Seawater Reverse Osmosis Pretreatment Research Articles

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

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 submerged system, because the pressurized system can use the hydraulic pressure generated from the seawater supply pump and air consumption is much lower than that of the submerged system. In addition, the result of LCC estimation shows that the pressurized system has the lower cost compared with the submerged system, by approximately 13%. This represented that the pressurized MF pretreatment system has economic advantage over the submerged system especially in SWRO desalination plant.

Algal bloom—critical to designing SWRO pretreatment and pretreatment as built in Shuwaikh, Kuwait SWRO by Doosan

The growing demand for fresh water in many areas in the world is due to drought, water shortages, population increases, and the desire for high- quality drinking water. The reverse osmosis (RO) process is pressure-driven and filtered seawater is pressurized beyond the osmotic pressure the solution to overcome the permeation barrier of membrane and the water molecules in the seawater able to pass through the membranes. In recent years, the number and size of these water projects have increased noticeably. RO membranes are expensive and susceptible to fouling due to contamination in the feed water; hence, it is utmost important to care for particular feed water treatment in maintaining ongoing performance and avoiding significant problems in downstream process equipments. In recent, days the additional risks are due to naturally occurring events like algal blooms or red tide, due to ingress of marine algae, planktonic bloom with small particles and colloidal material released from algae cause for pretreatment failure almost regularly. As algal bloom life cycle peaks and decays, a significant amount of organic material is released upon cell death. Also, bacteria feed on the decaying material and release their own extracellular polymeric substance (EPS) that has the potential to escape out pretreatment and foul RO membranes. There are many pretreatment procedures for seawater reverse osmosis (SWRO) plant, and the basis of selection of right system depends on seawater quality and the price. Doosan built facility in Shuwaikh in Kuwait is having the pretreatment configuration with combination of dissolved air flotation and ultrafiltration to take care of difficult water condition with highly suspended solid value arise for various reasons. Pretreatment combination is found to be working well in providing plant availability and quality. But the main concern is that it is impossible to avoid deposition of EPS on SWRO membrane surface with present pretreatment technology—it may happen in future with new generation of technology, it will be possible to overcome the situation at added cost.

Ceramic membrane filtration as seawater RO pre-treatment: influencing factors on the ceramic membrane flux and quality

Membrane filtration has been accepted as the preferred pre-treatment method in reverse osmosis (RO) processes in recent years. In this paper, a laboratory-scale ceramic membranes device, which has a potential to be used as pre-treatment for RO desalination, was employed to investigate the performance of ceramic membranes with different pore sizes and under different conditions. Ceramic membranes with pore sizes of 50, 200, 500, and 800nm were tested, and the effects of pore size, transmembrane pressure (TMP), coagulation method, and NaClO addition on the permeate flux and the permeate quality of ceramic membranes were studied. The results show that the pore size has an insignificant effect on the permeate flux of ceramic membranes but the coagulation method has a significant effect. Pore size and NaClO addition did not have significant effects on the turbidity of the ceramic membrane permeate, but they did affect the SDI15 (Silt Density Index) values of the ceramic membrane permeate. A pilot test was executed using a pilot ceramic membrane device with an approximate capacity of 330 m3/d. The TMP was stable with a constant flux of 150 L/m2h and a cross-flow velocity of 0.015 m/s, and the turbidity and SDI15 values were satisfactory for RO, suggesting that ceramic membranes can meet the demands of RO.

해수담수화 전처리로서 DAF공정에서 고온의 해수에 대한 영향 특성

Flocculation and flotation are used as pretreatment steps prior to the reverse osmosis (RO) process. During seawater treatment, high temperature can change the water chemistry of seawater during the process of coagulation. It also affects bubble volume concentration (BVC) and bubble characteristics. Coagulants such as alum and ferric salts at <TEX>$40^{\circ}C$</TEX> can also change flux rates in the seawater reverse osmosis (SWRO) process. In this study, the bubble characteristics in dissolved air flotation (DAF), used as a SWRO pretreatment process, were studied in synthetic seawater at <TEX>$20^{\circ}C$</TEX> and <TEX>$40^{\circ}C$</TEX>. The flux of an RO membrane was monitored after dosing the synthetic seawater with coagulants at different temperatures. Results showed that BVC increases as the operating pressure increases and as the salt concentration decreases. The bubble size released at <TEX>$40^{\circ}C$</TEX> is far smaller than that at <TEX>$20^{\circ}C$</TEX>The addition of a ferric salt is effective for turbidity removal in synthetic seawater at <TEX>$20^{\circ}C$</TEX>; it is more effective than alum. When synthetic seawater was dosed with a ferric salt, the RO membrane flux increased by 27 % at <TEX>$40^{\circ}C$</TEX>.

