Removal of sugars by activated sludge

Abstract

1. (1) The diurnal variation of concentration of sugars and volatile fatty acids in fresh and settled sewage at three sites was determined. Little loss of sugar occurred on settlement at two sites, where settlement was carried out aerobically. 2. (2) The sugars normally present in sewage were removed from solution by activated sludge at much the same rate as was added glucose (40–50 mg/g/hr). 3. (3) The Michaelis constants for sugars were in the region of 10 mg/l at 20°. 4. (4) No simple relation was found between BOD loading and the ability of a sludge to remove sugars, but in general the higher the “sugar loading” the greater the activity of the sludge. 5. (5) Activated sludge acquired very high, though variable, activity towards glucose on addition of this sugar to the sewage treated but, unlike pure cultures of two species of bacteria tested, the sludge lost this activity when fed with further amounts of the sugar alone in quick succession. 6. (6) Evidence of sequential oxidation of glucose and fructose was inconclusive. 7. (7) At the point of complete, or near complete, removal of sugar from solution, variable proportions of the theoretical amounts of oxygen were taken up, namely 10–30 per cent for glucose and 8–26 per cent for sucrose. 8. (8) No evidence of formation of significant amounts of poly-β-hydroxybutyric acid was found in activated sludge grown on sewage receiving normal amounts of glucose, though the presence of 0–5 per cent polymer in sludge was established. 9. (9) It is concluded that biochemical removal of soluble substrates is not a limiting factor in the activated-sludge process, so that any limitation on the load applied would appear to involve flocculation or separation of sludge particles.