RO Pretreatment Research Articles

Process improvement of sea water reverse osmosis (SWRO) and subsequent decarbonization

An enhanced RO desalination system is presented which improves the efficiency of the coagulation system and helps to maintain (or even increase) first-pass recovery ratios, while simultaneously reducing the need for industrial acids, and antiscalants in the second-pass that potentially cause biofouling. The aim is to eliminate the use of expensive industrial acids for acidification of seawater during RO pretreatment processes; instead carbon dioxide (CO2) is injected after capturing it from the exhaust of power plants. The injection of CO2 into seawater essentially reduces the carbon footprint of the RO process. CO2 addition reduces scaling potential of carbonates and allows a higher recovery operation, it will also make acid and antiscalant dosing obsolete. The dissolved CO2 in seawater passes through the RO membranes. Consequently, the CO2 addition also lowers the pH of the RO permeate and brine, the presence of additional CO2 in RO permeate reduces the need of food grade CO2 in the post-treatment process. Low pH brine stream is an ideal condition for further brine concentration processes. Based on the cost of the carbon capture technology, a Life-Cycle Cost Analysis (LCCA) has been performed to access different alternatives for seawater acidification and determine the most cost-effective option.

Ultrafiltration membranes from novel low-fouling copolymers for RO pretreatment applications (Part II)

Ultrafiltration membranes from novel low-fouling copolymers for RO pretreatment applications (Part II)

Surface modification of polyamide RO membrane for improved fouling resistance

This study investigates how surface modification of RO membranes enhances resistance to fouling. The standard mechanisms of membrane fouling are extended to identify RO pretreatment processes. The degree of fouling resistance of modified RO membranes are studied with respect to the modified fouling index (MFI). According to the definition of the MFI, the higher the MFI value of an RO membrane indicate the greater the fouling resistance.A polysiloxane system consisting of 3-glycidoxypropyltrimethoxysilane (GPPTMS) modified on a PA surface displays a complex structure. The fouling resistance of the GPPTMS-modified RO membrane was increased by using a hydrophilic epoxy compound, which forms hydrolyzed functional groups. The flux decline index (m) and the MFI decreased for GPPTMS concentrations less than 1.0wt%. These results prove that fouling of GPPTMS-modified RO membranes would be reduced when the concentration of GPPTMS was over 1.5wt%. The values of m and MFI for RO membrane are much higher than those for GPPTMS-modified RO membranes because more foulants are brought to the membrane surface.

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

For 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 performance was achieved, allowing the fibers to be operated at a substantially higher flux of up to 30%. This study underscores the importance of chemistry in obtaining low-fouling and high-performance UF membranes by modifying their surface properties.

Rosiglitazone ameliorates senescence-like phenotypes in a cellular photoaging model

BackgroundRosiglitazone (RO), a second-generation thiazolidinedione used mainly in the treatment of non-insulin-dependent diabetes mellitus, has been discovered to be a high-affinity ligand for peroxisome proliferator-activated receptor-γ (PPAR-γ). Several studies have revealed that PPAR-γ is also involved in the regulation of oxidative stress and chronic inflammation associated with aging process in vivo as well as with cellular senescence in vitro. We sought to investigate whether RO pretreatment will counteract the photoaging process using a well-established cellular photoaging model. MethodsMurine dermal fibroblasts (MDFs) were cultured in the absence or presence of RO for 48h, followed by exposure to repeated UVB irradiation. The senescent phenotypes were evaluated including cell viability, senescence-associated β-galactosidase (SA-β-gal) expression, cell morphology, ROS generation, cell cycle, production and degradation of extracellular matrix (ECM), and the potential mechanisms were discussed. ResultsPretreatment with RO (40μM) significantly decreased the staining intensity and the percentage of SA-β-gal-positive cells and reserved the elongated cell shape compared with UVB group. The cells pretreated with RO also showed decreased UVB-induced degradation of type I collagen by decreasing MMPs expressions. In addition, we observed counteraction of cell-cycle arrest and repression of UVB-induced p53 and p21 in the presence of RO. We further confirmed a significant decrease in ROS accumulation accompanied by an increase in catalase in RO group. ConclusionsRO, a potent PPAR-γ activator, counteracts senescence-like phenotypes, including long-term growth arrest, flattened morphology, degradation of ECM and SA-β-gal-positive staining in MDFs by inhibiting the expression of MMPs and increasing the synthesis of catalase when administered to repeated UVB irradiation. The novel application of RO may lead to innovative and effective anti-photoaging therapies.

