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Filter‐to‐waste optimization
Author(s) -
Soucie William J.,
Sheen Brett J.
Publication year - 2007
Publication title -
journal ‐ american water works association
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.466
H-Index - 74
eISSN - 1551-8833
pISSN - 0003-150X
DOI - 10.1002/j.1551-8833.2007.tb07935.x
Subject(s) - turbidity , filter (signal processing) , effluent , environmental science , sand filter , environmental engineering , pulp and paper industry , chemistry , wastewater , engineering , biology , ecology , electrical engineering
At the Central Lake County Joint Action Water Agency in Lake Bluff, III., the filter effluent turbidity goal is ≤ 0.10 ntu 100% of the time. This necessitates a filter‐to‐waste (FTW) step that occurs during filter ripening. An extended terminal subfluidization wash (ETSW) scheme was evaluated (Amburgey et al, 2003) in an effort to eliminate this step. The dual‐media filters use 4 ft (1.2 m) of 13‐year‐old biologically active carbon over 1 ft (0.3 m) of sand. Each filter is rated for up to 5 gpm/sq ft (3.4 mm/s) of ozonated, coagulated, flocculated, and settled Lake Michigan water. During this study 412 filter backwashes were examined. The FTW peak turbidity or maximum turbidity that occurred during filter ripening decreased 38% from an average 0.13 ntu in the control filters backwashed normally to an average 0.08 ntu in the test filters backwashed using ETSW. This scheme consumed an average 5% or 7,000 gal (26,000 L) more backwash water while filter off‐line time was reduced 14% or 11 min per backwash. The control filters exceeded an FTW peak turbidity of 0.10 ntu 95% of the time, whereas ETSW reduced occurrences of excess turbidity to just 4% of the time. However, because the FTW turbidity maximum did surpass 0.10 ntu, abandonment of FTW is not indicated. Instead, the FTW step should become relegated to an as‐needed step used only when filter effluent turbidity exceeds 0.10 ntu. The data suggest that the additional 7,000 gal of backwash water consumed would be offset by a savings of 22,000 gal (83,000 L) of pretreated FTW water while filter off‐line time would be reduced ≥ 30 min.