Section 811.860. Backwash wastewater from surface water treatment plants.

  Filter backwash wastewater from surface water treatment plants shall be disposed of by any of the following methods:

(1)   Recycling. Filter backwash wastewater may be returned to the inlet end of the plant in accordance with the requirements of s. NR 811.862 . Membrane filtration plants may not recycle backwash wastewater unless the waste goes through coagulation and settling processes prior to being applied to the membranes. Membrane manufacturers may have specific feed water quality parameter requirements that could limit recycling. Chemical cleaning waste from membrane plants may not be recycled unless specifically approved by the department. All plants recycling filter wastewater shall have an alternative means of disposing of wastewater available during challenging raw water quality periods.

(2)   Discharge to sanitary sewer. The wastewater program of the department may approve direct or controlled discharge to a sanitary sewer system if the discharge will not overload the facilities or adversely affect the wastewater treatment process.

(3)   Discharge to surface water. Suspended solids shall be removed from the filter backwash wastewater before the filter backwash wastewater is discharged to surface water. This will require settling and possibly coagulation. Any discharge requires a WPDES Permit. Chemical cleaning waste from membrane plants may not be discharged to surface water.

(4)   Treated by secondary membrane. The filter backwash water may be treated by a dedicated membrane system and sent to the clearwell if approved by the department in accordance with all of the following requirements:

(a) The membrane, as can be demonstrated by integrity testing conducted every 8 hours, shall provide a minimum 99.9997 percent (5.5-log) removal of Cryptosporidium .

(b) If the membrane cannot be demonstrated to provide a 99.9997 percent (5.5-log) removal of Cryptosporidium , UV shall be provided following the membrane. The membrane and UV together shall provide a minimum of 99.9997 percent (5.5-logs) of removal or inactivation of Cryptosporidium , or a combination of both.

(c) A target removal of less than 99.9997 percent (5.5-logs) of Cryptosporidium may be considered by the department if testing of the backwash water in accordance with s. NR 809.334 and bin classification in accordance with s. NR 810.34 would result in a bin classification less than Bin 4.

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