A high rate clarifier for load levelling in sewerage systems

The combining of chemically assisted clarification with a proprietary physical separation technology has led to a high rate process for clarifying flocculated sewage and other waste streams. This hybrid physico-chemical system, known as the CDS Fine Solids Separation (FSS) System, was developed over a two year period within a sewage treatment plant environment. This paper summarises the results of a recent field trial of the system with a Victorian water authority which experiences heavy loading of sewers in a coastal town during holiday periods. The trial sought to evaluate the FSS as a tool for smoothing the load on the 11 km long sewer to the sewage treatment plant (STP). The FSS system could possibly enable the costly augmentation of the sewer to be deferred, particularly as the capacity of the existing sewer pipe is satisfactory for most of the year. Water quality parameters were determined for a range of flowrates and operational conditions over a two month period. Large reductions were achieved in TSS, TP, FC, turbidity and BOD5, with only minimal reductions in NH3 and TON. These results showed that the FSS could meet the authority's objectives for load levelling and would provide a 20-25% increase in effective sewer capacity. The data are also discussed in terms of possible use of the effluent from the FSS for water reuse applications.