| (a) Cloth or disk filter systems must meet the requirements
in §217.190 of this title (relating to Filtration).
(b) Media Design.
(1) The average pore size of cloth or disk filter
media must not exceed 30 microns.
(2) The media thickness must be based on the manufacturer's
recommendations, considering frequent pressure changes. The manufacturer's
recommendations must be included in the engineering report.
(3) The media must be disinfectant-resistant if the
filter will be exposed to disinfectants.
(4) The media must be chlorine-resistant if the filter
will be exposed to chlorine.
(c) Filtration Rates and Hydraulic Requirements.
(1) The design filtration rate must be based on the
effective submerged surface area of the media. If the submerged surface
area of the media varies based on the operational mode, the design
filtration rate must account for the variability.
(2) The maximum design filtration rate for peak flow
must not exceed 6.5 gallons per minute per square foot of submerged
media.
(3) The filtration system must be able to treat the
design flow rate with one filter unit in backwash mode.
(4) The backwash flux rate must be at least 6.0 gallons
per minute per square foot of media, based on the portion of the filter
surface that is being actively backwashed.
(d) Disposal of Backwashed Material.
(1) Liquid filter backwash must be re-filtered or must
be returned to the headworks of the wastewater treatment facility
or to the influent lift station.
(2) Solid filter backwash material must be pumped to
the influent lift station, the headworks, the digester, or to another
location approved in writing by the executive director for processing
at least once per day.
(e) Monitoring and Controls.
(1) Cloth or disk filters must use an automatic control
system.
(2) An automatic control system must include manual
override capability.
(3) Each filter unit must monitor head loss across
the unit and must have a head loss gauge or readout.
(4) Each filter unit must monitor effluent turbidity
and have a turbidity gauge or readout.
(5) Gauges and readouts must be readable from the control
panel.
(f) Weather Resistance. Cloth or disk filter systems
must be protected from the environment. The engineering report must
describe how the system will be protected from freezing conditions,
ultraviolet light, and similar environmental concerns.
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