Seawater Reverse Osmosis Pretreatment Research Articles

Combination of activated carbon/ultrafiltration as pre-treatment for seawater reverse osmosis plants

Seawater Reverse Osmosis (SWRO) is a common technology to treat seawater to comply high freshwater demand. Currently, the main issue of seawater/brackish water as the potential sources for drinking water is vulnerable to organic pollutants. An effective pre-treatment is crucial to maintain the efficiency of SWRO for sustainable operation. Optimization of the process could be performed by a hybrid membrane combination using commercial Activated Carbon (AC) with based material coconut shell/coal and Ultrafiltration membrane (UF). For hybrid process, the activated carbon was continuously dosed into the pilot scale filtration employing PES Hollow Fiber membrane with active area of 4 m² and average pore size of 10 nm that represents a real operation filtration process (i.e., filtration flux, filtration time, backwashing, and cleaning in place), and was performed until 8 filtration cycle sequence. This study investigated membrane performance with combination technique PAC/UF and GAC/UF in Pilot scale experiments within resistance membrane and retention membrane. Combination of Activated Carbon/Ultrafiltration showed synergistic effects in the removal of organic content for COD 40%-96%, UV-VIS 43%-92% and Turbidity 73%-99%. High removal of organics pollutants (COD, UV-VIS and Turbidity) was attributed to small average pore distribution of Activated Carbon (<10 µm) that increase adsorption process. Moreover, hybrid Activated Carbon/UF adsorption kinetics can reduce filtration times to achieved optimal retention. Related to membrane performance, hybrid AC/UF resulted in less permeability declines almost double in first two filtration cycle and slightly less permeability decline until fifth cycle in comparison with single UF process. Better membrane performance can furtherly be explained from less irreversible fouling in case of AC/UF. Combination AC/UF enhanced the control of Irreversible fouling and resulted in better filtration performance as well as higher organic substance removal. Therefore, hybrid AC/UF could be seen as an effective system as pretreatment for SWRO.

Peroxymonosulfate based in situ chemical oxidation: An efficient strategy for mitigation of membrane fouling in real seawater reverse osmosis desalination

Persulfate based advanced oxidation processes (AOPs) is an emerging method to assist the pretreatment to prevent membrane fouling for seawater desalination. However, the present strategies which adopt activators (e.g., UV, heat, Fe) to generate kinds of free radicals, are energy-consuming and enhance the concerns of disinfection by-products (DBPs). Here, peroxymonosulfate (PMS) is adopted as a green, effective and economical pretreatment chemical for simultaneous microorganic pollutants degradation and microorganism inactivation in seawater reverse osmosis (SWRO) desalination without any external energy input. After adding into the seawater, 53% PMS could be activated by Cl- in situ to generate HClO at most with no other active species generated, which is verified by stoichiometric analysis and quenching experiments. Benefited from the residual PMS, not only could up to 89.6% of total organic carbon be removed in the real seawater, but also nearly 80% of DBPs could be degraded by simply adjusting pH from neutral to alkaline conditions. Meanwhile, all bacteria could be killed completely and hardly any regrowth appeared, which further proved the anti-fouling ability of the PMS/Cl- system. Consequently, the addition of PMS could maintain the flux for a long time in the practical SWRO application with significantly reducing the RO membrane fouling. Moreover, the operating cost of PMS is only 0.024 $/ton, which is comparable to NaClO. This study demonstrated the excellent performance of PMS in SWRO pretreatment, supplying a promising scheme in practical desalination processes.

