High Recovery Reverse Osmosis Research Articles

High recovery reverse osmosis design to minimize wastewater of ultra-pure water production process

High recovery reverse osmosis design to minimize wastewater of ultra-pure water production process

A new pretreatment approach for applying high-recovery reverse osmosis desalination to highly scaling brackish groundwater

A new approach is presented for pretreating very hard, divalent-ion-laden brackish-water, to allow applying reverse-osmosis desalination at reasonable recovery-ratio and competitive cost. The approach consists of a cation-exchange step applied on the raw-water to reduce the divalent-cation concentrations thereby enabling operation at high recovery (>80 %) without chemical scaling. For cost-effectiveness, the exhausted ion-exchange regeneration solution undergoes nanofiltration separations to recover the NaCl, enabling multi-cycle usage. The process was exemplified on brackish groundwater from New-Mexico's National-Desalination-Research-Facility. Two treatment alternatives were considered for the exhausted regeneration brine, consisting of several NF in series (alternative 1) and additional NF-retentate treatment (alternative 2). Following simulation and selection of alternative 1, empirical-evaluation and cost-assessment ensued. The results showed that when the regeneration-solution contained total-hardness < 2 % of the total-cation concentration (eq/eq), the cation-exchange breakthrough curves did not deteriorate. To maintain this criterion the exhausted regeneration-solution should undergo 3–4 sequential NF passes after each regeneration cycle. This approach enables operating the BWRO plant with RR = 81 % at additional cost of ∼US$0.4/m3 (CAPEX+OPEX), which ∼doubles the overall brackish desalination cost, but also produces more desalted water and much less retentate. The approach is competitive when the brackish water is laden with divalent ions and the retentate discharge-cost is high.

Solar energy powered high-recovery reverse osmosis for synchronous seawater desalination and energy storage

Solar energy is clean and sustainable to power our continuously developing society, but the intermittency and unpredictability lays a barrier on its direct connection to the grid. Seawater desalination is an effective path to consume dynamic solar energy to produce fresh water and stable salinity gradient energy simultaneously. Thus, a self-diluted 2-stage reverse osmosis with high recovery ratio is proposed to consume the renewable power from a dish solar Stirling engine to achieve more water production and energy storage. Based on theoretical derivation, system performance is evaluated under ideal membrane property and enough membrane area condition. The influence of hydraulic pressure difference and diluted fraction ratio on water production and energy storage performance are investigated. A performance optimization is further conducted and the corresponding performance are evaluated. Results revealed that self-diluted 2-stage configuration can improve the maximal recovery ratio from 25%, 57% and 70% to 39%, 62% and 72% under the maximal bearable pressure difference of 4, 7 and 10 MPa. Maximal salinity gradient energy of 3.84 MJ can be stored with an overall energy efficiency of 8.42% while desalinating 1 cubic meter seawater of 0.6 M. Theoretical analysis indicates that novel configuration is potentially an effective method to improve the upper separation limitation, which further produces more water and stores more solar energy in the desalination process of finite amount of source seawater.

An analysis of the effects of pressure-assisted osmotic backwashing on the high recovery reverse osmosis system

AbstractThe low cost simplified method for implementation of pressure-assisted osmotic (PAO) backwash (BW) for spiral wound reverse osmosis (RO) membrane module is presented in this work. The effect of membrane design and an operating parameter concerning the efficiency of PAO membrane BW is analyzed. The following design and operating parameters are considered in this study: (i) spacer thickness, (ii) dimension of the permeate channel, (iii) number of leaves, and (iv) BW water pressure. The performance of PAO BW with respect to membrane cleaning efficiency is analyzed for three different high recovery RO systems by purifying 1,500 liters of water. The membrane cleaning efficiency is measured by examining the rate of permeate quality and quantity decline using ASTM D4516 method. Finally, to quantify the membrane fouling with respect to different high recovery configurations, the thickness, and composition of foulants present in the used membrane's surface are measured by using field emission scanning electron microscope with energy dispersive X-ray (FESEM-EDX). The result concludes that the RO membrane operated at high recovery with PAO BW is found to have less fouling deposits than membrane without PAO BW.

