically under varying hydraulic retention times (HRTs) from 4 h to 24 h, and achieved over 90% removal of total suspended solids (TSS) for all HRTs tested with feed particle sizes below 1.7 mm. In parallel with the baffled reactor research, phototrophic membrane bioreactors (PMBRs) were tested with low aeration conditions to decrease their energy demand, which resulted in nitrification-dominated systems. A phototrophic technology was developed for increasing the pH of waste streams to potentially aid pH-sensitive nutrient recovery processes. Phototrophic pH increase from 6.42±0.13 to 8.87±0.06 was achieved using batch reactors, and an increase of pH from 6.73 to 8.61 was recorded during a continuous reactor trial. Finally, the CBR was combined with a post-CBR membrane filtration process, and two PMBRs treating the effluent and permeate streams from the CBR in order to achieve complete organic matter and nutrient removal. The combined systems were tested both for high strength-high HRT and low strength-low HRT scenarios. Using the combined CBR-PMBR system, over 90% TN and TP removal were possible for 10 d HRT operation at high-strength feed conditions, with post-CBR membrane filtration. COD removal over 90% was possible for both high-strength and low-strength scenarios under all conditions tested.

Les effluents de distillerie de mélasse de canne à sucre génèrent une pollution environnementale due à, d’une part de grands volumes et d’autres part à la présence de composés de couleur brune foncée, connus sous le nom de mélanoïdines. Dans cette étude, un consortium bactérien CONS8 isolé dans des sédiments de chute d'eau a été choisi comme consortium apte à la décoloration de la mélasse. On a montré que le consortium CONS8 pouvait décolorer, trois eaux usées synthétiques différentes, élaborées respectivement à base de Viandox (13,48% v/v), d’eau usée de mélasse de betterave (41,5% v/v) ou d’eau usée de mélasse de canne à sucre (20% v/v). Les décolorations obtenues en 2 jours seulement, en fioles d’Erlenmeyer sont respectivement de 9,5, à 8,02 et à 17,5%. Quatre bactéries prédominantes ont été identifiées dans le consortium CONS8 par l'analyse de l'rADN 16S. Sur la base de cette identification, et afin de réaliser la décoloration la plus élevée, un consortium bactérien artificiel MMP1 a été reconstruit avec Klebsiella oxytoca, Serratia mercescens (T2) et la bactérie inconnue DQ817737 (T4). Dans des conditions optimisées (aération, pH) le consortium bactérien MMP1 a permis de décolorer l'eau usée synthétique contenant de la mélanoidine à 18,3% en 2 jours. La comparaison de la décoloration par le consortium MMP1 avec un milieu abiotique a démontré que la décoloration était principalement due à l'activité biotique des cellules bactériennes, sans aucun phénomène d'adsorption. Un complément en minéraux et vitamines B n'a pas amélioré la décoloration de mélanoïdines avec le consortium bactérien MMP1. Enfin, les performances d'un bioréacteur à membrane pour traiter les eaux résiduaires synthétiques contenant de la mélanoïdine ont été évaluées à l’échelle du laboratoire. L'ensemencement du réacteur a été réalisé avec un inoculum sur la base du consortium MMP1. Le réacteur a fonctionné sous plusieurs conditions de temps de séjour hydrauliques (HRT) de 15, 20, et 40 heures. Les performances ont été analysées en termes de DCO (demande chimique en oxygène), décoloration et croissance de biomasse. Les résultats ont indiqué qu’une efficacité accrue d’élimination de la DCO et de la couleur ont été obtenues avec le HRT le plus long. / Distillery effluent from sugarcane molasses leads to an environmental pollution due to its large volume and the presence of dark brown colored compounds, known as melanoidins. In this study, a bacterial consortium CONS8 isolated from waterfall sediments in Maehongsorn province was selected as a molasses-decolorizing consortium. Consortium CONS8 was able to decolorize, only within 2 days, in Erlenmeyer flasks, three different synthetic wastewaters containing either Viandox sauce (13.5% v/v), beet molasses wastewater (41.5% v/v) or sugarcane molasses wastewater (20% v/v) at 9.5, 8.0 and 17.5%, respectively. Four predominant bacteria present in the consortium CONS8 were identified by the 16S rDNA analysis. To achieve the highest decolorization, the artificial bacterial consortium MMP1 comprising Klebsiella oxytoca, Serratia mercescens (T2) and unknown bacterium DQ817737 (T4), was constructed. Under optimized conditions (aeration, pH), the bacterial consortium MMP1 was