Wisconsin Administrative Code
Department of Natural Resources
NR 800 - Environmental Protection - Water Supply
Chapter NR 811 - Requirements For The Operation And Design Of Community Water Systems
Subchapter XII - Waste Disposal
Section NR 811.860 - Backwash wastewater from surface water treatment plants

Universal Citation: WI Admin Code § NR 811.860

Current through August 26, 2024

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 under 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. A plant recycling filter wastewater shall have an alternative means of disposing of wastewater available during periods when raw water quality precludes the ability to recycle all or some of the backwash water.

(2) DISCHARGE TO SANITARY SEWER. Backwash water may be discharged to a sanitary sewer system subject to the requirements under s. NR 811.85 (1) (a).

(3) DISCHARGE TO SURFACE WATER. Backwash wastewater from filtration for surface water treatment may be discharged to a surface water of the state subject to the requirements under s. NR 811.85 (1) (b) and all of the following requirements:

(a) Suspended solids shall be removed from the filter backwash wastewater prior to surface water discharge. This will require settling and may require coagulation as determined by the department on a case-by-case basis. Additional treatment may be necessary to meet the requirements of the WPDES permit.

(b) The solids removed during treatment of backwash water shall be land spread or discharged to a holding tank in accordance with the requirements under s. NR 811.85 (1) (b) and (c).

(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.

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