Contamination of natural waters due to nitrogenous wastes has become a crucial environmental problem due to deterioration of water quality and eutrophication in aquatic eco-systems. Thus, the reduction of nitrogen accumulation in the natural environment is vital to maintain a healthy eco-system. Bipolar membrane electrodialysis (BMED) is a promising technology for selective ammonia separation from high-strength wastewater, such as liquid digestates of food waste or wastewater sludge. This technology was recently studied for reducing membrane scaling problems associated with conventional electrodialysis (ED) systems due to the water splitting mechanism in the BPM interface. A bench-scale BMED stack was built using 5 pairs of cation exchange membranes (CEMs) and bipolar membranes (BPMs). Using the BMED stack, a simulated food liquid digestate solution was examined to separate ammonia with different voltage applications and inter-membrane distances. The highest ammonia recovery was obtained at a cell pair voltage of 5.83 V (81% separation). Experiments on investigation of optimal inter-membrane distance of BMED operation suggested that the inter-membrane distance could be increased up to 2.46 mm without a significant decrease in nitrogen recovery. The residual Ca2+ and Mg2+ in the CIP (clean-in-place) solution which explains the degree of the scaling problem in the BMED was observed consistently below 2% of the initial mass introduced to the system, indicating that BMED design and regular CIP were effective in scaling control. The ammonia loss through CEMs to the feed cell by back diffusion was minimized due to high pH in the base cell since uncharged free ammonia was dominant over ammonium cation in the base cell. The energy required for BMED operation was comparatively low; 1.93-6.93 kWh/kg-N within 90 mins. Therefore, BMED can be considered as a sustainable candidate for selective ammonia recovery at high energy efficiency with successful scaling control. / Thesis / Master of Civil Engineering (MCE)

Nitrogen pollution in the environment creates challenging problems globally and locally and can be effectively controlled by a significant reduction in nitrogen release into the natural water system. In addition, nutrients in high-strength wastewater can be recovered as valuable resources such as different types of ammonium solutions for industrial and agricultural utilizations. Selective ammonia separation from high-strength wastewater can be achieved by bipolar membrane electrodialysis (BMED), a relatively new ion exchange technology. A series of 8 bench-scale BMED experiments with bipolar membranes and cation exchange membranes were performed under various voltage applications. Ammonia in the wastewater was rapidly separated and recovered as a high purity ammonium hydroxide solution. BMED operation for 30 minutes at 5.0 V per cell pair was found to be ideal for high purity ammonium hydroxide production and low electrical energy consumption. Additionally, effective organic fouling control and low energy consumption were achieved. The experiments showed a decrease in the feed pH making it ideal for applications in solid-state anaerobic digestion with leachate recirculation. The application of leachate recirculation in solid-state anaerobic digestion (SSAD) has proven effective for mobilizing nutrients and diluting toxic byproducts to enhance biogas production. The leachate after recirculation contains accumulated ammonia and an increased pH and requires water and chemicals for dilution and pH adjustment prior to recirculation. The data from the experiments were used to construct a numerical model for a hypothetical lab-scale and pilot-scale bipolar membrane electrodialysis and solid-state anaerobic digestion with leachate recirculation (BMED-SSAD) system. A final ammonia concentration of less than 2000 mg-N/L in the reactor was found to be achievable by lab-scale (6 mA/cm2) and pilot-scale (12 mA/cm2) BMED-SSAD and low electric energy consumption. The results suggest that BMED is an attractive solution for ammonia separation from high-strength wastewater. / Thesis / Master of Applied Science (MASc)

