Laser Doppler Electrophoresis and electro-osmotic flow mapping: A novel methodology for the determination of membrane surface zeta potential

A novel technique employing an Uzigirs dip cell arrangement is used in conjunction with Laser Doppler Electrophoresis for the determination of the surface zeta potential for a UF, NF, and RO membrane. To the authors best knowledge this is the first study employing Laser Doppler Electrophoresis and Electro-osmotic Flow Mapping for membrane surface charge determination. High correlation of the regression fit (R2>0.95) for a carboxylated polystyrene latex particle electrophoretic mobility was achieved at low electrolyte concentrations (1mM and 10mM NaCl), but the reliability and accuracy of the extrapolated zeta potential values were problematic at higher concentration due to high measurement uncertainty (>10% in some cases). Changes in the applied electric field increased the phase resolution of 50mM NaCl electrolyte solutions between 0.5-2.0V. However, the effects of Joule heating at higher voltages compromised 50mM NaCl sample integrity. When compared with the established Tangential Streaming Potential method, Laser Doppler Electrophoresis measurements provided similar zeta potential values and trends indicating that this new methodology can indeed be employed for membrane characterization purposes; however, further research needs to be conducted in order to optimize this new technique and set appropriate operating limits

Utilising light-emitting diodes of specific narrow wavelengths for the optimization and co-production of multiple high-value compounds in Porphyridium purpureum

The effect of specific narrow light-emitting diode (LED) wavelengths (red, green, blue) and a combination of LED wavelengths (red, green and blue - RGB) on biomass composition produced by Porphyridium purpureum is studied. Phycobiliprotein, fatty acids, exopolysaccharides, pigment content, and the main macromolecules composition were analysed to determine the effect of wavelength on multiple compounds of commercial interest. The results demonstrate that green light plays a significant role in the growth of rhodophyta, due to phycobiliproteins being able to harvest green wavelengths where chlorophyll pigments absorb poorly. However, under multi-chromatic LED wavelengths, P. purpureum biomass accumulated the highest yield of valuable products such as eicosapentaenoic acid (~2.9 %DW), zeaxanthin (~586 μg g− 1 DW), β-carotene (397 μg g− 1 DW), exopolysaccharides (2.05 g/L-1), and phycobiliproteins (~ 4.8 % DW). This increased accumulation is likely to be the combination of both photo-adaption and photo-protection, under the combined specific wavelengths employed

Characterisation of Mass Transfer in Frontal Nanofiltration Equipment and Development of a Simple Correlation

This aim of this work was to investigate the effects of mass transfer in three commercially available frontal nanofiltration systems (Amicon, Sterlitech and Membranology) using the rejection of uncharged poly ethylene glycol (molecular weight 3400) at different pressures and stirrer speeds using a 4000 MWCO membrane. The real rejection was calculated from the observed rejection using the infinite rejection method and a comparison was made between experimentally obtained mass transfer coefficients and those obtained from commonly used ultrafiltration theory. A new mass transfer correlation was proposed that is more appropriate to account for the increased mass transfer effects observed with the larger pressures of nanofiltration. This new correlation is defined as NSh = j(NRe)n (NSc)0.33(1+(Jv/wr)x) is only a minor modification to existing theory and has an accuracy suitable for engineering design purposes

Valorising Nutrient-Rich Digestate as a Waste-Based Media for Microalgal Cultivation: Bench-Scale Filtration Characterisation and Scale-Up for a Commercial Recovery Process

