Section NR 811.495 - Filtration - pressure A pressure filter may not be used in the filtration of surface water, polluted waters, or following lime-soda softening as provided under s. NR 811.57. A pressure filter shall meet all of the following requirements:
(1) NUMBER. At least 2 filter units or cells shall be provided. Provisions shall be made to meet the plant design capacity at the approved filtration rate with one filter out of service. If only 2 units or cells are provided, each shall be capable of meeting the plant design capacity, normally the projected maximum daily demand.(2) RATE OF FILTRATION. The rate of filtration shall not exceed 4 gallons per minute per square foot of filter area except when pilot testing under s. NR 811.44 or full-scale testing as approved by the department has demonstrated adequate contaminant removal rates at the higher filtration rates, as determined by the department.(3) FILTER MATERIAL. The filter media material shall meet the requirements under s. NR 811.49 (1) (f).(4) DESIGN DETAILS. A filter shall be designed to provide for all of the following: (a) Loss of head gauges on the inlet and outlet pipes of each filter.(b) An easily readable meter of flow indicator on each battery of filters. Note: A flow indicator is recommended for each filtering unit.
(c) Piping that allows filtration and backwashing of each filter individually.(d) Minimum side wall shell height of 5 feet. A reduction in side wall height may be approved by the department when proprietary filter bottoms permit reduction of the gravel depth.(e) The top of the wash water collectors to be at least 18 inches above the surface of the media.(f) The underdrain system to efficiently collect the filtered water and to uniformly distribute the backwash water at a rate not less than 15 gallons per minute per square foot of filter area.(g) Backwash flow indicators and controls that are easily readable while operating the control valves.(h) An air release valve on the highest point of each filter cell. The discharge line from the relief valve shall be metal and terminate downward facing with a 24-mesh corrosion resistant screen, at least 24 inches above the floor.(i) An accessible manhole to facilitate inspection and repairs for each filter cell.(j) Means to observe the wastewater during backwashing.(k) Construction to prevent cross connection.Wis. Admin. Code Department of Natural Resources NR 811.495
Adopted by, CR 22-074: cr. Register January 2024 No. 817, eff. 2/1/2024 correction in (2) made under s. 35.17, Stats., Register January 2024 No. 817.