Tesi di Dottorato
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Item Experimental investigation of system performance for combined desalination processes with membrane capacitive deionisation (MCDI)(Università della Calabria, 2021-10-31) Cañas Kurz, Edgardo E.; Critelli, Salvatore; Gabriele, Bartolo; Figoli, Alberto; Hoinkis, JanThe water supply in many coastal regions worldwide is affected by progressive salinization. Here, the use of desalination technologies is a viable solution for obtaining freshwater. In this thesis, two modular concepts for brackish water (BW) desalination by the use of membrane capacitive deionization (MCDI) and low-pressure reverse osmosis (LPRO) were developed and tested at laboratory and pilot-scales with two pilot plants installed in Vietnam. The two concepts were developed by using computer-based calculations (software: WAVE) and evaluated in a socioeconomic and environmental multi-criteria analysis. The first plant consisting of subsurface arsenic removal (SAR) as pre-treatment and MCDI for desalination was installed in Tra Vinh, in the Mekong Delta for the treatment of arseniccontaminated groundwater with a concentration of total dissolved solids (TDS) of 1.65 g/L. Results showed the feasibility of the modular concept for producing drinking water (TDS<0.45 g/L) with a specific energy consumption (SEC) of <3 kWh/m³. The relationship between feed salinity and specific ion removal of the MCDI was evaluated in real environment and compared with laboratory experiments. The use of renewable energies such as solar and wind for autonomous supply was proven feasible for these technologies. The second pilot plant was installed in a riverine estuary in the region of Cần Giờ, where no access to freshwater is available due to the progressive salinization of river water and groundwater. Here, river water showed TDS concentrations of up to 25 g/L. The combined system consisted of UF pre-treatment, LPRO and MCDI to produce drinking water and product water with TDS of <0.45 g/L and <1.5 g/L, respectively with a total SEC of 5.8 kWh/m³. Additionally, the performance of the LPRO was compared to seawater-RO (SWRO) in pilot trials, which showed a SEC of 5.5 kWh/m³. Although the SEC of single-stage SWRO was lower, the separate production of drinking and product water by LPRO+MCDI showed different advantages including a reduced SEC of 5.2 kWh/m³ for product water and additional 0.6 kWh/m³ for drinking water. Finally, an optimization of the LPRO+MCDI can be possible by increasing the desalination efficiency of the MCDI, increasing the efficiency of LPRO-pump and the MCDI power supply, and by aiming at feed water qualities with lower salinity.Item Theoretical Models for Membrane Capacitive Deionization for the design of Modular Desalination Processes(Università della Calabria, 2021-12-08) Hellriegel, Ulrich; Critelli, Salvatore; Gabriele, Bartolo; Figoli, Alberto; Hoinkis, JanDue to climate change, water scarcity will be exacerbated around the globe. To increase the water availability in regions at risk, water desalination plants can be a solution. Especially in rural areas, energy e cient technologies are needed so that an operation with renewable energy as photovoltaic modules can be feasible. Recent publications showed that the novel technology membrane capacitive deionization (MCDI) can achieve a lower speci c energy consumption (SEC) than reverse osmosis (RO), for brackish water desalination with salt concentrations below 2.5 g L-1. There is still a gap in research between laboratory operation and applied commercial scaled desalination, regarding experimental but also theoretical model studies. Therefore the latter is elaborated in the present PhD thesis. Hereby, existing models are reviewed, adapted and further developed to t to applied MCDI operation for drinking water production. Two dimensional nite element methods (FEM) modelling of ion transport, according to the Gouy-Chapman-Stern theory for electrical double layers (EDL) as well as computational uid dynamics (CFD) is combined with an adjusted semi-analytical modi ed Donnan (mD) model, with a constant excess chemical potential att = 2:33 kT, for the electrosorption of ions into porous active carbon electrodes. It predicts the e uent salt concentration time-dependently for di erent inputs of applied electrical currents Icell and voltages as well as inlet concentrations and volume ows. Applied MCDI operation was optimized for drinking water production with practical experiments, which support the evaluation of the theoretical ndings. The model ts to experimental data for Icell = 20 A, however the equations for the voltage over the electrodes need to be re-assessed so that the model ts for further input parameters. A CFD model of the water ow through large scaled MCDI modules (> 50 pairs of electodes) shows the need of constructing spacer thicknesses Sp small enough, to ensure equal retention times of the water between the electrodes in the module, which is important for stable diluate concentrations. Furthermore, an analytical calculation tool is developed, by adjusting the mD model and introducing an e ective salt adsorption capacity salt; , to predict the maximum e cient charging time tmax,ch, removal- and recovery rate as well as SEC values for optimized operation of applied MCDI processes. The model reaches an accuracy of 87% for the prediction of salt removal, 86% for tmax,ch and 75% for SEC values, compared with an experimental study and thus can be used to optimize the process design of applied MCDI desalination plants.