Characterization and destabilization of spent filter backwash water particles

Inorganic and organic particles, including bacteria, viruses and parasites, which are retained within a granular filter during surface water filtration, are removed by backwashing the filter with clean water or water and air. The objective of the study was to characterize SFBW and determine its treatability by coagulation. Microbial and physical-chemical characterization of SFBW collected from a number of different water treatment plants was performed. Experiments to determine the impact of coagulation/flocculation on the SFBW samples were also conducted. SFBW was collected from six different water treatment plants and analyzed for microbial and physical parameters. Physical characterization was done on SFBW collected from all of the treatment plants. Turbidity and pH measurements were taken over the course of the backwash run, and the backwash samples were collected in two to four 20 L containers. A number of parameters were measured for the samples in each container, as well as for SFBW composites made by mixing equal portions of the container contents. The measured parameters included: turbidity, pH, TSS, DOC, UV-254 and alkalinity. Jar tests were carried out on individual containers, on SFBW composite and on SFBW composite that was allowed to settle for one hour. Turbidity and particle count data was collected for both settled and filtered samples.