Wirote Youravong

Critical Flux in Ultrafiltration of Skimmed Milk

The best operating conditions, using the critical flux concept during ultraflltration of skimmed milk, were evaluated for tubular membranes. It was found that irreversible fouling was greatly reduced by operating at or below the critical flux, but was not totally eliminated. The critical flux of skimmed milk was found to be the weak form. The critical flux at cross flow velocity 3.4ms–1 for MWCO 200 kDa membrane was 56.9 kgm–2h–1 while for MWCO 25 kDa membranes it was 45 kgm–2h–1 suggesting that membrane pore size influenced the flux. The critical flux increased with increasing wall shear stress and decreased with increasing protein concentration. Empirical equations, for predicting the critical flux (Jcrit) for skimmed milk with a protein concentration (Cb) in the range 3–7% w/w and wall shear stress (τw) in the range 7–60 Pa for MWCO 200 kDa and 25 kDa membranes were Jcrit = 5.1 (τw/Cb) and Jcrit = 4.0 (τw/Cb) respectively. In general, the rejections of protein and lactose at the critical flux were not affected by protein concentration,wall shear stress and membrane used, and they were similar to those found when operating at the limiting flux.

Effect of hydrodynamic and physicochemical changes on critical flux of milk protein suspensions.

The critical flux during ultrafiltration of whey protein concentrate and sodium caseinate suspensions was investigated. The weak form of critical flux was found for both suspensions. Critical flux of sodium caseinate was higher than that of whey protein concentrate. This could be due to the differences in particle size of the suspensions, resulting in a slower particle back transportation for small particles (whey proteins) compared to the larger casein micelles. Critical flux increased as crossflow velocity increased and decreased as concentration increased, suggesting that critical flux was determined by competition between rate of particle removal from the membrane surface and rate of particle movement towards the membrane surface. Influence of changing pH, addition of NaCl and CaCl2 on the critical fluxes of both protein suspensions was also studied. Increasing pH led to an increase in critical flux for both protein suspensions, suggesting that electrostatic repulsive forces are involved in determining critical flux in both cases. Addition of NaCl gave rise to a decrease in electrostatic interactions due to an increase in ionic strength and zeta potential, and resulted in a decrease in critical flux for sodium caseinate, but had no significant effect for whey protein concentrate. Addition of CaCl2 resulted in a decrease in the critical flux and had a more pronounced influence than NaCl. These results suggest that, in addition to electrostatic repulsive forces, other factors such as structure of protein may be involved in determining the critical flux.

Performance evaluation of novel PVDF–Cloisite 15A hollow fiber composite membranes for treatment of effluents containing dyes and salts using membrane distillation

The present study reports the performance of a novel PVDF–Cloisite 15A hollow fiber composite membrane for the treatment of effluents containing dyes and salts through a direct contact membrane distillation (DCMD) process. The performance of the membrane was evaluated by varying several important parameters during the DCMD process which included feed properties (type of dyes, dye and salt concentration) and process conditions (feed temperature and flow rate). The experimental results showed that the in-house made membrane was able to achieve stable fluxes and excellent dye rejections (>97%) when tested with feed solutions containing dyes of different classes and molecular weights (MW), except crystal violet (CV) dye. The lower rejection resulting from a CV-containing feed is likely due to its small MW coupled with its high diffusion rate in aqueous solution. With respect to feed concentration, it is found that an increase in salt concentration in the feed solution had a negligible effect on the membrane separation performance. Increasing the dye concentration in the feed however led to lower membrane water flux owing to the deposition of dye particles on the membrane surface which resulted in severe fouling. Meanwhile, increasing the feed temperature and its flow rate could improve the membrane flux without affecting the permeate quality. When tested using a dyeing solution containing 50 ppm acid red and 1.0 M NaCl, the membrane flux was reported to enhance by 200% and 25% on increasing the feed temperature from 50 to 90 °C and the flow rate from 0.010 to 0.023 m s−1, respectively.

Triple helical structure of acid-soluble collagen derived from Nile tilapia skin as affected by extraction temperature.

