Pilot-Scale Selective Electrodialysis for the Separation of Chloride and Sulphate from High-Salinity Wastewater.

The separation of chloride and sulphate is important for the treatment of high salt wastewater, and monovalent selective electrodialysis (MSED) has advantages in terms of energy consumption and pre-treatment costs compared to nanofiltration salt separation. Most of the research on monovalent anion-selective membranes (MASM) is still on a laboratory scale due to the preparation process, cost, and other reasons. In this study, a low-cost, easy-to-operate modification scheme was used to prepare MASM, which was applied to assemble a pilot-scale electrodialysis device to treat reverse osmosis concentrated water with a salt content of 4% to 5%. The results indicate that the optimum operating conditions for the device are: 250 L/h influent flow rate for the concentration and dilute compartments, 350 L/h influent flow rate for the electrode compartment and a constant voltage of 20 V. The separation effect of the pilot electrodialysis plant at optimal operating conditions was: the Cl- and SO42- transmission rates of 80% and 2.54% respectively, the separation efficiency (S) of 93.85% and the Energy consumption per unit of NaCl (ENaCl) of 0.344 kWh/kg. The analysis of the variation of the three parameters of selective separation performance during electrodialysis indicates that the separation efficiency (S) is a suitable parameter for measuring the selective separation performance of the device compared to the monovalent selectivity coefficient (PSO42-Cl-).

Monovalent selective electrodialysis: Modelling multi-ionic transport across selective membranes.

Monovalent selective electrodialysis (MSED) is a variant of conventional electrodialysis (ED) that employs selective ion exchange membranes to preferentially remove monovalent ions relative to divalent ions. This process can be beneficial when the divalent rich stream has potential applications. In agriculture, for example, a stream rich in calcium and magnesium is deemed beneficial for crops and can decrease the use of fertilizers that would otherwise need to be re-introduced to the source water prior to irrigation. MSED has been used for salt production, brine concentration, and irrigation. An experimentally validated computational model to predict its performance, however, is not available in the literature. The present work uses concepts from conventional ED modelling to build a high-resolution predictive model for the performance of MSED. The model was validated with over 32 experiments at different operating conditions and observed to fit the data to within 6% and 8% for two different types of membranes. All voltage predictions were within 10% of experiments conducted. The model was then used to predict permselectivity across different salinities and compositions. These values were extended to investigate the economic benefits of using MSED to save fertilizers for greenhouses across the U.S. Results showed an average of $4991 saved per hectare when employing MSED technology. These values aligned with predictions from two previous techno-economic studies conducted investigating MSED for agriculture.

Towards Water, Sodium Chloride and Natural Organic Matter Recovery from Ion Exchange Spent Brine.

Despite the tremendous success of the application of anion exchange resins (IX) in natural organic matter (NOM) removal over conventional removal methods, the considerable amount of brine spent during its regeneration cycle makes its sustainability questionable. This polluting saline stream can be challenging to manage and costly to discharge. Alternatively, and with the recent shift in perception of resource recovery, the produced spent brine can no longer be seen as a polluting waste but as an unconventional source of water, minerals and nutrients. In this research, for the first time, we evaluated the effectiveness of an integrated monovalent selective electrodialysis (MSED) and direct contact membrane distillation (DCMD) system in IX spent brine desalination and resource recovery. Of particular interest were the effects of operating time on the characteristics of the monovalent permselective ion exchange membranes, the impact of the DCMD stack configuration on minimizing heat loss to the ambient environment and the efficacy of the recovered NaCl in the regenerating cycle of the exhausted IXs. Our findings demonstrated that although the recovered NaCl from the stand-alone MSED can restore nearly 60% ion exchange capacity of the exhausted IXs, coupling MSED with DCMD led to minimizing the consumption of fresh NaCl (in the IX regeneration cycle) significantly, the potential application of NOM in agriculture and diminishing the risk of the IX spent brine disposal. In addition, the initial characteristics of the ion permselective membranes were maintained after 24 h of MSED and the transmembrane flux was increased when the feed/hot compartment (in the DCMD stack) was encapsulated on two outer ends with coolant/permeate compartments as a result of less heat loss to the ambient environment.