High-pressure Membrane Research Articles

Pilot study for the treatment of sodium and fluoride-contaminated groundwater by using high-pressure membrane systems

High-pressure membrane process is one of the cost-effective technologies for the treatment of groundwater containing excessive dissolved solids. This paper reports a pilot study in treating a typical groundwater in Huaibei Plain containing excessive sodium, sulfate and fluoride ions. Three membrane systems were set up and two brands of reverse osmosis (RO), four low-pressure RO (LPRO) and one tight nanofiltration (NF) membranes were tested under this pilot study. An apparent recovery rate at about 75% was adopted. Cartridge filtration, in combination with dosing antiscalent, was not sufficient to reduce the fouling potential of the raw water. All RO and LPRO systems (except for the two severely affected by membrane fouling) demonstrated similar rejection ratios of the conductivity (∼98.5%), sodium (∼98.5%) and fluoride (∼99%). Membrane fouling substantially reduced the rejection performance of the fouled membranes. The tight NF membrane also had a good rejection on conductivity (95%), sodium (94%) and fluoride (95%). All membranes rejected sulfate ion almost completely (more than 99%). The electricity consumptions for the RO, LPRO and NF systems were 1.74, 1.10 and 0.72 kWh·m−3 treated water, respectively. The estimated treatment costs by using typical RO, LPRO and tight NF membrane systems were 1.21, 0.98 and 0.96 CNY·m−3 finished water, respectively. A treatment process consisting of either LPRO or tight NF facilities following multi-media filtration was suggested.

Characterisation of algal organic matter produced by bloom-forming marine and freshwater algae

Algal blooms can seriously affect the operation of water treatment processes including low pressure (micro- and ultra-filtration) and high pressure (nanofiltration and reverse osmosis) membranes mainly due to accumulation of algal-derived organic matter (AOM). In this study, the different components of AOM extracted from three common species of bloom-forming algae (Alexandrium tamarense, Chaetoceros affinis and Microcystis sp.) were characterised employing various analytical techniques, such as liquid chromatography – organic carbon detection, fluorescence spectroscopy, fourier transform infrared spectroscopy, alcian blue staining and lectin staining coupled with laser scanning microscopy to indentify its composition and force measurement using atomic force microscopy to measure its stickiness. Batch culture monitoring of the three algal species illustrated varying characteristics in terms of growth pattern, cell concentration and AOM release. The AOM produced by the three algal species comprised mainly biopolymers (e.g., polysaccharides and proteins) but some refractory compounds (e.g., humic-like substances) and other low molecular weight acid and neutral compounds were also found. Biopolymers containing fucose and sulphated functional groups were found in all AOM samples while the presence of other functional groups varied between different species. A large majority (>80%) of the acidic polysaccharide components (in terms of transparent exopolymer particles) were found in the colloidal size range (<0.4 μm). The relative stickiness of AOM substantially varied between algal species and that the cohesion between AOM-coated surfaces was much stronger than the adhesion of AOM on AOM-free surfaces. Overall, the composition as well as the physico-chemical characteristics (e.g., stickiness) of AOM will likely dictate the severity of fouling in membrane systems during algal blooms.

Effects of different pretreatments on the performance of ceramic ultrafiltration membrane during the treatment of oil sands tailings pond recycle water: A pilot-scale study

Membrane filtration is an effective treatment method for oil sands tailings pond recycle water (RCW); however, membrane fouling and rapid decrease in permeate flux caused by colloids, organic matter, and bitumen residues present in the RCW hinder its successful application. This pilot-scale study investigated the impact of different pretreatment steps on the performance of a ceramic ultrafiltration (CUF) membrane used for the treatment of RCW. Two treatment trains were examined: treatment train 1 consisted of coagulant followed by a CUF system, while treatment train 2 included softening (Multiflo™ system) and coagulant addition, followed by a CUF system. The results indicated that minimum pretreatment (train 1) was required for almost complete solids removal. The addition of a softening step (train 2) provided an additional barrier to membrane fouling by reducing hardness-causing ions to negligible levels. More than 99% removal of turbidity and less than 20% removal of total organic carbon were achieved regardless of the treatment train used. Permeate fluxes normalized at 20 °C of 127–130 L/m2 h and 111–118 L/m2 h, with permeate recoveries of 90–93% and 90–94% were observed for the treatment trains 1 and 2, respectively. It was also found that materials deposited onto the membrane surface had an impact on trans-membrane pressure and influenced the required frequencies of chemically enhanced backwashes (CEBs) and clean-in-place (CIP) procedures. The CIP performed was successful in removing fouling and scaling materials such that the CUF performance was restored to baseline levels. The results also demonstrated that due to their low turbidity and silt density index values, permeates produced in this pilot study were suitable for further treatment by high pressure membrane processes.

