Full-scale Reverse Osmosis Research Articles

Detailed organic characterization of process water to evaluate reverse osmosis membrane fouling in industrial wastewater treatment

One of the major waste streams within the oil and gas (O&G) industry is produced and process water generated during hydrocarbon production and treatment, respectively. In gas production facilities, process water typically has lower salinity (i.e., <10,000 mg/L) which present opportunities for these wastewaters to be treated for beneficial reuse applications via advanced water treatment technologies, such as reverse osmosis (RO) membranes. One of the key challenges for RO membranes application to industrial wastewater treatment is fouling which is frequently attributed to the soluble organics present in the water and/or associated with field chemicals. In this study, a detailed organic characterization methodology, using liquid chromatography with organic carbon detector (LC-OCD) was applied to characterize the organics on a real process water collected from industrial wastewater treatment plant at a gas production facility. Additionally, a rigorous bench-scale testing procedure was implemented to assess the performance of a full-scale RO system with and without activated carbon filter (ACF) pretreatment, making this study the first one to apply LC-OCD methodology on real wastewater to evaluate the fouling of RO membranes deployed at an industrial treatment plant. Bench-scale RO results showed that in the absence of ACF pretreatment, a 12 % decline in membrane permeability (from 1.78 to 1.57 L/(m2-bar-h)) was observed, while no permeability decline was measured after ACF treatment. The organic fouling was confirmed by mass balance calculations on the bench scale experiments as well as Fourier Transform Infrared (FTIR) analysis on the membrane coupons. Moreover, LC-OCD analysis showed that the ACF inlet has a TOC concentration of approximately 3.06 mg/L; of those 1.29 mg/L (42 %) are hydrophobic, and 1.77 mg/L (58 %) are hydrophilic. After ACF treatment, the hydrophobic organics decreased to 0.65 mg/L, revealing that the ACF is removing >50 % of hydrophobic organics which are likely responsible for membrane fouling. Bench-scale operational and water quality results were comparable to the full-scale RO performance data validating the lab testing procedure implemented in this study.

A hybrid modelling approach for reverse osmosis processes including fouling

A novel hybrid modelling approach, combining the strengths of a mechanistic reverse osmosis (RO) model and a data-driven fouling model, is developed on a unique long-term dataset from a full-scale RO installation to predict its performance. The mechanistic solution-diffusion model describes well understood phenomena in RO such as concentration polarisation, osmotic pressure and solutes transport throughout the membrane. This solution-diffusion model is combined with a data-driven model to cover the gaps in knowledge related to fouling phenomena. Several fouling models are tested to predict the membrane resistance over time and a thorough analysis of important input features was performed. A non-linear recurrent neural network with long short-term memory (RNN-LSTM) clearly outperformed (RMSE = 1.01e13) a linear autoregressive integrated moving average with exogenous variables (ARIMAX) model (RMSE = 1.97e13) for an 8 month testing period. The best performance was achieved when including membrane cleaning as two separate features representing short and long CIPs. Moreover, recovery setpoint, concentrate flow rate, feed temperature, feed conductivity and feed calcium concentration were shown to be important model input features. Fouling sensitive parameters of the solution-diffusion model (the water permeability, the feed spacer channel height and the solute permeability - determined by a global sensitivity analysis) were made function of the output (membrane resistance) of the RNN-LSTM thus leading to a serial hybrid model. The predictions of the hybrid model showed a clear improvement for all output variables when compared to a solution-diffusion model including temperature correction. The model was developed, calibrated and trained on measurements of standard sensors and can thus be used for real-time applications such as advanced control and predictive scenario analysis in a digital twin context.

Membrane integrity monitoring on laboratory scale: Impact of test cell-induced damage on membrane selectivity

Defects in the active layer of reverse osmosis (RO) membranes play a crucial role in the passage of virus particles and microbial surrogates through the membrane systems. Prior research indicates that not only defects in the active layer but also a mechanical failure in the membrane module can compromise the performance of full-scale RO spiral wound systems. However, there have been no studies on the microbial passage in coupon-scale testing systems for highly selective RO membrane characterization on a laboratory scale. The capability of test cells to introduce defects on the membrane surface via contact zones is recognized for the first time in this study. This work focuses on membrane defects introduced by the sealing mechanism of the coupon-scale test. We show how defects arise at points of contact between the membrane, the O-rings, and the test cell body, occurring in both commercially available test cells as well as in-house developed test cells. These defects cause a marked decrease in membrane selectivity, compared to spiral-wound elements housing the same membranes. Membrane integrity was assessed by measuring the passage of viruses and fluorescent markers. We demonstrate that in almost all cases, detectable virus concentrations were found in the permeate due to non-selective transport through defects in the membrane. Failure to account for this non-selective transport leads to an overestimation of achievable selectivity by a factor of two or more, as seen in previously published studies. Lastly, we propose modifications to test cell design that reduce contact zones thus potentially safeguarding the membrane's selectivity.