Experiences from the Adelaide Desalination project: ultrafiltration cleaning optimisation—from pilot to full-scale operation

Membrane fouling remains a major concern for ultrafiltration (UF) pretreatment for seawater reverse osmosis (RO). The focus of this study was the optimisation of the chemical cleaning regime and any associated impact on the downstream cartridge filters (pre-RO). Different shock acidification/chlorination and maintenance wash (MW) regimes for the pilot UF were tested. The results of the study at the Adelaide Desalination Pilot Plant (ADPP) are summarised as follows:•Sulphuric acid shock dose alone at pH 4 was ineffective for prevention of UF biogrowth, when performed for one hour per week or less.•Shock chlorination provided an effective tool for limiting biogrowth in UF systems.•Relocating the sodium metabisulphite dechlorination dosing point downstream of the cartridge filters was essential for controlling biogrowth and to ensure stable operation of the filters.•Chlorine MWs provided better UF permeability and transmembrane pressure (TMP) recovery than sulphuric acid MWs.•A chlorine MW frequency once in every 4 days and sulphuric acid MW frequency more than once in every 2 weeks was chosen for the full-scale plant.•Addition of ferric sulphate into the UF feed significantly impaired operational performance with respect to TMP and permeability decay rate. This is most likely due to the low seawater turbidity and dissolved organic carbon levels. Data from the ADPP were used to optimise operation conditions for the full-scale plant during commissioning. The Operator of the Adelaide Desalination Plant, AdelaideAqua Pty. Ltd. used the pilot plant findings to assist with optimisation of the dose/frequency regime for chlorine and sulphuric MWs. A comparison of pilot operation and full-scale plant commissioning performance is discussed.

The performance of contact flocculation–filtration as pretreatment of seawater reverse osmosis

Deep bed filtration has traditionally been used as a pretreatment in seawater desalination. The performance of contact flocculation–filtration (CFF) as pretreatment of seawater reverse osmosis (SWRO) was evaluated in terms of pressure drop through the filter and removal of organics and turbidity. The average turbidity, total suspended solids, and dissolved organic carbon (DOC) of raw seawater were 0.92 NTU, 3.6, and 1.12 mg/L, respectively. The performances of CFF were experimentally evaluated with different flocculant doses (0.5–3.0 mg Fe3+/L) and rapid mixing times (1.7–14.4 s). Here rapid mixing was performed in a spiral flocculation unit which consisted of a PVC tube of length 0.5 m and internal diameters of 0.16 and 0.40 cm. The experimental results show that the filtration rate of 10.0 m/h led to an extensive increase in both head loss (pressure drop) and turbidity as compared to those at filtration rates of 5.0 and 7.5 m/h. The head loss also significantly decreased when the flocculant dose was reduced from 3 to 0.5 mg Fe3+/L. However, the organic matter (26% of DOC) removal was lower at a lower dose of ferric chloride (1.0 mg/L as Fe3+). The removal efficiency of DOC at low concentration of ferric was improved considerably through the improvement of rapid mixing. The application of CFF process also led to a significant decrease in ultrafilter-modified fouling index (UF-MFI).

