Unified Membrane Fouling Index Research Articles

Spectroscopic analysis and prediction of membrane fouling potential of NOM in the continuous membrane filtration-submersed (CMF[sbnd]S) reactor

The long-term running continuous microfiltration-submersed (CMFS) reactor was built and spectral indicators, organic matter, and fouling potential were monitored. The specific filtration volume decline rates (V0.5 and V0.25) and unified membrane fouling index (UMFI) were characterized as pore blocking, gel layer, and cake layer fouling potential, respectively. Spectral analysis results showed the parameters of both S275–295 (slope of log-transformed absorption coefficient with the range of 275–295 nm) and SR (the ratio of S275–295 and S350–400) were significant correlations with V0.5, V0.25, and UMFI. The humification index (HIX) had stronger correlations with UMFI, proving the humic acids (HA) had more significant impacts on the cake layer. The V0.5 and V0.25 had correlations with the ratio of peak T to peak C (fT/C) because the aromatic proteins (PN) were more involved in the pore blocking. Statistical analysis results showed that V0.5 and V0.25 were mainly contributed by the polysaccharide (PS) and the interactions of PS × PN × HA, while UMFI was mainly contributed by the HA and PS × PN × HA interactions. The multivariate linear regression (MLR), backpropagation neural network (BPNN), and support vector regression (SVR) models were successfully employed to achieve multiple signals fusion and prediction potential, with the SVR model having better accuracy, especially for UMFI.

Characterization of coagulant-induced ultrafiltration membrane fouling by multi-spectral fusion: DOM properties and model prediction based on machine learning

This study used the ultraviolet-visible (UV–vis), synchronous fluorescence, and excitation-emission matrix (EEM) spectroscopy coupled with zeta potential and particle size to explore the dissolved organic matter (DOM) solutions properties with the addition of two kinds of coagulants, including aluminum chloride and ferric chloride, in humic solutions and surface water. The results of zeta potential and particle size showed the size of aggregates became larger with the addition of coagulant. The binding sequence of coagulant to DOM was followed from aromatic amino acids to fulvic-like and humic-likes fractions. The results of the unified membrane fouling index (UMFI) were showed negatively correlated with the concentrations of coagulant due to the cake layers formed by aggregates being looser and more permeable. Among all the 12 spectral parameters, slope radio (SR) and specific fluorescence intensities (SFI) had the most significant correlation to UMFI. The multi-spectral fusion for predicting UMFI was established via multiple linear regressions and the backpropagation neural network (BPNN) by using the parameters with both SR and SFI with good accuracy and robustness. Sensitivity analyses results showed that SFI was more sensitive than SR in solutions with high protein-like substances, while SR was more sensitive than SFI with high humic-like substances.

Interplay of water temperature and fouling during ceramic ultrafiltration for drinking water production

Ceramic ultrafiltration (UF) is an emerging technology for drinking water production, but the interplay and influence of water temperature on fouling is lacking. This research investigates temperatures from 5 to 35 °C and explored the fouling impacts of humic, protein, and polysaccharide substances on a ceramic UF membrane. Water temperature not only affected water viscosity but also altered the fouling behavior of organics. At 5 °C, while approximately 50 % of the change in the unified membrane fouling index (UMFI) was attributed to the change in water viscosity the remaining 50 % was due to change in organic fouling behavior. Conversely, at 35 °C, the overall UMFI decreased relative to the 20 °C standard, of which 36–53 % of the decrease was associated with changes in fouling behavior. Constant flux blocking models determined that standard pore blocking dominated the first filtration cycle for all temperature cases, suggesting that material accumulation inside the pores was responsible for fouling during the initial stages of filtration. The standard blocking continued throughout filtration for 20 and 35 °C suggesting that fouling was mostly reversible. In contrast, at 5 °C condition, fouling transitioned to intermediate blocking, suggesting deposition inside the pores causing irreversible fouling. UMFI and carbon analysis showed lower backwash and chemical cleaning efficiencies at the 5 °C condition indicating higher irreversible fouling mass, while better cleaning was observed at the warmer water temperatures. The exacerbated fouling at low temperatures demonstrates that changes in membrane backwash and chemical cleaning should be implemented under fluctuating water temperature conditions.

