Reverse osmosis treatment of blow-down water for beneficial reuse and sustainable power generation

The project objective was to develop a cooling blowdown water (BDW) treatment process utilizing produced water (PW) and low-grade heat to maximize water reuse and saleable by-product generation while reducing chemical and energy footprints of the treatment. The proposed treatment process consists of mixing, softening, organics and suspended solids removal, reverse osmosis (RO), thermal desalination, and brine electrolysis. BDW samples collected from a local coal-fired power plant and PW samples from two shale gas production wells were used in this study. Each treatment unit was first designed and tested to quantify its treatment efficiency, and its chemical and energy requirements. In addition, a process model was developed and model simulations were conducted based on the experimental results and literature data to optimize the treatment process. A techno-economic analysis was conducted to quantify chemical and energy savings as well as production of 10-lb brine as a saleable product. With the field-collected BDW and PW samples, mixing experiments determined a volumetric mixing ratio 10:1 (BDW:PW) resulted in the best performance of multivalent ions removal and largest chemical savings for softening. Softening of the BDW/PW mixtures using alkaline chemicals (Na2CO3 and NaOH) achieved 95%-100% removal of scaling-forming cations (Ca, Mg, Fe, Ba, Sr) and 60% of silicon, and 10% of total organic carbon (TOC). The mixing and softening treatments yielded an effluent with total dissolved solids (TDS) concentration of 23 g/L. Activated carbon (AC) filtration removed TOC to a low level (< 3 mg/L) and further removed remaining scale-forming divalent metals and silica from the softened water. The AC filtration resulted in a slight reduction of TDS from 23 g/L to 20 g/L, leaving behind only mostly monovalent ions (i.e., sodium and chloride) in the filtered water. These pretreatments yielded a feed water that met the criteria of the downstream reverse osmosis (RO) to prevent membrane fouling. A cross-flow RO system was used to further concentrate the TDS of the AC effluent. Various factors including TDS, pH, and applied pressure were examined and optimal conditions were determined for the co-treatment process. An integrated process consisting of mixing, softening, AC filtration and RO was used to treat a continuous flow (0.25 – 1.2 L/min, or 0.07 – 0.32 gpm) and successfully generated RO permeate as product water (TDS < 0.5 g/L) for reuse in cooling operation, and a concentrate (TDS ~ 45 g/L) to be further treated in a thermal desalination unit. These flow rates meet the FOA’s criterion of 0.01 – 1 gpm. Overall, the co-treatment of BDW/PW allowed shorter ramp-up time compared to treatment of BDW alone. It resulted in 40% and 55% savings of Na2CO3(s) and NaOH, respectively, compared to treating the BDW and PW individually for the same level of softening. The co-treatment also resulted in a 29% energy saving compared to treatment of BDW only for the level of TDS concentration. A thermal desalination system was designed using CFD simulations and manufactured in the WVU Innovation Hub for further treatment of the RO concentrate to generate 10-lb brine. The system has a design flow rate of 2 gpm and has been successfully tested. A bench-scale brine electrolysis system was developed for on-site generation of chlorine/hypochlorite (Cl2/OCl-) and caustic soda (NaOH) as useful chemicals for the co-treatment process. Using salt solutions (0.5 M and 1 M), the system achieved faradaic efficiencies of 93%-97% and 70%-77% for caustic soda and chlorine/hypochlorite generation, respectively. An economic analysis showed that the electricity costs for on-site generation of these chemicals were significantly lower than the chemical prices offered by suppliers. An industrial-scale process model consisting of mixing, softening, AC filtration, RO, thermal desalination, and brine electrolysis was developed using the Aspen Plus V9 in conjunction with Aspen Custom Modeler V9. The model serves as a solvable Aspen Plus model and as basis to form the costing infrastructure. In addition, techno-economic analysis considering capital, operating, and transportation costs was conducted. An optimization solution showed that produced water for mixing is still advantageous in low quantities. The optimum solution approaches a leveled cost of water (LCW) of 2 $/m3 which becomes cost competitive with nominal water treatment prices.