A comparative study of ultrafiltration and physicochemical process as pretreatment of seawater reverse osmosis

A comparative study of ultrafiltration and physicochemical process as pretreatment of seawater reverse osmosis

A comparative study of ultrafiltration and physicochemical process as pretreatment of seawater reverse osmosis

Abstract The effectiveness of two pretreatments for open intake seawater reverse osmosis (RO), aerated spiral wound ultrafiltration (ASWUF) and physicochemical (PC) pretreatment, were evaluated. Their efficiency in removing particulate materials was assessed by SDI, turbidity and Particle Size Distribution. Aerobic bacteria levels indicated the effectiveness of bacterial removal. Organic matter was characterized by TOC and UV254. The apparent molecular weight (MW) distribution of organic matter was determined by centrifugal ultrafiltration fractionation and the effect of pretreated effl uent on seawater RO flux decline was evaluated by a bench-scale test. Both pretreatments lowered feed water SDI to 2 and turbidity to 0.4 NTU and were highly efficient in removing particles larger than 1 μm. In general, ASWUF was more effective than PC, although PC removed TOC more effi ciently. For both pretreatments, TOC fractions with a MW of under 3 kDa remained in treated water. Both pretreatments made effl uents of e...

Dual media filtration and ultrafiltration as pretreatment options of low-turbidity seawater reverse osmosis processes

Well-controlled laboratory scale experiments were carried out to estimate the performance of dual media filtration (DMF) and ultrafiltration (UF) as a pretreatment for seawater reverse osmosis (SWRO) processes. Raw seawater was taken from the place close to the construction site of the SEAHERO test-bed of 45,000 m3/d in capacity, which is planning to be operated from 2013. The raw seawater turbidity was rather low and the focus of this study is to find out the better process between DMF and UF for the pretreatment of low turbidity seawater. The UF process exhibited a good performance to produce qualified RO feed water and coagulation added the removal of aromatic organics and better resistance to the membrane fouling. However the DMF process could not make RO feed water to satisfy the SDI standard and variations in operation conditions did not change the product water quality. In order to enhance the performance of DMF process, a multi-pass design or an improved coagulation strategy for low turbidity wate...

Iron and manganese fouling in microfiltration as a pretreatment of seawater reverse osmosis processes

Two sets of pilot test were carried out to investigate the fouling behaviours of microfiltration (MF) system as a pretreatment for seawater reverse osmosis (SWRO) processes for about two years. One set used clean seawater as feed water while the other adopted surface water with lower quality than the seawater. Both systems introduced commercial hollow fiber MF modules from the same manufacturer. During the operation period, raw water quality parameters related to reverse osmosis (RO) performance were collected and analyzed. Regardless of raw water quality, the product water of both MF systems without coagulation exhibited high water quality as RO feed water. The MF system for SWRO pretreatment underwent more severe fouling than the MF system for surface water treatment although the tested seawater quality is much better than the tested surface water quality in terms of fouling potentials. Iron and manganese turned out to be main foulants through water analysis for discharged water from the chemical cleani...

Pretreatment for seawater desalination by flocculation: Performance of modified poly ferric silicate (PFSi-δ) and ferric chloride as flocculants

Submerged microfiltration system coupled with in-line flocculation as pretreatment for seawater reverse osmosis has the potential to remove organic compounds and mitigate fouling. The effect of flocculation on the performance of microfiltration (MF) was investigated using two flocculants, namely, modified poly ferric silicate (PFSi-δ) and ferric chloride (FeCl 3). The experimental results were analysed in terms of organic removal efficiency and critical flux. Both PFSi-δ and FeCl 3 were found to be suitable as pretreatment because of their capacity in removing organic compounds. The results show that PFSi-δ was better than FeCl 3 in terms of removing turbidity and dissolved organic carbon (DOC), particularly in removing hydrophilic compounds. The highest DOC removals of 68% and 57% were obtained when PFSi-δ at a dose of 1.2 mg Fe 3+/L and FeCl 3 at 3 mg Fe 3+/L were used, respectively. It was observed that PFSi-δ (1.2 mg Fe 3+/L) and FeCl 3 (3 mg Fe 3+/L) led to an increase of critical flux from 20 L/m 2 h to 35 L/m 2 h and 55 L/m 2 h, respectively.