Performance Evaluation of Ceramic Membrane on Ultrafiltration and Diafiltration Modes for Efficient Recovery of Whey Protein

The recovery of high-quality, valuable end products from cheese whey is a very important industrial process. The aim of this study is to improve the recovered protein content of concentrate stream in cheese whey. The experiments were conducted by using ceramic ultrafiltration (UF) membrane followed by diafiltration (DF) process with a 15kDa molecular weight cut-off (MWCO). The volume concentration factor (VCF) was set as 1.4, 2.0 and 3.3 by controlling the permeate and concentrate volume. It was observed that the protein concentration increased from 1.4 g/l in the feed solution to 9.9 g/l in the concentrate stream. After VCF optimization, two intermittent feed diafiltration (IFD) cycles were performed experimentally and a mathematical model with real-time function was applied for DF yield calculation. The maximum yield was found as 88% at the end of the second DF cycle. The protein content reached to 33% in the concentrate stream after applying the IFD process. During the fouling experiments of DF process, the indicative parameters were calculated with three different fouling models. Total resistance (RT), membrane fouling index (MFI), and unified membrane fouling index (UMFI) were found as 5.15x1014 m-1, 25x106, and 344 respectively. IFD process enhanced the overall performance of whey processing compared to normal UF process.

Effects of feed water temperature on irreversible fouling of ceramic ultrafiltration membranes

Temperature is known to influence the filtration performance of membrane systems through its direct impact on water viscosity. This research demonstrates that the changes in natural organic matter (NOM) fouling behavior with temperature are over and beyond simple viscosity changes in water. Constant flux experiments were performed in a tubular ceramic ultrafiltration (UF) system at 5, 20, and 35 °C. The unified membrane fouling index (UMFI) was used to identify NOM reversible and irreversible fouling mechanisms; while the modified UF fouling index (MFI-UF) was used to predict the fouling potential of NOM. The results showed that after correcting for viscosity to standard 20 °C compared to 5 °C, UMFI values were higher than expected and reflected the higher fouling irreversibility observed at the lower temperature. The lower water temperature resulted in an increase in NOM retention along with decrease in backwash and chemical cleaning effectiveness as determined by the UMFI and FEEM analyses. However, increased water temperature did not adversely impact existing backwash or chemical cleaning protocols. In addition, The MFI-UF exhibited the same trend as UMFI for establishing NOM fouling and retention, and therefore, the MFI-UF method is suitable for use as fouling predictor with ceramic membrane systems.

Impact of transmembrane pressure (TMP) on membrane fouling in microalgae harvesting with a uniform shearing vibration membrane system

A uniform shearing vibration membrane system can mitigate membrane fouling during algae filtration. In this paper, the effects of transmembrane pressure (TMP) on the membrane filtration performance at 8 kPa, 9 kPa and 10 kPa were investigated. The results of membrane fouling mechanisms predicted by Hermia's model surmised that membrane fouling is principally caused by the cake layer model, and the application of the Unified Membrane Fouling Index for quantitative evaluation of antifouling properties substantiating membranes in sub-critical condition exhibited superior antifouling properties. The reversible membrane fouling was largely dependent on polysaccharides due to size exclusion. Proteins tended to block the membrane pores and to cause irreversible fouling. It was also observed that high-molecular weight (>100 kDa) extracellular organic matters contributed a significant portion of membrane fouling. For greater insight, the CRiteria Importance Through Intercriteria Correlation (CRITIC) method was administered; it could be concluded that the removal of proteins was more responsible for the total fouling resistance than was the removal of polysaccharides, especially for membranes at the TMP of 9 kPa.

Polyethersulfone membranes modified with D-tyrosine for biofouling mitigation: Synergistic effect of surface hydrophility and anti-microbial properties

Biofouling is a critical issue in membrane separations. Development of novel approaches for biofouling mitigation is of crucial importance for membrane-based technologies. In this research, D-tyrosine was immobilized on a polyethersulfone (PES) ultrafiltration membrane (UF) to mitigate biofouling with the synergistic effects of surface hydrophilicity and anti-microbial properties. Results showed that the grafting of D-tyrosine increased the surface hydrophilicity and imparted a smoother surface to the membrane without altering its transport properties. During bovine serum albumen (BSA) filtration tests, the unified membrane fouling index (UMFI) of D-tyrosine-polydopamine (PDA)/PES membrane was only 0.00162, probably half of the PDA/PES membrane’s UMFI without D-tyrosine. The flux recovery ratio (FRR) of the D-tyrosine-PDA/PES membrane was up to 79%, higher than the virgin PES membrane. Moreover, the D-tyrosine-PDA/PES membrane showed better anti-biofouling performance when inoculated with E. coli culture. The proposed membrane surface modification technique paves the way toward realization of biological control for mitigating biofouling by simultaneously enhancing the anti-adhesive and antimicrobial properties of the membrane.

