Imhoff cone

Figure 11,5, Relationships between relative saturated hydraulic conductivity and percent dispersion index of two Kentucky soils (dispersion index = percent of total clay remaining waterborne after 1 hr of settling in an Imhoff cone) (from Marsi and Evangelou, 1991c, with...

The dispersion phenomenon in the two humid soils (Pembroke and Uniontown) was evaluated through the use of an Imhoff cone test and a permeameter. The Imhoff cone is commonly used by engineers to determine settleable solids (see Chapter 9). The results of clay dispersion obtained by the Imhoff cone test are expressed as a dispersion index (percent of total clays in the soil sample dispersed), which is correlated with relative saturated hydraulic conductivity. This is shown in Figure 11.5. It demonstrates that each of the soils, depending on its clay content (Pembroke 59% Uniontown 20%), exhibits unique saturated hydraulic conductivity behavior with respect to the dispersion index. Also, in each of the soils, various mechanisms (different line slopes) appear to control saturated hydraulic conductivity. 

Marsi, M. and V. P. Evangelou. 1991c. Chemical and physical behavior of two Kentucky soils III. Saturated hydraulic conductivity-Imhoff cone test relationships. J. Env. Sci. Health. A267 l 195-1215. 

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. 

Imhoff cone—A vessel shaped like a cone used to measure settleable solids. 

Settleable solids—The fraction of solids produced after settling for 30 minutes in a cone-shaped vessel called an Imhoff cone. 

An Imhoff cone is used to determine the settleable solids content of treated waste waters to check efficiency of treatment. This cone-shaped measuring device, of IL capacity and made of transparent glass or plastic, is graduated down the side to units of tenths of a milliliter at its lower apex. The sample is placed in the cone and allowed to stand for a period of 1 hr. Then the volume of the solids layer settled is read directly from the graduations on the side. 

Standard method 2540 F determines settleable solids either gravimetrically or volumetrically. In the volumetric method, all water sample is allowed to settle for 45 min in an Imhoff cone, then is very gently stirred to loosen any settleable particulates that adhere to the sides of the cone. After an additional 15 min of settling, the volume of the settled material is estimated from the marking on the cone. Do not count floating solids. 

The role of settleable matter and supracolloids in the absorbance of suspended solids of wastewater has been studied more precisely. A simple experience has been carried out. Raw wastewater has been introduced into an Imhoff cone over 1 h. Figure 7 presents the settling device used for the separation of four granulometric fractions. These fractions have been analyzed both with laser granulometry (laser diffraction) and with UV spectrophotometry (deconvolution method, see Chapter 2). 

Granulometric analysis of fractions 1, 2, 3 (Fig. 6) clearly shows that particles are mainly supracolloids, between 1 to 100 xm, with a mode value close to 30 xm. The fraction 4 (at the bottom of the Imhoff cone) presents the widest range size with particle larger than 100 im, and a multi-modal distribution. After 1 h of settling, the separation of settleable matter is achieved, as fractions 1 to 3 do not contain particles of size above 100 xm, even if, in the first fraction, some millimetric floating particles are present. One can note that no colloidal population is detected by laser granulometry. 

Imhoff cone removals indicate the percentage of algal biomass that will spontaneously flocculate and settle... 

In a similar manner, a 1 liter representative sample of the unfiltered used solvent can be placed in an Imhoff cone and evaporated to dryness. The volume of residue can be measured directly and used to compute the amount of contaminant extracted per square foot (meter) of surface area cleaned. Greater sensitivity can be... 

Detenninalion of Settleable Solids by Imhoff Cone Procedure... 

Mix the sample well and pour it into Imhoff cone up to 1-litre mark. Leave it undisturbed for 45 minutes gently stir the sides of the cone with a glass rod and let the material settle for another 15 minutes. Record the volume of the. material that settles and report the result in ml per litre. 

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