Effects of operating conditions on submerged hollow fibre membrane systems used as pre-treatment for seawater reverse osmosis

The potential of submerged hollow fibre membrane systems without the aid of coagulant was investigated as a pre-treatment for seawater reverse osmosis in this paper. The operation parameters such as filtration duration, backwash duration, backwash strength and the aid of air scouring during backwash were investigated in order to optimize the filtration performance and fouling control. The underlying fouling limitation mechanisms which result in those optimized operation parameters were also explored. It was found that periodical backwash with the permeate can provide effective removal of fouling layer and reduce the fouling rate during the filtration cycle. Results also indicated the strong inter-correlation among backwash strength and filtration duration and their effect on fouling rate. Excessive backwash strength was found unable to minimize fouling, and in fact, resulted in higher fouling rate during filtration. The percentage of removable fouling by backwash was also significantly affected by the inter-correlation between the backwash strength and backwash duration. By analyzing the composition of the feed, permeate and the solution after backwash, it was found that UF membrane (pore size 0.04 μm) can remove more than 60% of biopolymers. The biopolymers rejected by the UF membrane formed the cake on the membrane surface, and this fouling cake can be easily removed by periodical backwash.

Comparison of fouling indices in assessing pre-treatment for seawater reverse osmosis

In this study, different processes such as fl occulation with ferric chloride (FeCl3) and deep bed filtration (sand filtration and dual media filtration) as a pre-treatment were used for seawater desalination. The performance of these pre-treatments was determined in terms of silt density index (SDI) and modified fouling index by using microfilter (MF-MFI), ultrafilter (UF-MFI), and nanofi lter (NF-MFI) membrane. MFI and SDI indicated that deep bed filtration with in-line flocculation was better pre-treatment than flocculation alone as colloidal particles are removed after this pretreatment. UF-MFI and NF-MFI indicated that these pretreatment cannot remove dissolved organic matter as the fouling reduction was smaller. Detailed molecular weight distribution (MWD) of seawater organic matter was examined after different pretreatments. MWD of the initial seawater mainly ranged from 1510 Da to 130 Da. Deep bed filtration with in-line flocculation removed relatively large molecular weight of organic matter (151...

Membrane-based SWRO pretreatment: Knowledge discovery in databases using principal component analysis regression

At the time being there are several technological designs of membrane-based seawater reverse osmosis (SWRO) pretreatment systems on the desalination market. The abundance of different membrane materials and configurations (pressurized/submerged/inside-out/outside-in etc.) combined with site specific conditions make the unbiased assessment of their general performance a difficult task. In this paper we suggest a data mining method based on the principal component analysis (PCA) to serve as a more systematically logical regression tool on currently available literature data. PCA is a multivariate statistical method that uses a linear transformation for dimension reduction and pattern recognition. The results show how this method can be used effectively in the case of SWRO membrane based pretreatment for both literature data reconciliation and reconstruction, as well as for future data prediction.

Ultrafiltration pretreatment to reverse osmosis for seawater desalination — three years field experience in the Wangtan Datang power plant

Systems composed of ultrafiltration (UF) pretreatment for seawater reverse osmosis (SWRO) desalination are often termed “integrated membrane system” or “dual membrane system”. These systems promise to offer reliable handling of very difficult waters, also in regions which have traditionally experienced feed water and pretreatment problems such as Middle East and United States. Nevertheless, data sets presenting long-term integrated operation from a UF and SWRO point of view at a larger scale level, and hence validating the potential cost benefit of UF pretreatment, are very scarce. The dual membrane seawater desalination system at the Wang Tan Power Plant has been operating for three years and is an ideal case to present learnings. Despite some gaps in the data set, some operational problems, and an unconventional low flux and low chemicals operation approach, the authors believe that transparent sharing of this data set can significantly contribute to a better industry understanding of integrated operation. The data shows that UF system operation is possible using a low flux (25 L/m2;/h), low chemical approach. This approach totally eliminates the need for coagulation or chemical enhanced backwash, and uses only yearly clean in place operations. This requires higher upfront capital investment, but results in lower chemicals cost, lower sludge and chemical brine disposal, better ease of operation and higher safety level. This approach has allowed reliable water production in the DOW™ UF and FILMTEC™ SWRO unit for 3 years and should be interesting for very environmentally aware regions with difficult waters, such as Australia or United States. Based on limited data, turbidity removal rate was 98–99.5% and outlet SDI typically <2.5. On a water with very high temperature fluctuation, this enabled SWRO operation with slow pressure drop increase and normalized flux loss, hence resulting in low cleaning frequency of around yearly clean in place operation, and low replacement rate of 1%/a. The data also shows that care should be taken that chlorine employed in ultrafiltration backwash operations does not attack SWRO membranes — improved modes eliminating these problems are available and discussed within the paper. Ultimately, a one-year pilot trial in the SWRO plant shows that the combination of ultrafiltration and internally staged design, employing high productivity elements such as FILMTECTM SW30ULE-400i is synergistic and can enable unprecedented SWRO vessel productivity of 5 m2;/h and flux rate in the range of 25 L/m2;/h, while achieving excellent water quality in the range of below 500 µS/cm.

