Civil Engineering Reference
In-Depth Information
Filter Design Checklist
In designing a rapid rate filter, a number of design considerations must be addressed
to ensure proper filter operation. Following is a checklist of some of the more critical
design issues:
1. Filter media sizing and selection should be based on pilot tests. If this is not
possible, data should be obtained from similar applications to determine the
suitability of the media design.
2. In dual- and mixed-media and high-rate, deep monomedia filter systems, pro-
visions should be made for the addition of polyelectrolytes directly to the filter
influent.
3. The turbidity and / or particle count of each filter unit should be monitored
continuously and recorded.
4. The flow and headloss through each filter should be monitored continuously
and recorded.
5. Provisions should be made for the addition of disinfectant directly to the filter
influent.
6. Pressure filters must be equipped with pressure and vacuum air release valves.
7. Provisions should be made to divert any filter effluent of unsatisfactory quality
(i.e., provide a filter-to-waste cycle).
8. Provisions should be made for automatic initiation and completion of the filter
backwash cycle.
9. The filter controls and pipe galleries should be housed. Pipe galleries should
have humidity control systems.
10. Filter piping should be color-coded.
11. The filter system layout must enable easy removal of pumps and valves for
maintenance.
12. The backwash rate must be based upon the specific filter media used and the
backwash water temperature variations expected.
13. Filter backwash supply storage should have a volume at least adequate to com-
plete two filter backwashes.
14. Adequate surface wash or air-scour facilities must be provided.
15. There should be adequate backwash and surface wash pump capacity available
with the largest single pumps out of service.
16. Backwash supply lines must be equipped with air release valves.
17. A means should be provided to indicate the backwash flow rate continuously
and to enable positive control of the filter backwash rate. A means should also
be provided to limit the filter backwash rate positively to a preset maximum
value.
18. The filter design must incorporate underdrains and backwash wastewater col-
lection devices that ensure uniform distribution of backwash water and filter
influent.
19. The filter system should be equipped with an alarm system that will indicate
major malfunctions.
20. Construction details must prevent cross-connections and backflow.
