Reverse Osmosis Stage Research Articles

A Highly Efficient Waste-Free Technology of Water and Fuel Preparation for Thermal Power Stations

A highly efficient, economical, and waste-free technology for the purification of natural waters for thermal power plants has been developed. The preliminary purification of water involved microfiltration on tubular ceramic membranes made of clay minerals according to a technology developed at the Dumansky Institute of Colloid Chemistry and Water Chemistry, NAS of Ukraine; the degree of retention of suspended solids and iron and manganese compounds on the membranes was 99.9, 99.8, and 60%, respectively. The high separation capacity of such membranes is due to the modification of their surface by water contaminants with the formation of a self-organizing dynamic membrane that serves as an additional barrier. The dynamic membrane formation contributed to the retention of up to 24.0% of the co-occurring ions, Ca2+ in particular; this is typical for ultrafiltration membranes. Further desalination was performed with low-pressure reverse osmosis membranes; two stages of reverse osmosis turned out necessary to achieve a total ion content of 0.5 mg/dm3 in the make-up water of a steam turbine unit of a thermal power plant (TPP). The retentate of the second stage of reverse osmosis, for which the total ion content is 50–60 mg/dm3, can be used for technical purposes at TPPs. The salt content of the retentate formed after the first stage of reverse osmosis was ~3 g/dm3, and thus insufficient for further transformation into secondary material resources; however, the introduction of waste recycling systems is considered to be the modern direction in protecting the environment from technological influence. The retentate of the first stage of reverse osmosis was concentrated using an original concentrating electrodialyzer developed at the Dumansky Institute of Colloid Chemistry and Water Chemistry, NAS of Ukraine; some design modifications that distinguish this electrodialyzer from the conventional ones were proposed and patented. Electrodialysis treatment of the retentate for 2.5 hours at a current density of 2.5 A/dm3 enabled the production of a solution with the ion content of ~105 g/dm3. This brine can be converted into sodium hypochlorite or caustic soda and hydrochloric acid by electrolysis. The diluate with a mineralization of ~200.5 g/dm3 and a total organic carbon content of ~148.3 g/dm3 can be used for the preparation of coal-water slurry fuels for power generation and metallurgy. The basic technological schemes of make-up water purification for the needs of thermal power plants and the preparation of slurry fuel systems based on coal and reverse osmosis waste that contains organic substances are proposed.

Techno-economic evaluation of an element-scale forward osmosis-reverse osmosis hybrid process for seawater desalination

The forward osmosis (FO)-reverse osmosis (RO) hybrid process is gaining attention in the desalination market because it can purify diluted seawater and the RO unit functions at low pressure conditions, resulting in a reduced total operational cost. However, FO element configuration affects the process performance, minimum flow rate, inlet pressure, product capacity, and draw solution (DS) dilution rate. Moreover, economic evaluation of the FO-RO hybrid process in the Middle East, which is the largest seawater desalination market, is required to obtain representative results. Realistic economic evaluation can be achieved with a real-performance database (DB) and specific assumptions. In this study, a techno-economic evaluation of the FO-RO hybrid process was conducted using real element-scale FO DB and simulation DB, and the results were compared with those of a stand-alone two stage RO process. Spiral wound FO (SWFO) and plate and frame (PFFO)-RO hybrid processes were more economical by 8.84% and 3.73%, respectively, when compared to two-stage RO. In the Middle East, the total cost of SWFO-RO was 45.1 M$ lesser than that of PFFO-RO due to its higher water flux and DS dilution rate. Therefore, the FO-RO hybrid process has high economic potential in the Middle East and elsewhere.

