Research in the field of Forward Osmosis (FO) membrane technology has grown significantly over the last 10 years, but its application in the scope of wastewater treatment has been slower. Drinking ...water is becoming an increasingly marginal resource. Substituting drinking water for alternate water sources, specifically for use in industrial processes, may alleviate the global water stress. FO has the potential to sustainably treat wastewater sources and produce high quality water. FO relies on the osmotic pressure difference across the membrane to extract clean water from the feed, however the FO step is still mostly perceived as a “pre-treatment” process. To prompt FO-wastewater feasibility, the focus lies with new membrane developments, draw solutions to enhance wastewater treatment and energy recovery, and operating conditions. Optimisation of these parameters are essential to mitigate fouling, decrease concentration polarisation and increase FO performance; issues all closely related to one another. This review attempts to define the steps still required for FO to reach full-scale potential in wastewater treatment and water reclamation by discussing current novelties, bottlenecks and future perspectives of FO technology in the wastewater sector.
•Wastewater can be used as an alternative source of water and energy.•FO shows promise and concern in wastewater treatment and reclamation.•FO-wastewater technology has a long way to go before reaching full-scale potential.
Worldwide, the application of a (gas/liquid) two-phase flow in membrane processes has received ample scientific deliberation because of its potential to reduce concentration polarization and membrane ...fouling, and therefore enhance membrane flux. Gas/liquid flows are now used to promote turbulence and instabilities inside membrane modules in various membrane processes such as microfiltration, ultrafiltration, nanofiltration, reverse osmosis, membrane distillation, electrodialysis, and membrane bio-reactors. This paper provides a comprehensive and critical literature review of the state of the art in this research area. A total of 205 scientific papers published in peer-reviewed journals from 1989 to 2013 were collected. The data in 195 of these papers (published up to 2011) were compiled and analyzed. These data were analyzed and normalized based on gas and liquid superficial velocities, gas/liquid ratio and feed types, trans-membrane pressure and membrane module type in order to make a fair comparison and identify general characteristics. The objective was to identify key factors in the application of two-phase flows in aqueous separation and purification processes, deliver new insights in how to optimize operations for implementation of this technology in the industry, discuss the importance of energy saving, provide a brief overview of current commercial applications and suggest future directions for research.
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•A critical review on the use of two-phase flow in membrane processes is presented.•Two-phase flow cleaning can effectively improve membrane process performance.•Optimal conditions for using gas-liquid flow are derived from the analysis of literature data.•Technical and economical analyses show that two-phase flow is competitive.•Future research directions are suggested.
Cardiorespiratory fitness (CRF) is an independent predictor of mortality, and females typically achieve smaller improvements in CRF than males after exercise-based cardiac rehabilitation. ...High-intensity interval training (HIIT) has been shown to produce superior improvements in CRF than traditional cardiac rehabilitation, but the sex differences are unknown. The purpose of this systematic review and meta-analysis was to evaluate sex differences for changes in CRF and cardiometabolic health indicators after HIIT in adults with coronary artery disease (CAD).
A systemic search of five electronic databases for studies examining the effect of HIIT on measured CRF and cardiometabolic health indicators in adults with CAD was performed. Data (published and unpublished) from 14 studies were included in the meta-analyses with approximately eightfold greater male than female participation (n = 836 vs n = 103). Males with CAD achieved a near-significant absolute improvement in CRF (mean difference MD = 1.07, 95% confidence interval CI = -0.08 to 2.23 mL·kg-1⋅min-1, P = 0.07) after HIIT when compared with control; there were insufficient data to conduct such an analysis in females. Significantly smaller improvements in CRF were experienced by females than males (MD = -1.10, 95% CI = -2.08 to -0.12 mL·kg-1⋅min-1, P = 0.03); there was no sex difference for the relative (percentage) change in CRF after HIIT. Females achieved significantly smaller reductions in body mass index (MD = -0.25, 95% CI = -0.03 to -0.47 kg·m-2, P = 0.02) and fasting blood glucose (MD = -0.38, 95% CI = -0.05 to -0.72, P = 0.03); no sex differences were observed for other cardiometabolic health indicators.