A couple of processes for electrosynthetic production of expendable reagents, namely acids, bases, and oxidants, from the native salt content of raw waters and industrial wastes were investigated, and the composition of mixed acids and bases made of sodium sulfate or sodium chloride salts were predicted using a model predicated on conservation principles, mass action relations, and Pitzer equations. Electrodialysis with bipolar membranes (BMED) was used to produce acids and bases in a single pass. Product concentration was limited only by the salt content of the feed water. The current efficiency for acid production was slightly higher than that for base, but neither dropped below 75%. Acid and base current utilization showed the same trends with respect to feed salt content and flow velocity, with higher efficiency at higher feed salt concentrations and flow velocities. Operating the BMED stack near the limiting current density of the bipolar membrane (BLCD) or above the limiting current density of the diluate compartment (LCD) decreased current efficiency and increased electrical power dissipation. Electrodialytic acid and base production was approximately10 times cheaper than the chemicals' f.o.b. unit costs as quoted on Alibaba.com. The mechanism and cost of on site peroxodisulfuric acid production by electrolysis of sulfuric acid solutions with boron doped diamond film anodes was investigated experimentally and with molecular dynamics (MD) and density functional theory (DFT) simulations. The cost of on site peroxodisulfate production was approximately 4 times less expensive than purchasing a 25 lb bag. It was shown that direct discharge of sulfate species produces sulfate radicals, which subsequently combined to form peroxodisulfuric acid. The likely hood of these reactions was dependent on electrode surface condition. Sulfate radicals could also be produced in solution by reaction with hydroxyl radicals generated by water discharge.

Le présent travail est dédié à l’étude d’un procédé hybride couplant l’électrodialyse à membrane bipolaire et l’échange d’ions. Cette étude est appliquée au traitement de solutions diluées d’acide acétique. L’objectif est double : acquérir une compréhension théorique des processus de transfert et des mécanismes qui impactent la consommation énergétique de ce système hybride et, de façon plus appliquée, proposer une configuration de cellule qui permette d’éliminer l’acide de la solution traitée en la transférant vers un compartiment de concentration. Cette configuration doit permettre d’obtenir le taux de purification le plus élevé possible tout en minimisant la consommation d’énergie. Des critères visant à optimiser le choix des résines échangeuses d’ions (fortes ou faibles) dans les compartiments de dilution sont proposés. L’intérêt de l’utilisation d’une résine cationique forte sous forme H+ dans le compartiment de concentration est par ailleurs mise en évidence, conduisant à une diminution de la résistance du compartiment et de ce fait de la consommation d’énergie. Une étude réalisée sur des systèmes « couplés » et « découplés » a permis d’identifier les contributions résistives des différents éléments de l’empilement. Cette approche a conduit à la détermination des paramètres d’un modèle qui permet de prévoir la résistance électrique d’un lit de résine dans une solution donnée. Les consommations spécifiques d’énergie (kWh/kg d’acide transféré) ont été évaluées en fonction du taux de purification souhaité. L’ensemble de l’étude a permis d’établir des recommandations pour la conception de la cellule et pour le choix des paramètres opératoires. / This work is dedicated to the study of a hybrid separation process involving bipolar membrane electrodialysis and ion exchange. This study is applied to the treatment of diluted effluents. The aim is first to acquire a theoretical understanding of transfer processes and mechanisms that affect energy consumption of this hybrid system. Then, in a more applied way, the objective is to be able to propose a cell configuration that allows to remove the acid from the treated solution by transferring it to a concentration compartment. This configuration must allow to obtain the highest purification rates as possible while minimizing energy consumption. Criteria aiming at optimizing ion exchange resins (strong or weak) in dilution compartment are proposed. The interest of the introduction of strong cationic resin under H+ form in the concentrated compartment is highlighted, as it enables reducing compartment resistance and hence energy consumption. Furthermore, experimental measurements successively conducted with “decoupled” and “coupled” systems identified resistive contributions of the different elements of the stack. This approach led to the determination of parameters of a model which predicts the resin bed electrical resistance in a given solution. Specific energy consumption (kWh/Kg transferred acid) was evaluated as a function of the desired purification rate. All the work led to recommendations for the cell design and for the choice of operating parameters.