Pa Shear Stress Research Articles

Experimental test to evaluate performance of an anaerobic reactor provided with an external membrane unit

The coupling of a wastewater treatment anaerobic reactor with a microfiltration or ultrafiltration membrane is particularly attractive: lower sludge production than in an aerobic reactor, methane production and dissociation of the mean residence times of the different phases. However, the industrial development of such a process is hampered by membrane fouling which can be a result of many causes and require a comprehensive study especially fouling by anaerobic suspensions. In order to simplify the study, the different phases of anaerobic oxidation were separated and this work is focused on the filtration of an anaerobic suspension fed with acetic acid as the sole carbon source at 2 g/1 TOC. The effluent quality was excellent without sludge production in spite of large variation of the liquid phase space time. The tested filtration elements were tubular Carbosep membranes. The Ml4 membrane showed the greatest flux of 120 1/m2 h at 0.5 bar and 25 Pa shear stress and the flux increased to 180 1/m2 h when a baffle was introduced. The main fouling mechanism appears to be the particle deposition on the membrane surface as no flux decline was observed at higher cross-flow velocity.

Cross-flow filtration of an anaerobic methanogenic suspension

The coupling of a wastewater treatment anaerobic reactor with a microfiltration or ultrafiltration membrane is particularly attractive: lower sludge production than in an aerobic reactor, methane production and dissociation of the mean residence times of the different phases. However, the industrial development of such a process is hampered by the membrane fouling which can be a result of many causes and require a comprehensive study especially the fouling by anaerobic suspensions. In order to simplify the study, the different phases of the anaerobic oxidation were separated and this work is focused on the filtration of an anaerobic suspension fed with acetic acid as the sole carbon source at 2 g/l TOC. The effluent quality was excellent without sludge production in spite of large variation of the liquid phase space time. The tested filtration elements were tubular Carbosep membranes. The M14 membrane showed the greatest flux of 120 l/m 2 h at 0.5 bar and 25 Pa shear stress and the flux increased to 180 l/m 2 h when a baffle was introduced. The main fouling mechanism appears to be the particle deposition on the membrane surface as no flux decline was observed at higher cross-flow velocity.

Simulated Small‐Channel Bed Scour and Head Cut Erosion Rates Compared

AbstractConcentrated‐flow erosion is often a major part of cropland erosion. The concentrated‐flow processes of bed scour and head cut need improved characterization to better predict and prevent erosion. This study was conducted to compare the erosion rates due to simulated small‐scale bed‐scour (Db) and head‐cut (Dh) processes. A 6.4‐m‐long by 0.15‐m‐wide hydraulic flume was used to simulate concentrated‐flow erosion on five Midwestern soils: Barnes (fine‐loamy, mixed Udic Haploboroll), Forman (fine‐loamy, mixed Udic Argiboroll), Mexico (fine, montmorillonitic, mesic Udollic Ochraqualf), Sharpsburg (fine, montmorillonitic, mesic Typic Argiudoll), and Sverdrup (sandy, mixed Udic Haploboroll). For slopes of 1.5, 3.5, and 5.0%, flow rates of 3.78, 5.67, 7.65, 11.34, and 15.12 L min−1 were used to provide a range from low (0.5 Pa) to moderate (2.5 Pa) shear stresses (τ). Soil detachment rates are functions of slope, flow rate, and shear stress. Slope, flow, their squares, and the slope × flow interaction were highly significant predictors of Db. Only flow, its square, and its interaction with slope were significant predictors of Db. Nonlinear power regressions using τ as an independent variable were better predictors of detachment than simple linear regressions. Erodibility for the soils from this study does not relate well with soil erodibility calculated using the Universal Soil Loss Equation. Differences in the slope and intercept of detachment vs. τ exist among soils. The value of Db was at least four times greater than Db for all soils at equal slope and flow rate, indicating that head cutting is the main process of detachment for the conditions tested.

Effects of shear flow on photosynthesis in a dilute suspension of microalgae

This study investigates the effects of shear stress on photosynthesis in dilute suspensions of Spirulina platensis and Chlorella by measuring the oxygen production rate using a coaxial, double-rotating-cylinder apparatus that generates Couette shear flow. Our device enables up to 0.6 Pa shear stress to be applied, which has the hydrodynamic effect of generating the algal motion and acutely augmenting the oxygen production rate of Spirulina, primarily because the surface area of algae exposed to illumination is increased. However, there is shear-flow limitation on any increase in oxygen production, and the shear stress at maximum oxygen production rate tends to decrease with increasing temperature. The comparative study with Chlorella showed the reverse relationship between oxygen production and shear stress, and the cause of this difference is discussed in terms of several factors such as size, shape, hydrodynamic stress capacity and others.