Influence of water matrix on the retention of pharmaceuticals by high-pressure membrane filtration

Influence of water matrix on the retention of pharmaceuticals by high-pressure membrane filtration

Growth of anaerobic methane-oxidizing archaea and sulfate-reducing bacteria in a high-pressure membrane capsule bioreactor.

Communities of anaerobic methane-oxidizing archaea (ANME) and sulfate-reducing bacteria (SRB) grow slowly, which limits the ability to perform physiological studies. High methane partial pressure was previously successfully applied to stimulate growth, but it is not clear how different ANME subtypes and associated SRB are affected by it. Here, we report on the growth of ANME-SRB in a membrane capsule bioreactor inoculated with Eckernförde Bay sediment that combines high-pressure incubation (10.1 MPa methane) and thorough mixing (100 rpm) with complete cell retention by a 0.2-m-pore-size membrane. The results were compared to previously obtained data from an ambient-pressure (0.101 MPa methane) bioreactor inoculated with the same sediment. The rates of oxidation of labeled methane were not higher at 10.1 MPa, likely because measurements were done at ambient pressure. The subtype ANME-2a/b was abundant in both reactors, but subtype ANME-2c was enriched only at 10.1 MPa. SRB at 10.1 MPa mainly belonged to the SEEP-SRB2 and Eel-1 groups and the Desulfuromonadales and not to the typically found SEEP-SRB1 group. The increase of ANME-2a/b occurred in parallel with the increase of SEEP-SRB2, which was previously found to be associated only with ANME-2c. Our results imply that the syntrophic association is flexible and that methane pressure and sulfide concentration influence the growth of different ANME-SRB consortia. We also studied the effect of elevated methane pressure on methane production and oxidation by a mixture of methanogenic and sulfate-reducing sludge. Here, methane oxidation rates decreased and were not coupled to sulfide production, indicating trace methane oxidation during net methanogenesis and not anaerobic methane oxidation, even at a high methane partial pressure.

Aquifer recharge with reclaimed water: life-cycle assessment of hybrid concepts for non-potable reuse

Aquifer recharge with reclaimed water is a promising means to store and supply on demand reclaimed water of high quality for further non-potable reuse. The reuse applications may include indirect agricultural or landscape irrigation, saltwater intrusion barriers, subsidence mitigation or aquifer replenishment. As an alternative to high-pressure or double-membrane systems, hybrid schemes consisting of a disinfection/filtration step prior to aquifer recharge were assessed in this study regarding their environmental footprint and energy efficiency. A simplified life-cycle assessment (LCA) for a hypothetical case study in a water-scarce country was conducted to compare these hybrid schemes to a double-membrane system working under similar conditions. The results show that there is a significant margin for lowering the environmental impact, energy demand and operational costs if non-potable water quality is targeted. While the hybrid schemes outperform high-pressure membranes for these factors, land footprint and final water quality also need to be considered in the choice of solution for specific conditions.

Biofouling removal in spiral-wound nanofiltration elements using two-phase flow cleaning

Biofouling has detrimental effects on the feed channel pressure drop and the permeate flux in high-pressure membrane processes such as NF and RO. Two-phase flow cleaning is a chemical-free technique that is able to remove such biofilms. This paper presents a study into the effects of the gas/liquid ratio, feed spacer geometry, applied pressure and liquid velocity on the efficiency of two-phase flow cleaning in spiral-wound nanofiltration elements. A high-speed camera, optical coherence tomography and scanning electron microscopy were used to study biofouling and its removal. Our results show that two conditions must be met to ensure that a sufficiently high shear force is applied to biofilms on membrane and spacer surfaces. A good bubble distribution in the channel is the first requirement. While it is mainly the structure of the feed spacer that controls bubble flow and bubble size, a minimum gas/liquid ratio of 0.5 is necessary to achieve a good bubble distribution. The second condition is the use of a sufficiently high liquid velocity during cleaning. The bubble velocity was found to be 3.5–5.5 times as high as the used liquid velocity, and responsible for a marked improvement in the flux recovery.