Hybrid membrane system for desalination and wastewater treatment : Integrating forward osmosis and low pressure reverse osmosis

The reverse osmosis (RO) system is widely applied to produce reclaimed water for high-standard industrial use. Chlorine disinfection is the main biofouling control method in the RO systems for wastewater reclamation. However, researchers reported the adverse effects of chlorine disinfection which aggravated biofouling in laboratory-scale RO systems. In this study, four parallel 4-inch spiral wound RO membranes were used to study the effect of chlorine on biofouling in a pilot-scale RO system. The free chlorine dosages in four experimental groups were 0, 1, 2 and 5 mg/L, respectively. After continuous chlorination and dechlorination, the feed water entered the RO system. It was found that chlorine pretreatment caused a 1.9–36.7% increase in relative feed water pressure of the RO system, suggesting that chlorine aggravated the membrane fouling in the pilot-scale RO system. The microbial community structures of living bacteria in the feed water of the RO system were determined by the PMA (propidium monoazide)-PCR method and showed that the relative abundance of chlorine-resistant bacteria (CRB) was significantly increased after disinfection. Nine major genera which maintained higher relative abundance in experimental groups with high chlorine dosage were considered as possible key species causing membrane fouling, including Pedobacter, Clostridium and Bradyrhizobium.

During the last decade, water reuse has been widely recognized in many regions of the world. Fouling of ceramic membranes, especially hydraulically irreversible fouling, is a critical aspect affecting the operational cost and energy consumption in water treatment plants. In addition, the reverse osmosis (RO) membranes, that are often used for water reuse plant, frequently face the problem of bio-fouling. The main objective of this thesis is to develop innovative applications of the ceramic ultra- and nanofiltration membranes for water reuse purpose. Improving RO pre-treatment using tight ceramic UF or ceramic NF To prevent the biofouling often relies on pre-treatment technology, since frequent chemical cleaning does not only increase the operational cost but also destructs the polyamide skin layer of RO membrane. A good RO pre-treatment should aim at both particulate removal to release clogging in the module, and organic carbon or nutrient limitation to release biofouling in the RO. Intense pre-treatment has been applied to alleviate the biofouling in RO membranes during wastewater reclamation. Whereas, current filtration-based pre-treatment processes cannot adequately prevent biofouling due to their poor removal of nutrients and organic carbon from feed water. The tight ceramic UF and ceramic NF membranes can potentially be deployed for RO pre-treatment in order to constrain the biofouling in RO by removing the organic carbon and phosphate (as nutrient). Theoretical research on the phosphate rejection by the charged tight ceramic UF was conducted, and the results have emphasized the importance of electrostatic interactions between the negatively charged membrane and the phosphate. The results indicate that the rejection of phosphate is dependent on the pH of the solutions and the results can be interpreted by Donnan exclusion and formation of an electrical double layer in the membrane pores. The greater phosphate rejection due to electrostatic repulsion results from a stronger overlapping of the electrical double layers in membrane pores. A Debye ratio (ratio of the Debye length to the pore radius) can be used to evaluate double layer overlapping in tight UF membranes. However, the membrane fouling caused by organic matter and cations can potentially influence the phosphate rejection by the tight ceramic UF. The phosphate rejection appeared to be linearly correlated to the surface charge of the organics in the feed waters. In addition, the biopolymers in WWTP effluent water organic matter (EfOM) can adsorb phosphate with the bridging of multivalent cations, which leads to higher phosphate rejection by the EfOM-fouled membranes than humics-fouled membranes. Sewer mining using ceramic nanofiltration Ceramic NF can be used for direct municipal sewage filtration aiming at energy, fresh water and nutrient recovery, so called sewer mining. Over 80% of organic carbon substrates and 90% of dissolved phosphate were rejected by a ceramic NF membrane (450 Da), but only 10% for ammonia. Concentration of the municipal sewage using ceramic NF increases the efficiency in the energy and nutrient recovery during the anaerobic digestion. The fouling on the ceramic NF membranes during sewage filtration can be suppressed by chemical cleaning with NaClO (0.1%) and HCl (0.1 mol L-1), while the cleaning of polymeric NF membranes is reportedly far more difficult. As such, sewer mining with ceramic NF is believed as an innovative and viable technology for energy, fresh water and nutrient recovery.

