Michel Y. Jaffrin

Contribution of various constituents of activated sludge to membrane bioreactor fouling

Urban effluents were treated in a pilot membrane bioreactor (MBR) fed by raw wastewater from a sewage plant. The MBR consisted of an aerated tank fed with raw water containing a volume of 600 l of activated sludge which was recirculated through an external circuit containing a ceramic membrane of 0.25 m2 area with 0.1 μm pores. Suspended solids (SS) concentration was stabilized at 10 g/l. The sludge and hydraulic residence times (SRT and HRT) were 60 days and 24 h, respectively. Elimination of chemical oxygen demand was higher than 95%. Rheological tests showed that activated sludges from the MBR and from the aeration tank of a classical plant were non-Newtonian. In order to evaluate the contribution of various sludge fractions to fouling, SS were first separated from the sludge by settling, then colloids were separated from the supernatant by a combination of flocculation and settling. The relative contributions of SS, colloids, and dissolved molecules (DM) to the resistance to filtration caused by fouling were found to be 65%, 30% and 5%, respectively. The filtration resistance due to each constituent was also measured as a function of its concentration. The permeate flux did not decrease much when cellular concentration rose from 2 to 6 g/l. The measured total filtration resistance was then compared with the sum of resistances of each constituents at the same respective concentrations as in the sludge. This calculated sum was found to be 50% higher than the measured total resistance, indicating that fouling resistances caused by each constituent were not additive.

Body fluid volumes measurements by impedance: A review of bioimpedance spectroscopy (BIS) and bioimpedance analysis (BIA) methods

This paper reviews various bioimpedance methods permitting to measure non-invasively, extracellular, intracellular and total body water (TBW) and compares BIA methods based on empirical equations of the wrist-ankle resistance or impedance at 50 kHz, height and weight with BIS methods which rely on an electrical model of tissues and resistances measured at zero and infinite frequencies. In order to compare these methods, impedance measurements were made with a multifrequency Xitron 4200 impedance meter on 57 healthy subjects which had undergone simultaneously a Dual X-ray absorptiometry examination (DXA), in order to estimate their TBW from their fat-free-mass. Extracellular (ECW) and TBW volumes were calculated for these subjects using the original BIS method and modifications of Matthie[Matthie JR. Second generation mixture theory equation for estimating intracellular water using bioimpedance spectroscopy. J Appl Physiol 2005;99:780-1], Jaffrin et al. [Jaffrin MY, Fenech M, Moreno MV, Kieffer R. Total body water measurement by a modification of the bioimpédance spectroscopy method. Med Bio Eng Comput 2006;44:873-82], Moissl et al. [Moissl UM, Wabel P, Chamney PW, Bosaeus I, Levin NW, et al. Body fluid volume determination via body composition spectroscopy in health and disease. Physiol Meas 2006;27:921-33] and their TBW resistivities were compared and discussed. ECW volumes were calculated by BIA methods of Sergi et al. [Sergi G, Bussolotto M, Perini P, Calliari I, et al. Accuracy of bioelectrical bioimpedance analysis for the assessment of extracellular space in healthy subjects and in fluid retention states. Ann Nutr Metab 1994;38(3):158-65] and Hannan et al. [Hannan WJ, Cowen SJ, Fearon KC, Plester CE, Falconer JS, Richardson RA. Evaluation of multi-frequency bio-impedance analysis for the assessment of extracellular and total body water in surgical patients. Clin Sci 1994;86:479-85] and TBW volumes by BIA methods of Kushner and Schoeller [Kushner RF, Schoeller DA. Estimation of total body water by bioelectrical impedance analysis. Am J Clin Nutr 1986;44(3):417-24], Lukaski et al. [Lukaski HC, Bolonchuk WW. Estimation of body fluid volumes using tetrapolar bioelectrical impedance measurements. Aviat Space Environ Med 1988;59:1163-9], Hannan et al. [Hannan WJ, Cowen SJ, Fearon KC, Plester CE, Falconer JS, Richardson RA. Evaluation of multi-frequency bio-impedance analysis for the assessment of extracellular and total body water in surgical patients. Clinical Science 1994;86:479-85], Deurenberg et al. [Deurenberg P, van der Koy K, Leenen R, Westrate JA, Seidell JC. Sex and age specific prediction formulas for estimating body composition from bioelectric impedance: a cross validation study. Int J Obesity 1991;15:17-25] These volumes were compared against those given by BIS method and, in the case of TBW, with those by DXA. For ECW, a good agreement was found between various BIS methods and that of Sergi while Hannans values were higher. Both Matthies and Moissls methods gave mean TBW resistivities and volumes lower than those of Jaffrins and DXA methods. Kushner et al. method gave values of TBW not significantly different from those of Jaffrin et al. and DXA, as Hannans method in men, but Lukaski and Deurenberg methods led to an underestimation.