able to decolorize the synthetic melanoidins-containing wastewater at 18.3% within 2 days. The comparison of decolorization by the consortium MMP1 with abiotic control proved that the color removal for synthetic melanoidins-containing wastewater medium was mainly due to biotic activity of bacterial cells, without any adsorption phenomena. Supplement of nutrients and vitamin B did not promote melanoidins decolorization by bacterial consortium MMP1. Finally, the performance of a membrane bioreactor (MBR) for synthetic melanoidins-containing wastewater treatment was investigated at laboratory scale, with a mineral membrane. The reactor seeding was made with the MMP1 bacterial consortium inoculum. The reactor was performed with several hydraulic retention times (HRT) of 15, 20, and 40 hours. The performances were analyzed in terms of COD, color removal and biomass in the reactor. The results indicated that the higher COD and color removal efficiency were achieved with the longer HRT.

Lack of clean fresh water is one of the most pervasive problems afflicting people throughout the world. Efficient desalination of sea and brackish water and safe reuse of wastewater become an insistent need. However, such techniques are energy intensive, and thus, a good control design is needed to increase the process efficiency and maintain water production costs at an acceptable level. This thesis proposes solutions to the above challenges and in particular will be focused on two membranebased water systems: Membrane Distillation (MD) and Membrane Bioreactor (MBR) for wastewater treatment plant (WWPT). The first part of this thesis, Direct Contact Membrane Distillation (DCMD) will study as an example an MD process. MD is an emerging sustainable desalination technique which can be powered by renewable energy. Its main drawback is the low water production rate. However, it can be improved by utilizing advanced control strategies. DCMD is modeled by a set of Differential Algebraic Equations (DAEs). In order to improve its water production, an optimization-based control scheme termed Model Predictive Control (MPC) provides a natural framework to optimally operate DCMD processes due to its unique control advantages. Among these advantages are the flexibility provided in formulating the objective function, the capability to directly handle process constraints, and the ability to work with various classes of nonlinear systems. Motivated by the above considerations, two MPC schemes that can maximize the water production rate of DCMD systems have been developed. The first MPC scheme is formulated to track an optimal set-point while taking input and stability constraints into account. The second MPC scheme, Economic MPC (EMPC), is formulated to maximize the distilled water flux while meeting input, stability and other process operational constraints. The total water production under both control designs is compared to illustrate the effectiveness of the two proposed control paradigms. Simulation results show that the DCMD process produces more distilled water when it is operated by EMPC than when it is operated by MPC. The above control techniques assume the full access to the system states. However, this is not the case for the DCMD plant. To effectively control the closed-loop system, an observer design that can estimate the values of the unmeasurable states is required. Motivated by that, a nonlinear observer design for DCMD is proposed. In addition, the effect of the estimation gain matrix on the differentiation index of the DAE system is investigated. Numerical simulations are presented to illustrate the effectiveness of the proposed observer design. The observer-based MPC and EMPC are also studied in this work. Mathematical modeling of a wastewater treatment system is critical because it enhances the process understanding and can be used for process design and process optimization. Motivated by the above considerations, modeling and optimal control strategies have been developed and applied to the MBR-based wastewater treatment process. The model is an extension of the well-known Benchmark simulation models for wastewater treatment. In addition, model predictive control has been applied to maintain the dissolved oxygen concentration level at the desired value. In addition, a conventional PID controller has also been developed. The simulation results show that the both of controllers can be used for dissolved oxygen concentration control. However, MPC has better performance compared to PID scenario.