Novel high-rate processes for sewer overflow treatment

There is a demonstrated need for high-rate processes, for the treatment of storm induced sewer overflows, that are capable of removing particulate solids down to at least 10 microns in size. Chemical coagulation processes are capable of producing a high quality treated sewage effluent that would be suitable for discharge to a receiving water such as a separate stormwater system. Compact, high-rate methods of solids separation within these processes will make them more attractive for use in areas where land is expensive or unavailable for large storage basins or settling tanks. Two approaches that are being developed at the CSIRO, Division of Chemicals and Polymers, appear to fulfil this requirement; these are magnetic assisted sedimentation and a high-rate filtration process. Both approaches combine the advantages of chemical coagulation with a high-rate separation of the flocculated solids and are discussed in this paper.