There are no sex differences for relative improvements in CRF after HIIT; however, females are greatly underrepresented in trials. Future studies should increase female participation and perform sex-based analyses to determine sex-specific outcomes following HIIT.
This study investigated sorption and biodegradation behaviour of 14 organic micropollutants (OMP) in soil columns representative of the first metre (oxic conditions) of the river bank filtration ...(RBF) process. Breakthrough curves were modelled to differentiate between OMP sorption and biodegradation. The main objective of this study was to investigate if the OMP biodegradation rate could be related to the physico-chemical properties (charge, hydrophobicity and molecular weight) or functional groups of the OMPs. Although trends were observed between charge or hydrophobicity and the biodegradation rate for charged compounds, a statistically significant linear relationship for the complete OMP mixture could not be obtained using these physico-chemical properties. However, a statistically significant relationship was obtained between biological degradation rates and the OMP functional groups. The presence of ethers and carbonyl groups will increase biodegradability, while the presence of amines, ring structures, aliphatic ethers and sulphur will decrease biodegradability. This predictive model based on functional groups can be used by drinking water companies to make a first estimate whether a newly detected compound will be biodegraded during the first metre of RBF or that additional treatment is required. In addition, the influence of active and inactive biomass (biosorption), sand grains and the water matrix on OMP sorption was found to be negligible under the conditions investigated in this study. Retardation factors for most compounds were close to 1, indicating mobile behaviour of these compounds during soil passage. Adaptation of the biomass towards the dosed OMPs was not observed for a 6 month period, implying that new developed RBF sites might not be able to biodegrade compounds such as atrazine and sulfamethoxazole in the first few months of operation.
Reverse osmosis membranes are increasingly used in drinking water treatment. However, the production of a concentrate stream is the main disadvantage of its application. Increasing the recovery of ...the membranes in order to have the smallest amount of concentrate possible is an attractive approach. In the absence of bivalent cations in the feed water, silica and silica-derived precipitants are limiting factors in high-recovery reverse osmosis operations. The removal of silica in a separate pretreatment process might be the solution. Several methods were tested to remove silica. Precipitation of silica with Fe(OH)3, Al(OH)3 and silica gel was investigated, and also the removal of silica using a strongly basic anion (SBA) exchange resin.
Al(OH)3 was the most effective precipitant for silica, removing nearly all of the molecularly dissolved silica. However, a residual amount of aluminum remained in solution, and aluminosilicate colloids were not removed. The use of the SBA exchange resin also showed a good performance, removing up to 94% of the silica. However, further investigations, such as checking whether the residual small amounts of silica and aluminum can still cause scaling in the membrane, need to be conducted.
•Different methods to remove silica from solution were investigated.•Al3+ was the most efficient precipitant for silica, removing up to 99% of silica.•A strongly basic anion exchange resin removed silica up to 94%.•Monitoring residual silica and Al3+ is crucial to prevent scaling in membranes.
The properties and performance of a recently developed thin film nanocomposite (TFN), with inorganic nanoparticles incorporated in the active layer, and standard thin film composite (TFC) spiral ...wound seawater desalination reverse osmosis (RO) membranes were assessed by comparison on the scale of 4040 and 8040 membrane modules.
Scanning electron microscopy with energy-dispersive X-ray spectroscopy, contact angle-, and ζ-potential measurements did not show large differences between TFN membranes and a TFC membrane (SW30HRLE). Small scale pilot tests (4040 elements) showed that the TFN had a factor to higher water permeability as the TFC. Salt rejection was similar, but the TFC showed slightly better rejection of NDMA and glycerol. Larger scale pilot tests (multiple 8040 elements) confirmed the nearly twofold higher water permeability for the TFN as compared to aged TFC membranes (SW30XHR). However, the boron rejection of the TFN was lower than that of the aged TFC. Furthermore, an indirect comparison showed that the flux for the virgin TFN would be about 1.4 times that for the virgin TFC.
•A TFN membrane shows nearly a factor two higher water permeability than a standard TFC.•A standard TFC membrane shows better rejection of glycerol and NDMA than a TFN.•TFN membrane boron rejection is lower than that of a standard TFC.•The current generation of TFNs and TFCs shows comparable performances.