Influence of osmotic mediation on permeation of water in reverse osmosis: Experimental and numerical analysis

Osmotically mediated reverse osmosis (RO), whose concept is to lower the osmotic pressure difference (Δπ) across the membrane by supplying a “mediate” solution of low or equal concentration (relative to feed solution concentration) in the permeate side, has been recently suggested as a viable way to treat hypersaline brines. However, most of the studies on the osmotically mediated RO process have focused on numerical analyses or simulation. Accordingly, we experimentally delved deeper into the permeation of water through the membrane and numerically analyzed this permeation for the process. When Δπ across the membrane was mediated in the bulk phase for the feed solution of 0.2 to 1.2 M, the water flux significantly decreased with the feed solution concentration. Specifically, for the feed solutions of 0.6 and 1.2 M, the water fluxes of 22.1 and 5.76 L m-2 h-1 were obtained at ΔP of 40 bar and Δπ of 0 bar in the bulk phase, respectively. Numerical results showed that even when Δπ was mediated in the bulk phase, effective osmotic pressure difference (Δπeff) for each concentration increased with ΔP increase and increased further with the feed solution concentration. Nevertheless, the osmotically mediated RO process can be regarded as hydraulic dilution process. By virtue of this process, the high-pressure single stage RO process may be replaced by a moderate-pressure two-stage RO process for low-energy process.

Reuse of shale gas flowback and produced water: Effects of coagulation and adsorption on ultrafiltration, reverse osmosis combined process

The shale gas flowback and produced water (FPW) from hydraulic fracturing in the Sichuan province of China has relatively low to moderate levels of total dissolved solids (<20 g/L) and organics (<50 mg/L of dissolved organic carbon). As such, a combined ultrafiltration (UF), reverse osmosis (RO) system can be successfully applied to desalinate this feed water with the goal of reuse. However, the concentration of influent organic matter and particulates in the UF and RO stage is high, and the overall ionic and organics composition is highly complex, so that the membrane processes do not perform well, also due to fouling. To ensure the long-term and efficient operation of the UF-RO stages, a combined pretreatment of the FPW with coagulation and adsorption was investigated. The effect of different parameters on the performance on the system was studied in detail. Overall, the coagulation-adsorption pre-treatment greatly reduced fouling of the membrane processes, thanks to the high removal rate of turbidity (98.8%) and dissolved organic carbon (86.3%). The adsorption of organic matter by powdered activated carbon was best described by the Freundlich equilibrium model, with a pseudo second-order model representing the adsorption kinetics. Also, the various ions had competitive removal rates during the adsorption step, a phenomenon reported for the first time for FPW treatment. Also, an optimal dose of activated carbon existed to maximize fouling reduction and effluent quality. The overall treatment system produced a high-quality water streams, suitable for reuse.

Cold-cathode X-ray irradiation pre-treatment for fouling control of reverse osmosis (RO) in shale gas produced water (SGPW) treatment

For a more sustainable and environmental-friendly management of shale gas produced water (SGPW), it is essential to customize and optimize the treatment options since the characteristics of SGPW vary both spatially and temporally. However, fundamental studies on the foulants of SGPW and their control methods are lacking, particularly in connection with the RO-based process, which has been adopted increasingly in SGPW treatment. This study fundamentally evaluated the feasibility of novel cold-cathode X-ray irradiation as an additional fouling control process prior to the RO process using actual SGPW extracted from the Sichuan shale region (China) for the first time in literature. The foulants incapable of being removed by conventional pre-treatments (e.g., dissolved air flotation (DAF) and ultrafiltration (UF) membrane) induced organic fouling in the RO stage, and they were identified eventually as aliphatic hydrocarbon (oil) components. The fouling mechanism was deduced to be the formation of coalesced hydrocarbon layer on the RO membrane surface. In order to target these identified oily substances surgically, the novel cold-cathode X-ray irradiation process was employed since this technology offers much better energy efficiency compared to the existing thermionic X-ray irradiation. Our work demonstrated that the cold-cathode X-ray irradiation could efficiently remove the aliphatic hydrocarbon in the pre-treatment stage. This new X-ray irradiation process was optimized further with respect to energy consumption by investigating the effect of tube current and voltage. Our experimental observations suggest that the cold-cathode X-ray irradiation process could be an energy-efficient alternative for the treatment of organic-rich (oily) industrial wastewaters such as SGPW.

