RO Membrane System Research Articles

Application of different treatment systems for boron removal from industrial wastewater with extremely high boron content

The aim of the study is purification and environmental management of boron containing industrial wastewater wastewaters comparing the efficiency of chemical precipitation and membrane filtration systems on the removal of boron at high concentrations from wastewater coming from boric acid production process and ground water. In order to eliminate adverse effects and find optimum treatment system, chemical precipitation, electrocoagulation and reverse osmosis processes have been studied. Different chemical precipitants such as poly aluminum chloride (PACl), lime, calcium chloride (CaCl2) and barium chloride (BaCl2) and hydrogen peroxide as oxidant were used. When solution pH was adjusted at 10, boron removal increased to 99.5 %. With application of electrocoagulation, 9 % of SO42-, 80 % of Si and 45 % of B were removed from spring water. At membrane-system, single and double pass BWRO/SWRO membrane system operations were carried out in order. Boron-removal increased 98 % by increasing pH up to 10, and DP-SWRO membranes system at 10-pH was found to be the best system. Obtaining a sufficient result for boron removal from spring water, a hybrid membrane process which contains an electrocoagulation process as a pre-treatment method and a double pass RO membrane system has been developed as an attractive technology.

Municipal-to-Industrial Water Reuse via Multi-Stage and Multi-Pass Reverse Osmosis Systems: A Step from Water Scarcity towards Sustainable Development

Wastewater reclamation is a promising solution to growing pressure on limited water resources. In this study we evaluated the efficiency of boron removal from effluent at a water resource recovery facility (WRRF) using a two-stage/two-pass RO membrane system. We propose using measurements of electrical conductivity (EC) as a proxy for boron concentration. We tested our approach to boron estimation and the proposed split partial second pass (SPSP) system at an established WRRF and a pilot plant we constructed at the same location. Results showed that boron in the effluent was directly related to the concentration of EC. The proposed regression equation (y = 4.959 × 10-5x + 0.138) represents a rule of thumb for wastewater plant operators. The proposed SPSP system was optimized through manipulation of operating conditions, achieving a promising total water recovery of 64% at maximum boron rejection (over 85% removal) in a manner that was both cost-effective and flexible. This study demonstrates that two-stage/two-pass split-partial permeate treatment with a high pH for boron removal offers a sustainable freshwater supply option suitable for use by the semiconductor industry.

Evaluation of the benefit of practically operating reverse osmosis system in the factory: taking the recycling of KI solution and water of the screen polarizing plate as an example

Abstract In recent years, with the advocacy of the circular economy and the rising awareness of environmental protection, energy saving, water saving and carbon reduction have become important topics for discussion today. The high-tech semiconductor, photoelectric, solar and other electronic industries involve high energy and water consumption. In addition to responding to the energy saving, water saving and carbon reduction, one of the main purposes of this system development is to reduce the use of materials and make the process chemicals reusable. In the practical factory operation, a large amount of water is used in the polarization process, and the wastewater generated in etching and pickling is discharged continuously. In order to recycle the water discharging from the manufacturing process, the reverse osmosis membrane system (RO membrane system) is often used for wastewater recycling. In this study, the KI waste liquid discharging from the process of a polarizing plate factory was concentrated with anti-fouling RO membrane. The quantity and arrangement of RO system membranes were simulated and designed with software, and the results, such as water volumes and pressures of inflow and outflow water for the membrane, changes of membrane pressure difference (ΔP), changes of permeating water quality, chemical cleaning frequency and water collection time, were discussed and the optimal parameters of RO membrane, such as the best water collection volume and time, chemical cleaning frequency, best concentration, time and temperature matching with cleaning in process (CIP) were inferred so as to improve the stability of the RO membrane system, enable RO permeating water to enter the water purifying system for reuse, reduce the treatment cost of wastewater recycle and improve the permeating water output efficiency of treatment equipment, accommodating effective utilization of water resources and economic benefits and to sustainable development of the industry.

Reducing the Impacts of Biofouling in RO Membrane Systems through In Situ Low Fluence Irradiation Employing UVC-LEDs.