Development and Industrial-Scale Fabrication of Next-Generation Low-Energy Membranes for Desalination

Spiral-wound modules have been the most common configuration of packing flat-sheet membranes since the early development of polyamide (PA) membranes for water treatment applications. Conventional spiral-wound modules (SWMs) for desalination applications typically consist of several leaf sets, with each leaf set comprising feed spacers, membranes, and a permeate carrier (PC) wrapped around a permeate-collecting tube. The membrane area that can be packed into a given module diameter is limited by the overall leaf set thickness, restricting module productivity for a given membrane permeability. We describe here a novel industrial-scale method for successfully coating the polysulfone (PSf) ultrafiltration (UF) support layer directly onto a permeate carrier, instead of conventional non-woven fabric, as a precursor to the polyamide TFC coating, resulting in twofold benefits: (a) drastically simplifying the membrane fabrication process by eliminating the use of non-woven fabric and (b) increasing the throughput of each membrane module by facilitating the packing of a larger membrane area in a standard module housing. By combining the permeate carrier and membrane into a single sheet, the need for the non-woven support layer was eliminated, leading to a significantly reduced leaf set thickness, enabling a much larger membrane area to be packed in a given volume, leading to lower energy consumption per cubic meter of produced water. Molecular-weight cutoff (MWCO) values in the range of 36–96 kDa were found to be dependent on PC thickness and material. Nevertheless, the reinforced membranes were successfully fabricated with a ~9% reduction in membrane leaf thickness compared to a conventional membrane. Preliminary trials of coating a thin-film composite PA layer resulted in defect-free reverse osmosis (RO) membranes with a salt rejection of 94% and a flux of 40 L m−2 h−1 when tested against a 2000 mg/L NaCl feed solution at an operating pressure of 15 bar. Results from the testing of the 1812 and 2514 elements validated the novel concept and paved the way for further improvements towards full-scale RO membranes with the potential to be the next low-energy workhorse of the water industry.

Modeling and evaluating performance of full-scale reverse osmosis system in industrial water treatment plant

Practical modeling for assessing the efficiency of a full-scale reverse osmosis (RO) system may be a challenging task. This is because the operating conditions of RO systems can change significantly in actual practice owing to high seasonal variations and different progress of membrane fouling during long-term filtration. Accordingly, it is difficult to reliably model the RO performance if such conditions are excluded. In this study, we model a full-scale installation of a RO membrane system, considering actual operations of the industrial water treatment plant. A numerical model is built to describe spatiotemporal behavior of (water, salt, and foulant) mass transport inside a full-dimension pressure vessel. By performing a global sensitivity analysis, we evaluate the relative importance of key influential factors on model accuracy and specific energy consumption (SEC). The model and its parameters are optimized based on the sensitivity result and validated using best-fitted time-series measurement data of 3875 h. The results demonstrate the practical behaviors of fouling development and separation performance of the primary RO process. A regression tree analysis of SEC for 27 different operational scenarios in simulations may benefit decision making for energy efficient RO. Results reveal the high dependence of SEC on cleaning frequency in the feed temperature range.

Numerical Simulations of Calcium Sulphate Scaling in Full-Scale Brackish Water Reverse Osmosis Pressure Vessels Using Computational Fluid Dynamics.

