Section 811.862. Recycling backwash wastewater.

  Filter and contactor backwash wastewater may be recycled if approved by the department in accordance with all of the following requirements:

(1)  The filter and contactor backwash wastewater shall be settled in a settling tank or equalization basin prior to being returned to the inlet end of the plant. For surface water systems, a coagulant or polymer may be required to enhance settling to prevent protozoans such as Giardia lamblia and Cryptosporidium from concentrating. Tanks and basins shall meet all of the following minimum requirements:

(a) The tanks shall contain the anticipated volume of backwash wastewater produced by the plant when operating at design capacity.

(b) The tanks shall be of adequate size to contain the total waste washwater from 2 consecutive backwashes to provide operation flexibility.

(2)  The settled filtered backwash wastewater shall be returned to the head end of the plant at a maximum rate of 10% of the instantaneous flow rate at which raw water is entering the plant. All of the following requirements shall be met:

(a) The point of recycle shall be prior to all treatment and chemical addition except chemical treatment for zebra mussel control at the intake.

(b) A meter shall be provided on the recycle line.

(c) A means shall be provided for controlling the rate at which the settled backwash wastewater is returned.

(3)  For systems treating groundwater, the settled filtered backwash wastewater shall be disinfected prior to or at the time that it is returned to the head end of the plant.

(4)  Reservoirs to be used to settle backwash wastewater for plants treating potable groundwater shall be constructed to potable reservoir construction standards as required by subch. IX . The discharge of any wastewater or sludge, or both, from such a reservoir to a sanitary or storm sewer main, manhole, or other collection structure, whether by pump or by gravity, shall not be made through a direct connection. The discharge piping shall terminate downward with a one-foot free air break over the receiving structure as required in s. NR 811.64 (4) .

(5)  For surface water systems that recycle their backwash wastewater, all of the following reporting and record keeping requirements apply:

(a) A current plant schematic showing the origin of all recycle streams, how any recycle streams are transported, and where the recycle streams enter the treatment process shall be maintained on file with the department.

(b) Information on the typical recycle flow rate, the highest observed plant flow rate each year, and the design flow rate of the plant shall be available to the department upon request.

(c) The information in pars. (a) and (b) along with all of the following information shall be maintained on file for a minimum of 10 years: dates when recycle flow rate has exceeded 10 percent of raw water flow rate entering the plant; how recycle flow rate is controlled; dimension and volume of backwash equalization basin; typical detention time in equalization basin; type of coagulant fed prior to equalization basin; and means of sludge removal from the equalization basin.

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