Effectiveness of ceramic ultrafiltration as pretreatment for seawater reverse osmosis

The Gulf Cooperation Council (GCC) region's considerable reliance on seawater reverse osmosis (SWRO) for freshwater production is amplifying with increasing population and industrial growth. Nonetheless, harsh seawater conditions in the region coupled with ineffective pretreatment have triggered frequent SWRO plant shutdowns, premature RO membrane and cartridge filter replacements, and low plant availability. To improve plant performance and sustainability, an effective pretreatment is needed; a promising option is the use of ceramic membranes. To investigate their effectiveness for handling variable seawater conditions experienced in the region — specifically harmful algal blooms (HAB) — this work presents a pilot scale ceramic UF (CUF) pretreatment study. Operational reliability and treated water quality of CUF was evaluated against existing polymeric MF and UF pretreatment in adjacent SWRO plants. CUF operated at full capacity during HAB season, compared to 30–40 % reduction for the MF/UF plants. Furthermore, it produced superior permeate quality, despite variations in feedwater conditions — for instance, it removed over 5× more Dissolved Organic Carbon (DOC) and 1.5× more Transparent Exopolymer Particles (TEP) than the polymeric membranes. These results indicate the potential for CUF as an effective pretreatment for SWRO to minimize plant downtime and ensure consistent permeate quality during all seawater conditions.

D (+)-Glucosamine (DGA) based polyesteramide TFC NF membrane for the pretreatment of reverse osmosis seawater desalination

Reverse osmosis is an effective seawater desalination way extending the available sources of fresh water, but challenged by the gypsum scaling. Herein, D (+)-glucosamine (DGA) was rationally selected and utilized to prepare a novel polyesteramide (PEA) NF membrane that can reject SO42− but release Ca2+. Then it was employed in the pretreatment of seawater reverse osmosis to spatially isolate SO42− and Ca2+, thus removing the “foundation” for forming gypsum. Compared to the referenced NF270, the optimized sample denoted as DGA-PEA-NF has a looser structure with stronger negative charge, as well as a higher resistance to both organic fouling and chlorine attack. During the pretreatment of seawater, both the water permeability and SO42−/Ca2+ selectivity of the DGA-PEA-NF membrane were much higher than those of NF270; the seawater permeance and SO42−/Ca2+ selectivity of DGA-PEA-NF were 10.25 L m−2·h−1·bar−1 and 7.62, respectively, while those of NF270 were only 5.11 L m−2·h−1·bar−1 and 2.08. Consequently, the DGA-PEA-NF membrane effectively reduced the gypsum scaling both in NF and RO stages rather than just transferring the fouling problem forwards to NF stage. The implementation of this research is expected to provide guidance for a targeted fabrication of NF membranes, as well as support for the sustainable development of seawater desalination.

Comprehensive analysis of a hybrid FO-NF-RO process for seawater desalination: With an NF-like FO membrane

Process optimization is a popular strategy to improve efficiency, reduce the energy consumption and total cost of the seawater reverse osmosis (SWRO). Forward osmosis (FO) process with a nanofiltration (NF)-like membrane has emerged as a cost-effective technology for seawater desalination pretreatment, due to its high water permeability and low energy consumption compared to RO-like FO membrane. The present work comprehensively evaluated the potential of using an NF-like FO membrane for SWRO pretreatment and analyzed the feasibility of the NF-like membrane-based FO-NF-RO process for seawater desalination. The performance of the FO-NF-RO integrated process was investigated with MgSO4, Na2SO4, and Mg(CH3COO)2 as draw solute, respectively. Besides, the energy consumption and total cost of the hybrid process were also estimated on the laboratory and large scale. The NF-like membrane-based FO process could effectively remove organic molecules and divalent ions effectively. The hybrid process product water could reach the drinking water standard in China (TDS ≤ 1000 mg/L). When water recovery was 42.0%, the hybrid process could produce freshwater with specific energy consumption of 2.99 kWh/m3 and specific water cost of 0.92 $/m3, which were comparable with the conventional SWRO process. Overall, our study revealed the feasibility of the FO-NF-RO process for seawater desalination.