Examination of the Anti-Inflammatory, Antioxidant, and Xenobiotic-Inducing Potential of Broccoli Extract and Various Essential Oils during a Mild DSS-Induced Colitis in Rats

Phytogenic compounds with antioxidant and anti-inflammatory properties are currently discussed as promising complementary agents in prevention and treatment of inflammatory bowel disease (IBD). Our study aimed to evaluate possible protective and curative effects of broccoli extract (BE) and of the essential oils of turmeric (Cuo), thyme (To), and rosemary (Ro) in a rat model with a mild dextran sulphate sodium- (DSS-) induced colitis. Therefore Wistar rats were fed a diet without an additive (Con) or diets with the addition of BE, Cuo, To, and Ro during the whole experiment. Pretreatment with Ro, Cuo, and To increased the expression of the tight junction protein Cldn3. All additives reduced mRNA of VCAM-1 which plays a crucial role in the first state of inflammatory response. Only Ro pretreatment affected the expression of the antioxidant enzymes HO1, GPx2, and of glutathione-S-transferases. All additives counteracted the DSS-induced rise in COX2 and VCAM-1 expression. Colonic IL-10 was increased by Cuo, To, and Ro. During the recovery phase DSS pretreatment increased NFκB, VCAM-1, and MCP-1: This response was counter-regulated by all additives. We conclude that the phytogenic additives tested have a promising anti-inflammatory potential in vivo and a particular role in the prevention of IBD.

SDI: is it a reliable fouling index?

The ASTM considers the silt density index (SDI) test as a standard test for fouling potential of RO and NF feed waters. Up to date, the SDI is used at many full- and pilot-scale installations. The design and choice of the applied RO pretreatment is to a large extent based on the SDI test on the raw feed water. Comparing and monitoring UF/MF membrane performance is another SDI application. From a practical point of view, the SDI of RO feed water preferably should be lower than 3. The SDI has several disadvantages making it an unreliable test. The SDI has a non linear relationship with the colloidal concentration in the water and it is not corrected for the feed water temperature. Besides that, the SDI is not based on any filtration model. SDI is trying to simulate the RO fouling using dead-end MF membrane. The modified fouling index (MFI) is another fouling index. The MFI is based on the cake filtration model, can be corrected for pressure and temperature and is therefore used as a promising alternative for the SDI. Nevertheless, the procedure of measuring a MFI is more difficult and not directly suitable for carrying out “in the field”. The objective of this study therefore is to determine a theoretical relationship between SDI and MFI, and to validate this with experimental results. This relationship can be used to investigate the influence of membrane and testing parameters on SDI under cake filtration conditions, implying this model is valid for cake filtration mechanism and a particle rejection of 100%. In order to calculate the SDI, the times t 1 and t 2 for collecting the first and second sample are predicted using the measured MFI value and the MFI definition. In this research, the influence of several parameters (such as temperature, membrane resistance, etc.) on the SDI will be shown. The experimental results show a good agreement with the theoretical work, but only if the cake filtration start builds up directly at the beginning of the experiment. In general, this work clearly demonstrates that SDI currently is not reliable test for RO fouling. Either corrections for the SDI are necessary to give a more reliable index, or a new index has to be developed.