Electrocoagulation for the purification of highly concentrated brine produced from reverse osmosis desalination of coal seam gas associated water

The ability of electrocoagulation (EC) at facilitating salt recovery from brine resultant from reverse osmosis (RO) desalination of coal seam gas (CSG) associated water is described. The aim was to reduce the presence of high concentrations of dissolved silicate which inhibit salt recrystallization by forming precipitates on equipment. The hypothesis was that EC could operate effectively in brine solutions and provide high silicate removal; thus facilitating a zero liquid discharge strategy. A benchtop EC unit equipped with either aluminium, iron or mixed iron-aluminium electrodes was used to treat simulated brine from a high recovery RO process. Up to 98.9% of silica was removed when aluminium or aluminium-iron electrodes were used. Significant reduction in concentrations of alkaline earth ions were also recorded (Ba > Sr > Ca > Mg) especially with iron electrodes. It appeared that silicate removal was via aluminosilicate formation. Hydraulic retention time was a key variable with 20 s recommended on the basis of performance/cost trade-off. Polarity reversal did not substantially change removal performance but impacted power consumption. For iron and iron-aluminium electrodes 1 min polarity reversal was preferred whereas for aluminium electrode 5 min was optimal. However, a thick coating was formed on the electrode surface and this may inhibit performance if longer tests are conducted. All flocs formed settled relatively rapidly (<20 min) which was in a time frame suitable for industrial application.

Mitigation of saltwater intrusion by ‘integrated fresh-keeper’ wells combined with high recovery reverse osmosis

Most countermeasures to mitigate saltwater intrusion in coastal, karstic or fractured aquifers are hindered by anisotropy, high transmissivities and complex dynamics. A coupled strategy is introduced here as a localized remedy to protect shallow freshwater reserves while utilizing the deeper intercepted brackish water. It is a double sourcing application where fresh-keeper wells are installed at the bottom of a deepened borehole of selected salinized wells, and then supported by high recovery RO desalination. The RO design has <1kWh/m3 energy consumption, and up to 96% recovery in addition to low scaling propensity without use of any anti-scalant. A feasibility study is presented as an example for a salinizing, brackish well (TDS ~1600mg/L) in the Damour coastal aquifer in Lebanon. The concept is expected to produce ca. 1000m3/d of freshwater from this well by pumping 250m3/d of fresh groundwater from the top well screen and 800m3/d of brackish groundwater (to be later desalinized) from the fresh-keeper well screen below. Cost analysis shows that the capital cost could be returned back in 1 to 4years depending on the choice of produced water (bottled or tap) and available market. As an alternative, water from the RO plant could be blended with lower quality water, for instance untreated brackish groundwater (if unpolluted), to supply 3 more volumes for domestic use. The usage of brackish groundwater from integrated fresh-keeper wells thus serves 3 purposes: production of high quality drinking water, financial gain and mitigation of water stress by overpumping.

Silica scale formation and effect of sodium and aluminium ions -29Si NMR study

Silica scale formation on reverse osmosis (RO) membrane surface is a significant problem for operation of high recovery RO desalination plant.

Silica removal to prevent silica scaling in reverse osmosis membranes

Reverse osmosis membranes are increasingly used in drinking water treatment. However, the production of a concentrate stream is the main disadvantage of its application. Increasing the recovery of the membranes in order to have the smallest amount of concentrate possible is an attractive approach. In the absence of bivalent cations in the feed water, silica and silica-derived precipitants are limiting factors in high-recovery reverse osmosis operations. The removal of silica in a separate pretreatment process might be the solution. Several methods were tested to remove silica. Precipitation of silica with Fe(OH)3, Al(OH)3 and silica gel was investigated, and also the removal of silica using a strongly basic anion (SBA) exchange resin.Al(OH)3 was the most effective precipitant for silica, removing nearly all of the molecularly dissolved silica. However, a residual amount of aluminum remained in solution, and aluminosilicate colloids were not removed. The use of the SBA exchange resin also showed a good performance, removing up to 94% of the silica. However, further investigations, such as checking whether the residual small amounts of silica and aluminum can still cause scaling in the membrane, need to be conducted.

