Liquid flow through sands: reliability of tortuosity measured from electrical conductivity and the importance of evaluating effective porosity

International audienc

Liquid Flow through Sands:Reliability of Tortuosity Measured from Electrical Conductivity and the Importance of Evaluating the Effective Porosity

International audienceSand beds are commonly used in many industrial applications, mainly as a filtering medium, and in civil engineering. However, predicting the pressure drop of liquid flow through sand beds with simple models remains elusive. Among the many factors that explain this failure is the difficulty of determining tortuosity and effective bed porosity. This work investigates the experimental determination of hydraulic tortuosity of different natural sands from electrical conductivity. Different protocols are tested and discussed. They underline the importance of a proper determination of effective porosity, i.e., the fraction of bed volume concerned by fluid flow. Correct determination of the effective porosity may help to reconcile actual bed parameters with those determined from pressure data using a capillary-type flow model

Performances of a seawater desalination plant made up of a sand filter, ultrafiltration and reverse osmosis membranes during a planktonic bloom

International audienc

Performance of nonwoven geotextiles on soil drainage and filtration

International audienceThe selection of a geotextile to prevent the soil suffusion in a civil engineering work is a classical problem. The internal erosion is a key factor as the migration of fine particles damages the integrity of the soil structure. This work deals with the problem of using a draining system consisting of a layer of soil and a geotextile sheet in order to prevent soil suffusion. It proposes a methodology which allows ordering the performance of nonwoven geotextiles. A range of experimental approaches were implemented including seepage flow tests under controlled flow rates. A detailed analysis of the data shows that intrinsic properties of geotextiles are not sufficient to predict their behaviour in a draining system. Moreover, the classical flow tests of the draining systems are not sufficient to adequately discriminate the three geotextile specimen used here. On the other hand, it seems important to use the history of the hydraulic gradient with respect to the flow rate variation. Thus, the present data of normalised relative pressure drop and normalised relative variation of flow rate are arranged in terms of a dimensionless criterion. This methodology enables evaluating and discriminating the performances of the geotextiles used here in terms of filtration and drainage functions

Effect of filtration rate on coal-sand dual-media filter performances for microalgae removal

International audienc

Impact of granular filtration on ultrafiltration membrane performance as pre-treatment to seawater desalination in presence of algal blooms

International audienc

Impact of granular filtration on ultrafiltration membrane performance as pre-treatment to seawater desalination in presence of algal blooms

To mitigate fouling of the ultrafiltration (UF) membrane and improve permeate quality, we coupled granular filters (GF) with UF membrane as a pre-treatment for reconstituted seawater in the presence of algal bloom. Mono and bilayer granular filtrations were led at a mean velocity of 10 m h−1 over a 7-hour period. Both GF gave the same algal cell retention rate (∼63%) after 7 hours of filtration. Turbidity reduction rate was 50% for the monolayer filter and 75% for the bilayer filter. Resulting organic matter removal rate was 10% for the monolayer filter and 35% for the bilayer filter. Dissolved organic carbon removal was low (20%) with the bilayer filter and non-existent with the monolayer filter. GF-coupled UF reduced humic acids in the permeate (20%) compared with UF alone. Peak pressure of 3 bars was reached at the end of 30 minutes of UF in both direct UF or UF after monolayer GF. The filtrate from the bilayer GF enables UF over a longer period (7 hours)

Performance of a sand filter in removal of algal bloom for SWRO pre-treatment

International audienc

Performances of dead-end ultrafiltration of seawater: from the filtration and backwash efficiencies to the membrane fouling mechanisms

The present work investigates the fouling mechanisms of PVDF hollow fibre membrane (0.03 μm) during the dead end ultrafiltration at a fixed permeate flux (outside to inside configuration) of complex synthetic seawater composed by humic acids, alginic acids, inorganic particles and numerous salts at high concentrations. Short term ultrafiltration experiments at 100 L.h-1.m-2 show that the optimal specific filtered volume seems to be equal to 50 L.m-2. A residual fouling resistance equal to 2.1010 m-1 is added after each cycle of filtration during 8h of ultrafiltration at 100 L.h-1.m-2 and 50 L.m-2. Most of the fouling is reversible (80%). Organics are barely (15% of humic acids) retained by the membrane. Backwash efficiency drops during operation which induces less organics into backwash waters. Humic acids could preferentially accumulate on the membrane early in the ultrafiltration and alginic acids after the build-up of a fouling pre-layer. Colloids and particulates could accumulate inside a heterogeneous fouling layer and/or the concentrate compartment of the membrane module before being more largely recovered inside backwash waters