Occurrence of perfluoroalkyl and polyfluoroalkyl substances in the water environment and their removal in a water treatment process

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) such as perfluorooctanoic acid (PFOA), and perfluorooctane sulfonate (PFOS) are found in aquatic environments worldwide. The presence of these compounds in the water environment is still unclear, even though direct or indirect discharges of these compounds from industries to the aquatic environment are the potential routes. In this paper, PFOA and PFOS contamination of aquatic ecosystems, and their removal efficiency by different water treatment processes are reviewed. Typically, PFOS and PFOA contamination levels are higher in industrialized countries than in non-industrial countries. Coagulation, sand filtration, sedimentation, oxidation and disinfection are mostly ineffective in removing PFASs from drinking and wastewater. Granular activated carbon demonstrated the removal of PFASs and the extent of removal depends on operational conditions, such as temperature, operational life period and empty bed contact time. High-pressure membrane systems are the most suitable processes for removing the PFOS and PFOA in water sources. In the high-pressure membrane, removal of those chemicals occurs through rejection via electrostatic interaction. The extent of the reduction efficiency depends on the solution chemistry of the sample; lower pH and higher calcium ion addition in the water sample enhance the reduction efficiency in the high-pressure membrane application.

In-line coagulation to reduce high-pressure membrane fouling in an integrated membrane system: a case study

Membrane fouling is a critical problem for many nanofiltration (NF) membrane plants. This study demonstrated that the poor spaces of the NF membrane were decreased for the deposition of natural organic matter (NOM) on the membrane surface. In-line coagulation was added prior to the low-pressure filtration step to remove more organic material by microfiltration (MF), thereby improving the quality of the feed-water entering the NF membranes. Three different types of coagulants, i.e. aluminum sulfate, ferric chloride, and polyaluminum chloride, with their different levels at different pH values were used for this study. The optimal dose of each coagulant was determined, and the impact on the NF membrane was assessed by batching and running 20 L of post-coagulation MF permeate through a bench-scale NF membrane for 200 h. Ferric chloride was found to perform the best of these three tested coagulants to reduce NF pressure fouling by reduction of NOM in the NF feed-water. High performance size exclusion chromatography study revealed that higher molecular weight fractions of NOM removed preferentially due to in-line coagulation processes. The scanning electron microscopy analysis of the fouled NF membrane trial revealed that the foulant layer consisted of a very large quantity of inorganic and organic matter, bacteria, which resulted in a very rough surface topography.

Simultaneous production of high-quality water and electrical power from aqueous feedstock’s and waste heat by high-pressure membrane distillation

A new membrane distillation (MD) concept (MemPower) has been developed for the simultaneous production of high-quality water from various aqueous feedstocks with cogeneration of mechanical power (electricity). Driven by low-grade heat (waste, solar, geothermal, etc.) a pressurized distillate can be produced by operating TNO’s Memstill® process at high hydraulic pressures. These pressures are theoretically limited by the liquid entry pressure (LEP) of the membrane. The proof of principle has been shown and is based on the transport of water vapor against a hydraulic pressure gradient. Various commercially available membranes have been evaluated in order to obtain high yields in water flux and power densities. Power densities have been measured which are sufficient to drive the pumps in MD. This allows standalone Memstill® units without electricity consumption to be possible, which are fully driven by waste heat. The application of new incompressible hydrophobic membranes, combining a high permeance with a high LEP, will allow for much higher power densities.

Three-dimensional numerical modeling on high pressure membrane reactors for high temperature water-gas shift reaction

This study presents a three-dimensional numerical model that simulates the H2 production from coal-derived syngas via a water-gas shift reaction in membrane reactors. The reactor was operated at a temperature of 900 °C, the typical syngas temperature at gasifier exit. The effects of membrane permeance, syngas composition, reactant residence time, sweep gas flow rate and steam-to-carbon (S/C) ratio on reactor performance were examined. Using CO conversion and H2 recovery to characterize the reactor performance, it was found that the reactor performance can be enhanced using higher sweep gas flow rate, membrane permeance and S/C ratio. However, CO conversion and H2 recovery limiting values were found when these parameters were further increased. The numerical results also indicated that the reactor performance degraded with increasing CO2 content in the syngas composition.

Chemical precipitation and ammonia air stripping as effective pre-treatment methods before membrane filtration of co-digestion effluents

The aim of the research presented was to develop an effective treatment method of highly polluted post-digestion effluents, to a degree allowing the treated waters to be directly released into a natural reservoir. The post-digestion effluents characterized by varied ammonia–nitrogen content underwent high-pressure membrane filtration (nanofiltration [NF], reverse osmosis [RO]) and chemical precipitation (struvite)/ammonia stripping as pre-treatment steps. The application of struvite precipitation and ammonia stripping turned out to be an effective method of binding nitrogen and phosphorus compounds from post-digestion liquors. Waters met all discharge limits after struvite precipitation at stoichiometric ratio of reagents, ammonia stripping of 2–8 h (depending on the initial NH4+ concentration) and RO as a post-treatment. Introducing air stripping between struvite precipitation and membrane filtration allowed to reduce the amount of reagents used during struvite precipitation in order to remove the ammonia–nitrogen below discharge limit. The waters purified with NF as a post-treatment did not meet the discharge limits; however, their reuse as technological waters should be taken into consideration.