Hybrid filtration method for pre-treatment of seawater reverse osmosis (SWRO)

Hybrid processes combining fibre filter with deep bed filtration process such as (i) fibre filter and sand filter, (ii) fibre filter and anthracite and (iii) fibre filter and dual media filter were investigated as pre- treatments to SWRO. Seawater was drawn from Chowder Bay, Sydney. The effect of different pretreatment hybrid systems was investigated in terms of silt density index (SDI 10), modified fouling index (MFI), headloss across the filters and reduction in turbidity and dissolved organic carbon (DOC). The in-line flocculation in fibre filter improved the performance of the pretreatment hybrid system as measured by the MFI, SDI 10, headloss, turbidity and DOC removal. The lowest SDI 10 and MFIwere found with a fibre filter operated at a filtration velocity of 40 m/h followed by dual media filter operated at a filtration velocity of 5 m/h. The lowest headloss and turbidity was found with a fibre filter operated at a filtration velocity of 40 m/hr followed by anthracite operated at a filtration velocity of 5 m/h. This system also gave an effluent with the lowest DOC of 0.64 mg/L corresponding to a removal efficiency of about 70%.

SWRO pre-treatment systems: Choosing between conventional and membrane filtration

Seawater pre-treatment is an integral part of every seawater reverse osmosis (SWRO) desalination plant, used to remove particulates, debris, micro-organisms, suspended solids and silt from the source seawater. But with conventional and membrane filtration as choices, which is right for you? Nicolay Voutchkov compares the options.

Effect of ozone on microfiltration as a pretreatment of seawater reverse osmosis

The main purpose of this study is to evaluate a combined ozone and microfiltration (MF) membrane process as pre-treatment of a seawater reverse osmosis (SWRO) system. During the filtration of seawater (SW) with the MF membranes, membrane fouling on both hydrophilic (PHI) and hydrophobic (PHO) MF membranes (PVDF, 0.22 μm pore size) was investigated by measuring the variation of flux. A significant decline of flux was observed in both PHI and PHO membranes, showing much higher fouling in the PHO membrane than the PHI membrane, with and without pre-filtration. Ozonation of the SW was performed to investigate the effect of ozone on fouling of the MF membrane. Reduction of membrane fouling by ozone occurred in only the PHO membrane. In the case of the PHI membrane, pre-ozonation of the SW led to more severe fouling during filtration than was the case for non-ozonated SW.

Economic evaluation of a new ultrafiltration membrane for pretreatment of seawater reverse osmosis

Numerous tests around the world have proven that ultrafiltration (UF) provides optimum pretreatment for seawater desalination based on reverse osmosis membranes (SWRO). Ultrafiltration will remove all suspended solids and will provide a substantial reduction in micro biological activities. Plugging of RO spacers is completely eliminated and the RO cleaning frequency can be substantially reduced. The main obstacle against the use of ultrafiltration membranes for SWRO pretreatment has always been the higher operating cost of ultrafiltration when being compared with conventional pretreatment. Up until now this higher cost has prevented implementation of UF in all but a few SWRO plants. A new membrane has been designed with the aim of tailoring it towards lowest total cost of ownership. Typical operating conditions have been used to quantify the following parameters for a potential large scale desalination system (UF + SWRO): amortization of investment in UF membranes and equipment; operating costs of the UF system; reduction in operating costs of the SWRO desalination plant, when being compared against a conventional pretreatment + SWRO system; the increased output of the SWRO desalination plant due to higher availability and shorter construction time. The total cost of ownership of a UF based SWRO desalination plant has been determined (expressed in US$/m 3 of water produced). Taking all factors into account the total cost of ownership of a dual membrane desalination plant (Seaguard UF + SWRO) will be 2–7% lower than the total cost of ownership of a SWRO plant based on conventional pretreatment.