The potential environmental and health risks of engineered nanoparticles such as buckminsterfullerene C60 in water require their removal during the production of drinking water. We present a study ...focusing on (i) the removal mechanism and (ii) the elucidation of the role of the membrane pore size during removal of nC60 fullerene nanoparticle suspensions in dead-end microfiltration and ultrafiltration mimicking separation in real industrial water treatment plants. Membranes were selected with pore sizes ranging from 18 nm to 500 nm to determine the significance of the nC60 to membrane pore size ratio and the adsorption affinity between nC60 and membrane material during filtration. Experiments were carried out with a dead-end bench-scale system operated at constant flux conditions including a hydraulic backwash cleaning procedure. nC60 nanoparticles can be efficiently removed by low pressure membrane technology with smaller and, unexpectedly, also by mostly similar or larger pores than the particle size, although the nC60 filtration behaviour appeared to be different. The nC60 size to membrane pore size ratio and the ratio of the cake-layer deposition resistance to the clean membrane resistance, both play an important role on the nC60 filtration behaviour and on the efficiency of the backwash procedure recovering the initial membrane filtration conditions. These results become specifically significant in the context of drinking water production, for which they provide relevant information for an accurate selection between membrane processes and operational parameters for the removal of nC60 in the drinking water treatment.
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•Membrane processes are a viable barrier in minimizing human exposure to fullerene.•Effect of pore size was significant in removal and removal mechanism of nC60.•Membranes with pore sizes similar/larger than nC60 pore size show >99% removal.•Backwash can remove accumulated cake-layer when cake resistance is higher than membrane resistance.
Cleaning of high pressure RO/NF membranes is an important operational tool to control biofouling. Quantitative information on the efficacy of cleaning agents and protocols to remove biomass is ...scarce. Therefore, a laboratory cleaning test to assess the efficiency of cleaning procedures to remove attached biomass was developed. The major components of the test are (i) production of uniform biofilm samples, (ii) the quantification of the biomass concentrations with robust parameters and (iii) a simple test procedure with optimal exposure of the biofilm samples to the chemicals. The results showed that PVC-P is a suitable substratum for the production of uniform biofilm samples. ATP and carbohydrates (CH) as major components of the biofilm matrix for nucleotides (living bacterial cells) and extracellular polymeric substances EPS, respectively, were selected as robust biomass parameters. The removal of ATP and CH with the NaOH/Sodium Dodecyl Sulfate (SDS) mixture, selected as a standard treatment at pH 12.0, was reproducible. The resistance of the EPS matrix against chemical cleaning was demonstrated by a low CH removal (32.8 ± 6.0%) compared to the ATP removal (70.5 ± 15.1%). The inverse relationship of biomass removal with the CH to ATP ratio (μg/ng) of the biofilms demonstrated the influence of the biomass characteristics on cleaning. None of the 27 chemicals tested (analytical-grade and commercial brands) in single step or in double-step treatments were significantly more effective than NaOH/SDS. Oxidizing agents NaOCl and H2O2, the latter in combination with SDS, both tested as common agents in biofilm control, showed a significantly higher efficiency (70%) to remove biofilms. In the test, simultaneously, the efficiency of agents to remove precipitated minerals such as Fe can be assessed. Validation tests with Cleaning in Place (CIP) in 8 and 2.5-inch RO membrane pilot plant experiments showed similar ranking of the cleaning efficiency of cleaning protocols as determined in the laboratory tests. Further studies with the laboratory test are required to study the effect of cleaning conditions such as duration, temperature, shear forces as well as chemical conditions (concentrations, alternative agents or mixtures and sequence of application) on the efficiency to remove attached biomass.
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► A laboratory test is available to quantify biofilm removal efficiency of agents and protocols used in membrane cleaning. ► Carbohydrate (EPS) removal by common used cleaning agents was lower than 50%. ► Ranking of the cleaning efficiency of chemicals by the test was similar to the ranking observed in CIP of membrane elements.