Biofouling is a major concern for numerous reverse osmosis membrane systems. UV pretreatment of the feed stream showed promising results but is still not an established technology as it does not maintain a residual effect. By conducting accelerated biofouling experiments in this study, it was investigated whether low fluence UV in situ treatment of the feed using UVC light-emitting diodes (UVC-LEDs) has a lasting effect on the biofilm. The application of UVC-LEDs for biofouling control is a novel hybrid technology that has not been investigated, yet. It could be shown that a low fluence of 2 mJ∙cm−2 delays biofilm formation by more than 15% in lab-scale experiments. In addition, biofilms at the same feed channel pressure drop exhibited a more than 40% reduced hydraulic resistance. The delay is probably linked to the inactivation of cells in the feed stream, modified adsorption properties or an induced cell cycle arrest. The altered hydraulic resistance might be caused by a change in the microbial community, as well as reduced adenosine triphosphate levels per cells, possibly impacting quorum sensing and extracellular polymeric substances production. Due to the observed biofilm attributes, low fluence UV-LED in situ treatment of the feed stream seems to be a promising technology for biofouling control.

A review on sources, types, mechanisms, characteristics, impacts and control strategies of fouling in RO membrane systems

A review on sources, types, mechanisms, characteristics, impacts and control strategies of fouling in RO membrane systems

Diffusiophoresis contributes significantly to colloidal fouling in low salinity reverse osmosis systems

Diffusiophoresis is the migration of particles in salt gradients, and depends on the particle charge and the difference in diffusion coefficients of major ions making up the salt. This phenomenon is ubiquitous where salt gradients and charged particles exist and has been studied for several decades. However, this phenomenon has not been explored in RO membrane systems and could be relevant for low salinity feed solutions (such as brackish water or reclaimed wastewater), where significant salt gradients arise next to the membrane and where charged colloidal particles exist natively. Here we demonstrate through experiments and modeling that under low salinity feed conditions, diffusiophoresis contributes significantly to particle transport and cake formation. We further propose that particulate fouling due to diffusiophoresis will increase in a positive feedback loop over time due to cake enhanced concentration polarization.

Pressure retarded osmosis for power generation and seawater desalination: Performance analysis

The present study evaluated the performance of pressure retarded osmosis–reverse osmosis (PRO–RO) process for power generation and seawater desalination. Two pre-developed software were used separately to estimate the performance of forward osmosis (FO) and RO process. The draw and feed solutions in the FO process were seawater and low-quality water; i.e. wastewater effluent and brackish water. The simulation results showed that the FO performance increased with increasing seawater salinity and decreased with increasing feed water TDS. Increasing the feed and draw solution flow rate resulted in an increase in the FO performance especially when brackish water was used as a feed solution in the FO process. Power generation from the PRO process was found to increase with increasing the TDS of seawater and the flow rate of feed and draw solutions. The simulation results, however, showed that the PRO process was more sensitive to the increase in the seawater TDS than the flow rate of feed and draw solutions. For fresh water supply, the diluted seawater from the FO process was treated by RO membrane system. Up to 31% decrease in the desalination power consumption can be achieved by the PRO–RO process. It was also found that the increase in the draw solution flow rate resulted in an increase of the permeate concentration and power consumption. This issue should be considered in the operation of the PRO–RO system in order to reduce the overall treatment cost.

Critical flux analyses on differently pretreated olive vegetation waste water streams: Some case studies

One of the main disadvantages of batch membrane processes is the increase of the pollutant concentration in the feedstock throughout the operation. Operating the plant at constant process conditions leads in many cases to weaker performances and, moreover, to heavy fouling on the membranes. Critical flux-based methods are one of the most used approaches to overcome fouling problems. Within critical flux conditions, only reversible fouling can occur, which can be periodically soft-cleaned. This work studies the relationship between particle size distributions in the feed stream and critical flux values when different pretreatment processes are applied to an olive vegetation waste water stream. The considered pretreatment processes were: coagulation (with aluminum hydroxide and aluminum sulphate), aerobic biodigestion (by means of fungi) and photocatalytic organic matter reduction (by means of nanometric titanium dioxide anatase powders irradiated by UV light). The study was carried out at pilot plant scale (100 L batch capacity). These results were compared with performances and effects on the critical flux value for MF, UF and NF membranes. The different pretreatment on the same waste water stream shifts differently the particle size distribution mainly by organic matter degradation, and this influences heavily the critical flux value and thus the filtration outcome. Finally, the purification of the olive vegetation waste water stream can be performed with a MF, UF, NF and RO membrane system in series, being very careful in choosing the correct operating conditions to avoid the quick formation of an unsustainable fouling.