A South African developed tubular cellulose acetate reverse osmosis (RO) system from Membratek (Pty) Ltd was evaluated for the treatment of nickel rinse water and mixed electroplating effluent. Spiral wrap polyamide (DuPont) and thin film composite (FilmTec) membranes were evaluated for cadmium and chromium rinse water treatment, respectively. Preliminary laboratory results have shown that nickel rinse water should be treated economically with tubular RO. Approximately 92% of the rinse water could be recovered for reuse. The RO brine is of suitable quality for reuse in the electroplating process. Plant payback for a 5 m3/h nickel/water recovery RO plant was determined to.be 1.3 years (approximately 2 000 mg/ℓ Ni in feed). No severe membrane fouling was encountered during the investigation. However, membrane fouling can affect the process adversely and this will be studied further. Approximately 90% water, of suitable quality for reuse as rinse water in the plating process, could be recovered from mixed electroplating effluent. Effluent volume for subsequent treatment with lime was significantly reduced. It may also be possible to treat cadmium and chromium rinse waters with RO. Approximately 92% and 91% water, of suitable quality for reuse as rinse water, could be recovered with spiral wrap polyamide and thin film composite membranes, respectively. Membrane fouling was experienced during cadmium rinse water treatment. However, water flux could be restored by chemical cleaning. Very little fouling was experienced during chromium rinse water treatment. The fouling potential of the rinse waters for the membranes and subsequent cleaning procedures will be studied further. Preliminary results have shown that payback for 5 m3/h RO cadmium/water and RO chromium/water recovery plants should be 3 and 7 years, respectively. Reverse osmosis has been shown to be a very effective technology for water and chemical recovery and for effluent volume reduction. The electroplating industry causes serious pollution and wastes large volumes of water. Consequently, RO is a technology that may be applied to good effect in the electroplating industry to control pollution and to save scarce water.

Simple program for the estimation of scaling potential in RO systems

Discussion on calculation of maximum water recovery in nanofiltration system

Fouling reduction in MBR-RO processes: the effect of MBR F/M ratio

Resource recovery from liquid digestate of swine wastewater by an ultrafiltration membrane bioreactor (UF-MBR) and reverse osmosis (RO) process