Modeling UF fouling and backwash in seawater RO feedwater treatment using neural networks with evolutionary algorithm and Bayesian binary classification

A machine learning approach to describing the dynamics of ultrafiltration performance in pretreatment of seawater reverse osmosis (RO) feedwater was explored via ensemble back propagation neural network (BPNN) model. The BPNN model was developed with Alopex evolutionary algorithm (AEA) optimization and AdaBoost strategy. The progression of ultrafiltration (UF) membrane resistance during both filtration and backwash, along with backwash efficiency were modeled via the ensemble BPNN-AEA approach relying on 422 days of operational data for an integrated SWRO UF-RO system. Model performance, for UF membrane resistance and backwash efficiency, evaluated over a wide range of operating conditions and coagulant dosing strategies, revealed excellent performance with a forecasting capability even for cases of temporally variable water quality. The performance level attained with the current machine learning modeling approach, which is particularly suited for handling the dynamics of UF operation, should prove useful for (a) determining UF performance deviation from intended baseline performance, (b) forecasting expected UF performance due to anticipated changes in water quality, and (c) providing a basis for model-based control of UF operation.

Monitoring Biofouling Potential Using ATP-Based Bacterial Growth Potential in SWRO Pre-Treatment of a Full-Scale Plant.

Several potential growth methods have been developed to monitor biological/organic fouling potential in seawater reverse osmosis (SWRO), but to date the correlation between these methods and biofouling of SWRO has not been demonstrated. In this research, the relation between a new adenosine triphosphate (ATP)-based bacterial growth potential (BGP) test of SWRO feed water and SWRO membrane performance is investigated. For this purpose, the pre-treatment of a full-scale SWRO plant including dissolved air flotation (DAF) and two stage dual media filtration (DMF) was monitored for 5 months using BGP, orthophosphate, organic fractions by liquid chromatography coupled with organic carbon detection (LC-OCD), silt density index (SDI), and modified fouling index (MFI). Results showed that particulate fouling potential was well controlled through the SWRO pre-treatment as the measured SDI and MFI in the SWRO feed water were below the recommended values. DAF in combination with coagulation (1–5 mg-Fe3+/L) consistently achieved 70% removal of orthophosphate, 50% removal of BGP, 25% removal of biopolymers, and 10% removal of humic substances. Higher BGP (100–950 µg-C/L) in the SWRO feed water corresponded to a higher normalized pressure drop in the SWRO, suggesting the applicability of using BGP as a biofouling indicator in SWRO systems. However, to validate this conclusion, more SWRO plants with different pre-treatment systems need to be monitored for longer periods of time.

Study of 3D-Printed Pressure Release Nozzle for Microbubble Formation in Full-Scale Dissolved Air Flotation (DAF)

Pressure-release equipment for the formation of microbubbles is an important part of any DAF system. In this study, 3D printing was employed to produce new nozzles, followed by testing to find the optimum pressure and flowrate. The flowrate through the nozzle affected both the empty bed residence time (EBRT) of the saturator and also the nucleation of bubbles. With the increase of flow rate, the total number of bubbles was seen to increase. This is a significant observation meaning that the enhanced precipitation of bubbles outweighs the reduced EBRT. This fact can improve equipment sizing and reduce CAPEX. Meanwhile, DAF is a technology that can help extend membrane life and reduce operational issues in seawater reverse osmosis (SWRO). So for further validation, a full-scale DAF was built and tested for SWRO pretreatment on the coast of the Persian Gulf. The system was tested with/without coagulation as well as with/without filtration media embedded inside the DAF tank. The results showed that the use of coagulation alongside DAF reduced the turbidity by more than 60% while using a DAF with embedded filtration could reduce the turbidity to less than 1 NTU. In comparison to common media filters, the proposed setup showed better performance.

Ozone enhanced ceramic membrane filtration for wastewater recycling

Abstract The Water Corporation of Western Australia uses polymeric ultrafiltration (UF) membranes across a range of applications including surface waters with high natural organic matter (NOM), recycling of secondary treated wastewater and pre-treatment for seawater reverse osmosis (SWRO). These challenging raw water conditions require expensive chemical dosing and clean-in-place (CIP) regimes, high frequency of membrane replacement and reduced membrane life. The greater durability of ceramic membranes, with optimal ozone and coagulant dosing, offer a potential capital and operating advantage over polymeric UF membranes. The Water Corporation collaborated with PWN Technologies (PWNT) to establish a ceramic membrane pilot plant at the Beenyup Wastewater Treatment Plant (WWTP). Optimised performance of the pilot plant was established and compared with existing UF membranes treating secondary treated wastewater prior to reverse osmosis (RO) in an indirect potable wastewater recycling application. Findings show a sustainable flux rate of 150 L/m2/h is achievable with ceramic MF membranes while filtering secondary treated wastewater. Higher flux rates up to 250 L/m2/h have been tested and are possibly sustainable, however, other bottlenecks in the pilot plant (ozone generator capacity) prevented longer test runs at this flux. Comparable design flux rates for polymeric UF membranes are 50 L/m2/h.

