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A preliminary study was carried out on the morphological design of tubular single-channel alumina membranes prepared by stereolithography, an additive manufacturing process. The geometry of the ring-patterned inner surface of membranes was optimized using computational fluid dynamics calculations and validated in microfiltration tests with aqueous suspensions of P. aeruginosa. Patterning of the inner surface of tubular membranes helped reduce cake formation at a higher value of the average crossflow velocity. The results highlight benefits of stereolithography-based approach to the morphological design of ceramic membranes. [Display omitted] • 3D-printed patterned tubular ceramic membranes are prepared by stereolithography. • CFD modeling guides membrane surface morphology design at the mesoscale. • Ring-patterning of the feed-facing surface helps alleviate membrane fouling. • Crossflow microfiltration tests with P. aeruginosa corroborate CFD predictions. • Additive manufacturing shows promise for morphological design of ceramic membranes. [ABSTRACT FROM AUTHOR]

Membrane fouling is an endemic problem in ultrafiltration used for many applications. Recently water-hammer pulsing has been shown to reduce membrane fouling. Rapid solenoid-valve closure on the retentate or permeate side of a membrane generates a pressure front that propagates and reflects at the system boundaries at the speed-of-sound. However, the mechanism whereby this mitigation occurs is not well-understood. A predictive model is developed for mitigating fouling using pulsed solenoid-valve closure in the ultrafiltration of particulates. The model assumes the boundary-layer flow that develops after the first pressure-front reflection at the upstream boundary causes an enhanced shear stress on the fouled membrane. This increased shear stress typically occurs for less than 0.01 s during each solenoid-valve closure that occurs once every several seconds. However, it has a significant effect on removing the fouling deposits because it is orders-of-magnitude larger than the shear stress of the steady state crossflow velocity. This model correlates with a Coefficient-of-Determination of 0.997 the fractional flux increase for 44 experiments spanning a range of fluxes, foulant concentrations, pressures, and solenoid-valve-closure frequencies for an aqueous whey-protein feed. The fractional flux increase was 10.7%–124% and averaged 51.2%. However, the model indicates that considerably higher flux increases are possible. Predicted fractional permeation flux increase (J ′‒ J)/ J as a function of αf / J for mitigating membrane fouling in the ultrafiltration of an aqueous whey-protein feed using water hammer; J ′ and J are the permeation fluxes in the presence and absence of water hammer, respectively, f is the solenoid-valve closure frequency, and α is a semiempirical parameter. [Display omitted] • Pulsed solenoid-valve closure can increase UF flux in the presence of fouling by as much as 124%. • Mechanism proposed for mitigation of particulate membrane fouling in the presence of water hammer. • Boundary layer generated by pressure-front reflection causes high shear stress that mitigates fouling. • Predictive model advanced that incorporates effects of flux, valve-closure frequency, pressure, and concentration. • Model correlates 44 data with CoD of 0.997 for UF concentration of aqueous whey-protein feed. [ABSTRACT FROM AUTHOR]

A new model based on the removal mechanism of loose/compact cake and the re-deposition mechanism of foulants was proposed to predict the instantaneous fouling resistance (R f (t)) in the rinsing process of 0.1 μm PAN membrane fouled with activated sludge. The variation trend of R f (t) was also analyzed by the removal rate of loose/compact cake (r r-loose / r r-compact) and the re-deposition rate of foulants (r re-deposition). Moreover, the model was validated by using other foulants (yeast, actual activated sludge, HA and SA) and membranes (0.1 μm PES and PVDF membranes). The results showed that the model predictions had good agreements with experimental data at different cross-flow velocities (1.0, 1.5, 2.0 and 2.5 m/s) or temperatures (25, 30, 35 and 40 °C) (R 2 >0.9900). Besides, the variation trend of R f (t) could be divided into three stages: (i) R f (t) quickly decreased and the removal of loose cake was almost completed at rinsing time of t 1 (first transition point) (r r-loose = 0); (ii) R f (t) slowly decreased and R f (t) reached to minimum (r r-compact = r re-deposition) at t 2 (second transition point); (iii) R f (t) slightly increased after t 2 (r r -compact (t)< r re -deposition (t)). This model would provide an accurate method to analyze the variation trend of R f (t) in the rinsing process and a theoretical basis for the optimization of rinsing conditions. [Display omitted] • A rinsing model was proposed to predict instantaneous fouling resistance (R f (t)). • The effect of rinsing mechanism on the variation trend of R f (t) were was studied. • Two transition points on the variation curve of R f (t) were determined by the model. • The removal of loose cake depended mainly on the cross-flow velocity. • The increase of temperature mainly promoted the removal of compact cake. [ABSTRACT FROM AUTHOR]

Fouling continues to be a limiting factor in membrane processes. Pulsating feed flows have the potential to decrease fouling while maintaining a constant pressure drop over the module. This study quantifies the impact of pulsating flows on particle deposition in a forward osmosis system with spacers at a mean crossflow velocity of 14 cm s−1 and permeate water flux of 18 L m−2 h−1. Carboxylate modified polystyrene beads were tracked by fluorescence microscopy in situ and real-time during the first 4 h of deposition with feed flow pulsations up to a frequency of 10 Hz, while experiments were conducted with a constant crossflow velocity as a reference. Imaging at 30 s intervals revealed deposition rates of up to 2.6 times higher at steady state, as compared to flow pulsations of 10 Hz. Consequentially, average deposition was reduced by a factor of 3.5 from steady state (109 ± 67 beads mm−2) to pulsating feed flow (31 ± 17 beads mm−2) after 4 h of deposition. The results of this research provide new fundamental insights related to the constraints and advantages of using pulsating flows for fouling mitigation in forward osmosis systems. [Display omitted] • In-situ and real-time investigation of cake layer formation in forward osmosis. • Quantification of particle deposition with fluorescence microscopy. • Pulsating flows are a promising approach for fouling mitigation in forward osmosis. • A higher pulsation frequency and amplitude leads to less deposition on the membrane. • Pulsation parameters have a significant influence on the spatial distribution of deposition. [ABSTRACT FROM AUTHOR]