Upon impact: the fate of adhering Pseudomonas fluorescens cells during nanofiltration.

Nanofiltration (NF) is a high-pressure membrane filtration process increasingly applied in drinking water treatment and water reuse processes. NF typically rejects divalent salts, organic matter, and micropollutants. However, the efficiency of NF is adversely affected by membrane biofouling, during which microorganisms adhere to the membrane and proliferate to create a biofilm. Here we show that adhered Pseudomonas fluorescens cells under high permeate flux conditions are met with high fluid shear and convective fluxes at the membrane-liquid interface, resulting in their structural damage and collapse. These results were confirmed by fluorescent staining, flow cytometry, and scanning electron microscopy. This present study offers a "first-glimpse" of cell damage and death during the initial phases of bacterial adhesion to NF membranes and raises a key question about the role of this observed phenomena during early-stage biofilm formation under permeate flux and cross-flow conditions.

Ozonation pretreatment for stabilized landfill leachate high-pressure membrane treatment

Laboratory-scale experiments were conducted to determine the effectiveness of ozonation as a pretreatment option for treating stabilized landfill leachate using reverse osmosis and nanofiltration membranes. Leachate from three different landfills was collected and characterized as stabilized leachate with a ratio of biochemical oxygen demand to chemical oxygen demand in the range of 0.02 to 0.12. Batch ozonation experiments were conducted by using an ozonation dose of 66.7gm−3 for duration of 5 to 30min. A maximum reduction of 78% UV-254 absorbing compounds and 23% dissolved organic carbon was observed for all three leachates. An effective ozonation time of 10min at an ozone dose of 66.7gm−3 was selected for leachate pretreatment before membrane operation. Even though the ozone-treated leachate contained approximately 50% fewer UV-254 absorbing compounds than raw leachate, ozonation of leachate prior to membrane treatment resulted in a greater reduction in permeate flux as compared to raw leachate. The cause of increased permeate flux reduction with the ozonated leachate was assessed by using a flux decline analysis alongside Hermia's crossflow filtration model. Hermia's crossflow filtration model indicated that each fouling mechanism occurred. The flux decline analysis suggested that distinct stages of fouling did not develop. While the cause of the increased fouling is suspected to be the coagulation of calcium and natural organic matter, further investigation is needed to determine the primary source of fouling.

Removal of the cyanotoxin anatoxin-a by drinking water treatment processes: a review.

Anatoxin-a (ANTX-a) is a potent alkaloid neurotoxin, produced by several species of cyanobacteria and detected throughout the world. The presence of cyanotoxins, including ANTX-a, in drinking water sources is a potential risk to public health. This article presents a thorough examination of the cumulative body of research on the use of drinking water treatment technologies for extracellular ANTX-a removal, focusing on providing an analysis of the specific operating parameters required for effective treatment and on compiling a series of best-practice recommendations for owners and operators of systems impacted by this cyanotoxin. Of the oxidants used in drinking water treatment, chlorine-based processes (chlorine, chloramines and chlorine dioxide) have been shown to be ineffective for ANTX-a treatment, while ozone, advanced oxidation processes and permanganate can be successful. High-pressure membrane filtration (nanofiltration and reverse osmosis) is likely effective, while adsorption and biofiltration may be effective but further investigation into the implementation of these processes is necessary. Given the lack of full-scale verification, a multiple-barrier approach is recommended, employing a combination of chemical and non-chemical processes.

Impact of spacer thickness on biofouling in forward osmosis

Forward osmosis (FO) indirect desalination systems integrate wastewater recovery with seawater desalination. Niche applications for FO systems have been reported recently, due to the demonstrated advantages compared to conventional high-pressure membrane processes such as nanofiltration (NF) and reverse osmosis (RO). Among them, wastewater recovery has been identified to be particularly suitable for practical applications. However, biofouling in FO membranes has rarely been studied in applications involving wastewater effluents. Feed spacers separating the membrane sheets in cross-flow systems play an important role in biofilm formation. The objective of this study was to determine the influence of feed spacer thickness (28, 31 and 46 mil) on biofouling development and membrane performance in a FO system, using identical cross-flow cells in parallel studies. Flux development, biomass accumulation, fouling localization and composition were determined and analyzed. For all spacer thicknesses, operated at the same feed flow and the same run time, the same amount of biomass was found, while the flux reduction decreased with thicker spacers. These observations are in good agreement with biofouling studies for RO systems, considering the key differences between FO and RO. Our findings contradict previous cross-flow studies on particulate/colloidal fouling, where higher cross-flow velocities improved system performance. Thicker spacers reduced the impact of biofouling on FO membrane flux.