Coal mine waters often have high salinity, hardness and alkalinity. The treatment of coal mine water requires careful management of multi-stage reverse osmosis (RO) systems to achieve effective recovery of water for domestic reuse, as well as zero liquid discharge to minimise the impact to the local environment. Design of RO systems for coal mine water treatment has been limited to the use of commercial design packages provided by membrane manufacturers, which do not provide insights into the impact of operating parameters such as feedwater salinity, concentrations of sparingly soluble salts, feed pressure and their interactions with different RO modules on the fouling/scaling potential of RO membranes. This also restricts the use of novel RO products and the delivery of an optimum design based on real needs. In this work, a mathematical model was developed to simulate a standard brackish water RO pressure vessel consisting six full-size RO membrane elements, using computational fluid dynamics (CFD). The model can be used to predict the permeate flowrate, water recovery levels, as well as the spatial information of the accumulation and scaling potential of sparingly soluble salts on the membrane surface. The results obtained from the model showed good agreement with the results obtained from the commercial RO design software WAVE. The CFD model was then used to predict the scaling threshold on various positions of a full-scale RO element, at different operating conditions, using parametric simulations based on Central Composite Designs. Outputs from this work not only provide insights into the microscopic flow characteristics of multiple full-scale elements in the RO pressure vessel, but also predicts the position where scaling would occur, at different feed conditions, for any RO products.

Analysis of Concentration Polarisation in Full-Size Spiral Wound Reverse Osmosis Membranes Using Computational Fluid Dynamics.

A three-dimensional model for the simulation of concentration polarisation in a full-scale spiral wound reverse osmosis (RO) membrane element was developed. The model considered the coupled effect of complex spacer geometry, pressure drop and membrane filtration. The simulated results showed that, at a salt concentration of 10,000 mg/L and feed pressure of 10.91 bar, permeate flux decreased from 27.6 L/(m2 h) (LMH) at the module inlet to 24.1 LMH at the module outlet as a result of salt accumulation in the absence of a feed spacer. In contrast, the presence of the spacer increased pressure loss along the membranes, and its presence created vortices and enhanced fluid velocity at the boundary layer and led to a minor decrease in flux to 26.5 LMH at the outlet. This paper underpins the importance of the feed spacer’s role in mitigating concentration polarisation in full-scale spiral wound modules. The model can be used by both the industry and by academia for improved understanding and accurate presentation of mass transfer phenomena of full-scale RO modules by different commercial manufacturers that cannot be achieved by experimental characterization of the mass transfer coefficient or by CFD modelling of simplified 2D flow channels.

Robust Spatial Modeling of Thermodynamic Parameters in a Full-Scale Reverse Osmosis Membrane Channel.

Full-scale reverse osmosis (RO) units usually consist of a set of pressure vessels holding up to six (1 m long) membrane modules in series. Since process parameters and water composition change substantially along the filtration channel in full-scale RO units, relevant thermodynamic parameters such as the ion activities and the osmotic coefficient change as well. Understanding these changes will lead to more accurate fouling prediction and to improvement in process and equipment designs. In this article, a rigorous thermodynamic model for RO concentrates in a full-scale module is developed and presented, which is capable of accounting for such changes. The change in concentrate composition due to permeation of water and ions is predicted locally in the membrane filtration channel. The local ionic composition is used to calculate the local activity coefficient and osmotic coefficient along the membrane channel through the Pitzer model for each modeled anion and cation. The approach developed was validated against related literature data, showing that Pitzer coefficient predictions were satisfactory. The spatial variation model was verified experimentally. It was found under the modeled conditions of high recovery that individual solute activity coefficients could be diminished up to 65%, in our case for sulfate, from their initial value from the membrane inlet to the outlet, and the water osmotic coefficient increased 3% as concentrate salinity increased from the membrane inlet to the outlet. Modeled at moderate recovery, the sulfate still achieved a statistically significant drop of 34% and an opposing trend of a decrease of 0.5% for the osmotic coefficient. These variations in internal water chemistry along the channel can significantly impact predicted recovery, fouling propensity, and permeate quality. Fouling prediction with our approach was also assessed through a theoretical fouling index to demonstrate the significance of ion activity over concentration-based calculations. Additionally, data from a pilot plant RO filtration channel was used to carry out a sensitivity analysis to show the capability of the developed model.

Reactivity of the Polyamide Membrane Monomer with Free Chlorine: Role of Bromide.