Membrane Filtration technique is being accepted worldwide as an environment friendly and energy efficient technique in Desalination Industry as compared to Thermal Desalination techniques. However, the performance of membranes which include permeate flux and rejection is affected by the membrane fouling. The properties of membrane and surface features such as porous structure, hydrophilicity/hydrophobicity charge, polymer characteristics, surface roughness determine the fouling potential of the membrane. The hydrophilic and smooth membrane surface is usually considered desirable in tackling membrane fouling issues. Therefore, many studies have focused on to enhance surface characteristics of membranes by surface coating with polymers and nanomaterials. Since, membrane coating is not done during fabrication of the most commercially available membranes, therefore, it is also important to determine the surface features of the commercially available membranes to investigate their membrane fouling potential. Thus, the objectives of this study were (1) to perform membrane surface characterization of commercial Reverse Osmosis (RO) and Nanofiltration (NF) membranes using techniques such as SEM, AFM, FTIR and XPS; (2) to measure hydrophilicity/hydrophobicity of commercial RO and NF membranes through water contact angle measurement using sessile drop method and (3) to measure the flux and percentage rejection of NF and RO membranes using Dead end filtration technique. Here, the characterization of membrane surface in terms of surface roughness, using SEM and AFM, showed that the commercial RO membrane had more ridge and valley structures and higher average surface roughness i.e. 71.24 nm as compared to NF membranes (6.63 nm). In addition, water contact angle measurements showed that the NF membrane was more hydrophilic as compared to RO membrane. The average contact angle found for RO membrane was 59.94°. On the other hand, it was observed that NF membrane is extremely hydrophilic in nature. Due to which, contact angle value was not obtained for most of the runs. The droplet could diffuse in less than 5 seconds. In addition, the dead-end filtration experiments showed that the RO membrane had much lower flux as compared to NF membrane. This can be associated with the pore structure of these membranes. Since, the NF membrane has porous structure, in oppose to RO membrane, the flux of the NF membrane is usually higher than the RO membranes. As the membrane surface roughness and hydrophobicity makes it more susceptible to the fouling leading to reduction in membrane flux and performance, it can be concluded from this study that there is a need for surface coating of RO membrane with suitable nanomaterials such as graphene oxide to improve its hydrophilicity and surface smoothness. This will eventually make the membrane more resistant to membrane fouling and will establish the use of membrane filtration technique in desalination industry in Qatar in the future. Microorganisms have been isolated from Gulf sea water, identified and differentiated and are being used to study the biofouling of RO and NF membranes, that would be coated to limit the fouling problems. Acknowledgement: This research was made possible by NPRP grant # [9-318-1-064] from the Qatar National Research Fund (a member of Qatar Foundation). The findings achieved herein are solely the responsibility of the author[s].

Electromagnetic field (EMF) is a cost-effective, simple, and energy-efficient method for scale control in reverse osmosis (RO) systems. However, its effects on gypsum and silica scaling, as well as the underlying mechanisms, remain poorly understood. This study systematically investigates the effects of EMF treatment on gypsum and silica scaling in RO systems, utilizing synthetic brackish water and natural RO concentrate (ROC) from a desalination facility. For gypsum, EMF changes the crystal morphology, resulting in the formation of a porous, less compact scaling layer. It is more readily removed through hydraulic flushing (HF), enhancing scaling reversibility and water recovery. In the case of silica scaling, EMF promotes homogeneous polymerization in the bulk solution, producing larger silica particles that inhibit the formation of a dense, cross-linked gel layer on the membrane surface, mitigating flux decline. This study thus demonstrates EMF's effectiveness in controlling gypsum scaling in undersaturated feedwaters when combined with HF and in mitigating silica scaling under both HF and non-HF conditions for supersaturated feedwaters. These findings underscore EMF's versatility as a nonchemical approach for scale control in RO desalination and show its substantial potential to enhance membrane performance and operational efficiency in real-world water treatment applications.