A conceptual NF/RO arrangement design in the pressure vessel for seawater desalination

The main objective of this study is to understand the operation mechanisms of reverse osmosis (RO) membrane and optimization of the operating mechanisms of the RO system in order to reduce the membrane fouling and/or energy requirements. Typically, the high-pressure RO membrane vessel is loaded with membrane elements having the same flux and salt rejection rate. It has been conceived that when different types of RO elements are loaded into the pressure vessel in a special arrangement according to their permeability and salt rejection rate, this arrangement has the potential for reducing the energy consumption of the RO plant. Here, a conceptual design is introduced to describe this new idea. The effects of feed salinity and temperature were investigated in this paper using the reverse osmosis system analysis filmtec membrane design software. A two pass membrane treatment process was designed for desalting seawater at different salinities varied from 35,000 ppm to 43,000 ppm. The results showed a net energy saving from 2.5 to 3% (depends on the feed salinity) could be achieved. The effect of the feed temperature was also investigated, and the new design was found to be more energy efficient. Membrane scaling was also investigated in this study, and it was found that the new membrane arrangement design was less efficient than old design at feed salinity 35,000 ppm and vice versa at feed salinity 45,000 ppm. This was attributed to the use of high membranes permeabilities in the new design.

Powerplant Design and Performance Analysis of a Manned All-Electric Helicopter

This paper describes the conceptual design of three all-electric powerplants—a battery-only, a fuel-cell-only, and a battery–fuel cell hybrid powerplant—for a manned ultralight utility helicopter (Robinson R 22 Beta II-like) and carries out a comparative evaluation of performance delivered by each. The new powerplants consist of a combination of high-pressure proton exchange membrane fuel cells, 700 bar type-4 hydrogen storage, a compressor–expander, lithium-ion batteries, and an alternating current synchronous permanent magnet motor. The key conclusion is that a hybrid powerplant that combines high specific power of batteries in hover and high calorific value of hydrogen in cruise delivers a superior performance compared to either system alone. The efficiency is higher than current rotorcraft piston engines but the key limitation is its low specific power, which is half of the current engines. Only 60% of the original payload can be flown (90 kg solo pilot) for a duration of 35 min (including 11 min hover) over a range of 47 km under high/hot () conditions. The paper lays the foundations of performance analysis for all-electric rotorcraft, benchmarks the best performance achievable with current state of the art, and quantifies future technology targets to enable performance comparable to existing internal combustion engines.

H2 recovery and CO2 capture after water–gas shift reactor using synthesis gas from coal gasification

In this study, a combined test of the WGS (water–gas shift) reactor and a Pd-based composite membrane was carried out for pre-combustion CO2 capture in a coal gasifier. The two series of WGS reactions, i.e., a high-temperature shift and a low-temperature shift, were performed under a gas composition of 60% CO and 40% H2 at 2100 kPa to imitate coal gasification. The CO2 enrichment and H2 recovery tests at 673 K and 2100 kPa with the high-pressure membrane module after the WGS reaction presented the enriched CO2 concentration and H2 recovery ratios of ∼92% and ∼96%, respectively. The long-term stability test showed that the CO2 concentration decreased to 78.2%, and CO was generated and reached to 8.8% in the retentate stream after 47 h because of reverse WGS and CO2 hydrogenation reaction on 316L stainless steel module. The stability test for ∼3137 h showed that these catalytic activities could be successfully prevented using steel with higher Cr and Ni contents, such as 310S. The WGS-membrane combination test using the outlet gas from a real coal gasifier was continued for ∼100 h and showed that the WGS catalysts and membrane module made of 310S would be stable under real conditions.

Effects of various emulsification methods on the oxidation of methyl linoleate.

The effects of mechanical stress during emulsification on the oxidation of methyl linoleate were investigated by four methods (high-pressure homogenization, high-speed stirring, ultrasonic homogenization, and membrane emulsification). The oxidation rates and induction periods were almost constant, regardless of the emulsification method, except for membrane emulsification, by which the induction period was prolonged when a cellulose acetate membrane was used.