Direct measurement of ATP in seawater and application of ATP to monitor bacterial growth potential in SWRO pre-treatment systems

The use of adenosine triphosphate (ATP) to monitor bacterial growth potential of seawater is currently not possible as ATP cannot be accurately measured at low concentration in seawater using commercially available luciferase-based ATP detection. The limitation is due to interference of salt with the luciferin–luciferase reaction, which inhibits light production. This research demonstrates that new reagents developed for (i) ATP extraction from microbial cells and (ii) ATP detection in seawater are able to reliably detect Microbial ATP as low as 0.3 ng L–1 in seawater. The luminescence signal of the new detection reagent is significantly higher (>20 times) than the luminescence signal of the freshwater reagent, when applied in seawater. ATP can now be used to monitor bacterial growth potential (BGP) through pre-treatment trains of seawater reverse osmosis (SWRO) plants. The level of detection of the new BGP test is significantly lower than the estimated threshold value required to prevent biofouling in SWRO systems. The new reagents have been used to monitor Microbial ATP in coastal North Sea water. Moreover, Microbial ATP has been applied to monitor the bacterial growth potential (using indigenous bacteria) through the pre-treatment train of an SWRO desalination plant. A significant reduction (>55%) of the bacterial growth potential was found through the dual media filtration with 4.5 mg-Fe(III) L–1 coagulant. Overall, the new reagents can detect low Microbial ATP concentrations in seawater and can be used to monitor bacterial growth potential in seawater desalination plants.

Performance of flocculation titanium salts for seawater reverse osmosis pretreatment

Performance of flocculation titanium salts for seawater reverse osmosis pretreatment

Dynamic membrane filtration using powdered iron oxide for SWRO pre-treatment during red tide event

Shut-down or reduced treated water supply of a seawater reverse osmosis (SWRO) plant due to membrane fouling during a red tide event is currently an important issue in regions where red tide frequently occurs. Algal organic matter (AOM) released by algae through metabolic activity is known as a major membrane foulant and the primary cause of the suspension of SWRO plants. In this study, iron oxide was utilized to develop an AOM removal process in seawater since activated carbon and advanced oxidation process (AOP) have limited removal efficiencies due to the high ionic strength of the seawater. Dynamic membrane filtration was applied as an iron oxide application method because additional process is not required for temporary operation during only algal bloom. The results showed that the dissolved organic carbon (DOC) removal efficiencies of the iron oxide were improved at high ionic strength compared to organics removal in fresh water. Although only a partial adsorption rate (below 50%) was achieved using iron oxide, significant reduction of the ultrafiltration (UF) membrane fouling was observed through the continuous operation of dynamic membrane filtration since relatively high molecular weight faction of organics was more readily adsorbed in the oxide surface. Given the continuous lab-scale experimental results and economic aspect, dynamic membrane filtration using powdered iron oxide can be a potential option as an emergency plan during a red tide event.

