Section 811.853. Backwash wastewater from iron and manganese filters.

 

(1)   Discharge to sanitary sewer. Backwash wastewater from iron and manganese removal filters may be discharged to a sanitary sewer if the discharge will not overload the facilities or adversely affect the wastewater treatment process. The radionuclide content of the wastewater shall comply with s. NR 811.856 . An equalization tank shall be provided when it is necessary to prevent overloading the sewers or wastewater treatment plant.

(2)   Discharge to sand filters. All of the following requirements apply when sand filters are used to treat backwash wastewater from iron and manganese removal filters:

(a) Filters shall be designed for a maximum rate of 35 gallons per square foot per day except if testing indicates that higher rates will not cause excessive plugging of the media and a quality effluent can be maintained. Sufficient surface area shall be provided so that during any filtration cycle the wastewater depth over the media does not exceed 2 feet. The filters shall be sized to handle the entire backwash volume from all of the filters at the treatment plant unless the filters are washed on a rotating schedule.

(b) No filter, regardless of the volume of water to be handled, may be smaller than 100 square feet in area. Multiple units may be necessary to facilitate cleaning.

(c) The filter media shall consist of a minimum of 12 inches of sand, 3 to 4 inches of supporting small gravel or torpedo sand, and 9 inches of gravel in graded layers. All fines shall be removed from the media by washing. The filter sand shall have an effective size of 0.3 to 0.5 mm and a uniformity coefficient not exceeding 3.5.

(d) An adequate underdrainage collection system shall be provided. Provision shall be made for sampling the filter effluent.

(e) A cover shall be provided which prevents freezing during the winter months.

(f) The filter shall be located in an area not subject to flooding, and the site shall be graded to prevent ponding of surface runoff. Finished grade elevation shall be designed to facilitate maintenance, cleaning, and removal or replacement of surface sand. An overflow may not be provided.

(g) The radionuclide content of the wastewater shall comply with s. NR 811.856 .

(3)   Discharge to lagoons. Lagoons used to settle backwash wastewater from iron and manganese removal filters shall meet all of the following design requirements:

(a) Lagoons shall be designed with a volume which is 10 times the total quantity of wastewater discharged during any 24-hour period.

(b) Lagoon length shall be 4 times the width, and the width shall be at least 3 times the depth.

(c) Adequate inlet and outlet devices shall be provided so that velocity currents are minimized.

(d) The radionuclide content of the wastewater shall comply with s. NR 811.856 .

(4)   Discharge to detention tanks. Detention tanks used to settle backwash wastewater from iron and manganese removal filters shall meet all of the following design requirements:

(a) Detention tanks shall be designed to maximize settling by means of inlet piping and baffling configurations. Tanks shall be of sufficient capacity to hold at least 2 complete backwash cycles. The floor shall be sloped to a sump and access manholes provided to facilitate cleaning. A cover shall be provided to prevent freezing.

(b) Pumps shall be provided to discharge the decant water to a storm sewer or receiving watercourse over approximately a 24-hour period. A convenient means of sampling the effluent shall be provided. Any discharge requires a WPDES permit. The radionuclide content of the wastewater shall comply with s. NR 811.856 .

(c) Decant water to be returned to the water treatment plant shall meet the requirements of s. NR 811.862 .

(d) Settled sludge removed from detention tanks shall be disposed of at a wastewater treatment plant unless the department approves an alternate disposal location on a case-by-case basis.

History: CR 09-073 : cr. Register November 2010 No. 659 , eff. 12-1-10.