SECTION 252:656-16-2. Attached growth systems

(a)   Rotating biological contactors (RBC). An RBC can only be installed to replace or to add to an existing RBC.

(1)   Winter protection. Enclose RBC units in a corrosion resistant structure to protect biological growth from cold temperatures and excessive heat loss.

(2)   Pretreatment. Provide primary clarifiers with scum and grease collecting devices. Bar screening and/or comminution alone are not suitable pretreatment.

(3)   Staging. Provide at least four stages for secondary treatment applications, with more stages for greater nitrification and BOD removal.

(4)   Loading.

(A)   Hydraulic. Equalize flow where the ratio of peak flow to average flow is 2.5 or greater. For secondary treatment hydraulic loading shall be from 2 to 4 gpd/ft and shall not exceed 0.75 to 2.0 gpd/ft where nitrification is required.

(B)   Organic. First stage loading rates shall be from 2.5 to 4.0 lbs. of soluble BOD/day/1,000 ft. 3.0 lbs. is recommended.

(5)   Tanks. Provide at least 0.12 gal/ft of media for RBC tanks to maintain a hydraulic load of 2 gpd/ft. Provide a side water depth of 5 feet or submerge the media at least 40%.

(b)   Trickling filters. Trickling filters may be installed to pretreat high-strength waste only, or to add to or replace existing trickling filters. Provide primary clarifiers with scum and grease collecting devices before filters so the influent will be relatively free from settleable, floating, or suspended matter. Design secondary clarifiers to meet the criteria of Appendix B of this Chapter.

(1)   Design basis. Filters are termed standard or high rate on the basis of hydraulic and biological loading. High rate filters may be used to pretreat wastewater before further biological treatment. High rate systems can withstand highly variable hydraulic overload conditions without significant deterioration of the biological growth. For design criteria, see Appendix A, Design Tables.

(2)   Hydraulics. Sewage application shall be continuous. Provide all pump stations with a backup.

(A)   Head requirements. For reaction type distributors, a minimum head of 24 inches above the center of the arms is required. Design distributors to uniformly distribute wastewater over at least 90% of the surface area.

(B)   Clearance. Provide at least 6 inches of clearance between the media and distributor arms.

(C)   Piping system. Design the piping system, including dosing equipment and distributor, for the peak hourly flow rate, including recirculation.

(3)   Media.

(A)   Quality. Plastic media or its approved equivalent shall be used. Manufactured media must also be resistant to ultraviolet degradation, disintegration, erosion, aging, common acids and alkalies, organic compounds, and fungus and biological attack.

(B)   Depth. Media depth for standard rate filters must be 6 to 8 feet deep and, for high rate filters, from 10 to 30 feet. Depths that deviate from the above criteria must be justified by a pilot study.

(4)   Underdrain system. The underdrain system shall cover the entire floor of the filter. Inlet openings into the underdrains shall have an unsubmerged gross combined area at least 15 percent of the surface area of the filter.

(A)   Hydraulic capacity and ventilation. Underdrains shall slope at least 1%. Design effluent channels to produce a minimum velocity of 2 fps of the average daily application rate. Design the underdrain system, effluent channels and effluent pipe to allow free air passage. Not more than 50% of the cross sectional area for all drains, channels and pipe may be submerged under the design hydraulic loading.

(B)   Flushing. Design the underdrains to be flushed.

(5)   Freeboard. Provide two feet of freeboard to prevent splashing and to protect the distributor. Structures taller than 25 feet shall have 4 feet of freeboard to contain windblown spray.

(6)   Recirculation. Recirculate effluent to maintain an active biological growth and to increase overall efficiency.

(7)   Dosing rate. The dosing rate on a trickling filter is the depth of liquid discharged on top of the packing for each pass of the distributor. For a standard rate filter, the dosing rate shall be in the range of 0.4 inches per pass to 1.2 inches per pass. For high rate filters, the rate shall be in the re range of 0.6 inches per pass to 7.0 inches per pass.

(c)   Whole effluent toxicity failures. Attached growth systems may not consistently provide ammonia removal through the nitrification process so the effluent from these facilities may be toxic to aquatic life and thus cause whole effluent toxicity test failures.

[Source: Added at 23 Ok Reg 937, eff 6-15-06; Added at 28 Ok Reg 1282, eff 7-1-11]