BACKGROUND Fish skin has become a new source of collagen. It is usually extracted at low temperature. Increasing the extraction temperature can increase the collagen yield. However, high temperature might cause degradation of the triple helical structure of collagen, which is related to its functional biomaterial. This work thus aimed to investigate the effect of extraction temperature on the extraction efficiency and characteristics of acid-soluble collagen (ASC), particularly its triple helical structure. RESULTS ASC was extracted at 5 ± 1, 15 ± 1 and 25 ± 1 °C for 0-24 h with 0.3 or 0.5 mol L(-1) acetic acid. The results showed that extraction with 0.5 mol L(-1) acetic acid gave a higher extraction efficiency than that in 0.3 mol L(-1) acetic acid (P < 0.5). Extraction at 25 ± 1 °C for 5 h with 0.5 mol L(-1) acetic acid gave a higher extraction efficiency (73.73 ± 1.28%), which is higher than that of 5 ± 1 °C by about 1.7-fold. All ASC obtained were identified as type I collagen and showed similar physicochemical properties. CONCLUSION The results showed that extraction temperature strongly affected extraction efficiency. Extraction at 25 °C did not affect the triple helical structure, which was confirmed by the results of Fourier transform infrared, circular dichroism spectrum and collagen self-assembly.

Permeate Flux Enhancement in Ultrafiltration of Tofu Whey Using pH-Shifting and Gas-Liquid Two-Phase Flow

Tofu whey contains nutrients such as proteins and oligosaccharides, and ultrafiltration (UF) was employed to recover protein and to obtain UF-permeate containing oligosaccharides. The experiments were carried out using hollow fiber membranes with different molecular weight cutoff (MWCO) to evaluate protein and saccharide retentions. The MWCO100 kDa gave higher permeate flux and lower saccharides retention compared with 30 kDa membrane. Further away pH from isoelectric point (pH4.5) resulted in higher flux improvement. Flux increased with CFV and TMP. In addition, the use of gas-liquid two-phase flow with gas injection factor of 0.45, could enhance flux up to 45.1%.

Applications and characterization of silicalite-1/polydimethylsiloxane composite membranes for the pervaporation of a model solution and fermentation broth

Abstract Ethanol recovery via pervaporation is greatly influenced by membrane separation performance, which can be enhanced by adding hydrophobic fillers such as silicalite-1. Silicalite-1 was prepared by controlling the gel molar composition in hydrothermal synthesis, and it was incorporated into a polydimethylsiloxane (PDMS) membrane on Teflon. The silicalite-1 Si-O-Si structures interacted with the -Si(CH3)2-O- backbone of the PDMS chain. The thermal gravimetric analysis results showed that the silicalite-1 improved the thermal stability and raised the initial decomposition temperature from 405°C to 450–470°C. Increasing silicalite-1 content from 5 to 20 wt% enhanced the relative ethanol/water swelling from 1.33% to 1.52% and advanced the contact angle from 112.6° to 138.6°. Addition of 20 wt% silicalite-1 improved the separation factor in broth from 2.55 to 5.56. When using 20 wt% silicalite-1/PDMS membrane and replacing the ethanol solution with broth, fouling reduced the flux from 597 to 482 g m−2 h−1, but the broth composite increased the separation factor from 3.14 to 5.56. The overall pervaporation separation index with a santol broth of the 20 wt% silicalite-1/PDMS and commercial PDMS membranes were 2199 and 2110. The prepared membranes had similar overall performance as a commercial membrane.

The Anticoagulant and Angiotensin I-Converting Enzyme (ACE) Inhibitory Peptides From Tuna Cooking Juice Produced By Alcalase