Silica scale mitigation for high recovery reverse osmosis of groundwater for a mining process

The feasibility of silica removal in RO treatment of groundwater from a Western Australian mining and processing operation to prevent scaling and enhance water recovery was investigated. This study has shown that it is possible to decrease the silica concentration in RO concentrate to levels that would allow an overall water recovery of 90% to 95% using 10g/L of regenerable activated alumina adsorbent. Regeneration of the adsorbent using 2% NaOH was found to be effective for at least three regeneration cycles. A preliminary costing of the high water recovery RO process using silica removal by adsorption indicated product water (permeate) costs of $5.6/kL and savings due to a reduction in brine volume from the current 40% of feed volume to 5–10% of feed volume. It also allows better utilisation of a scarce groundwater resource, allowing the production of up to 1.6 times more low salt water from a given volume of groundwater. These results warrant larger scale investigation of silica removal and adsorbent regeneration for high recovery RO processing for mining operations, and application of silica removal to RO treatment of other silica laden waters such as coal seam gas produced water.

Kinetics of Gypsum Precipitation for Designing Interstage Crystallizers for Concentrate in High Recovery Reverse Osmosis

Treating desalination concentrates by precipitating sparingly soluble salts is a promising method for extending water recovery limits of such processes and thereby reducing concentrate volumes. One of more common technologies for carrying this out is the use of fluidized bed crystallizers, often with sand grains as the crystallizing surface. Most of the works done to date on such crystallizers for water treatment purposes have been on water softening, and little has been done on use of such crystallizers for precipitation of gypsum. This study was on the crystallization kinetics of gypsum at initial supersaturation levels typical of reverse osmosis (RO) concentrates, in the presence of silica sand grains or gypsum seeds, in a batch stirred tank crystallizer. The findings show that silica sand grains were efficient primary heterogeneous nucleators for gypsum. Crystallization kinetics increased with larger grain size or higher grain number concentration. Considering the different nucleation mechanisms, a ce...

Coal seam gas associated water treatment and management—opportunities and limitations

Coal seam gas (CSG) is a new major export for Australia. The production of CSG releases a significant amount of brackish water to the surface, known as associated water. Queensland’s Department of Environment and Heritage Protection (DEHP) has predicted that the peak yearly flow of the associated water could range between 100-280 gigalitres (GL) per year. This presents a major challenge to the CSG industry in water and its by-product (brine) management. CSG water quality varies across regions, but is typically high in total dissolved solids, bicarbonate, hardness, and silica. Consequently, CSG water without treatment is unsuitable for beneficial uses. To date, reverse osmosis (RO) desalination processes with suitable pre-treatment steps have been employed to remove elevated salts and other compounds before CSG water can be used beneficially. One type of beneficial reuse of the treated water that has gained acceptance and prominence in recent times is the irrigation of agricultural crops and forestry. RO brine, a highly saline stream, requires a managed response to ensure a socially, environmentally and financially sound outcome. Conventional evaporation in brine ponds is not considered favourably under existing government directions and, consequently, alternative solutions are sought. Thermal processes, such as brine concentrators, have been used in the treatment of CSG RO brine. The resulting high-quality distillate produced by thermal processes can be used in a number of applications along with a greater proportion of water recovered from such processes. This peer-reviewed paper concludes that a thermal process in conjunction with a high-recovery RO membrane plant, configured as a hybrid membrane/thermal configuration, is probably a suitable solution to meet policy direction by improving system recovery as a precursor to advance associated water treatment and brine management. The discussion is generated out of MWH’s experience with CSG water treatment and management processes, which totals a number of significant projects in the CSG industry.

