Determination settleable solids

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. 

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. 

For wastewater samples, a number of additional solid determinations are typically performed, including total dissolved solids, volatile solids, and settleable solids. Total dissolved solids are the total solids minus the suspended solids and are determined in a manner similar to total solids, but after filtering out the suspended solids. Thus, a volume of the filtrate is measured into the evaporating dish and the water evaporated in a drying oven. 

For settleable solids, a sample of the wastewater is taken after the suspended solids are allowed to settle for a specified time. The solids in this sample are then measured in a manner similar to that for total solids. These are the nonsettleable solids. The settleable solids are then determined by subtracting from the total solids determined previously. See Workplace Scene 3.2. 

The term settleable solids applies to suspended solids that settle under quiescent conditions because of the influence of gravity. Their measurement is important in engineering practice to determine the need for sedimentation units and the physical behavior of waste streams entering natural water bodies. Colloidal particles do not settle readily and cause the turbidity found in many surface waters. 

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. 

In the gravimetric method, the TSS is determined from the original sample and also from the supernatant liquid above the settled material. The settleable solids are computed as ... 

Settleable solids To determine those solids that will settle by gravity in a specific time period test data used for design of sedimentation facilities... 

If the biochemical oxygen demand of the settleable solids is to be determined, it may in the case of primary sludge be calculated from the loss on ignition of the settleable solids. According to Imhoff, 30 g organic substances cause 20 g BOD5 in primary sludge. 

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