Long-term operation of biological activated carbon pre-treatment for microfiltration of secondary effluent: Correlation between the organic foulants and fouling potential

The impact of long-term (>2 years) biological activated carbon (BAC) treatment for mitigating organic fouling in the microfiltration of biologically treated secondary effluent was investigated. Correlation between the organic constituents and hydraulic filtration resistance was investigated to identify the major components responsible for fouling. Over two years operation, the removal efficiency for dissolved organic carbon (DOC) by the BAC treatment was fairly consistent (30 ± 3%), although the reduction in UVA254 gradually decreased from 56 to 34%. BAC treatment effectively decreased the organic foulants in the effluent and so contributed to the mitigation of membrane fouling as shown by reduction in the unified membrane fouling index (UMFI). BAC consistently removed biopolymers whereas the removal of humic substances decreased from 52 to 25% after two years of BAC operation, and thus led to a gradual decrease in UMFI reduction efficiency from 78 to 43%. This was due to gradual reduction in adsorption capacity of the activated carbon as confirmed by analysis of its pore size distribution. Hence humics also played an important role in membrane fouling. However, there was a good correlation between protein and carbohydrate contents with hydraulically reversible and irreversible filtration resistance, compared with UVA254, turbidity and DOC. Although the mitigation of membrane fouling decreased over time, this study demonstrated that the long-term use of BAC pre-treatment of biologically treated secondary effluent prior to microfiltration has potential to reduce the need for frequent chemical cleaning and so increase membrane life span.

Aluminum-induced changes in properties and fouling propensity of DOM solutions revealed by UV–vis absorbance spectral parameters

The integration of pre-coagulation with ultrafiltration (UF) is expected to not only reduce membrane fouling but also improve natural organic matter (NOM) removal. However, it is difficult to determine the proper coagulant dosage for different water qualities. The objective of this study was to probe the potential of UV–vis spectroscopic analysis to reveal the coagulant-induced changes in the fouling potentials of dissolved organic matter (DOM) and to determine the optimal coagulant dosage. The Zeta potentials (ZPs) and average particle size of the four DOM solutions (Aldrich humic acid (AHA), AHA-sodium alginate (SA), AHA-bovine serum albumin (BSA) and AHA-dextran (DEX)) coagulated with aluminum chloride (AlCl3) were measured. Results showed that increasing the aluminum coagulant dosage induced the aggregation of DOM. Meanwhile, the addition of aluminum coagulant resulted in an increase in DSlope325-375 (the slope of the log-transformed absorbance spectra from 325 to 375 nm) and a decrease in S275-295 (the slope of the log-transformed absorption coefficient from 275 to 295 nm) and SR (the ratio of Slope275-295 and Slope350-400). The variations of these spectral parameters (i.e., DSlope325-375, S275-295 and SR) correlated well with the aluminum-caused changes in ZPs and average particle size. This implies that spectral parameters have the potential to indicate DOM aggregation. In addition, good correlations of spectral parameters and membrane fouling behaviors (i.e., unified membrane fouling index (UMFI)) suggest that the changes in DSlope325-375, S275-295 and SR were indicative of the aluminum-caused alterations of fouling potentials of all DOM solutions. Interestingly, the optimal dosage of aluminum (40 μM for AHA, AHA-BSA, and AHA-DEX) was obtained based on the relation between spectral parameters and fouling behaviors. Overall, the spectroscopic analysis, particularly for the utilization of spectral parameters, provided a convenient approach for the exploration of combined coagulation and UF systems for DOM removal.