The production of biologically stable drinking water is challenging in conventional surface water treatment plants. However, attainment of biological stability is essential to avoid regrowth in ...disinfectant-free distribution systems. A novel application of ultrafiltration as a posttreatment step to enhance biological stability of drinking water produced in an existing conventional surface water treatment plant was investigated. The conventional full-scale plant comprised coagulation/sedimentation/filtration, UV-disinfection, biological activated carbon filtration and chlorine dioxide post-disinfection. The produced water exhibited substantial regrowth of Aeromonads, invertebrates and colony counts in the distribution network. Recent literature attributes this phenomenon to the specific presence of slowly biodegradable, high molecular weight (MW) biopolymeric organic compounds. Hence, the aim of this study is to enhance the biological stability of conventionally treated surface water by reducing the concentration of high-MW organic compounds. For this purpose, biological active carbon filtrate was subjected to ultrafiltration with membrane pore sizes of 10 kDa, 150 kDa and 0.12 μm respectively, operating in parallel. The UF performance was evaluated in terms of the achieved reduction in particulate and high-MW organic carbon (PHMOC); the biopolymer fraction in Liquid Chromatography-Organic Carbon Detection; biomass (cells, ATP); Assimilable Organic Carbon (AOC) by the AOC-P17/NOX method for easily biodegradable, low-MW compounds and by the AOC-A3 method for slowly biodegradable, high-MW compounds; and overall microbial growth potential (MGP) as assessed by Biomass Production Potential (BPP) and Bacterial Growth Potential (BGP) bio-assays. Results showed increasing removal of high-MW organic carbon with decreasing UF pore size, i.e., 30%, 60% and 70% removal was observed for the 0.12 μm, 150 kDa and 10 kDa membranes, respectively. Biomass and particulates retention was more than 95% for all UF membranes. AOC-A3, BPP and BGP were substantially reduced by 90%, 70% and 50%, respectively. These respective reductions were similar for all three UF membranes despite their difference in pore size. Easily biodegradable organic compounds (as AOC-P17/NOX) were not reduced by any of the membranes, which was in accordance with expectations considering the low MW of the compounds involved. Based on the obtained results, growth potential appears to be largely attributable to high-MW organic compounds which are retained by a 0.12 μm UF membrane. Furthermore, the quality of all three UF permeates was equal to or better than in reference cases (literature data) which exhibit little regrowth in their disinfectant-free distribution networks. The results demonstrate that ultrafiltration posttreatment in conventional surface water treatment plants is a potentially promising approach to enhance the biological stability of drinking water.
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•Surface water posttreatment by Ultrafiltration (UF) was found to be promising.•Ultrafiltration posttreatment reduces high-MW Organic Carbon and biomass.•Ultrafiltration posttreatment enhances the biological stability of drinking water.•Permeate quality compared well to reference cases of low microbial regrowth.•Ultrafiltration over comparatively large pores of 0.12 μm was effective.
The effects of surface water pretreatment on membrane fouling and the influence of these different fouling types on the rejection of 21 neutral, positively and negatively charged pharmaceuticals were ...investigated for two nanofiltration membranes. Untreated surface water was compared with surface water, pretreated with a fluidized anionic ion exchange and surface water, pretreated with ultrafiltration. Fouling the nanofiltration membranes with anionic ion exchange resin effluent, resulted in the deposition of a mainly colloidal fouling layer, with a rough morphology. Fouling the nanofiltration membranes with ultrafiltration permeate, resulted in the deposition of a smooth fouling layer, containing mainly natural organic matter. The fouling layer on the nanofiltration membranes, caused by the filtration of untreated surface water, was a combination of both colloids and natural organic matter.
Rejection of pharmaceuticals varied the most for the membranes, fouled with the anionic ion exchange effluent, and variations in rejection were caused by a combination of cake-enhanced concentration polarisation and electrostatic (charge) effects. For the membranes, fouled with the other two water types, variations in rejection were smaller and were caused by a combination of steric and electrostatic effects.
Changes in membrane surface hydrophobicity due to fouling, changed the extent of partitioning and thus the rejection of hydrophobic, as well as hydrophilic pharmaceuticals.
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