Silica and silicate precipitation as limiting factors in high-recovery reverse osmosis operations

This paper investigated silica and silicate precipitation as limiting factors in high-recovery membrane operations. For this purpose a cation exchange pretreatment is proposed to reduce Ca2+, Ba2+, Mg2+ levels to prevent scaling of salts containing these ions during subsequent NF and RO filtration, in which RO is fed with NF concentrate. In a pilot plant experiments were carried out at total (NF+RO) water recovery of 91, 94, 96 and 98% with locally available tap water which contains 20mg/L of silica as feed water. Autopsy studies were performed with the RO membranes after each experiment in which the fouling layer was studied using SEM–EDX to determine the structure and the composition of the fouling deposits. A thin cake layer was observed which covered approximately half of the membrane surface after operating for 20 days at 91 and 94% recovery. At 96 and 98% recovery the fouling layer was thicker and completely covered the membrane surface. EDX analysis indicated that the fouling layer was mainly composed of Si, Al, Fe and O, most likely due to the presence of iron oxides, iron hydroxides, silica and aluminosilicates. To be able to work at these high recoveries for an extended period, further measures need to be taken to prevent silica and aluminosilicate scaling.

Enhancement of reverse osmosis water recovery using interstage calcium precipitation

The feasibility of removing calcium scale precursor ions from reverse osmosis (RO) concentrate by accelerated seeded precipitation (ASP) was investigated with the goal of increasing product water recovery and minimizing the volume of concentrate disposal from inland municipal wastewater desalination plants. Three seed materials were tested in laboratory trials — calcium carbonate, calcium sulfate and calcium phosphate. Calcium carbonate and calcium sulfate seed were not effective. The addition of calcium phosphate seed particles at 20gL−1 or phosphate ion in stoichiometric excess of the calcium concentration (250mgL−1 Ca=6.25mM Ca2+, 650mgL−1 HPO42−=6.7mM) decreased the calcium content in the RO concentrate to 10mgL−1. Evaluation of the accelerated seeded precipitation process using in-situ generated calcium phosphate seed at the pilot scale was performed on a 25kLday−1 pilot plant consisting of dissolved air flotation, ultrafiltration and reverse osmosis. The treated concentrate was filtered by a ceramic filtration system. Preliminary cost analyses indicate that high recovery RO using calcium phosphate precipitation can only be justified in inland situations where restrictions on concentrate disposal drive smaller evaporation pond storage volumes to offset the higher chemical and energy running costs.

Accelerated desupersaturation of reverse osmosis concentrate by chemically-enhanced seeded precipitation

A two-step chemically-enhanced seeded precipitation (CESP) process was demonstrated for accelerated desupersaturation of antiscalant-containing, gypsum-supersaturated model solutions, which mimicked reverse osmosis (RO) concentrate from RO desalting of agricultural drainage water of high mineral scaling propensity. In the CESP process, CaCO 3 precipitation is first induced via lime dosing for antiscalant scavenging, followed by subsequent CaSO 4 precipitation via gypsum seeding for concentrate desupersaturation. It was demonstrated that lime-precipitated CaCO 3 particles were able to scavenge generic and commercial polycarboxylic-acid antiscalants, thereby facilitating subsequent CaSO 4 precipitation to progress with minimal retardation. The study demonstrated via a series of batch CESP cycles that gypsum particle recycling can sustain CaSO 4 precipitation, suggesting that a continuous CESP process could be feasible. Process analysis suggests that CESP can be significantly less chemical-intensive than conventional precipitation softening and, with its integration as an intermediate RO concentrate demineralization process, can enable desalination water recovery enhancement via secondary RO desalting. For the present case of gypsum-saturated RO feed water, enhancement of overall water recovery from 63% up to 87% or higher appears to be feasible. The study suggests that there is merit for developing a continuous CESP process for high recovery RO desalting of brackish water of high gypsum scaling propensity.