Using UV–vis absorbance spectral parameters to characterize the fouling propensity of humic substances during ultrafiltration

Ultrafiltration (UF) can achieve excellent removal of natural organic matter (NOM), but the main challenge for this process is the limited understanding of membrane fouling. The objective of this study is to explore the potential of UV–vis spectroscopic analysis for the detection of membrane fouling caused by humic acids (HA) at different solution chemistries (i.e., calcium ions (Ca2+) and pH). In the presence of Ca2+, several spectral parameters, including the DSlope325–375 (the slope of the log-transformed absorbance spectra over 325–375 nm), S275–295 (the slope of the absorption coefficient over 257–295 nm) and SR (the ratio of S275–295 to S350–400) of various HA solutions, were correlated with the molecule aggregation and the membrane fouling potential. Interestingly, increased DSlope325–375 and decreased S275–295 and SR were observed for the HA-Ca2+ interaction under alkaline conditions (i.e., pH = 9) relative to those in lower pH environments (i.e., pH = 7 or 6), suggesting that spectral parameters were able to predict HA-Ca2+ interactions under varying pH conditions. The strong correlations between the spectral parameters and the unified membrane fouling index (UMFI) obtained from UF experiments further corroborated that the spectral parameters were able to predict the membrane fouling potential. Moreover, the spectral parameters were also found to well reveal the fouling extent of the mixture of HA and Suwannee River NOM (SRNOM) or the pure SRNOM added with varying calcium concentrations, implying that the spectroscopic analysis was also available for the indication of practical NOM fouling. In addition, the measurement of S275–295 and SR of the permeate solution suggests an increasing proportion of small-molecule HA in the permeate during the UF process. This study not only expands our knowledge of NOM-Ca2+ aggregates as well as their role in membrane fouling behavior but also provides an approach for the in situ characterization of membrane performance.

Contribution of effluent organic matter (EfOM) to ultrafiltration (UF) membrane fouling: Isolation, characterization, and fouling effect of EfOM fractions

EfOM has been regarded as a major organic foulant resulting in UF membrane fouling in wastewater reclamation. To investigate fouling potential of different EfOM fractions, the present study isolated EfOM into hydrophobic neutrals (HPO-N), colloids, hydrophobic acids (HPO-A), transphilic neutrals and acids (TPI), and hydrophilics (HPI), and tested their fouling effect in both salt solution and pure water during ultrafiltration (UF). Major functional groups and chemical structure of the isolates were identified using Fourier transform infrared spectroscopy (FT-IR) and solid-state carbon nuclear magnetic resonance (13C NMR) analysis. The influence of the isolation process on the properties of EfOM fractions was minor because the raw and reconstituted secondary effluents were found similar with respect to UV absorbance, molecular size distribution, and fluorescence character. In membrane filtration tests, unified membrane fouling index (UMFI) and hydraulic resistance were used to quantify irreversible fouling potential of different water samples. Results show that under similar DOC level in feed water, colloids present much more irreversible fouling than other fractions. The fouling effect of the isolates is related to their size, chemical properties, and solution chemistry. Further investigations have identified that the interaction between colloids and other fractions also influences the performance of colloids in fouling phenomena.

Study of the relation between kinematic viscosity and SDI in polyethylene glycol solutions for predicting membrane fouling: preliminary test

Nowadays, membrane technology plays an essential role in water treatment as a method of producing good-quality water. Its success is due to its ease of implementation, high efficiency and low cost. However, fouling of the active layer of the membranes is one of the main problems of this technology because it affects the operation conditions of the process, requires maintenance and limits the useful lifetime of membranes. Several parameters have been developed for the prediction of fouling being the most used Silt Density Index (SDI). However, it has some limitations that have prompted the search for alternative parameters such as Modified Fouling Index, Modified Fouling Index-UF, Mini Plugging Factor Index and Unified Membrane Fouling Index, among others. In this work, a prediction methodology of colloidal fouling is studied by means of a direct, simple and immediate measure of the combination of kinematic viscosity and SDI. To perform the tests, synthetic solutions of polyethylene glycol at a concentration ranging between 0.1 and 0.75 g/l were used. In kinematic viscosity tests, a Cannon–Fenske viscometer was used and SDI measurements were performed using a standard testing system. Results show that there is a linear relationship between the kinematic viscosity values and SDI in the concentration range studied. These preliminary results can be used to introduce a new parameter for predicting fouling potential in membranes based on the measurement of the kinematic viscosity in the feed water.