Aromatic polyamide-based membranes are widely used for reverse osmosis (RO) and nanofiltration (NF) treatment but degrade when exposed to free chlorine (HOCl/OCl-). The reaction mechanisms with free chlorine were previously explored, but less is known about the role of bromide (Br-) in these processes. Br- may impact these reactions by reacting with HOCl to form HOBr, which then triggers other brominating agents (Br2O, Br2, BrOCl, and BrCl) to form. This study examined the reactivities of these brominating agents with a polyamide monomer model compound, benzanilide (BA), and a modified version of it, N-CH3-BA. The results indicated that all these brominating agents only attacked the aromatic ring adjacent to the amide N, rather than the amide N, different from the previously examined chlorinating agents (HOCl, OCl-, and Cl2) that attacked both sites. Orton rearrangement was not observed. Species-specific rate constants (ki, M-1 s-1) between BA and HOBr, Br2O, Br2, BrOCl, and BrCl were determined to be (5.3 ± 1.2) × 10-2, (1.2 ± 0.4) × 101, (3.7 ± 0.2) × 102, (2.2 ± 0.6) × 104, and (6.6 ± 0.9) × 104 M-1 s-1, respectively, such that kBrCl > kBrOCl > kBr2 > kBr2O > kHOBr. N-CH3-BA exhibited lower reactivity than BA. Model predictions of BA loss during chlorination with varied Br- and/or Cl- concentrations were established. These findings will ultimately enable membrane degradation and performance loss following chlorination in mixed halide solutions to be better predicted during pilot- and full-scale NF and RO treatment.

Cost of fouling in full-scale reverse osmosis and nanofiltration installations in the Netherlands

The economic impact of fouling in spiral wound membranes is not yet well explored. There has been an established assumption that the cost of fouling in membrane processes is significant, but this hypothesis has not been thoroughly evaluated. We conducted an economic analysis on seven full-scale installations, four nanofiltration (NF) and three reverse osmosis (RO), to estimate the cost of fouling in industrial plants. The cost of fouling was calculated in detail, including costs of increase in feed channel pressure drop, water permeability reduction, early membrane replacement, and extensive cleaning-in-place (CIP). The estimated cost of fouling was expressed as a fraction of operational expenses (OPEX) for each plant and the major cost factors in fouling and CIP costs were identified.The selected NF plants were fed with anoxic ground water, while the feed water to RO plants was either surface water or municipal wastewater effluent. All the NF plants produce drinking water, while the RO plants produce demineralized water for industrial applications. We found that the cost of fouling in the RO plants was around 24% of OPEX, while the fouling related costs in NF cases was only around 11% due to the low biofouling potential of the anoxic ground water. The major factor in the cost of fouling is the early membrane replacement cost, followed by additional energy and with only a minor contribution from the cleaning costs. The down-time cost (caused by the interruption of water production during a CIP event) can be the major CIP cost factor for the plants with frequent cleaning events, while the cost of chemicals dominates in the plants with non-frequent CIP. In case of manual cleaning-in-place, the cost of fouling is increased by around 2% for the RO plants with frequent CIP. The manual execution of CIP cleaning is an attention point to reconsider, as the reviewed plants hold an automated CIP cleaning, providing membrane productivity advantages.

Enhanced hydraulic cleanability of biofilms developed under a low phosphorus concentration in reverse osmosis membrane systems

A critical problem in seawater reverse osmosis (RO) filtration processes is biofilm accumulation, which reduces system performance and increases energy requirements. As a result, membrane systems need to be periodically cleaned by combining chemical and physical protocols. Nutrient limitation in the feed water is a strategy to control biofilm formation, lengthening stable membrane system performance. However, the cleanability of biofilms developed under various feed water nutrient conditions is not well understood.This study analyzes the removal efficiency of biofilms grown in membrane fouling simulators (MFSs) supplied with water varying in phosphorus concentrations (3 and 6 μg P·L-1 and with constant biodegradable carbon concentration) by applying hydraulic cleaning after a defined 140% increase in the feed channel pressure drop, through increasing the cross-flow velocity from 0.18 m s-1 to 0.35 m s-1 for 1 h. The two phosphorus concentrations (3 and 6 μg P·L-1) simulate the RO feed water without and with the addition of a phosphorus-based antiscalant, respectively, and were chosen based on measurements at a full-scale seawater RO desalination plant. Biomass quantification parameters performed after membrane autopsies such as total cell count, adenosine triphosphate, total organic carbon, and extracellular polymeric substances were used along with feed channel pressure drop measurements to evaluate biofilm removal efficiency. The outlet water during hydraulic cleaning (1 h) was collected and characterized as well. Optical coherence tomography images were taken before and after hydraulic cleaning for visualization of biofilm morphology.Biofilms grown at 3 μg P·L-1 had an enhanced hydraulic cleanability compared to biofilms grown at 6 μg P·L-1. The higher detachment for biofilms grown at a lower phosphorus concentration was explained by more soluble polymers in the EPS, resulting in a lower biofilm cohesive and adhesive strength. This study confirms that manipulating the feed water nutrient composition can engineer a biofilm that is easier to remove, shifting research focus towards biofilm engineering and more sustainable cleaning strategies.