Reverse Osmosis Network Rigorous Design Optimization

In this work, we propose a methodology to solve a nonlinear mathematical model for the optimal design of reverse osmosis (RO) networks, which ameliorates the shortcomings of the computational performance and sometimes convergence failures of commercial software to solve the rigorous mixed integer nonlinear programming (MINLP) models. Our strategy consists of the use of a genetic algorithm to obtain initial values for a full nonlinear MINLP model. In addition, because the genetic algorithm based on the rigorous model equations is insurmountably slow, we use metamodels to reduce the mathematical complexity and considerably speed up the run. We explore the effects of the feed flow, seawater concentration, number of reverse osmosis stages, and the maximum number of membrane modules in each pressure vessel on the total annualized cost of the plant.

The valorization of biogas slurry with a pilot dual stage reverse osmosis membrane process

Biogas slurry is an environmental pollution source if it is discharged without proper treatment. In this work, a membrane system is designed to concentrate, and hence to recover the nutrient in the biogas slurry. The effects of pre-treatment technology, pH, temperature, operating pressure and module types of the reverse osmosis unit were studied via analyzing the chemical oxygen demand (COD), ammonia nitrogen, total nitrogen, conductivity in the permeate and retentate, and the volume concentration ratio. A dual stage reverse osmosis (RO) process is also applied to further enhance the performance, the concentration ratio reaches above 5 within 80 mins of operation, while the nutrient recovery and water recovery rates are 98% and 92.52%, respectively. The COD and ammonia nitrogen rejection rates are 99.41% and 99.11%, respectively; the quality of the permeate is in accordance with the national standard for water discharging.

Study on Application of Membrane Technology in Treatment of Effluent from Dyeing Industries in Erode, TamilNadu

The textile dyeing industry is one of the hazardous polluting industries which uses water as the major source for their production and substantially the generation of wastewater leads to be a huge burden in treatment. The existing treatment methods adopted in most of the dyeing industries are said to be very old and its efficiency of removal is very less and at the same time it does not meet the standards for trade effluent discharge as prescribed by the regulatory boards. The study carried out on the application of Activated Carbon Filter (ACF) outlet in three stages of Reverse Osmosis results in reduction of 52% and the Total Dissolved Solids (TDS) is reduced to 226 ppm under the operation time of 10 hours. Significance reduction in pH, BOD, COD, TSS and Sulphates. The results say that the new technology of applying Nano-filtration and ultra-filtration will increase the efficiency of treatment. The effluent characteristics with the help this technology satisfy the standards.

Process economics and operating strategy for the energy-efficient reverse osmosis (EERO) process

The energy-efficient reverse osmosis (EERO) desalination process was recently developed for cost-effective high total water recovery. It feeds the retentate from one or more single-stage reverse osmosis (SSRO) stages in series to a countercurrent membrane cascade with recycle (CMCR) consisting of a terminal reverse osmosis (RO) stage and one or more low salt-rejection stages. The CMCR permits retentate refluxing in the low salt-rejection stages and multi-pass processing of permeate. The novel 2-2 EERO process is advanced that involves two SSRO stages in series with a 2-stage CMCR. To address problems encountered in a pilot-scale test of the EERO process, it develops an operating strategy involving boosting the pressure to the low salt-rejection stage of the CMCR to compensate for using membranes with a higher salt rejection than required. A process embodiment for mitigating concentration polarization is also advanced. The first estimate of the total cost of water production for three EERO process configurations is made. The EERO process can reduce the osmotic pressure differential by 50% relative to conventional SSRO for the same total water recovery and can achieve 75% total water recovery at a lower total cost of water production than conventional SSRO operated at just 50% water recovery.

Unlocking High-Salinity Desalination with Cascading Osmotically Mediated Reverse Osmosis: Energy and Operating Pressure Analysis.