Online estimation of fouling development for SWRO system using real data

Fouling is one of the most serious problems in seawater desalination using reverse osmosis (SWRO) which is important to lower the production cost of desalinated water. For efficient operation of the SWRO plant, accurate models are crucial to decide the optimal operating condition and cleaning operation. The model for RO membrane system has been studied by many researchers and its usefulness has been increased as its accuracy has been improved. However, the prediction of fouling is difficult due to its extremely complicated mechanism of growth involving various foulants. In this study, the development of the fouling is predicted by monitoring the membrane resistance across the membrane and the friction coefficient through spiral-wound membrane from the operation data. Using nonlinear recursive least-squares (NRLS) method, the two properties are identified from the operating data based on the one-dimensional model of the SWRO system. By this method, the degree of fouling can be inferred from the two properties and potential cleaning time can be predicted. It can also assess the effectiveness of membrane cleaning. Using the actual data of an existing plant, the trends of resistance and friction coefficient could be monitored and the effect of cleaning pattern of the real plant can be evaluated by recursive parameter estimation online.

Ozonation of reverse osmosis concentrate: Kinetics and efficiency of beta blocker oxidation

Reverse osmosis (RO) concentrate samples were obtained from a RO-membrane system that uses effluents of wastewater treatment plants (WWTP) as feed water for the production of drinking water. A number of different pharmaceuticals (e.g. antibiotics, contrast media, beta blockers) were found in the WWTP effluent as well as in the RO-concentrate. Overall, a concentration factor (feed:concentrate) of approximately 3–4 was measured. Beta blockers (acebutolol, atenolol, bisoprolol, celiprolol, metoprolol, propranolol, timolol) were found in the range of low ng/L to low μg/L. Because metoprolol and propranolol are classified as potentially toxic to aquatic organisms and all beta blocker molecules have moieties, which are reactive towards ozone (amine groups, activated aromatic rings), it was tested whether ozonation can be applied for their mitigation. Rate constants for the reaction of acebutolol, atenolol, metoprolol and propranolol with ozone and OH radicals were determined. At pH 7 acebutolol, atenolol and metoprolol react with ozone with an apparent second-order rate constant ( k O 3 ) of about 2000 M −1 s −1, whereas propranolol reacts with ∼10 5 M −1 s −1. The rate constants for the reaction of the selected compounds with OH radicals were determined to be 0.5–1.0×10 10 M −1 s −1. Experiments with RO concentrate showed that an ozone dose of only 5 mg/L resulted in a quantitative removal of propranolol in 0.8 s and 10 mg O 3/L oxidized 70% of metoprolol in only 1.2 s. Tests with chlorinated and non-chlorinated WWTP effluent showed an increase of ozone stability but a decrease of hydroxyl radical exposure in the samples after chlorination. This may shift the oxidation processes towards direct ozone reactions and favor the degradation of compounds with high k O 3 .

Integrating Membrane Contactors Technology and Pressure-Driven Membrane Operations for Seawater Desalination: Energy, Exergy and Costs Analysis

Membrane science and technology has nowadays become the dominant technology in water desalination. In this context, Reverse Osmosis, in combination with other pressure-driven membrane operations (i.e., microfiltration, ultrafiltration and nanofiltration), represents the most diffuse practice. Despite this success, specific actions are requested in order to solve problems related to water recovery factors, brine disposal, cost and quality of the water. In this paper, a MF–NF–RO membrane system is integrated with membrane distillation/crystallization units. The use of these membrane contactors devices, operated on the NF and/or RO retentate, permits to increase the water recovery factor up to 92.8% without a significant increase of the costs if waste thermal energy is already available to the process. In addition, the sale of salt crystals grown in high concentrated brines might potentially reduce the overall desalination cost, thus confirming the potential interest for the proposed approach. Energy and exergy analysis permitted to individuate the points of higher entropic losses and low thermodynamic efficiency for the systems, and possible solutions based on the use of energy recovery devices have been discussed in detail.

