The distribution of chemical constituents within the sewage settling velocity grading curve

Over the past decade there has been an increase in legislation relating to the quality of effluent discharges. The legislation, which contains higher standards for metals, nutrients and organic matter has prompted a need for sewage treatment works to upgrade existing processes. For a significant improvement in process efficiency there is a need for a better understanding of the characteristics of sewage, in particular the association of chemical constituents with solids. This research has used a settling column to determine a profile of the chemical constituents associated with solids in crude sewage. The results indicate that the particulate concentration of Chemical Oxygen Demand (COD) and Phosphorous are associated with solids which have settling velocities in the range 0.04-0.90 cm/sec.