Current practice of using thermally driven methods to treat hypersaline brines is highly energy-intensive and costly. While conventional reverse osmosis (RO) is the most efficient desalination technique, it is confined to purifying seawater and lower salinity sources. Hydraulic pressure restrictions and elevated energy demand render RO unsuitable for high-salinity streams. Here, we propose an innovative cascading osmotically mediated reverse osmosis (COMRO) technology to overcome the limitations of conventional RO. The innovation utilizes the novel design of bilateral countercurrent reverse osmosis stages to depress the hydraulic pressure needed by lessening the osmotic pressure difference across the membrane, and simultaneously achieve energy savings. Instead of the 137 bar required by conventional RO to desalinate 70 000 ppm TDS hypersaline feed, the highest operating pressure in COMRO is only 68.3 bar (-50%). Furthermore, up to ≈17% energy saving is attained by COMRO (3.16 kWh/m3, compared to 3.79 kWh/m3 with conventional RO). When COMRO is employed to boost the recovery of seawater desalination to 70% from the typical 35-50%, energy savings of up to ≈33% is achieved (2.11 kWh/m3, compared to 3.16 kWh/m3 with conventional RO). Again, COMRO can operate at a moderate hydraulic pressure of 80 bar (25% lower than 113 bar of conventional RO). This study highlights the encouraging potential of energy-efficient COMRO to access unprecedented high recovery rates and treat hypersaline brines at moderate hydraulic pressures, thus extending the capabilities of membrane-based technologies for high-salinity desalination.

Removal of fouling species from brackish water reverse osmosis reject stream

ABSTRACTBrine disposal from reverse osmosis (RO) systems remains a major challenge for the desalination industry especially in inland areas where discharge options are very limited. Solutions will entail the introduction of economic treatment processes that will alleviate the brine’s negative impact on the environment and reduce its discharge volume. Such processes could act as an intermediary treatment process for the recycling of the brine through an additional RO stage which, for brackish water (BW) desalination, could lead to saving valuable water while reducing the amount of brine discharge. In this context, the study at hand attempts to evaluate the effectiveness of a one-step chemical process for the treatment of BWRO brine. This study seeks to determine optimal operating conditions relative to type, ratio, and dosage of alkalizing chemicals, pH and temperature, for substantially reducing the concentrations of scaling parameters such as calcium, magnesium, silica, and strontium. The results indicate that precipitation softening at pH = 11.5 using combined chemical dosages of NaOH and Na2CO3 in a ratio of 2:1 leads to substantial removal of calcium and magnesium (>95%) and moderately high removal of strontium and silica (>71%).

The exergetic efficiency as a performance evaluation tool in reverse osmosis desalination plants in operation

Exergetic efficiency characterizes the performance of a system or a system component from the second-law of Thermodynamics viewpoint. Although this parameter can be used in the comparison of the operation of similar components working under similar conditions, there are not many articles in the literature dealing with this purpose. In this paper, a desalination plant located in Gran Canaria (Canary Islands, Spain) is considered. Different configurations are possible in the ten reverse osmosis production lines of the plant, depending on the procedure used for the energy recovery, the number of reverse osmosis stages, the technologies applied to the intake and filtration processes, or the components involved in feed water pressurization. Using real data, the exergetic efficiency is assessed as a performance evaluation tool. Through the comparison of the exergetic efficiency of similar devices, though different production lines, the components with operation defects that should be repaired are identified: the most inefficient pelton turbines, intake pumps, high pressure pumps, booster pumps, reverse osmosis membrane modules, and pressure exchanger modules. This way, exergetic efficiency can be successfully used to control and to improve the operation of the plant.

Advanced Microscopy of Inorganic Colloids Sampled From Consecutive Stages of RO Filtration

Understanding the phenomena governing silica scaling in reverse osmosis (RO) relies on properly characterising the water matrix. One of the challenges to characterising water samples is the presence of inorganic nanoparticles, which are difficult to detect and analyse. In this work we develop a straightforward approach for nanoparticle trapping, detection, visualisation and elemental analysis by means of electron microscopy. The new approach is applied to characterise samples from three consecutive stages of RO in a water treatment facility. Transmission electron microscopy grids are employed with and without carbon films, to capture nanoparticles. We find that film coated traps are more effective in collecting colloids, and the colloids collected are of similar size. For the waters tested, the nanoparticles are rich in silica and the number of particulates increases with the advancement of the RO process.