Inhibition of CaCO 3 scaling on RO membranes by trace amounts of zinc ions

Anti-scalants, which are widely used for scale control in desalination processes, are essentially impurities capable of inhibiting scale precipitation and weakening scale adhesion on a flow surface. Many basic studies indicate that metallic ion impurities, notably Zn ions, can hinder significantly CaCO 3 precipitation from hard waters and alter crystal morphology. Recent studies demonstrate a substantial potential for suppressing CaCO 3 scale formation in hard water heating systems by trace concentrations of Zn ions. The objective of the present work was to explore the possibility of controlling CaCO 3 scale formation in RO membrane systems by a similar technique. Results obtained with a tubular RO system are most promising. A Zn ++ concentration of the order of 2 PPM was able to exert a marked suppression effect on both bulk precipitation of CaCO 3 and on membrane scaling on waters of moderate hardness.

Raisin grower cuts wastewater costs with RO membrane system

The installation of a membrane filtration plant from ITT Sanitaire's PCI Membrane Systems division, helped the National Raisin Co, based in California, USA, to successfuly combat its rising wastewater disposal costs, as well as create an additional revenue source for the company.

Biofuoling in RO membrane systems Part 1: Fundamentals and control

Membrane separation systems are widely used to purify water of different qualities including brackish water, seawater and wastewater. Dissolved and particulate matter in the feed water can deposit on the membrane surface. This phenomenon is identified as fouling. Several types of fouling can occur in the membrane systems, e.g. inorganic fouling or scaling, particulate and colloidal fouling, organic fouling and finally biological fouling or biofouling. Biofouling is usually ascribed to the accumulation of microorganisms such as bacteria, algae and fungi on the membrane surfaces forming the harmful biofilms, via multi-step and complex formation process. In fact; biofouling has a lot of adverse effects on the RO membrane systems like flux decline of the RO plant, significant increase in the pressure drop of the RO modules, increase in salt passage and membranes biodegradation and failure. No doubt that biofouling is one of the most serious problems associated with the RO membrane systems which has not yet been effectively solved. Moreover, this biofouling phenomenon is most critical in RO systems operating with feed water above 25°C which is typical of RO plants in the Gulf countries like Saudi Arabia. In the present work, more attention is given to the fundamental and engineering aspects of this biofouling phenomena covering the basic various mechanisms of its multisteps formation processes and its negative effects on the plant performances. The interaction between feed water quality and membrane biofouling is also discussed and analyzed. Corrosion problems induced by biofouling are also tackled in the present work due to their harmful effects in the actual practice of RO plants. Finally, various techniques for befouling minimization and control are recommended with special attention to the proper pretreatment systems by which feed water properties are precisely adjusted before entering to the membrane modules.

RO and NF membrane systems for drinking water production and their maintenance techniques

Elaboration of drinking water supply strategies is closely connected with expansion of private housing, as well as country farms and industries that require water treatment facilities. As a rule, the majority of ground well waters does not meet modern drinking standards due to high content of iron, hardness, strontium, nitrates, fluoride and TDS. Thus, a special respect should be given to small portable and economically reasonable point-of-entry water treatment systems that produce quality water meeting WHO standards. Membrane treatment techniques are based on simultaneous rejection of all types of ionic and molecular water species by semipermeable (RO) polymeric membranes which is more advantageous compared to conventional treatment techniques. The continuous theoretical and experimental research conducted in VODGEO research institute from 1992 to 1999 resulted in development of drinking water production techniques from different natural waters, using Russian-made and foreign polymeric membranes. Computer calculation techniques are developed that enable us to determine optimum characteristics of membrane water treatment systems, such as pressure, recovery, membrane type etc. corresponding to optimum quality water composition (required hardness, fluoride, chloride and TDS content). As a result, water purification techniques were developed providing facilities with operational guidelines to reduce greatly membrane fouling and simplify pretreatment. This demonstrates considerable cost savings and membrane efficiency compared to conventional iron removal and ion exchange softening techniques.

