Abstract
Our previously reported exploration (Journal of Membrane Science 565 (2018) 241–253) on the differences between fouling in reverse osmosis (RO) and forward osmosis (FO), used alginate as a foulant with initial conditions that ensured that the starting fluxes were the same. That study found that for a cellulose triacetate (CTA) membrane the extent of fouling, based on the analysis of foulant resistance, was greater when the membrane was part of a FO system. Herein, using the same methodology, results for a thin film composite membrane with alginate as the foulant are presented and these confirm the same general conclusion namely that the extent of foulant accumulation in FO mode is more severe than in RO mode. Furthermore the specific fouling resistance with alginate fouling in FO is more than for RO. However examining the overall operation including cleaning as well as fouling, this study suggests that FO operation is potentially less sensitive to fouling phenomena than RO for similar feed materials. This is due to the driving force compensation coming from a changing level of ICP. Some preliminary work including that with silica particles is also reported.
Highlights
From early in the twenty-first century, pressure retarded osmosis (PRO) and forward osmosis (FO) and have received considerable attention [1]
The cellulose triacetate (CTA) membrane could be operated at a hydraulic pressure of 27.5 bar in reverse osmosis (RO) mode and it was found that this was sufficient to generate some initial fouling—see Fig. 2
It was concluded that these observations could be related to the fact that the critical flux [29] was greater than 25 LMH and this value could not be exceeded in the FO experiments but could be exceeded in the RO run
Summary
From early in the twenty-first century, pressure retarded osmosis (PRO) and forward osmosis (FO) and have received considerable attention [1]. The conceptual simplicity of both processes, and the ambition to have more sustainable processes with a lower carbon footprint, has generated this interest The former is concerned with power production, and its commercial viability is in doubt with the world’s first pilot plant closed and viability being questioned [2, 3]. It has been suggested that a hybrid FO system that incorporates a DS regeneration process may outperform conventional RO when treating challenging feedwaters (e.g., the feedwater with high salinity or specific challenging contaminants) [9, 10] These suggestions regarding outperformance are dependent upon a key assumption regarding the regeneration process, namely that is uses ‘waste’ heat.
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