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Removal of scale-forming ions (e.g., Ca2 +, Mg2 +) from seawater using a bioelecrochemical system (BES) was investigated in a fed-batch and a continuous mode. In the fed-batch mode, Ca2 + removal with different anolyte buffers at different external resistances (10 Ω and 1 kΩ) was evaluated. As a result, Ca2 + was effectively removed with PBS (phosphate buffer solution) and PIPES (piperazine-N,N′-bis(2-ethanesulfonic acid) buffer solution. However, the removal of Ca2 + with PBS was not solely due to current generated from the anode but also from precipitation induced by combining Ca2 + with phosphate ions transferred from the anode chamber while the removal of Ca2 + with PIPES entirely relies on a cathodic reaction. Continuous removal of Ca2 + and Mg2 + with PIPES was more effective than the fed-batch mode with removal efficiencies of > 97 ± 2% (Ca2 + removal) and 98 ± 1% (Mg2 + removal). The XRD spectra revealed that the precipitates were mainly composed of brucite (Mg(OH)2), calcite, and aragonite (CaCO3). These results indicate that BES could be a promising way to remove scale-forming ions that can promote inorganic fouling in membrane-based processes.

The generation of salinity gradient power (SGP) is a promising technique to extract energy from either seawater or reverse osmosis (RO) brine. There are two methods for harvesting SGP, including reverse electrodialysis (RED) and pressure retarded osmosis (PRO). Although they have been individually investigated, few works have been done to compare their fouling behaviors under similar conditions. Accordingly, this study intended to compare RED and PRO processes using various low salinity (LS) solutions and high salinity (HS) solutions in terms of power density and fouling potential. Experiments were carried out in bench-scale RED and PRO systems. Three types of LS solutions including deionized water (DW), wastewater (WW), and wastewater reverse osmosis brine (WB) and two types of HS solutions including seawater (SW) and seawater reverse osmosis brine (SB) were considered. The power density was measured under non-fouling (initial) and fouling conditions. Results indicated that the power density for the PRO was higher (1.09– 3.24 W/m2) than that for the RED (0– 1.66 W/m2) under the non-fouling condition. However, the loss of power density due to fouling was smaller in RED (0– 11.2%) than in PRO (14.2– 58.7%). The use of WB as the LS solution resulted in low power density in both RED process (

Reverse electrodialysis (RED) is an emerging electrochemical process for harnessing salinity gradient power. For the commercialization of the RED process, the development of a highly efficient RED stack at a given flow rate is crucial. For this purpose, we first evaluated the performance of a RED stack according to the number of cell pairs at a given flow rate to improve the net power and specific energy (SE). Integrating the number of cell pairs at a given flow rate caused an increase in the electrical potential, and the net power was converged to the limiting value. The net SE was 0.06 kWh/m3 with 100 cell pairs at a flow rate of 100 mL/min. The levelized cost of electricity (

The fouling characteristics of dissolved organic matter (DOM) in the fresh water and seawater compartments of the reverse electrodialysis (RED) system were investigated under natural water conditions. The salinity gradient power generation was governed monovalent ions whereas multivalent ions strongly contributed to the fouling formation of the ion-exchange membranes (IEMs). The partial deposition of DOM within the membrane pores during its passage from the fresh water compartment to the seawater compartment facilitated the fouling formation of the IEMs. Despite of the similar DOC losses in fresh water (DOC loss = 20%) and seawater (DOC loss = 22%) through the RED system, the colour variations of the anion-exchange membranes (AEMs) and spacers in contact with fresh water were more noticeable than those in contact with seawater. These results indicate that the deposition of hydrophobic DOM components onto the AEM surfaces water may lead to the increases in the pressure drop of the fresh water compartment and the decreases in the power density of the RED system. Therefore, an appropriate pre-treatment strategy capable of mitigating membrane fouling by hydrophobic DOM components seemed to be indispensable to maintain constantly the performance of the RED system under natural water conditions.

Energy and cost effective pretreatment of seawater is essential for any desalination plant to convert seawater into clean water successfully. This study shows a way to pretreat seawater without excessive input of electrical energy or high pressure; it uses a bioelectrochemical cell with two chambers, divided by an anion exchange membrane (AEM). When bacteria attached on the anode produce current using organic matter as a source of fuel, hydroxyl ions can be generated in the cathode chamber, which can increase the alkalinity of the catholyte (seawater); scale-forming ions such as Ca 2 + and Mg 2 + in seawater can be removed by forming precipitates in the cathode chamber. Our results show that 84% of Ca 2 + and 37% of Mg 2 + in seawater can be effectively removed while treating wastewater in the anode chamber. These results indicate a new method to pretreat seawater without external energy input since the cell accomplishes selective removal of divalent cations using an electrochemical cathode reaction. This study provides evidence that this new method can be a viable option for membrane based seawater pretreatment and desalination processes to significantly mitigate scale problems of membranes.