Cultivating microalgae requires a nitrogen and phosphorous feed source. Anaerobic digestion waste (digestate) provides a cheap sustainable feedstock for these materials. Previous studies have successfully demonstrated the feasibility of nutrient recovery and subsequent algae growth. There is now a need to fully characterise digestate filtration to improve our understanding of this process prior to its commercialisation. In this work, digestate filtration is characterised at bench scale using frontal (dead-end) filtration and a 100 kDa MWCO ultrafiltration membrane. Our experiments demonstrated rapid cake formation causing significant flux decline. The steady-state permeate flux for digestate was 2.4 to 4.8 L m−2 h−1, a reduction of ~90% compared to clean water flux. The specific cake resistance was ~1015 m kg−1 and the compressibility index 1.07. A series of four filtration and cleaning cycles showed 90% flux recovery following a clean water wash. Digestate filtration was then evaluated at a commercial scale using crossflow and the KOCH ABCOR® tubular membrane (100 kDa MWCO). The results were similar to those at the bench scale, i.e., rapid initial fouling leading to a period of steady-state flux (approximately 7 L m−2 h−1). The commercial membrane was flushed with water and diluted bleach after each use, and a digestate permeate flux decline of only 4.8% over a 12-month active use period was observed. The present research provides bench scale characterisation and demonstrates the commercial scale operation of anaerobic digestate filtration using ultrafiltration. The overall filtration performance was excellent, and the process can now be scaled to any operational capacity

Minimizing the Energy Requirement of Dewatering Scenedesmus sp. by Microfiltration: Performance, Costs, and Feasibility

The harvesting of the microalgae Scenedesmus species using a 200 L pilot-scale microfiltration system was investigated and critically assessed. The energy requirement was determined and correlated to the different operating parameters, such as transmembrane pressure (Δ<i>P</i>), membrane area, temperature, and initial biomass concentration. A filtration model was developed and showed a strong correlation with experimental data up to 20.0 g of dry cell weight (DCW)/L. The non-optimized filtration system had an energy requirement of 2.23 kWh/m³ with an associated cost of $0.282/kg of microalgae. The investigation into the influence of the operating parameters and scale-up effects showed that the energy requirement could be substantially reduced to 0.90 kWh/m³ and$0.058/kg of microalgae harvested. Maintenance costs associated with cleaning were estimated to be 0.23 kWh or $0.029/batch of microalgae processed. Dependent upon the operating conditions, harvesting may represent 6–45% of the energy embedded in the microalgae with a carbon footprint of 0.74–1.67 kg of CO₂/kg of microalgae. Microfiltration was demonstrated to be a feasible microalgae harvesting technology allowing for more than 99% volume reduction. The energy requirement and associated carbon footprint of microalgae harvesting reported here do not forfeit the need for an industrial-scale study; however, the information provided presents a more realistic approximation than the literature reported to date

Laser Doppler electrophoresis and electro-osmotic flow mapping for the zeta potential measurement of positively charged membrane surfaces

Successful characterization of membranes is of paramount importance for the development and improvement of novel membranes and membrane processes. The characterisation of membrane charge is key to understanding charge interactions between the process stream and the membrane and is typically represented by the surface zeta potential. In a previous paper (Thomas et al., 2017), a novel technique employing an Uzigirs dip cell arrangement used in conjunction with Laser Doppler Electrophoresis was used to characterize the surface of several negatively charged membranes. In this paper, positively charged modified PTFE membranes are fabricated and the novel zeta potential measurement technique is utilised to quantify the resultant membrane charge by use of a positively charged amidine tracer particle. The amidine particles were characterised and shown to have a positive zeta potential of 12.4 mV for the experimental conditions used. A comparative analysis was made between the novel laser Doppler electrophoresis measurements and tangential streaming potential measurements for the positive membrane and the agreement was good. The phase plot and mobility-displacement were of good quality for the data set, with the surface equivalent mobility being 0.632 μmcm/Vs with R2 = 0.977. In addition, a series of experiments were conducted to explore the operating envelope and highlight the pitfalls of the technique, i.e. oppositely charged particles to the surface should not be used. Overall, this work expands the application of the novel zeta potential measurement technique to span all membrane charge types. Thus providing a real benefit to the practicing scientist or engineer by having a reliable, fast and simple zeta potential technique that uses only a very small membrane sample