(a) Reasons for Use.
- (1) Permit Requirements. A facility with tertiary effluent limitations must use filtration as a unit of operation to supplement suspended solids removal.
- (2) Specific Water Quality Requirements. At facility with secondary or advanced secondary effluent limitations may use filtration as a unit of operation to supplement suspended biological floc removal and intermittent filter operation if filters are not necessary to meet permitted effluent limitations.
(b) Redundancy.
- (1) A facility using filtration to provide tertiary treatment for a permit requirement must have a minimum of two filter units.
- (2) A design must specify the required filter surface area based on peak flow through the filters with the largest filter unit out of service.
- (3) If a filter is being provided to polish wastewater for situations where permit compliance does not depend on the use of a filter, such as some cases of reclaimed water usage, one filter is allowed.
- (c) Source of Backwash Water. A filtration system must use filtered effluent as the source of backwash water.
- (d) Disposition of Backwash Water. A filtration system must return backwash water containing material cleaned from a filter to the head of the facility for processing.
(e) Sequence of Treatment Units.
- (1) A final clarifier must precede a filter, in accordance with Subchapter F of this chapter (relating to Activated Sludge Systems).
- (2) A filter system may be used in conjunction with a disinfection tank to provide additional detention time, provided a filter is backwashed to the headworks of the facility.
- (f) Overload Conditions. A design must prevent effluent or partially treated effluent from overflowing from any filtration unit.
- (g) Control of Slime Growth. A filtration system must provide periodic disinfectant in the influent stream to a filter to control slime growth in the filter and backwash storage tank.
Source Note:The provisions of this §217.190 adopted to be effective August 28, 2008, 33 TexReg 6843.