Membranes are widely applied in water and waste water treatment as they provide an absolute barrier against the contaminants. Membranes are offered in wide pore size range and they are applied vastly due to their versatile and cost effective operation in dealing with wide range of streams. However, membranes, like any other filtration systems, suffer from fouling. Fouling layer, accumulation of rejected materials over time on membrane surface, is often called the main bottleneck of membrane processes. Fouling formation reduces water flux, increases energy consumption and leads to the early membrane replacement. To better control and mitigate fouling layer formation, better understanding of fouling mechanism and properties are required. Fouling properties can be categorized into hydraulic properties, mechanical properties, structural properties, chemical properties. These properties can be impacted by operational conditions, feed water quality and membrane properties. Moreover, these properties influence membrane performance parameters such as water flux, energy consumption and eventually the plant expenses. Therefore, the fouling properties, their inter-relations, their impacts on performance parameters should be further studied. We used novel modelling techniques and experimental measurements in laboratory and full-scale plants to study fouling properties and their impacts on membrane performance parameters. We also discussed the opportunities and challenges for future fouling study.Chapter 2. To evaluate the relation between structural, hydraulic and mechanical properties of fouling layer in the membrane systems, a novel method to extract these properties was developed to extracted fouling properties in a non-destructive and in-situ technique. The performance parameters of a dead-end UF system with integrated OCT imaging (in-situ) was coupled with a fully-coupled fluid-structural interaction (FSI) model. The dead-end UF was operated under a compression-relaxation cycle to evaluate how fouling properties changes under different applied pressure. Several mechanical models were evaluated to find the most suitable mechanical model to explain the fouling layer behaviour under compression-relaxation cycle in the dead-end UF. The results indicate that the hydraulic resistance of homogeneous biofilms under UF was much more affected by change in permeability than by the fouling layer thickness. Interestingly, we also found that even a poroelastic model (relatively simple model) can fairly good explain behaviour of the fouling layer in this study under different applied pressures. Compression of the fouling layer in UF systems can significantly increase hydraulic resistance of the membrane systems. In Chapter 2, a new technique was developed to extract fouling properties of the smooth surface biofilms. In Chapter 3 the new technique was further expanded to extract the mechanical properties of rough surface fouling layer under dead-end UF. We observed for the fouling layer which is fed with real surface water (i.e., river water), a dual-layer fouling structure with a thin and dense base layer and a thick and porous top layer could best explain the observed results. We also introduced a new fouling structure indicator, the fraction of exposed base layer, as a good indicator in the determination of water flux in UF systems.In Chapter 4 the chemical properties of fouling layer (e.g., composition) and their impacts on chemical cleaning efficiency in Reverse Osmosis (RO) systems were evaluated. Chemical cleaning protocols (often referred as CIP protocols) are usually developed under laboratory conditions (synthetic feed water, short-term experiments) and then are applied in the full-scale RO installations. This often leads to significant differences in CIP efficiency in the lab and full-scale installations. Thus, we compared the fouling layer properties and CIP efficiency of typical laboratory conditions RO and several full-scale RO plants. The results show that CIP efficiency in the full-scale RO plants are much lower than lab conditions RO. Later, we correlated such differences in CIP efficiency to their significantly different extracellular polymeric substance (EPS) properties. The EPS extracted from lab RO had different composition and adherence properties than the EPS extracted from full-scale RO. Therefore, we concluded that CIP protocols should not be developed under lab conditions. In the Chapter 5 we suggested a new method to better develop CIP protocols and study fouling properties with more industrial applications. We installed several new RO modules in the full-scale installation and they were operated for 30 days under identical conditions as the full-scale installation. Later, the fouling properties and CIP efficiency (in-situ measurement of permeability and pressure drop recovery) were compared between new RO modules (after 30 days of operation) and old RO modules (&amp;gt;2 years of operations). The new proposed fouling simulation method show promising results in both CIP efficiency results and fouling properties. Although fouling is inevitable part of filtration processes, its economic impacts on membrane systems is not well evaluated. In Chapter 6 cost of fouling in several RO and NF systems in The Netherlands has been calculated using plant performance data. All the cost factors contributing to cost of fouling such as CIP cost, energy cost, down cost were considered. We observed that for the RO plants, around a quarter of OPEX is caused by fouling, as oppose of around 10% for anoxic NF plants. The most important factor in the cost of fouling was considered the early membrane replacement cost, followed closely by additional energy cost. CIP costs have a minor contribution to the overall cost of fouling. Reuse of municipal wastewater effluent is part of solution to deal with water scarcity challenges. In Chapter 7 a fit-for-purpose approach to water reuse was proposed. We developed full techno-economic analysis on membrane-based Water reuse plant for municipal wastewater treatment effluent in the Netherlands. The impact of fouling and its properties and fouling cost have been integrated in all the membrane systems. A novel approach on design of water reuse plant has been offered to not only inherently reduce fouling impact but also increase plant robustness and water recovery. In chapter 8 a summarized and generalized conclusions of the previous chapters is presented. We also presents our suggestions and opportunities for the future membrane and fouling research.