Body composition determination by bioimpedance: an update

Purpose of reviewTo review various methods for measuring body composition by bioimpedance and their limitations, as well as available impedance meters, including body fat analyzers for home use. Recent findingsBioimpedance spectroscopy, which requires multifrequency impedance meters, is preferable for fluid volume measurements, especially extracellular fluid, whereas bioimpedance analysis at 50 kHz is more widely used for measuring fat-free mass. A method for using bioimpedance spectroscopy equations with 50 kHz impedance meters has been recently proposed and successfully tested. Low cost foot-to-foot impedance meters (body fat analyzers) with plantar electrodes on a body scale, that are easy and fast to use, have been compared with medical impedance meters and with dual X-ray absorptiometry measurements and found reasonably accurate, except for individuals with very low or high BMI. SummaryBody composition by bioimpedance is gaining acceptance in nutrition, hemodialysis, gerontology and sports medicine. Body fat analyzers that have been validated by comparison with dual x-ray absorptiometry could be useful to general practitioners, nutritionists and cardiologists.

A two-stage ultrafiltration and nanofiltration process for recycling dairy wastewater.

A two-stage ultrafiltration and nanofiltration (UF/NF) process for the treatment of model dairy wastewater was investigated to recycle nutrients and water from the wastewater. Ultracel PLGC and NF270 membranes were found to be the most suitable for this purpose. In the first stage, protein and lipid were concentrated by the Ultracel PLGC UF membrane and could be used for algae cultivation to produce biodiesel and biofuel, and the permeate from UF was concentrated by the NF270 membrane in the second stage to obtain lactose in retentate and reusable water in permeate, while the NF retentate could be recycled for anaerobic digestion to produce biogas. With this approach, most of dairy wastewater could be recycled to produce reusable water and substrates for bioenergy production. Compared with the single NF process, this two-stage UF/NF process had a higher efficiency and less membrane fouling.

Permeate flux enhancement by pressure and flow pulsations in microfiltration with mineral membranes

Abstract We have investigated the possibility of permeate flux enhancement with mineral membranes using pressure and flow pulsations superimposed on the inlet flow of the filtration module. These pulsations are generated by a piston in a cylinder; various pressure wave shapes, generated by controlling the piston motions, have been tried. One wave form (fast piston return followed by a fast forward stroke) was found to yield the largest permeate flux increase, up to 45%, at 1 Hz frequency and with stroke volumes smaller than the internal volume of the membrane. Carefully chosen pulsation decrease the hydraulic power dissipated in the retentate per unit volume of permeate by up to 30%.

Simultaneous Convective and Diffusive Mass Transfers in a Hemodialyser

The mass transfer in a hemodialyser in the presence of combined dialysis and ultrafiltration has been calculated by integration of mass fluxes across the boundary layers in blood and dialysate phase taking into account the partial rejection of solute as well as changes in local blood flow and ultrafiltration flux along the membrane. Clearances of creatinin, vitamin B12, and myoglobin have been calculated as a function of blood and ultrafiltrate flow rate and were found to be in good agreement with in vitro measurements. The data suggest the following empirical correlation for the hemodiafiltration clearance.

Cake growth mechanism in cross-flow microfiltration of mineral suspensions

Abstract This paper describes the fouling mechanism in cross-flow filtration of a mineral CaCO3 suspension. Since the minimum particle size (1 μm for a mean of 6 μm) was larger than the pore size (0.2 μm) of the ceramic membrane, fouling is in this case exclusively superficial and Brownian diffusion effects are negligible. The transmembrane pressure was increased and decreased in steps at constant velocity to form successive cycles. The permeate flux variation presented a hysteresis which is interpreted as an irreversible compression of the cake deposited on the membrane. Cake resistance was measured as a function of the pressure in the permeation experiments. The porosity was calculated from Erguns equation and found to be a function of the pressure gradient in the cake. The mean cake thickness in the microfiltration experiments was calculated as a function of the pressure drop across the cake using the porosity data from the permeation experiments. The thickness was found to be a significant fraction of the membrane radius (up to 38%). This result suggested that the cake growth was limited by the shear stress acting on its surface. The cake grew as long as the top particle layer obeyed the Coulomb friction equilibrium. When due to an increase in shear stress by lumen reduction the Coulomb equilibrium was not satisfied, incident particles were ripped off the surface and the cake ceased to grow. However, subsequent pressure reduction did not decrease the cake thickness because of its irreversible compressibility.

