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Water Res ; 204: 117646, 2021 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-34543974


Membrane capacitive deionization (MCDI) is an emerging electric field-driven technology for brackish water desalination involving the removal of charged ions from saline source waters. While the desalination performance of MCDI under different operational modes has been widely investigated, most studies have concentrated on different charging conditions without considering discharging conditions. In this study, we investigate the effects of different discharging conditions on the desalination performance of MCDI electrode. Our study demonstrates that low-current discharge (1.0 mA/cm2) can increase salt removal by 20% and decrease volumetric energy consumption by 40% by improving electrode regeneration and increasing energy recovery, respectively, while high-current discharge (3.0 mA/cm2) can improve productivity by 70% at the expense of electrode regeneration and energy recovery. Whether discharging electrodes at the low current or high current is optimal depends on a trade-off between productivity and energy consumption. We also reveal that stopped flow discharge (85%) can achieve higher water recovery than continuous flow discharge (35-59%). However, stopped flow discharge caused a 20-30% decrease in concentration reduction and a 25-50% increase in molar energy consumption, possibly due to the higher ion concentration in the macropores at the end of discharging step. These results reveal that an optimal discharging operation should be obtained from achieving a balance among productivity, water recovery and energy consumption by varying discharging current and flow rate.

Eletricidade , Purificação da Água , Adsorção , Eletrodos , Membranas , Águas Salinas , Cloreto de Sódio
Water Res ; 203: 117498, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34371229


A novel design for a flow-electrode capacitive deionization (FCDI) system consisting of tubular electrodes in a shell and tube heat exchanger configuration is proposed. Each electrode consists of a metallic mesh current collector along the inner circumference of a tubular ion-exchange membrane. This tubular FCDI design is suitable for scale-up as it consists of easily manufactured components which can be assembled in an array. An apparatus with 4 tubular electrodes with a large effective area (202.3 cm2) was constructed and shown to provide a high net salt (NaCl) removal rate (0.15 mg s-1 at 1.2 V applied voltage and ∼2000 mg L-1 influent total dissolved solids concentration). A computational fluid dynamics (CFD) model incorporating ion migration and transport mechanisms was developed to simulate the ion concentration and electrical potential profiles in the water channel. The results of CFD modelling highlighted the need to maximize regions of both high potential gradient and high hydraulic flow in order to achieve optimal salt removal. In brief, this study presents a new design approach for FCDI scale-up and provides a computational tool for optimization of this design and future innovative FCDI designs.

Purificação da Água , Adsorção , Eletricidade , Eletrodos , Troca Iônica , Cloreto de Sódio
Membranes (Basel) ; 10(5)2020 May 25.
Artigo em Inglês | MEDLINE | ID: mdl-32466224


In an effort to improve performances of forward osmosis (FO) systems, several innovative draw spacers have been proposed. However, the small pressure generally applied on the feed side of the process is expected to result in the membrane bending towards the draw side, and in the gradual occlusion of the channel. This phenomenon potentially presents detrimental effects on process performance, including pressure drop and external concentration polarization (ECP) in the draw channel. A flat sheet FO system with a dot-spacer draw channel geometry was characterized to determine the degree of draw channel occlusion resulting from feed pressurization, and the resulting implications on flow performance. First, tensile testing was performed on the FO membrane to derive a Young's modulus, used to assess the membrane stretching, and the resulting draw channel characteristics under a range of moderate feed pressures. Membrane apex reached up to 67% of the membrane channel height when transmembrane pressure (TMP) of 1.4 bar was applied. The new FO channels considerations were then processed by computational fluid dynamics model (computational fluid dynamics (CFD) by ANSYS Fluent v19.1) and validated against previously obtained experimental data. Further simulations were conducted to better assess velocity profiles, Reynolds number and shear rate. Reynolds number on the membrane surface (draw side) increased by 20% and shear rate increased by 90% when occlusion changed from 0 to 70%, impacting concentration polarisation (CP) on the membrane surface and therefore FO performance. This paper shows that FO draw channel occlusion is expected to have a significant impact on fluid hydrodynamics when the membrane is not appropriately supported in the draw side.

Water Res ; 144: 642-655, 2018 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-30096690


The consumption of saline groundwater has contributed to a growing incidence of renal diseases, particularly in coastal communities of India. Although reverse osmosis (RO) is routinely used to remove salt from groundwater, conventional RO systems (i.e. centralized systems using spiral wound RO elements) have limited utility in these communities due to high capital and maintenances costs, and lack of infrastructure to distribute the water. Consequently, there is a need to develop an appropriate solution for groundwater treatment based on small-scale, mobile and community-led systems. In this work, we designed a mobile desalination system to provide a simple platform for water treatment and delivery of goods to rural communities. The system employs tubular RO membranes packed in a single, low-profile vessel which fits below the cargo space. The low-profile enables minimal intrusion on the space available for the transportation of goods. Pressure is delivered by a belt driven clutch pump, powered by the engine. Water is treated locally by connecting the intake to the village well while the vehicle idles. A combined numerical and experimental approach was used to optimise the module/system design, resulting in ∼20% permeate flux enhancement. Experimental results revealed that the system can produce 16 L per square meter of membrane area per hour (LMH) at a salinity level of 80 ppm from a ∼2000 ppm groundwater when it is feed at 1 m3/h at 8 bars. This indicates that a vehicle equipped with 12 m2 of tubular RO membranes can deliver 1 m3 of drinkable water by using ∼0.9 L of diesel. Assuming eight such systems could be implemented in a community to fulfil the water demands for a village with 2000 residents, a social business study revealed that a payback time of 2.5 years is achievable, even if the sale price of the water is relatively low, USD 0.18 (Rs 12, which is half of the lowest market price) per 20 L, including providing a goods transportation service at price of USD 5.25 (Rs 350) per 100 km.

Água Subterrânea , Purificação da Água , Humanos , Índia , Membranas Artificiais , Osmose , População Rural