Control and Monitoring of a High Recovery Reverse Osmosis Desalination Process

Model-based control and monitoring such as feed-forward/feedback control, fault detection and isolation (FDI), and fault-tolerant control (FTC) techniques that utilize Lyapunov-based control laws are implemented on a high recovery reverse osmosis desalination plant model. A detailed mathematical model of a high recovery reverse osmosis plant is developed. This model incorporates the large spatial variations of concentration and flow rate that occur in membrane units during high recovery operation. Bounded nonlinear feedback and feed-forward controllers are developed and applied to this system. The application of these controllers with FDI and FTC is demonstrated in the context of a high recovery reverse osmosis process simulation. The first set of simulations demonstrates the ability to compensate for the effects of large time-varying disturbances in the feed concentration on specific process outputs with and without feed-forward control. The second set of simulations demonstrates the ability of FDI and F...

Rotating reverse osmosis and spiral wound reverse osmosis filtration: A comparison

Wastewater produced by the crew members on a long-term space mission needs to be recovered as potable water. Reverse osmosis (RO) has long been in use as a physical membrane separation technology for wastewater treatment. However, membrane fouling and concentration polarization have limited the efficiency for high recovery reverse osmosis systems. An advanced high pressure rotating RO device was designed to minimize these problems by the rotation of the cylindrical RO filter producing shear and Taylor vortices in the annulus of the device. We compare the performance of the rotating RO device to a standard spiral wound RO module using a commercially-available RO membrane under conditions of very high recovery and similar permeate flux. The studies were conducted using 0.01N sodium chloride solution and biological water processor effluent (BWPE) as model wastewaters. The results for 100% recovery of water from 0.01N sodium chloride solution show that the spiral wound RO has poor rejection (<5%) compared to more than 75% rejection for the rotating RO over a period of 2 days. Similar differences in rejection were observed for BWPE for a 5-day test at high recoveries. The overall ion rejection, dissolved organic carbon (DOC) rejection, and ammonium ion rejection from BWPE was typically two times higher for the rotating RO system than for spiral wound RO at 70–80% recovery. Thus, while rotating RO is a more complicated system than spiral wound RO, it provides better rejection of contaminants at very high recoveries.

The Way to Sea Water Desalination by High Recovery Reverse Osmosis

The Way to Sea Water Desalination by High Recovery Reverse Osmosis

Features of High Recovery Reverse Osmosis System for Sea Water Desalination

Features of High Recovery Reverse Osmosis System for Sea Water Desalination

High recovery reverse osmosis using a recycle loop

A single-pump configuration with feedback has been found useful in reaching high brine osmotic pressures in continuous-flow operation. Enhanced brine concentration, and enhanced product/feed water recovery fraction, can be obtained by recycle of a second-stage permeate of intermediate quality. For spaceflight recycling of hygiene water this permits lower pressure-vessel ratings, or higher water recovery, or both. With feed of 1,000 ppM concentration, recoveries of 95–97% are achieved at a pressure of 1.65 MPa. With feed of seawater concentration, recoveries of 50% to 70% have been achieved using a single pump at 5.5 MPa. Membrane performance parameters have been obtained for high water recovery operation in the pressure range up to 1.4 MPascals (200 psig) for system modeling. Simple equations can be fitted to these measurements, from which RO system performance can be predicted, or simulated as part of a model of system performance.

High recovery reverse osmosis

As a means to minimize or eliminate brine disposal problems, high recovery RO must be accompanied by pre- or post-treatment to avoid scale precipitation, almost entirely by CaSO 4. All such methods will add to water cost. However, rigorous comparison must be made with the costs and constraints of brine disposal at recoveries low enough not to require these treatments. Such examination is invariably and totally site-specific. Prior to detailed design of any large RO facility, it is always prudent to invest in a pilot plant testing program, whereby membrane performance under varying recovery and flux may be evaluated on the raw feed to be used at full scale. Because of the even tighter design limits imposed at high recovery, pilot tests of combined membrane and treatment processes are absolutely essential.