Transparent exopolymer particles (TEP) removal efficiency by a combination of coagulation and ultrafiltration to minimize SWRO membrane fouling

This study investigated the impact of coagulation on the transformation between colloidal and particulate transparent exopolymer particles (TEP) in seawater; and the effectiveness of a combined pretreatment consisting of coagulation and UF on minimizing TEP fouling of seawater reverse osmosis (SWRO) membranes. Coagulation with ferric chloride at pH 5 substantially transformed colloidal TEP (0.1–0.4) into particulate TEP (>0.4) leading to a better membrane fouling control. Both 50 and 100 kDa molecular weight cut-off (MWCO) UF membranes removed most of particulate and colloidal TEP without the assistance of coagulation, but coagulation is still necessary for better UF fouling control. The improvement of combined SWRO pretreatment with coagulation and 50 kDa UF membranes was not that much significant compared to UF pretreatment with 50 KDa alone. Therefore, the minimal coagulant dosage for seawater containing TEP should be based on the UF fouling control requirements rather than removal efficiency.

Use of innovative inge® Multibore® ultrafiltration membranes for the treatment of challenging seawater

AbstractUltrafiltration (UF) has established itself as one of the key technologies in the water treatment industry over the last decade, providing superior filtrate water quality regardless of fluctuations in the feedwater quality and protecting downstream treatment steps. UF has demonstrated its advantages as seawater reverse osmosis pre-treatment for desalination application improving reverse osmosis membranes performances while extending their service life. In-depth knowledge of polymeric chemistry is mandatory for developing, manufacturing and operating new membranes. On-site evaluation of membrane performance on real water is also essential. Seawater properties can vary significantly depending on location and region. This makes it very important to pilot in order to understand the challenges and how to address them. This paper presents results obtained at different sites operating on seawater under particularly difficult conditions using inge® Multibore® membranes. The study describes membrane behavi...

Novel ultrafiltration membranes from low-fouling copolymers for RO pretreatment applications

AbstractFor a consistent and reliable ultrafiltration (UF) membrane operation, the membrane flux level has always been determined conservatively so that fouling rate is controllable, and therefore, chemical cleaning requirements are minimized. A better solution is to prevent the fouling to happen in the first place by modifying the surface properties of the membrane materials. This paper presents novel approaches to improve the fouling-propensity performance of existing UF membranes based on polyethersulfone. More hydrophilic membranes and anti-adhesive membranes were developed by using various novel copolymers as base membrane materials or as an additive in the spinning process. Incorporating these copolymers, improved Multibore® fibers were produced and validated in multiple pilot trials for various applications, namely surface and wastewater purification and seawater reverse osmosis pretreatment for desalination. The paper demonstrates that, for each application, a reduced fouling propensity performanc...

Environmental and economic assessment of beach well intake versus open intake for seawater reverse osmosis desalination

This paper presents a comparative life cycle assessment (LCA) and levelised cost (LC) analysis of two scenarios: an open intake scenario in which a seawater reverse osmosis (SWRO) desalination plant employs an open intake and membrane pre-treatment prior to RO, and a beach well scenario in which feedwater is extracted from the subsurface using beach well intake and cartridge filtration prior to RO. In both scenarios, desalination plants with 35,000m3/day capacities were modelled. Results indicate that the beach well intake plant life cycle environmental burdens and LC were as much as 31% and 13% lower respectively, compared with the open intake plant. A detailed contribution analysis revealed that the better environmental performance of the beach well intake plant was significantly influenced by its comparatively low electricity use in the simplified pre-treatment process. The better economic performance of the plant with beach well intake was mostly due to savings in chemical use. The results are based on site specific assumptions. However, the LCA and LC framework developed herein could be used to determine the optimum SWRO seawater intake and pre-treatment configuration at plant sites with different characteristics to those modelled herein, provided sufficient data is available.

Gravity-driven membrane filtration as pretreatment for seawater reverse osmosis: Linking biofouling layer morphology with flux stabilization