Seawater pretreatment for reverse osmosis: Chemistry, contaminants, and coagulation

The paper addresses the effects of salinity and temperature on the chemistry of important parameters affecting coagulation pretreatment including the ion product of water, acid-base chemistry, dissolved metal speciation, and precipitation reactions for aluminum and iron coagulants. The ion product of seawater is greater than for freshwaters and affects chemical hydrolysis and metal-hydroxide solubility reactions. Inorganic carbon is the main cause of seawater alkalinity and buffer intensity but borate B ( OH ) 4 1 − also contributes. Buffer intensity is an important parameter in assessing coagulation pH adjustment. Mineral particles are relatively unstable in seawater from electrical double layer compression, and when present these particles are easily coagulated. Algal-particle stability is affected by steric effects and algal motility. Dissolved natural organic matter from algae and humic substances causes fouling of RO membranes and pretreatment removal is essential. Aluminum coagulants are not recommended, and not used, because they are too soluble in seawater. Ferric coagulants are preferred and used. The equilibrium solubility of Fe with amorphous ferric hydroxide in seawater is low over a wide range of pH and temperature conditions. Ferric chloride dosing guidelines are presented for various raw seawater quality characteristics. The effect of pH on coagulant dose and the role of buffer intensity are addressed. A dual coagulation strategy is recommended for treating seawater with moderate to high concentrations of algae or seawater with humic matter. This involves a low and constant dose with high charge-density cationic polymers using Fe as the main coagulant where it is varied in response to raw water quality changes.

Identifying, Evaluating, and Implementing Antiscalants in RO Reuse Applications

AbstractThe Orange County Water District (OCWD) operates a 70-mgd RO system as part of the Groundwater Replenishment System (GWRS), an advanced wastewater purification facility. Each of 15 5-mgd RO units consists of a three-stage array, operating at 85 percent recovery. As part of the operating strategy, antiscalant and pH suppression are used to limit third-stage precipitation of sparingly soluble mineral salts. Identifying successful antiscalants is extremely challenging. A variety of antiscalants with varying chemistries and capabilities present opportunities for optimizing RO processes, pricing, dosage, and pH adjustment. Recognizing the potential savings in RO pretreatment chemical cost, OCWD began antiscalant pilot-scale trials in 2009. However, failure to identify an effective product led to the trial's cancellation. Concurrently, the GWRS RO facility began experiencing third-stage permeability loss in all 15 RO units because the antiscalant was ineffective. This article discusses fast-track testin...

Design aspects of small-scale photovoltaic brackish water reverse osmosis (PV-BWRO) system

Clean drinking water is essential for survival and good health. Reverse osmosis is a very effective way to produce clean drinking water. Designing small scale photovoltaic powered brackish water reverse osmosis system (PV-BWRO) requires feed water characterization, proper pre-treatment setup, module design configuration, energy consumption evaluation and reject water management. Feed water characterization is done for optimum RO module arrangements and pre-treatment design to prevent fouling and scaling. Success of small scale PV-BWRO system designation depends on ability to minimize cost of water produced. Among all the parameters effecting cost, energy is the most influential. Energy consumption is reduced by including energy recovery device (ERD) in the system. It can be further reduced by including battery for stable supply of energy enabling the pumps to operate at optimum level. Problem with battery is energy loss during charging/discharging and high cost of maintenance and replacing. Instead of storing energy, another option is to store produced fresh water in storage tank. The capacity of the tank is determined based on average consumption of water by the population at the location of the system build. Reject water from RO system need to be managed properly. Improper disposal will cause contamination and disturb ecosystem. Powering RO systems with PV panels have a lot of advantages which includes maintenance free, easy installation and last up to 25 y.

The Study of PAFSSB on RO Pre-Treatment in Pulp and Paper Wastewater

Reverse osmosis approach was used to dispose pulp and paper wastewater from a papermaking company. To meet the requirements of reverse osmosis membranes for water quality, a proper pretreatment had been done before raw water into RO membranes. A new efficient composite flocculant named PAFSSB had been used in the pre-treatment of pulp and paper wastewater. In the paper, the results showed that the treatment effect of PAFSSB was better, COD content was down to 10mg/L and COD removal rate was up to 75%. The pre-treatment process was simplified and processing costs were reduced.