Background: Tuna Cooking Juice (TCJ) is a by-product of canned tuna industry. It usually was either used as protein source of feed meal or directly discharged to wastewater treatment system. However, the soluble proteins in TCJ could be used for producing bioactive peptides by enzymatic hydrolysis. The aims of this study were to produce and purify the anticoagulant and ACE inhibitory peptides from TCJ. Methods: The bioactive peptides were prepared from tuna cooking juice by enzymatic hydrolysis. In this study, four commercial proteases including alcalase, flavourzyme, pancreatin and pepsin were used for enzymatic hydrolysis of tuna cooking juice. Six biological activities including angiotensin I-converting enzyme inhibitor, anticoagulant, calcium binding, hypocholesterolemic, antioxidant, and antidiabetes were determined. The hydrolysate was performed in an in vitro digestive system. The bioactive peptides were purified by size exclusion chromatography and then high performance liquid chromatography. Results: The alcalase hydrolysate at the hydrolysate time of 240 and 120 min showed the highest ACE inhibitory of 96.9±0.54% and anticoagulant activities of 92.0±0.75%, respectively. Both ACE inhibitory and anticoagulant peptides from tuna cooking juice hydrolysate were able to survive in an in vitro digestive tract and improve its activities. The molecular weight range of peptides exhibited highest ACE inhibitory and anticoagulant activities was 238-829 and 1355-1880 Da, respectively and these peptides still showed high activities. Conclusion: Therefore, tuna cooking juice is a potential source of bioactive peptides production used for functional food and neutraceutical ingredients.

Influence of gas–liquid two‐phase flow on angiotensin‐I converting enzyme inhibitory peptides separation by ultra‐filtration

BACKGROUND Membrane fouling is a major problem in ultra-filtration systems and two-phase flow is a promising technique for permeate flux enhancement. The objective of this research was to study the use of an ultra-filtration (UF) system to enrich angiotensin-I converting enzyme (ACE) inhibitory peptides from tilapia protein hydrolysate. To select the most appropriate membrane and operating condition, the effects of membrane molecular weight cut-off (MWCO), transmembrane pressure (TMP) and cross-flow velocity (CFV) on permeate flux and ACE inhibitory peptide separation were studied. Additionally, the gas-liquid two-phase flow technique was applied to investigate its effect on the process capability. RESULTS The results showed that the highest ACE inhibitory activity was obtained from permeate of the 1 kDa membrane. In terms of TMP and CFV, the permeate flux tended to increase with TMP and CFV. The use of gas-liquid two-phase flow as indicated by shear stress number could reduce membrane fouling and increase the permeate flux up to 42%, depending on shear stress number. Moreover, the use of a shear stress number of 0.039 led to an augmentation in ACE inhibitory activity of permeates. CONCLUSIONS Operating conditions using a shear stress number of 0.039 were recommended for enrichment of ACE inhibitory peptides.

Electroless Plating of Pd on Macro-Porous Alumina Support for H2 Purification

In this work, Pd metal layer was deposited on in-house prepared macro-porous disc alumina support by electroless plating. The in-house prepared support were repeatedly seeded for 4 cycles to obtain Pd nuclei before repeatedly electroless plated for 4 cycles. The 4-cycle Pd plating was to obtain the full layer of Pd metal observing from changing support surface from black to light grey. The plated membrane samples were annealed at 550 and 600oC for using in high-temperature H2 separation. The annealed samples were observed morphology by SEM and confirm the occurrence of Pd layer with EDS. The SEM images revealed incomplete Pd layer. The over 4 cycles of plating were needed to form complete Pd layer since the numerous Pd ions diffused into macro-pores alumina support instead of depositing on the surface of macro-porous support. The higher annealing temperature of 600oC led to denser layer of Pd with the presence of small cracks due to the contraction of Pd particles.

Energy Consumption for Brine Solution Recovery in Direct Contact Membrane Distillation

Direct contact membrane distillation (DCMD) process was applied for brine solution recovery. The energy consumption of the process was evaluated as varying feed temperature and cross flow velocity (CFV). The evaporation efficiency and energy consumption were also studied. The experiments was carried out using a hollow fiber PVDF membrane with pore size of 0.1 μm and NaCl 3.5 %wt as feed solution. The operating feed temperature and CFV were in range of 40 °C-70 °C and 0.14-0.42 m/s (laminar and transition flow region), respectively. The temperature and CFV of permeate were fixed at 20 °C and 1.97 m/s respectively. It was found that the flux rate was in function with the temperature, CFV and temperature polarization coefficient (TPC). The best result in terms of energy consumption and evaporation efficiency were obtained at CFV and temperature of 0.28 m/s and 70 °C about 188.6 W and 41.1 %, respectively.