Settled volume index

Surprisingly, good separation can be achieved in the decanter on a good (SVI, settled volume index, of 120 or less) activated municipal effluent, without the use of a flocculant. This is possibly due to the homogenous nature of an activated sludge. 

A very important parameter ia routine control of the process is the ratio of the MLSS volume to the dry weight, called the Sludge Volume Index (SVI). A weU operating plant has an SVI of 50 to 100, but operational difficulties occur when the SVI approaches 150. At this poiat the sludge settles poorly. 

The settleable fraction is the volume of the solids after settling for 30 minntes in a cone-shaped vessel called an Imhoff cone. The volume of solids that settled, in milliliters, divided by the corresponding grams of solids mass is called the sludge volume index, SVI. Settleable solids are an approximate measure of the volume of sludge that will settle by sedimentation. Figure 2.4 shows a photograph of Imhoff cones. 

Sludge volume index (SVI)—The volume of solids that settled, in milliliters, divided by the corresponding grams of solids mass. 

The Hausner ratio and compressibility index are calculated from the measured bulk volume or poured volume (Vo) and tapped volume or settled volume (Vt) and are defined by Equations 8.4a and 8.4b, respectively. The bulk volume can be determined by filling a known amount of powder in a graduated cylinder, while the tapped volume is obtained by mechanically tapping a measuring cylinder containing a powder sample in a controlled way. A Hausner ratio close to 1 or a low-compressibility index indicates good flow properties, while a Hausner index >1.35 or a compressibility index >26% would indicate poor flow properties. For a more detailed classification. ... 

The Mohlman index or sludge volume index (SVI) expresses the volume of 1 g of activated sludge settled for 30 min and is calculated by the ratio ... 

An unresolved problem that should be mentioned is that, when the high-pressure phase of Am is indexed as the a-U structure, the volume difference between the low- and high-pressure phases is much smaller than the volume difference to be expected between f-bonding and non-bonding states. This problem has been investigated in some detail by Eriksson and Wills (1992), who were led to question the correctness of the crystal structure assignment for Am. Further experimental and theoretical work will be required to settle this question. 

With respect to the emulsification properties of biosurfactants, one parameter that is often reported in the literature is the emulsification efficiency (E%). To measure this parameter, equal volumes of oil and water are vortexted for 1 minute and then left to settle for 24 hours (E24). After that time, the percentage of the total volume of the liquid occupied by the emulsion is reported (E24%) [35]. This emulsification index can be measured, in principle, against any oil but most of the studies use kerosene as the reference oil. In the work of Benincasa and Accorsini [32], the rhamnolipid produced from sunflower soapstock had an E24 index of 50 (or 50%) against kerosene. In the work of Mercadd et al. [35], who used wastewater from olive oil mills, they obtained E24 indices ranging from 15 to 75 with kerosene. 

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