Sediment-water system Superior

PCBs in biological samples are usually extracted by a Soxhlet column and with a nonpolar solvent such as hexane. The sample is first mixed with sodium sulfate to remove moisture. The extraction of PCBs from sediments was tested with sonication, with two sonications interspersed at a 24-h quiescent interval, with steam distillation, or with Soxhlet extraction (Dunnivant and Elzerman 1988). Comparison of the recoveries of various PCB mixtures from dry and wet sediments by the four techniques and the extraction efficiency of four solvents showed that the best overall recoveries were obtained by Soxhlet extraction and the two sonication procedures. In comparisons of solvent systems of acetone, acetonitrile, acetone-hexane (1+1), and water-acetone-isooctane (5+1.5+1), recoveries of lower chlorinated congeners (dichloro- to tetrachloro-) were usually higher with acetonitrile and recoveries of higher chlorinated congeners (tetrachloro- to heptachloro-) extracted with acetone were superior (Dunnivant and Elzerman 1988). The completeness of extraction from a sample matrix does not seem to discriminate against specific isomers however, discrimination in the cleanup and fractionation process may occur and must be tested (Duinker et al. 1988b). 

Two-Box Model for Lake/Sediment System Box 23.3 Solution of Linear Water-Sediment Model PCBs in Lake Superior (Part 3)... 

Figure 6.29. Conversion of substrate in the liquid phase (Cs,l) measure of purification effect in waste water treatment versus mass loading rate per unit mass in case of CSTR and CPFR operation Compared are systems operating with one common sedimentation tank (SED), exhibiting only a small difference in conversion, and systems with separated SED, called contact stabilization or sludge-reaeration, in which case the CPFR is superior to the CSTR. (Adapted from F. Moser, 1977.)...

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