Cost estimation of landfill leachate treatment by reverse osmosis in a Brazilian landfill.

The reverse osmosis (RO) process has been increasingly applied to landfill leachate treatment. The published literature reports several studies that investigated the technical feasibility of RO. However, information about process costs is scarce. Also, companies that run leachate treatment plants do not provide actual costs. To fill this gap, this study aimed to evaluate the treatment costs of a full-scale RO for the treatment of landfill leachate located in Rio de Janeiro State, Brazil. A procedure was proposed to estimate the capital expenses (CAPEX), operational expenses (OPEX), and specific total treatment cost, the total cost per m3 of treated leachate, of the leachate treatment by membrane process, and the results obtained are discussed. The CAPEX for this full-scale RO was estimated at MUS$ 1.413, and OPEX ranged from US$ 0.132 to US$ 0.265 m-3 per year. The cost of leachate treatment has been estimated at US$ 8.58 m-3 considering the operation of the RO-unit for 20 years after landfill closure.

A generic reverse osmosis model for full-scale operation

Mathematical models can be a powerful tool in the operation of reverse osmosis (RO) facilities which is often challenged by a varying feed water quality. Most models, however, do not consider both full-scale and good modelling practice, which makes them less suited in practice. In this paper, a generic steady state model for RO was set-up and applied to a unique three-year data set from a full-scale RO process according to state-of-the-art good modelling practice. It was found that the model outputs are most sensitive towards the water and the solute permeability, and the feed spacer channel height, and therefore, only these parameters were calibrated. Furthermore, manufacturer's tests do not always reflect the full-scale situation, which highlights the importance of calibration. The model was validated with online conductivity data as input taking into account the uncertainty originating from online sensors, and compared to the commercial software Winflows. Despite the lack of long-term predictive power since fouling was not included, the model with online conductivity data as input showed satisfactory results, i.e. an average deviation from the data of 2.7%, 12.7%, 34.1% and 18.7% for respectively the recovery, the concentrate pressure, the permeate and concentrate solute concentration.

Chemistry of inorganic scaling in full-scale reverse osmosis plants treating brackish groundwater

Abstract An extensive chemical analysis was conducted on water samples and fouled membranes of community Reverse Osmosis plants of Rajasthan, India facing accelerated scaling. Calcium carbonate was the major foulant as evidenced by the rhombohedral crystalline structure with sharp edges in SEM images of membranes of one of the plants while the other membrane had deposits of aragonite having outward-oriented needles. The reverse solubility of CaCO3 with temperature was the major reason behind carbonate scaling as the area witnesses ambient temperatures of more than 40 °C for many months of the year. To further explain the scaling process, a detailed chemical analysis of five recently established plants was carried out and verified by ion balance. It was found that consecutive combination of Ca2+ and Mg2+ with F−, CO32- and SO42- would give the best quantification of scale formation. Extent of CaCO3 scaling was also verified through Langelier Saturation Index and Ryznar Stability Index. The earlier part of this study resulted in promotion of the use of antiscalants in these plants, leading to sharp increase in the membrane life. Therefore, reject and raw samples were analyzed in presence and absence of antiscalant in the feed supply. The molar ratios of ions clearly revealed the inefficiency of antiscalant in arresting the growth of sulfate scales. As a result, many other inorganic deposits besides carbonates require further research inputs.