Flux enhancement of RO desalination processes

The simple model proposed by Kennedy et al. was modified so as to improve its ability to predict the periodic performance operation of RO systems. The modified model was validated using data from the literature as well as data obtained from experiments in this work. The predicted permeate rates compared well with the experimental values for the considered forcing functions: sine and asymmetric square waves. Periodic and steady-state experimental runs were performed on a spiral-wound RO membrane system at three average pressures: 20, 25 and 30 bars. For the case of periodic operation, the operating pressure was varied according to an asymmetric square wave having a period of 5 min. The duration of each run was 30 min. The effect of the time split, γ, of the forcing wave on the permeation rate as well the salt rejection was investigated. The results showed that periodic operation leads to improvements in the permeation rate. For the tested pressures, the overall maximum water production rates occurred at a time split approximately equal to 0.65. It was also found that cyclic operation may lead to small reductions in the salt passage.

Development of boron reduction system for sea water desalination

Since boron has been showing to induce male reproductive impediments in laboratory animals, the 1993 WHO guidelines for drinking water quality set the recommended guideline value at 0.3 mg boron/l based on the NOEL (no-observed-adverse-effect level). Since boron is not effectively removed by the conventional water treatment not only for drinking water and domestic wastewater treatment, the concentration in ambient water as well as drinking water is affected by its consumption such as for soaps and detergents in the catchment area. Boron is also affected by leaching from the surrounding geology, drinking water derived water sources affected by a weak alkali spring contains high level of boron. Since the rejection ratio of boron is extremely less than that of salts in RO membrane system applying to drinking water supply in the areas where scarce a fresh water resources, desalinated water contains higher level of boron than that of WHO drinking water quality guidelines. In order to develop of boron treatment system either fresh water or desalinated water, multi stage RO membrane treatment system has studied by using a pilot plant. The boron rejection of RO membrane depends greatly upon pH and driving pressure of RO process. However, the boron rejection does not depends upon its concentration of raw water. Therefore, it is necessary to apply multi stage RO membrane treatment system for producing a finished water that meets the WHO drinking water quality guideline level of boron. Since the secondary and third RO membrane treat less dissolved salt concentration such as observed in fresh water, the driving pressure of RO process for removing boron can operate at low pressure such as about 0.6 to 1.3 MPa. Therefore, multi stage RO membrane sea desalination process and a low pressure RO process can be recommendable for boron management with a reasonable additional cost in drinking water supply.

Prediction of RO membrane performance for Arabian Gulf seawater

Arabian Gulf seawater is characterized by its high average seasonal temperatures, silt density index (SDI), and total dissolved solids (TDS), in addition to other parameters such as level of pollution and type and magnitude of marine microorganisms. The overall effect of these on RO membrane performance is very significant and complex as well. Hence, the primary objective of this paper is to present a mathematical model for the prediction of RO membrane performance for Arabian Gulf seawater under the prevailing local conditions. A complete system of equations that can be used for the prediction of product water flow rate and separation of ions present in seawater for a given RO membrane was obtained on the basis of the Kimura-Sourirajan analysis. Solution of this system for the purpose of performance prediction requires prior knowledge of certain parameters that are specific to the RO membrane under consideration and pertinent to the ions present in the seawater. A computer program has been developed to evaluate such parameters, solve the obtained system of equations, and process the performance predictions utilizing experimental data available from the operation of two RO membrane systems, spiral wound and hollow fiber, at the Doha Desalination Research Plant (DRP). Comparisons between predicted and experimental data at standard conditions have shown reasonable agreement for product flow rates and very good agreement for the rejection of total salts and ions present in the seawater.