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.

No abstract

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.