Reverse osmosis pretreatment alternatives: Demonstration plant in the seawater desalination plant in Carboneras, Spain

This paper presents the results of a demonstration study for the RO pretreatment that was performed on an AcuaMed open intake desalination plant in Carboneras (Almería, Spain). The main goal was to test different configurations of conventional pretreatments in order to establish the limit of each process as well as their reliability. The pretreatment processes tested were Actiflo® (a process that consists of coagulation, polymer and microsand injection, maturation and settling of microsand ballasted flocs), multimedia filtration at atmospheric pressure, pressurized dual-media filtration and pressurized three-layer filtration. During the tests, the silt density index (SDI) of the filtered water was regularly measured and then evaluated in probability graphs. The raw seawater SDI ranged from 4.5 to 25. The results from this study showed that the Actiflo® system followed by two pressurized multimedia filters (dual-media and three-layer filters) in series, provided effluent SDI values lower than 3 with a reliability of 95% under the optimized operating conditions. These results were obtained when the Actiflo® system included coagulation, flocculation (with flocculant and microsand addition) and maturation stages or just working as a coagulation stage.

REUSE OF REFINERY TREATED WASTEWATER IN COOLING TOWERS

In this report, experimental investigation of waste water treatment by reverse osmosis to enable its reuse in cooling tower is presented. A polyamide spiral wound RO membrane followed by three filters as RO pretreatment (two activated carbon and one cartridge filter) and samples of Tehran refinery treated waste water have been used. The effect of operating conditions such as pressure difference, temperature and feed concentration on permeation flux, permeate concentration and fouling have been studied. The results show that continuous operation with a pressure difference of 6 bar and a temperature of 30 °C are the best operating conditions. Analysis of the water treated by RO represents 95 %, 100 %, 93 % and 97 % reduction in TDS, TH, Cl - and SiO2, respectively. Comparison between the treated wastewater analysis and city water used in cooling tower as make up water shows the suitability of reverse osmosis method for the above mentioned purpose.

UF/MF as RO pre-treatment: the real benefit

Ultrafiltration (UF) and microfiltration (MF) are theoretically the best pre-treatment upstream reverse osmosis, removing from the feed water most of the potential elements responsible of desalinating membranes fouling such as particles, turbidity, bacteria and large molecular weight organic maters. Those clarification membranes reduce also significantly the silt density index below 3 (100%) [1–6] and generally below 2. Many papers present results about the efficiency of UF/MF regarding clarification efficiency. UF/MF can be an economical option for RO pre-treatment. Several evaluations of the cost of UF/MF upstream RO demonstrate the interest of this pre-treatment technology on average to bad water qualities, compared to a double filtration steps conventional pre-treatment. In that case, and on a long-term operation basis, the treatment line is economically viable [7]. However, UF/MF remains more costly than a single filtration on mono or multimedia filter: UF/MF is not economically applicable on the best water quality to pre-treat. Nevertheless, UF/MF technology has some limits. If this technology is economically viable on average to bad water qualities, UF/MF direct filtration can overpass the technical limits of the process, generating the need of frequent cleanings. In that case, the RO fouling is moved upstream to the pre-treatment stage. Moreover, the clarification membranes, with cut off generally higher than 100,000 kd, do not remove the smaller organic matter molecules responsible of the biofouling development on RO membranes. In this situation, it is very difficult to demonstrate the real technical advantage of UF/MF on the RO operation, since this demonstration needs a long-term study (more than one year depending on the application) with side-by-side technologies to compare, and the results appear to be site specific. Solution of this double problem, UF/MF fouling on average to bad surface seawater and biodegradable organic matters removal, can be found in the treatment line, enhancing the UF/MF treatment by adding a pre-coagulation/settling of flotation. The benefits of this association of technologies are multiples, as it was developed for the treatment on surface water one decade ago for drinking water production. Moreover, the benefit of the coagulation/separation on the design (filtration flux) and operation (frequency of cleaning, membrane life duration) can significantly improve the economical balance of the process. It also allows a definitive advantage concerning RO membrane fouling and its related impact on cleaning frequency, RO membrane replacement and plant availability.

Introduction to membranes: Water and wastewater – RO pre-treatment

In the sixth of a series of articles looking at membrane filtration technology in water and wastewater treatment, Graeme Pearce examines the case for using membrane filtration as pre-treatment to reverse osmosis.