High Permeate Recovery for Concentrate Reduction by Integrated Membrane Process in Textile Effluent.

The textile dyeing industry consumes a significant amount of high-quality water for processing, which stresses water resources. In recent decades, technologies have been developed to recover water from wastewater. This study describes the high recovery (greater than 92%) of reusable water from an industrial-scale hosiery dye-water recovery facility, consisting of three stages of reverse osmosis and ultrafiltration. The effluent was pre-treated before the membrane process was performed to prevent biofouling. The process performance results in the generation of a consistent water quality that is required for dyeing operations. An average feed flux of 15 l/m2h was maintained in the reverse osmosis membrane by regular chemical dosing and cleaning. The integrated membrane process achieved a permeate with a pH of 6.5 and total dissolved solids (TDS) of 160 mg/l, with no other contaminants, which is of sufficient quality for reuse in the cotton hosiery dyeing process.

A novel brine precipitation process for higher water recovery

A three-step demineralization process for removing scale-forming substances from brine solutions produced from nanofiltration (NF) of water was developed. The process is designed to remove substances that would lead to scale and membrane fouling during additional stages of NF or reverse osmosis (RO). Tests were performed to determine the most suitable dosages and mixing times for each reagent. The first step in the demineralization process employs ferric chloride for removing phosphonate scale inhibitors via co-precipitation with ferric hydroxide. The second step of the process increases the solution pH value to promote carbonate mineral precipitation. The third step involves barium sulfate precipitation promoted by barite seed crystals. Saturation indices for precipitation of mineral solids were simulated using the Phreeqc thermodynamic modeling program. Water recovery from the treated brines was modeled using the ROSA package for simulating permeate and concentrate compositions for NF processes. The three-step demineralization process allowed the recovery rate for the brine solution to be as high as the initial feed water, and achieved a total water recovery of >97%.

Impact of Protein Removal by an Upstream Ultrafiltration on the Reverse Osmosis of Skim Milk and Sweet Whey

AbstractConcentration of milk and whey by ultrafiltration and reverse osmosis (RO) in cascade mode is an amendment of evaporation for high volume reduction ratios (VRR) prior to drying. This study investigated the impact of a prior protein removal and the transmembrane pressure (TMP) on the RO stage, compared to skim milk and sweet whey. It could be found that removal of the protein fraction of both skim milk and sweet whey improved the efficiency of the RO. An upstream ultrafiltration resulted in higher VRR as well as an increased permeate flux.

Characterization of microbial communities in water and biofilms along a large scale SWRO desalination facility: Site-specific prerequisite for biofouling treatments

Biofouling impacts seawater reverse osmosis (SWRO) desalination plants by hindering module performance, increasing energetic demands, and incurring further costs. Here we investigated the spatial–temporal dynamics of microbial communities along the feedwater, pretreatment, and reverse osmosis stages of a large-scale SWRO desalination facility. While the composition of water-based microbial communities varied seasonally, the composition of biofilm microbial communities clustered by locations. Proteobacteria dominated throughout the water and biofilm communities while other dominant phyla varied seasonally and spatially. The microbial community composition significantly differed along the pathway locations of feedwater, rapid sand filtration (RSF), cartridge filters (CF), and the reverse osmosis (RO) membranes. Biofilms on the RSF and CF were composed of more diverse microbial populations than RO biofilms as determined by the effective number of species. Biofilms that developed along the treatment pathway (CF) served as inocula enhancing biofouling downstream on the RO membranes. Subsequently, we believe that prior to the development of advanced antibiofouling treatments for the desalination industries, the site-specific microbial community of feedwater, pretreatment and RO biofouling should be characterized. Site specific identification of these communities will enable optimization of pretreatment and cleaning procedures and can ultimately reduce chemical usage and incurred costs.

