How to Measure Specific Deposit Washout and Backwash Efficiency of Granular Filters

摘要

Practical experience shows that water treatment filters develop problems over time due to the routinenrunning of the filter, including backwashing. There are difficulties in maintaining filters in good condition, givennthe eutrophic state of many South African raw waters, high water temperatures and the development ofndifficult-to-remove biofilm as a result. Such difficulties are often related to deposits accumulated on the filternmedia and it is, therefore, expected that the backwash system should be good enough to ensure that the filternis kept clean in the long run. This paper deals with a fairly simple operational option to significantly improvenbackwash efficiency at treatment plants where air and water are used consecutively.nThe paper describes methods used and typical results obtained in the testing of the quantitative benefitsnof multiple wash cycles. Multiple washing shows great promise for improving backwash efficiency, with annaverage of an additional 40% to 50% of the solids that would have been washed out with a single wash,nremoved by a second wash. Furthermore, third and even fourth washes continue to remove additional dirtnfrom the filter. Multiple washing, therefore, may be a useful tool for the effective rehabilitation of a filter, asnwell as for routine operation procedures.