Coagulation–bubbling–ultrafiltration: Effect of floc properties on the performance of the hybrid process

A novel hybrid process of coagulation–bubbling–ultrafiltration was proposed to study membrane fouling phenomena by surface water. Relationship of bubbles, flocs and the hollow fibers was explored. When applying less than 20mL/min gas flow rate, membrane fouling was accelerated with air bubbles introduced. When gas flow rate increased further to 40mL/min and 60mL/min, TMP showed a two-stage development trend, which was a fast development in the first few hours followed with a relatively slow development after about 4h. Unified membrane fouling index (UMFI) increased from 0.00216 (without bubbles) to 0.00274m2/L (40mL/min gas flow rate) and 0.00219m2/L (60mL/min gas flow rate). As gas flow rate increased, bubble size became bigger, and its distribution range became wider, resulting in higher shear rate in the ultrafiltration column, which led to severe floc breakage. Flocs of small size and compact structure accelerated membrane fouling, resulting in highest UMFI value under 40mL/min gas flow rate. However, under 60mL/min gas flow rate, with largest bubbles and highest shear rate examined in this study, concentration polarization was effectively limited. As a result, TMP development slowed down when pore blockage reached equilibrium.

Comparison of the performance of ceramic microfiltration and ultrafiltration membranes in the reclamation and reuse of secondary wastewater

Advanced treatment of secondary wastewater generally has been achieved using polymeric microfiltration and ultrafiltration membranes. Newly developed ceramic membranes offer distinctive advantages over the currently employed membranes and were recently introduced for the purpose. This paper presents results of a pilot study designed to investigate the application of ceramic microfiltration (MF) and ultrafiltration (UF) membranes in the recovery of water from secondary wastewater. Synthetic wastewater similar to the quality of secondary treated wastewater was fed to ceramic MF and UF system in a cross-flow mode. The filtration experiments revealed that the flux recovery through tubular ceramic MF membrane was more sensitive to the variation in TMP compared with the tubular ceramic UF membrane over the range of TMP studied. The resistance in series model was used for the evaluation of the resistance to the permeate flux. The results revealed that for ceramic UF membrane, the contribution to the total resistance of fouling was higher than the inherent of the clean membrane resistance. However, both the clean membrane resistance and the fouling resistance contribute equally in the case of MF membrane. Various wastewater indices were measured to evaluate the effectiveness of the filtration treatment. The ceramic UF membrane consistently met water quality in the permeate in terms of colour, turbidity, chemical oxygen demand and absorbance, suggesting that the permeate water could be made to be reused or recycled for suitable purposes. However, MF membrane appeared to be incompetent with respect to the removal of colour. The unified membrane fouling index (UMFI) was used to measure the fouling potential of both the membranes. The result showed that for UF membrane, the value of UMFI is one order of magnitude higher than MF membrane. The overall results suggest that there were significant differences in the performance of both the ceramic UF and MF membranes that are likely to impact on the operation and maintenance of the membrane system.

Comparison of fouling mechanisms in low-pressure membrane (MF/UF) filtration of secondary effluent

Membrane filtration in municipal wastewater treatment is being increasingly used to improve the quality of water and increase the productivity of existing plants. However, membrane fouling encountered in reclamation of municipal wastewater represents serious design and operational concern. There are several fouling models which are being developed and used as a powerful tool to increase the understanding of the fouling mechanisms and its key characteristics that influence the design of optimal process and operating conditions. This study investigates and compares the fouling mechanisms of three different types of polymeric and ceramic ultrafiltration (UF) and microfiltration (MF) membranes in the recovery of water from secondary effluent. The result demonstrated that ceramic UF membrane produced very high quality of water compared to polymeric UF and ceramic MF membranes. Out of four fouling models used to fit the experimental flux data, cake filtration and pore narrowing and complete pore blocking models predicted the initial fluxes of polymeric UF membrane more accurately. On the other hand, the cake filtration and pore narrowing models predicted the performance of ceramic UF membrane. Whereas, pore narrowing model predicted the performance of ceramic MF membrane more precisely compared to other three models. Further, the application of unified membrane fouling index (UMFI) was used to assess the fouling potential of the membranes. Good agreement between UMFI and other models was found.