A comparison between chemical cleaning efficiency in lab-scale and full-scale reverse osmosis membranes: Role of extracellular polymeric substances (EPS)

Chemical cleaning is vital for the optimal operation of membrane systems. Membrane chemical cleaning protocols are often developed in the laboratory flow cells (e.g., Membrane Fouling Simulator (MFS)) using synthetic feed water (nutrient excess) and short experimental time of typically days. However, full-scale Reverse Osmosis (RO) membranes are usually fed with nutrient limited feed water (due to extensive pre-treatment) and operated for a long-time of typically years. These operational differences lead to significant differences in the efficiency of chemical Cleaning-In-Place (CIP) carried out on laboratory-scale and on full-scale RO systems. Therefore, we investigated the suitability of lab-scale CIP results for full-scale applications. A lab-scale flow cell (i.e., MFSs) and two full-scale RO modules were analysed to compare CIP efficiency in terms of water flux recovery and biofouling properties (biomass content, Extracellular Polymeric Substances (EPS) composition and EPS adherence) under typical lab-scale and full-scale conditions. We observed a significant difference between the CIP efficiency in lab-scale (~50%) and full-scale (9–20%) RO membranes. Typical biomass analysis such as Total Organic Carbon (TOC) and Adenosine triphosphate (ATP) measurements did not indicate any correlation to the observed trend in the CIP efficiency in the lab-scale and full-scale RO membranes. However, the biofilms formed in the lab-scale contains different EPS than the biofilms in the full-scale RO modules. The biofilms in the lab-scale MFS have polysaccharide-rich EPS (Protein/Polysaccharide ratio = 0.5) as opposed to biofilm developed in full-scale modules which contain protein-rich EPS (Protein/Polysaccharide ratio = 2.2). Moreover, EPS analysis indicates the EPS extracted from full-scale biofilms have a higher affinity and rigidity to the membrane surface compared to EPS from lab-scale biofilm. Thus, we propose that CIP protocols should be optimized in long-term experiments using the realistic feed water.

Long-term performance and economic evaluation of full-scale MF and RO process – A case study of the changi NEWater Project Phase 2 in Singapore

The Changi NEWater Project Phase 2 purifies the secondary effluent of an urban sewage treatment plant using a two-stage microfiltration membrane (MF) and reverse osmosis (RO) process to produce NEWater for industrial use and to supplement drinking water sources. The total recovery rate of the system was 73.5%. The turbidity removal rate of the MF unit was 93.4% and the silt density index (SDI) value of MF product water was stable below 3. The performance of the pretreatment unit met the design standards. After reverse osmosis treatment, the total organic carbon removal rate was 99.4% and the desalination rate was greater than 99%. The quality of the NEWater was superior to the drinking-water standards of Singapore and the World Health Organization. Because of its advanced automatic control system, the Changi NEWater Project Phase 2 required a staff of only 15 operation and management personnel. The total operational cost was between 0.08 and 0.15 $/m³, of which energy consumption, chemical consumption, maintenance costs, and labor costs accounted for 62.9%, 20.2%, 7.3% and 9.6%, respectively. The energy consumption was between 0.6 and 0.8 ​kWh/m³. The Changi NEWater Project Phase 2 represents a milestone in water cycle engineering practice because of its excellent process design, superior product water quality, high degree of automatic control, and low operational energy consumption.

Analysis of long-term performance of full-scale reverse osmosis desalination plant using artificial neural network and tree model

The reverse osmosis (RO) technology is currently the leading desalination method. However, until recently, application of RO technology on a large scale has been primarily limited by membrane fouling. The mechanism of fouling is complex, which is not well understood in full-scale plants. Although many studies about modeling and prediction of fouling have been done, in most cases, the experimental data set of lab or pilot scale systems, which may not show fouling characteristics well in full-scale systems were used. In this study, both artificial neural network (ANN) model and tree model (TM) was evaluated to analyze long-term performance of full scale reverse osmosis desalination plant. The results of application of the ANN and TM indicated high correlation coefficients between the measured and simulated output variables. However, it is not easy to use ANN for the full scale plant operation because the final model is not expressed as a form of mathematical functions. TM has advantages over ANN because the model can be obtained as forms of simple function and it showed reasonably high &lt;i&gt;R&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt;. Therefore, TM is shown to be more adequate than ANN for developing models in which the full-scale RO plant data is considered as an input.

Pilot-Scale Assessment of Urea as a Chemical Cleaning Agent for Biofouling Control in Spiral-Wound Reverse Osmosis Membrane Elements.

