Pressure-driven membrane processes are often used for the separation and purification of organic compounds originating from biomass. However, membrane fouling remains a challenge as these biobased streams have a very complex composition and comprise a high fouling tendency. Conventional, the fouling is monitored based on either a decrease in flux or an increase in pressure over time. Those conventional techniques provide no information on the location, composition or amount of fouling. As fouling is often cumulative, it will be detected as a loss of performance. Once fouling becomes irreversible, it is often not possible to clean the membrane without chemicals and the filtration/separation process has to be stopped eventually. In situ real-time monitoring of membrane fouling could provide dynamic information on the development of fouling, allowing optimization of the process. This paper reviews the state of the art in in situ monitoring techniques that could be applied to membrane processes in the biotechnology, biorefinery and food sectors and briefly reflects on the current awareness of in situ monitoring techniques among experienced industrial users of membrane processes. The physical principles as well as the strengths and weaknesses are addressed, and potentially, promising techniques are identified.

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The rapid and accurate detection of food pathogens plays a critical role in the early prevention of foodborne epidemics.Current bacteria identification practises, including colony counting, polymerase chain reaction (PCR) and immunological methods, are time consuming and labour intensive; they are not ideal for achieving the required immediate diagnosis. Different SERS substrates have been studied for the detection of foodborne microbes. The majority of the approaches are either based on costly patterning techniques on silicon or glass wafers or on methods which have not been tested in large scale fabrication. We demonstrate the feasibility of analyte specific sensing using mass-produced, polymer-based low-cost SERS substrate in analysing the chosen model microbe with biological recognition. The use of this novel roll-to-roll fabricated SERS substrate was combined with optimised gold nanoparticles to increase the detection sensitivity.Distinctive SERS spectral bands were recorded for Listeria innocua ATCC 33090 using an in-house build (785 nm) near infra red (NIR) Raman system. Results were compared to both those found in the literature and the results obtained from a commercial time-gated Raman system with a 532 nm wavelength laser excitation. The effect of the SERS enhancer metal and the excitation wavelength on the detected spectra was found to be negligible. The hypothesis that disagreements within the literature regarding bacterial spectral results from conditions present during the detection process has not been supported. The sensitivity of our SERS detection was improved through optimization of the concentration of the sample inside the hydrophobic polydimethylsiloxane (PDMS) wells. Immuno-magnetic separation (IMS) beads were used to assist the accumulation of bacteria into the path of the beam of the excitation laser. With this combination we have detected L i s t e r i a w i t h g o l d e n h a n c e d S E R S i n a l a b e l f r e e m a n n e r f r o m s u c h l o w s a m p l e c o n c e n t r a t i o n s a s 1 0 4 CFU/ml.Figure 10. a) A normalised concentration series for LOD estimation. b) An exponential fit for the normalised concentration series in logarithmic scale for the entire series and a linear fit for the small concentrations. c) Comparison of the 737 cm -1 peak intensity for different concentration series with 5 -10 µl dried IMS bound L. innocua ATCC 33090 samples placed with AuNPs into a 1 -1.5 mm PDMS well on top of SERS substrate. d) Comparison of baseline corrected Raman intensities for three of the concentration series. All figures are a mean of 9 measurement points with mean absolute deviations.

Membrane fouling is the major factor limiting the wider applicability of the membrane-based technologies in water treatment and in separation and purification processes of biorefineries, pulp and paper industry, food industry and other sectors. Endeavors to prevent and minimize fouling requires a deep understanding on the fouling mechanisms and their relative effects. In this study, Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption technique was applied to get an insight into pore-level membrane fouling phenomena occurring in ultrafiltration of wood-based streams. The fouling of commercial polysulfone and polyethersulfone membranes by black liquor, thermomechanical pulping process water and pressurized hot-water extract was investigated with BET analysis, infrared spectroscopy, contact angle analysis and pure water permeability measurements. Particular emphasis was paid to the applicability of BET for membrane fouling characterization. The formation of a fouling layer was detected as an increase in cumulative pore volumes and pore areas in the meso-pores region. Pore blocking was seen as disappearance of meso-pores and micro-pores. The results indicate that the presented approach of using BET analysis combined with IR spectroscopy can provide complementary information revealing both the structure of fouling layer and the chemical nature of foulants.

Adsorptive fouling, by phenolic compounds, is a serious issue regarding the development and use of membrane based filtration technologies for water purification and wastewater treatment. We have developed a novel, combined, protocol of Raman spectroscopy and surface plasmon resonance (SPR) experiments, along with molecular dynamics (MD) simulation, to study the interaction of vanillin, a model phenolic compound, with the polyethersulfone (PES) surface of a membrane. The adsorption of vanillin to the PES surface was found to be highly pH dependent; the source of this was determined, by MD simulation, to be the stronger interaction with the protonated form of vanillin, predominant at low pH. Vanillin interacts with the PES surface, both through entropy driven, hydrophobic, interactions and, for the case of the protonated form, H-bonding of the hydroxyl group with the sulphur oxygens of the PES molecules. In addition to general insight into the fouling process that can be used to develop new methods to inhibit adsorptive fouling, our results also elucidate the specific interaction of the PES membrane with vanillin that can be used in the development of anti-fouling coatings, based on the structure of vanillin.

In this study cellulose-rich membranes were fabricated from untreated and treated hardwood biomass solutions in 1-ethyl-3-methylimidazolium acetate ([Emim][OAc])—dimetylsulfoxide (DMSO) system via wet phase separation. Wood treatment methods aimed to get purified cellulose fraction of wood. Treatment sequence was as followed: deep eutectic solvent pretreatment, sodium chlorite bleaching, and alkaline treatment. Resulted biomass after each treatment step was characterized by chemical composition and crystalline fraction content. Flat-sheet membranes were produced from biomass samples after each treatment step. Characterization of membranes included measurements of pure water permeability and (poly)ethyleneglycol 35 kDa retention, Fourier-transform infrared and Raman spectroscopy, X-ray diffraction measurements and thermogravimetric analysis. The study revealed that it was possible to fabricate membrane from untreated wood as well as from wood biomass after each of treatment steps. The resulted membranes differed in chemical composition and filtration performance. Membrane prepared directly from untreated wood had the highest permeability, the lowest retention; and the most complex chemical composition among others. As treatment steps removed lignin and hemicelluloses from the wood biomass, the corresponding membranes became chemically more homogeneous and showed increased retention and decreased permeability values.

Fouling as an intricate process is considered as the main obstacle in membrane technologies, and its control is one of the main areas of attention in membrane processes. In this study, a commercial polyethersulfone ultrafiltration membrane (MWCO: 4000 g/mol) was surface modified with different concentrations of vanillin as an antifouling and hydrophilicity promoter to improve its performance. The presence of vanillin and its increasing adsorption potential trends in higher vanillin concentrations were clearly confirmed by observable changes in FTIR (Fourier transform infrared) spectra after modification. Membranes with better hydrophilicity (almost 30% lower contact angle in the best case) and higher polyethylene glycol solution (PEG) permeability were achieved after modification, where a 35–38% increase in permeability of aqueous solution of PEG was perceived when the membrane was modified at the highest exposure concentration of vanillin (2.8 g/L). After filtration of wood extract, surface modified membrane (2.8 g/L vanillin) showed better antifouling characteristics compared to unmodified membrane, as indicated by approximately 22% lower pure water flux reduction, which in turn improved the separation of lignin from the other organic compounds present in wood extract.

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