In this study gravity-driven membrane (GDM) ultrafiltration is investigated for the pretreatment of seawater before reverse osmosis (RO). The impacts of temperature (21 ± 1 and 29 ± 1 °C) and hydrostatic pressure (40 and 100 mbar) on dynamic flux development and biofouling layer structure were studied. The data suggested pore constriction fouling was predominant at the early stage of filtration, during which the hydrostatic pressure and temperature had negligible effects on permeate flux. With extended filtration time, cake layer fouling played a major role, during which higher hydrostatic pressure and temperature improved permeate flux. The permeate flux stabilized in a range of 3.6 L/m2 h (21 ± 1 °C, 40 mbar) to 7.3 L/m2 h (29 ± 1 °C, 100 mbar) after slight fluctuations and remained constant for the duration of the experiments (almost 3 months). An increase in biofouling layer thickness and a variable biofouling layer structure were observed over time by optical coherence tomography and confocal laser scanning microscopy. The presence of eukaryotic organisms in the biofouling layer was observed by light microscopy and the microbial community structure of the biofouling layer was analyzed by sequences of 16S rRNA genes. The magnitude of permeate flux was associated with the combined effect of the biofouling layer thickness and structure. Changes in the biofouling layer structure were attributed to (1) the movement and predation behaviour of the eukaryotic organisms which increased the heterogeneous nature of the biofouling layer; (2) the bacterial debris generated by eukaryotic predation activity which reduced porosity; (3) significant shifts of the dominant bacterial species over time that may have influenced the biofouling layer structure. As expected, most of the particles and colloids in the feed seawater were removed by the GDM process, which led to a lower RO fouling potential. However, the dissolved organic carbon in the permeate was not be reduced, possibly because some microbial species (e.g. algae) could convert CO2 into organic substances. To further improve the removal efficiency of the organic carbon, combining carrier biofilm processes with a submerged GDM filtration system is proposed.

Long-term effect on membrane fouling in a new membrane bioreactor as a pretreatment to seawater desalination.

Submerged membrane adsorption bio-reactors (SMABR) were investigated as a new pretreatment for seawater reverse osmosis (SWRO) desalination. They were tested with different doses of powder activated carbon (PAC) on-site for a long-term. The biofouling on the membrane was assessed in terms of DNA (cells) and polysaccharide distribution. MBR without PAC addition resulted in severe fouling on membrane. When PAC is added in the MBR, PAC could reduce the organic fouling. Hence the biofilm formation on membrane was reduced without any membrane damage. PAC also helped to remove low molecular weight (LMW) organics responsible for biofouling of RO membrane. A linear correlation between assimilable organic carbon (AOC) and LMW organics was observed. A small amount of PAC (2.4-8.0g of PAC/m(3) of seawater) was sufficient to reduce biofouling. It indicated that SMABR is an environmentally-friendly biological pretreatment to reduce biofouling for SWRO.

Dynamic shift in community structures of biofilm-forming bacteria by the pre-treatment systems of seawater reverse osmosis processes

In this study, the bacterial compositions of raw seawater and permeates from the conventional pre-treatment system and the membrane-based microfiltration system were examined during the seasons of autumn, winter and spring. The biofilm-forming potential was calculated based on the relative abundances of the putative biofilm-forming bacteria for the two seawater reverse osmosis pre-treatment systems. The cloning and sequencing analysis of the 16S rRNA gene reveals the dynamic shift in bacterial community structure to the genera capable of biofilm-formation through the pre-treatments. The highly diverse bacterial community structure of the raw seawater and the permeates hinders the statistical analysis for generalizing the bacterial components according to the sources or the seasons. This study proposes that the operational regimes of pre-treatment systems should be reconsidered based on the target bacterial groups of key biofilm formers.

Economic feasibility study for MF system as a pretreatment of SWRO in test bed desalination plant

Abstract The test bed for seawater reverse osmosis (SWRO) desalination plant having a capacity of 10 million imperial gallons per day, located in the southeast of South Korea, is under construction by Doosan Heavy Industries and Construction. The feed water for first pass SWRO train will be pretreated by a microfiltration (MF) membrane system and conventional dual media filtration system. For the MF pretreatment system, it is necessary to evaluate the economic feasibility between the submerged and the pressurized membrane systems to apply the filtration mode of membrane modules. This article evaluates the economics using the life cycle cost (LCC) analysis method. Although many researchers reported that the submerged MF system has economic advantages over the pressurized system because the submerged system consumes lower energy, the result of this article presents on the contrary to this. The result shows that the total capital cost and operation cost of the pressurized system are lower than those of the s...