Routine chemical cleaning with the combined use of sodium hydroxide (NaOH) and hydrochloric acid (HCl) is carried out as a means of biofouling control in reverse osmosis (RO) membranes. The novelty of the research presented herein is in the application of urea, instead of NaOH, as a chemical cleaning agent to full-scale spiral-wound RO membrane elements. A comparative study was carried out at a pilot-scale facility at the Evides Industriewater DECO water treatment plant in the Netherlands. Three fouled 8-inch diameter membrane modules were harvested from the lead position of one of the full-scale RO units treating membrane bioreactor (MBR) permeate. One membrane module was not cleaned and was assessed as the control. The second membrane module was cleaned by the standard alkali/acid cleaning protocol. The third membrane module was cleaned with concentrated urea solution followed by acid rinse. The results showed that urea cleaning is as effective as the conventional chemical cleaning with regards to restoring the normalized feed channel pressure drop, and more effective in terms of (i) improving membrane permeability, and (ii) solubilizing organic foulants and the subsequent removal of the surface fouling layer. Higher biomass removal by urea cleaning was also indicated by the fact that the total organic carbon (TOC) content in the HCl rinse solution post-urea-cleaning was an order of magnitude greater than in the HCl rinse after standard cleaning. Further optimization of urea-based membrane cleaning protocols and urea recovery and/or waste treatment methods is proposed for full-scale applications.

Genome-resolved metagenomic analysis reveals roles of microbial community members in full-scale seawater reverse osmosis plant

Biofouling of Reverse Osmosis (RO) membrane is a significant issue for the water treatment industry. In this study, we apply the metagenomic shot-gun sequencing technology to characterise the composition and functional potential of the microbial community in a full-scale RO plant, at different stages of seawater treatment. We find Proteobacteria, Bacteroidetes and Planctomycetes to be the most abundant bacterial phyla. The genetic potential of the RO membrane microbial community shows the enrichment of genes involved in biofilm formation, representing the selective pressure of the biofilm formation process. We recover 31 metagenome-assembled genomes (MAGs) from intake (raw seawater), fouled RO membranes (leading and middle RO module) and brine reject water. A total of 25 MAGs are recovered from the biofilm samples (leading and middle RO modules), with 9 of them (36%) belonging to Planctomycetes. We investigate all 25 MAGs for genes (pili, flagella, quorum sensing, quorum quenching and nitrate reduction) that play an important role in biofilm formation and sustenance of cells. We show that Planctomycetes contain genes for the formation of flagella and pili, and the reduction of nitrate. Although genes for quorum sensing are not detected, quorum quenching genes are identified in the biofilm MAGs. Our results show that Planctomycetes, along with other microbes, play an important role in the formation and sustenance of biofilms on seawater RO membranes.

N-nitrosomorpholine in potable reuse

As potable reuse guidelines and regulations continue to develop, the presence of N-nitrosamines is a primary concern because of their associated health concerns. In this study, bench-, pilot-, and full-scale tests were conducted to focus on the occurrence and treatment of N-nitrosomorpholine (NMOR) in United States (U.S.) potable reuse systems. Out of twelve U.S. wastewater effluents collected, ambient NMOR was detected in eleven (average = 20 ± 18 ng/L); in contrast, only two of the thirteen surface water and stormwater samples had NMOR. Across all of these samples maximum formation potential by chloramination produced an average increase of 3.6 ± 1.8 ng/L. This result underscores the need to understand the sources of NMOR as it is not likely a disinfection byproduct and it is not known to be commercially produced within the U.S. At the pilot-scale, three potable reuse systems were evaluated for ambient NMOR with oxidation (i.e., chlorination and ozonation), biofiltration, and granular activated carbon (GAC). Both pre-oxidation and biofiltration were ineffective at mitigating NMOR during long-term pilot plant operation (at least eight-months). GAC adsorbers were the only pilot-scale treatment to remove NMOR; however, complete breakthrough occurred rapidly from <2000 to 10,000 bed volumes. For comparison, a full-scale reverse osmosis (RO) potable reuse system was monitored for a year and confirmed that RO effectively removes NMOR. Systematic bench-scale UV-advanced oxidation experiments were undertaken to assess the mitigation potential for NMOR. At a fluence dose of 325 ± 10 mJ/cm2, UV alone degraded 90% of the NMOR present. The addition of 5 mg/L hydrogen peroxide did not significantly decrease the UV dose required for one-log removal. These data illustrate that efficient NMOR removal from potable reuse systems is limited to RO or UV treatment.