Variability and limits of the unified membrane fouling index: application to the reduction of low-pressure membrane fouling by ozonation and biofiltration

The impacts of ozone (0–8 mg O3 L-1) and filtration with biological activated carbon on membrane fouling by surface waters were investigated using three low-pressure membranes (two ceramics—UF or MF—and one polymeric—UF). The unified membrane fouling index (UMFI) was used to quantify the reversibility and irreversibility of membrane fouling. Minimum UMFI were calculated and repeatability assays were performed in order to evaluate the analytical detection limit and the precision of the method, respectively. The lowest ozone dose tested (1 mg O3 L-1) reduced the total fouling by 44, 63, and 41% for the polymeric membrane, the UF ceramic membrane, and the MF ceramic membrane, respectively. Further increase of the dose led to minor or no improvement, except for the ceramic MF membrane. For the ceramic membranes, a similar trend to that observed for total fouling was observed for hydraulically irreversible fouling. For the polymeric membrane, the hydraulically and chemically irreversible fouling were too low to be measured. Although biofiltration reduced the average dissolved organic carbon and turbidity by 25 and 50%, respectively, no significant fouling reduction was observed. The results indicate that irreversible fouling measurements are highly variable and most of the time below the analytical detection limit.

Membrane foulants and fouling mechanisms in microfiltration and ultrafiltration of an activated sludge effluent

Membrane fouling in microfiltration (MF) and ultrafiltration (UF) of an activated sludge (AS) effluent was investigated. It was found that the major membrane foulants were polysaccharides, proteins, polysaccharide-like and protein-like materials and humic substances. MF fouling by the raw effluent was governed by pore adsorption of particles smaller than the pores during the first 30 minutes of filtration and then followed the cake filtration model. UF fouling could be described by the cake filtration model throughout the course of filtration. Coagulation with alum and (poly)aluminium chlorohydrate (ACH) altered the MF fouling mechanism to follow the cake filtration model from the beginning of filtration. The MF and UF flux improvement by coagulation was due to the removal of some of the foulants in the raw AS effluent by the coagulants. The MF flux improvement was greater for alum than for ACH whereas the two coagulants performed equally well in UF. Coagulation also reduced hydraulically irreversible fouling on the membranes and this effect was more prominent in MF than in UF. The unified membrane fouling index (UMFI) was used to quantitatively evaluate the effectiveness of coagulation on membrane flux enhancement.

Novel approach for the analysis of bench-scale, low pressure membrane fouling in water treatment

The concept of the unified membrane fouling index (UMFI) was introduced recently for assessing the fouling of low pressure membranes (LPM) used in water treatment. The major advantages of the UMFI over most other fouling indices are the universality (independent of filtration scale or mode) and specificity (based on the actual membrane of interest for full-scale application). This study applied the concept of the UMFI to the assessment of fouling results obtained in a bench-scale fouling study. This study was conducted with combinations of four commercially available LPMs and four natural waters (including secondary wastewater effluent) under systematically varied hydrodynamic conditions. It was found that, with the adoption of the UMFI, the fouling potential of different membrane and water combinations can be presented in a unified, concise, and quantitative way, enabling quantitative and integrated assessment of the fouling data and their relationships with different potential fouling factors. Expansion of the UMFI concept to other studies is anticipated to assist in the integration of the vast amount of bench-scale fouling results obtained with different LPMs; this integration is crucial to the mechanistic understanding of LPM fouling.

Unified Membrane Fouling Index for Low Pressure Membrane Filtration of Natural Waters: Principles and Methodology

Membrane filtration is considered an important technology that can contribute to the sustainability of water supplies. However, its continued development necessitates the establishment of proper techniques for the assessment of membrane fouling. Unified Membrane Fouling Index (UMFI) was developed in this study in order to quantify and assess the fouling of low-pressure membranes (LPM) observed at various scales of water treatment. The foundation of UMFI is a revised Hermia model applied to both constant pressure and constant flux filtration. The adoption of UMFI makes it possible to simplify and standardize the bench-scale testing of membrane fouling potential by directly using the commercial LPM of interest. This approach can overcome a major challenge to fouling assessment, i.e., the membrane-specificity of fouling potential, which has not been wholly addressed by existing fouling indices. The fundamentals of UMFI are presented in this paper, together with the methodology for bench-scale testing. The application of UMFI to the assessment of the fouling of a LPM by a natural surface water is also discussed. Good agreement between bench-scale UMFI and pilot-scale UMFI was found, suggesting the validity of this new scientific concept for environmental applications.