The influence of added saccharide, protein and lipid on the sedimentation of E. coli bacteria using aluminium sulphate and polyacrylamides

The chemical sedimentation of E. coli bacteria has been studied in the presence of polymeric impurities such as occur in domestic waste-water (proteins, lipids, saccharides). Chemical sedimentation was carried out at pH 7 using aluminium sulphate and various polyacrylamides. Sedimentation was followed from the turbidity of samples from a sedimentation vessel as a function of time after polyacrylamide addition. The results show that protein and lipid increase, whilst polysaccharide reduces the sedimentation rate to extents that depend on the dosages and types of polyacrylamides used. In particular, at a fixed dosage level of a given polyacrylamide, variations in concentrations of polymeric impurities may lead to variations in sedimentation rate of ca. 30 per cent. In order to obtain reproducible sedimentation, it is therefore necessary to vary the polyacrylamide dosage to compensate for changes in the levels of protein, lipid and polysaccharide which occur in domestic waste-water.