Integration of nanofiltration and reverse osmosis for metal separation and sulfuric acid recovery from gold mining effluent

Abstract This work assessed the viability of implementing sequential stages of microfiltration (MF), nanofiltration (NF) and reverse osmosis (RO) to recover sulfuric acid, separate noble metals, and produce high quality reuse water from a gold mining effluent, specifically from a pressure-oxidation process effluent. Additionally, lime demand for neutralization of the proposed treatment streams and current lime demand were compared. It was observed that the NF attained high sulfuric acid permeation, equivalent to 82%, and a substantial acid purification of approximately 77% in relation to feed solution. Moreover, the RO increased the acid content by 99% in relation to feed solution considering a recovery rate of 50%. The final RO permeate had low conductivity and reduced content of total solids and contaminants, thus showing promising potential for industrial reuse. Furthermore, the acid recovery did not led to an important loss of metals of high commercial value which were present in the raw effluent since their retention in the concentrates of the MF and NF was above 95%. The neutralization of the MF and NF concentrates allowed for a 20% reduction in lime consumption in relation current demand.

Phosphate adsorption on granular ferric hydroxide to increase product water recovery in reverse osmosis-desalination of secondary effluents

Calcium phosphate precipitation, and in particular calcium hydroxyapatite (HAP)-Ca5(PO4)3OH scaling, is a major factor limiting high recovery in reverse osmosis (RO) of treated effluents. This study evaluated the feasibility of phosphate adsorption in continuous regime on granular ferric hydroxide (GFH) from 2-fold concentrated RO-brines (1st stage of a 2-stage RO desalination train) of secondary effluents. Fixed bed adsorption on granular media was chosen to ensure low turbidity and preserve brine pressure for the 2nd RO stage. Optimal hydraulic conditions for adsorption and a method for GFH regeneration were formulated. Simultaneous analysis of bed mass transfer zone and adsorbent concentration yielded optimum at empty bed contact time (EBCT)>3.5min and 10<hydraulic load (HL)<15m/h. Breakthrough P-concentration was set at 0.2mg/L to maintain HAP-solubility index ≤7. A constant adsorption rate of 1.6mg P/g GFH was maintained during nine adsorption/regeneration cycles at feed phosphate concentration of 9.3±0.9mg/L (as P), approx. 3300 bed volumes (BV) per batch. A NaOH regeneration solution was effectively recycled over 2300 BV until reactivation was required. Considering that phosphate concentration in effluents of well performing wastewater treatment plants is far below 10mg/L, in practice column capacity will be considerable higher than 3300 BV.

Bacterial profiling in brine samples of the Emalahleni Water Reclamation Plant, South Africa, using 454-pyrosequencing method.

A metagenomic approach was applied using 454-pyrosequencing data analysis for the profiling of bacterial communities in the brine samples of the water reclamation plant. Some physicochemical characteristics of brine samples were also determined using standard methods. Samples ranged from being lightly alkaline to highly alkaline (pH 7.40-10.91) throughout the various treatment stages, with the salinity ranging from 1.62 to 4.53 g L(-1) and dissolved oxygen concentrations ranging from 7.47 to 9.12 mg L(-1). Phenotypic switching was found to occur due to these physicochemical parameters. Microbial diversities increased from those present in Stage I reactor (six taxonomic groups) to those in Reverse Osmosis (RO) stage I (17 taxonomic groups), whereas in the second phase of the treatment, it increased in Stage II clarifier (14 taxonomic groups) followed by a decrease in RO stage II (seven taxonomic groups). Overall, seven phyla were detected, apart from many bacterial sequences that were unclassified at the phylum level. The most dominant phylum found was Proteobacteria accounting for 59% of the total sequences. A blastn sequence similarity search showed that the majority of the sequences (56%) were homologous to the uncultured bacterial species, underlining the vast untapped bacterial diversity.