Experimental Research On Direct Filtration Of Low Turbidity Water With Superimposed Filter

The superimposed filter which contained quartz sand and comet fiber filtrationmedium was designed in this paper. It was used to treat the water with low turbidityby micro-flocculation direct filtration. The raw water was filtrated by superimposedfilter after dosing PAC. The experiment results show as follows:The total height of the filter layer is800mm. Considering the superimposed filterfiltering effect and filter fiber costs, when the thickness of the upper filter is400mmand the thickness of the under filter is400mm and the quartz particle size rangebetween0.95mm and1.35mm, the superimposed filter has better filter performance,further more, both filter layers take full advantage of the interception capability.When the initial filtration rate is15m/h, the water production of superimposedfilter is the largest in the entire filtration cycle, and the water quality can meet thenational standards within filtration cycle. The removal rate of turbidity, CODMn,ammonia and nitrite nitrogen is97%,58%,75%and81%respectively.The superimposed filter is backwashed by the manner of gas-water combination,making the layer of quartz sand in a suspended state and the layer of comet fiberfiltration medium in a uniform agitation state. The entire Backwashing is lasted11min.when the water washing strength is14L/(m~2×s) and gas washing strength is35L/(m~2×s), the backwash water consumption rate is1.37%, the remaining deposition rateis1.36%.Based on a large number of test data, the superimposed filter’s three performancecurves are plotted: the curve of the relationship between water yielding per day(Qm)and initial filter filtration rate(V), the curve of the relationship between filtrationcycle(T) and initial filter filtration rate(V), the curve of the relationship betweenfiltration head loss(△H) and initial filter filtration rate(V). When the raw waterquality or water yielding change, the operator can adjust the operating parametersaccording to the overall performance curves.