Ultrafiltration with self-generated RO concentrate pulse backwash in a novel integrated seawater desalination UF-RO system

Abstract

Ultrafiltration as a pretreatment for RO feedwater with enhanced UF backwash, which combines continuous with pulse backwash, was investigated in a novel UF-RO process integration. Direct supply of RO concentrate to the UF module served for UF backwash which was further enhanced with pulse backwash generated using bladder-type hydraulic accumulators. Model analysis of the hydraulic accumulator operation, which was validated via a series of field experiments, demonstrated a capability for accumulator charging directly from the RO concentrate stream within a period of 30-40 s. Moreover, pulse backwash over a short period (~5 s) which was added to the continuous UF backwash (directly from the RO brine stream), enabled peak UF backwash flux that was up to a factor of 4.2-4.6 higher than the normal filtration flux. The above mode of UF operation with multiple consecutive backwash pulses was found to be more effective than with a single pulse, while inline coagulation further increased the UF performance. Relatively long-term field operation (over eight days where) of the UF-RO system with self-adaptive triggering of UF backwash, whereby the number of consecutive pulses increased when a higher membrane fouling resistance was encountered, was highly effective enabling stable UF operation over a wider range of water quality conditions and without the need for chemical cleaning. These encouraging results suggest that direct UF-RO integration with enhanced pulse UF backwash is an effective approach for dead-end UF filtration without sacrificing water productivity.

A perspective on reverse osmosis water desalination: Quest for sustainability

“…Effective self‐adaptive RO feed pretreatment that can handle temporal variability of raw feed water quality and production demand is also likely to lead to significant reduction in the use of feed treatment chemicals while reducing the frequency of membrane cleaning and replacement. All of the above would benefit from real time monitoring of membrane fouling and mineral scaling . It is also stressed that real‐time monitoring of feed and product water quality (e.g., w.r.t emerging contaminants) and of membrane integrity would contribute to establishing effective operational strategies to mitigate fouling/scaling and toward gaining acceptability of RO for direct potable reuse applications.…”

“…Current practice of membrane fouling prevention emphasizes the removal of potential foulants, prior to any RO desalting unit operations, using conventional flocculation/coagulation, disinfection (e.g., via chlorine dosing or UV pretreatment), media filters or membrane filtration (microfiltration or ultrafiltration) processes for RO feed water pretreatment. 16,32,43,48,50,51 In some cases, sodium metabisulfite, sodium bisulfite, or activated carbon may also be used for dechlorination of the RO feed to avoid RO membranes degradation due to chlorine; 52,53 it is noted, however, that the use of chlorine in RO feed is now typically avoided in modern plants. 11 These feed pretreatment processes, while effective for minimizing membrane fouling due to particulate deposition, organic adsorption, and biological growth, do not remove mineral scale precursors.…”

“…All of the above would benefit from real time monitoring of membrane fouling and mineral scaling. 44,51,77,[101][102][103] It is also stressed that real-time monitoring of feed and product water quality (e.g., w.r.t emerging contaminants) and of membrane integrity 104,105 would contribute to establishing effective operational strategies to mitigate fouling/scaling and toward gaining acceptability of RO for direct potable reuse applications.…”

Air Backwash Efficiency on Organic Fouling of UF Membranes Applied to Shellfish Hatchery Effluents

“…Many improvements have been developed to overcome this phenomenon by manipulating membrane structure or by enhancing the efficiency of backwashing [ 7 , 8 ]. This procedure was studied using the filtration of natural water, with a combination of surface modifications of membranes [ 9 ] or for seawater treatment [ 10 ]. Backwash understanding and optimization was studied to link the key backwash parameters and characteristics of feed water [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ].…”

Physico‐Chemical Processes

“…The results showed that they impacted the permeate flux. Gu et al (2016) incorporated the ultrafiltration with reverse osmosis in one system, in which, the UF represented the pretreatment for salt water desalination. Pulsed and continuous back washing were applied to the UF membrane, which removed the fouling without the use of chemicals.…”