This thesis presents a comprehensive research report on microbiological aspects of biofouling occurrence in full-scale reverse osmosis (RO) systems. Biofouling is a process in which microorganisms attach to membranes and develop into a thick film that can choke the entire RO system. Management of this problem requires basic understanding of the mechanism of this phenomenon. The basic questions of this PhD research project therefore addressed the origin, succession and spatiotemporal development of biofilms in full-scale RO systems, in particular in relation to operational aspects of RO systems. The multifaceted research strategy involving acquisitions of representative samples and use of many molecular and microscopic analysis techniques in parallel was employed. The investigation showed that biofilms are able to grow on any surface in a full-scale RO plant. This gives local niches for detachment of biomass, either as single cells or cell clumps, and results in a spreading of bacteria to the further stages of the plant. In the RO membrane modules, the enriched bacteria might more easily colonise the surfaces since they will be better adapted to growth in the system than bacteria present in the feed water. Initially, the single cell colonizers (sphingomonads) form a number of flat and abundantly EPS-embedded cell monolayers over the entire membrane surface. The clumps-associated pioneers (mainly Beta- and Gammaproteobacteria) appear to be trapped mainly in the first part of the module, most likely due to a filtering action of the spacer. In time, these bacteria develop in pillar-like structures and slowly spread throughout the whole membrane module on top of the established sphingomonads biofilm. The secondary colonisers (bacteria and eukaryotes) occur in the resulting biofilm formations. Although composition of the biofilm microbial community undergoes a succession in time, the architecture of an established biofilm appears to be rather stable. Conventional treatment of RO membrane modules with chemicals did not lead to cleaning: the sphingomonads cells can be detected under the collapsed but obviously not removed biofilm EPS matrix. After cleaning, the biofouling layer seemed to grow faster (within 6 days) than a fresh biofilm (16 days). To conclude, biofouling is a complex phenomenon with two appearances: a fouling layer on the membrane limiting the water flux and a fouling layer on the spacer limiting the water flow through the spacer channel and resulting in an increased pressure drop. It became clear that cleaning strategies should focus more on the removal of accumulated biomass and not only on the killing of cells. Moreover, the basal Sphingomonas layer requires further research to appropriately control biofouling in RO systems. It might also be possible to design the RO - membrane module in a different manner, leading to a different biofilm morphology which gives less rise to operational problems.

The fate of Transparent Exopolymer Particles (TEP) in integrated membrane systems: Removal through pre-treatment processes and deposition on reverse osmosis membranes

This paper presents a case study of a natural gas production site covering various technical issues related to selection of an appropriate Reverse Osmosis (RO) system. The long-term field experience indicates the necessity of the selection of appropriate pretreatment systems for fouling-free RO operational conditions. The produced water has a variety of impurities such as oil and grease, process chemicals used for corrosion and scaling control, and dehydration of natural gas, etc. This situation leads to a complicated and extremely difficult task for a membrane specialist to design RO systems, especially the pre-treatment section. Here as part of the pretreatment selection, two types of UF membrane modules viz. spiral wound and hollow fibre, with MWCO of 8000 and 50,000 Dalton respectively, were tested in parallel with NF membranes of the spiral wound type with MWCO 200 Dalton. The UF permeate is used as feed for RO compatibility testing. Both configurations of UF failed to be compatible, due to irreversible fouling of the RO membrane. The NF membrane, however, showed interesting results, due to membrane stability in terms of cleaning and fouling. The NF plant with 50% capacity gave a recovery of 75% and the RO plant gave a recovery of 60% versus the expected 92–95%. The long-term tests have indicated that the reminder of the membranes could be installed to achieve full capacity of the plant. This study also demonstrates the importance of selection of proper pre-treatment set-up for the RO system design.