Comparative seawater RO pretreatment evaluation using bench‐ and pilot‐scale testing

Desalination using seawater reverse osmosis (SWRO) technology is an important option available to water‐scarce coastal regions. Recent full‐scale experiences have shown that pretreatment is the key for this application of RO technology. In this article, a unique series of bench‐ and pilot‐scale tests are presented. These tests were conducted to determine the effect of pretreatment on SWRO performance. Seawater in the San Diego, Calif., region was first characterized to elucidate the difference between open‐ocean and enclosed‐bay water quality with respect to selection of an appropriate site for an SWRO plant. Two pretreatment schemes for SWRO—conventional pretreatment (coagulation/media filtration) and membrane filtration—were then evaluated using water obtained from two locations within the San Diego Bay, and the effluent water quality from these pretreatments was characterized. RO systems were then operated on these pretreated waters to evaluate the effect of pretreatment type on RO fouling and to correlate the pretreated water quality with the extent of RO fouling. The results show that for both source water types the seawater treated by microfiltration caused lower RO flux decline when compared with conventionally treated seawater. It was also found that the pretreated water silt density index was generally a good indicator of RO fouling for the experiments conducted.

Membrane Bioreactors for RO Pretreatment

Membrane Bioreactors for RO Pretreatment

Study of seawater alkalization as a promising RO pretreatment method

Inorganic fouling is a major challenge in seawater RO desalination due to its relatively high SO 4/HCO 3 molar ratios. In most of the recorded cases, if not all, calcium sulfate scale is dominating (>90% wt/ wt) other scale types such as CaCO 3, MgSO 4, MgCO 3, MgSiO 3, SiO 2 and CaPO 4. However, the standard pretreatment practice in RO plants depends on the acidification of seawater in order to remove the minor carbonate and bicarbonate. Meanwhile, solubility of the major sulfate species decreases considerably because of acidification. The present study investigated the application of NaOH alkalization on the Red Sea surface water instead. It was found that the method has many technical and economical advantages, such as removal of hard chemical species (i.e. hard carbonate, bicarbonate, sulfate, silicate, phosphate and iron), removal of suspended solids and colloids, bacterial disinfection, cleaning and wetting of a membrane surface, increasing permeate recovery, lower sludge volume of environmentally chemical nature, and the possibility of instant preparation of NaOH in-line by seawater electrolysis. The alkalization method is fast, clean and economic. The proposed model as well as chemical equations are presented in detail.

Water quality assessment for indirect potable reuse: a new methodology for controlling trace organic compounds at the West Basin Water Recycling Plant (California, USA)

The West Basin Water Recycling plant (California; USA) was built to increase the region's water resource availability. The plant influent is produced at Los Angeles Hyperion wastewater treatment plant and is treated through two parallel treatment processes depending on the end use: (1) Title 22 water for industrial and urban use, and (2) barrier treatment for groundwater recharge. A new methodology was applied to monitor the fate of base neutral compounds in the water barrier treatment train. The methodology included large sample volumes coupled with integrated chromatographic analysis (ICA). Data indicated a 25% increase in concentration of base neutral compounds after RO pretreatment, followed by a 70% removal efficiency after RO. The increase in concentration after RO pretreatment appears to be linked to the use of lime clarification.

Assessment of UF pretreatment prior RO membranes for seawater desalination

Among the desalination technologies available, reverse osmosis is currently considered as the most economical process. However, while RO membranes have been continuously improved over the years, they have had one major shortcoming; the susceptibility to fouling. Indeed, it appears that RO technology is limited in hydraulic performance by the raw water quality. In the case of direct seawater intake, extensive treatment is required upstream the RO process. Thus, the objective of this study was to evaluate the ultrafiltration membrane process as a RO pretreatment. The trials were conducted at Fuerteventura, Canary Island. The preliminary results showed that the Aquasource® UF membrane does not seem sensitive to high salinity of the seawater. Indeed, the mechanical resistance, as well as the specific flux of the UF membrane, remained stable. The dead-end filtration mode coupled with operation at low pressure allowed for very low power consumption, approximately 0.1 kWh per m3 of permeate. Concerning the RO membrane evaluations, the hollow fine fiber (HFF) membrane was more efficient in terms of salt rejection, but the thin film composite spiral wound (SW) membrane operated at lower pressure (i.e. lower energy consumption). To date, the study continues in order to develop an integrated membrane system (UF/RO) to treat surface seawater.