Abstract
Reverse electrodialysis (RED) is a process to harvest renewable energy from the salinity gradient obtained by the controlled mixing of river and seawater. When using natural waters, (bio)fouling is an inevitable process which has a negative impact on the obtained power density. Specific characteristics of RED do not allow the direct transfer of knowledge from previous fouling studies in other membranes process. More insight on how fouling is impacting RED is needed to design effective pre-treatment solutions. In this study, fresh water was fractionated based on particle size for 54 days, revealing the impact that specific foulants have on the RED process. A combination of turbidity and particle size measurements coupled with stack performance throughout the experiment showed that particles with an average diameter of 10 μm are responsible for a reduction in obtained stack power density of around 25%. Visualization of extracellular microbial polymers by confocal laser scanning microscopy confirmed that the role of biofouling only was of lesser concern compared to the impact of these suspended particles. According to these results, the removal of suspended particles >10 μm using a dual media filter has shown to be a simple and effective pre-treatment for fresh water in RED applications.
Highlights
In the last decades, Salinity Gradient Power (SGP) – called Blue Energy – has been receiving substantial attention as an alternative renewable energy source
Each sample was characterized by its turbidity, Total Suspended Solids (TSS), average particles size, ion composition, and total carbon, inorganic carbon and total organic carbon (TOC) and the results are presented in Tables 2 and 3
The dual media filter allows for a more constant number of suspended particles in the effluent when compared to the drum filter, as seen in lower standard deviation in the measurement related to the dual media filter (Table 2)
Summary
Salinity Gradient Power (SGP) – called Blue Energy – has been receiving substantial attention as an alternative renewable energy source. In RED a fresh and a saltwater stream are separated by ion-exchange membranes, and the concentration difference between the two water streams results in an electrochemical potential difference over the membranes [1,2,3,4]. One of the main effects of fouling is an increase of pressure drop over a stack's feed compartment, resulting in a higher energy consumption to pump the feed waters through the stacks. This increased energy consumption leads to a reduction of the overall net power density produced by the RED process [2,5,10,11]. Fouling of the ion-exchange membranes can hinder ion transport and thereby increases the internal resistance of the stack, reducing the power density that can be harvested [2]
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