Extracellular and intracellular volume variations during postural change measured by segmental and wrist-ankle bioimpedance spectroscopy

Extracellular (ECW) and intracellular (ICW) volumes were measured using both segmental and wrist-ankle (W-A) bioimpedance spectroscopy (5-1000 kHz) in 15 healthy subjects (7 men, 8 women). In the 1st protocol, the subject, after sitting for 30 min, laid supine for at least 30 min. In the second protocol, the subject, who had been supine for 1 hr, sat up in bed for 10 min and returned to supine position for another hour. Segmental ECW and ICW resistances of legs, arms and trunk were measured by placing four voltage electrodes on wrist, shoulder, top of thigh and ankle and using Hanais conductivity theory. W-A resistances were found to be very close to the sum of segmental resistances. When switching from sitting to supine (protocol 1), the mean ECW leg resistance increased by 18.2%, that of arm and W-A by 12.4%. Trunk resistance also increased but not significantly by 4.8%. Corresponding increases in ICW resistance were smaller for legs (3.7%) and arm (-0.7%) but larger for the trunk (21.4%). Total body ECW volumes from segmental measurements were in good agreement with W-A and Watson anthropomorphic correlation. The decrease in total ECW volume (when supine) calculated from segmental resistances was at 0.79 l less than the W-A one (1.12 l). Total ICW volume reductions were 3.4% (segmental) and 3.8% (W-A). Tests of protocol 2 confirmed that resistance and fluid volume values were not affected by a temporary position change.

Microfiltration and ultrafiltration of UHT skim milk with a vibrating membrane module

Abstract Dairy applications of a vibratory shear-enhanced (VSEPPUR) filtration system were investigated using a 500 cm 2 membrane area pilot. Commercial UHT skim milk was ultrafiltered with a 50 kDa PES membrane for concentrating total proteins. The effect of mean membrane shear rate γ w was investigated by lowering the vibration frequency. The permeate flux was found to vary as γ w 0.533 at initial concentration and as γ w 0.567 at a volume reduction ratio (VRR) of 1.8. The permeate flux decayed with the logarithm of concentration and the maximum VRR calculated by extrapolation to zero flux was 8.66. The critical flux for stable filtration was found to be 76 l h −1 m −2 at the maximum frequency of 60.75 Hz, corresponding to a mean shear stress on the membrane of 50 Pa. Microfiltration tests were carried out with a 0.1 μm pores Teflon membrane for separating casein micelles. The permeate flux increased with γ w , but with a lower exponent than in UF, especially at high frequency. The critical flux at 60.75 Hz and initial concentration was 64 l h −1 m −2 , thus lower than in UF. A comparison with critical fluxes reported in the literature for UF and MF of skim milk indicates a larger domain of filtration stability for the VSEPPUR than for cross-flow filtration with tubular membranes.

Optimization of ultrafiltration and diafiltration processes for albumin production

This paper presents a model of the combined ultrafiltration-diafiltration process used by plasma fractionation centers to prepare human albumin by Cohns ethanol precipitation technique. This process consists of a predilution to lower the ethanol concentration Ca from 40 to 20%, a preconcentration phase to raise albumin concentration to ∼ 80 g/l, a diafiltration to reduce ethanol concentration to 0.1 g/l and a final concentration of albumin to 210 g/l. Laboratory scale experiments were run with water-ethanol solutions of bovine albumin at various concentrations to determine, for each membrane tested, a correlation for the permeate flux as a function of Ca and Cp. The model was used to determine the effects of initial dilution and albumin concentration at diafiltration on a normalized process time, which is defined as the time necessary to process 1 kg of albumin with 1 m2 of membrane. Optimal initial ethanol concentrations were found to depend upon the membrane material (30% for polysulfone, 16% for cellulose acetate) and the minimum process time was generally obtained when diafiltration was carried out at the maximum albumin concentration.