Mixed liquor, definition

Depth tends to be determined from the retention time and the surface overflow rate. As surface overflow rates were reduced, the depth of sedimentation tanks was reduced to keep retention time from being excessive. It was recognized that depth was a valid design parameter and was more critical in some systems than retention time. As mixed-liquor suspended-solids (MESS) concentrations increase, the depth should also be increased. Minimum sedimentation-tank depths for variable operations should be 3.0 m (10 ft) with depths to 4.5 m (15 ft) if 3000 mg/L MESS concentrations are to be maintained under variable hydraulic conditions. With MESS concentrations above 4000 mg/L, the depth of the sedimentation tank should be increased to 6.0 m (20 ft). The key is to keep a definite freeboard over the settled-sludge blanket so that variable hydraulic flows do not lift the solids over the effluent weir. 

The selection of the most appropriate mean treatment time, reaction temperature and dissolved oxygen level to be maintained in the aerated mixed liquor requires a clear definition of the treatment objectives for each particular farm enterprise. These are the... 

With the solvent composition selected as the controlling factor, the given mixture is dissolved in a rather excessive quantity of an appropriate hot solvent, which may be one pure liquid, or a mixture consisting of two or more liquids mixed together in a definite proportion. After collecting the first crop of crystals yielded by the hot solution as a result of its cooling, small quantities of a second liquid are added to the mother liquor whereby the altered solvent composition would yield a second crop of crystals which also is collected. Further crops, or fractions, will be obtained by repeating the aforesaid series of steps several times. 

It is important to note that either clear liquor volume or slurry volume can he taken os a besis for the definition of n, For example, if clear liquor volume is taken as the besis, VT becomes the volume of dear liquor in the control volume. With this definition of the population density, it can be shown thet the population balance on a well-mixed continuous crystallizer is given by... 

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