R317-3-12. Effluent Filtration

12.1. Granular Media Filters. Granular media filters may be used as a tertiary treatment device for the removal of residual suspended solids from secondary effluents. A pretreatment process such as chemical coagulation and sedimentation or other acceptable process must precede the filter units, where effluent suspended solids requirements are less than 10 milligrams per liter, or where secondary effluent quality can be expected to fluctuate significantly, or where filters follow a treatment process and where significant amounts of algae will be present. 12.2. Design Considerations. The plant design should incorporate flow-equalization facilities to moderate filter influent quality and quantity. The selection of pumping equipment ahead of filter units should be designed to minimize shearing of floc particles. A. Filter Types. Filters may be of the gravity or pressure type. Pressure filters shall be provided with ready and convenient access to the media for treatment or cleaning. Where greases or similar solids which result in filter plugging are expected, filters should be of the gravity type. B. Filtration Rates. Filtration rates shall not exceed 5 gallons per minute per square foot. (3.4 liters per square meter per second) based on the maximum hydraulic flow rate applied to the filter units. C. Number of Units. Total filter area shall be provided in two or more units, and the filtration rate shall be calculated on the total available filter area with one unit out of service. D. Filter Backwash 1. Backwash Rate. The backwash rate shall be adequate to fluidize and expand each media layer a minimum of 20 percent based on the media selected. The backwash system shall be capable of providing a variable backwash rate having a maximum of at least 20 gallons per minute per square foot, (13.6 liters per square meter per second) and a minimum backwash period of 10 minutes. 2. Backwash Pumps. Pumps for backwashing filter units shall be sized and interconnected to provide the required rate to any filter with the largest pump out of service. Filtered water should be used as the source of backwash water. Waste filter backwash shall be returned to the treatment process or otherwise adequately treated. E. Filter Media 1. Selection. Selection of proper media size will depend on the rate of filtration rate, the type of pretreatment, filter configuration, and effluent quality objectives. In dual or multi-media filters, media size selection must consider compatibility among media. 2. Media Specifications. Table R317-3-12.2(E)(2) provides minimum media depths and the normally acceptable range of media sizes. The applicant has the responsibility for selection of media to meet specific conditions and treatment requirements relative to the project under consideration. 12.3. Filter Appurtenances. The filters shall be equipped with wash water troughs, surface wash or air scouring equipment, means of measurement and positive control of the backwash rate, equipment for measuring filter head loss, positive means of shutting off flow to a filter being backwashed, and filter influent and effluent sampling points. If automatic controls are provided, there shall be a manual override for operating equipment, including each individual valve essential to the filter operation. The underdrain system shall be designed for uniform distribution of backwash water (and air if provided) without danger of clogging from solids in the backwash water. Provision shall be made to allow periodic chlorination of the filter influent or backwash water to control slime growths. 12.4. Reliability. Each filter unit shall be designed and installed so that there is ready and convenient access to all components and the media surface for inspection and maintenance without taking other units out of service. The need for enclosing filter units shall depend on expected extreme climatic conditions at the treatment plant site. As a minimum, all controls shall be protected from adverse process and climatic conditions. The structure housing filter controls and equipment shall be provided with adequate heating and ventilation equipment to minimize problems with excess humidity. 12.5. Backwash Surge Control. The rate of waste filter backwash water return to treatment units shall be controlled such that the rate does not exceed 15 percent of the design average daily flow rate to the treatment units. The hydraulic and organic loads from waste backwash water shall be considered in the overall design of the treatment plant. Where waste backwash water is returned for treatment by pumping, adequate pumping capacity shall be provided with the largest unit out of service. 12.6. Backwash Water Storage. Total backwash water storage capacity provided in an effluent clearwell or surge tank or other unit shall equal or exceed the volume required for two complete backwash cycles. Additional storage capacity should be considered for operational flexibility. 12.7. Proprietary Equipment. Where proprietary filtration equipment, not conforming to the preceding requirements is proposed, data which supports the capacity of the equipment to meet effluent requirements under design conditions shall be submitted for review and approval by the Director. TABLE R317-3-2.3(D)(4). Minimum Slopes Sewer Size, Minimum Slope, inch (centimeter) feet per feet or meter per meter 8 (20) 0.00334 9 (23) 0.00285 10 (25) 0.00248 12 (30) 0.00194 14 (36) 0.00158 15 (38) 0.00144 16 (41) 0.00132 18 (46) 0.00113 21 (53) 0.00092 24 (61) 0.00077 27 (69) 0.00066 30 (76) 0.00057 36 (91) 0.00045 TABLE R317-3-4.4(H)(1). Painting Service Color Sludge Brown Gas Orange Potable Water Blue Non-Potable Water Blue with a 6-inch (15 centimeters) red band spaced 30 inches (76 centimeters) apart Chlorine Yellow Compressed Air Green Sewage Gray TABLE R317-3-6.2(B)(3)(d). Loadings for Final Settling Tanks Following Activated Sludge Process Process Average Surface Surface Design Loading, Loading, Rate of gallons per pounds Flow, day per day million per square per square gallons foot foot per day (cubic (kilograms (cubic meters per day meters per day per square per day) per square meter) meter) Contact 0.5 (1,893) 400 (16.3) Stabilization to 1.5 to 600 (5,678) (24.5) Greater than 500 (20.4) or equal to to 700 1.5 (5,678) (28.5) Extended Less than 200 (8.2) Aeration or equal to to 400 0.5 (1,893) (16.3) 0.5 (1,893) 300 (12.3) 25 (122.1) to 1.5 to 500 (5,678) (20.4) Greater than 400 (16.3) or equal to to 600 1.5 (5,678) (24.5) Other than Less than 400 (16.3) Contact or equal to to 600 Stabilization 0.5 (1,893) (24.5) and Extended Aeration 0.5 (1,893) to 500 (20.4) 25 (122.1) 1.5 (5,678) to 700 (28.5) Greater than 600 (24.5) or equal to to 800 1.5 (5,678) (32.6) TABLE R317-3-7.1(E)(3)(a)(2). Media Grading Percent by Weight Passing 4-1/2 inch (11.4 centimeters) screen 100 Retained on 3 inch (7.6 centimeters) screen 95 - 100 Retained on 2 inch (5.1 centimeters) screen 98 TABLE R317-3-7.1(K)(1). Hydraulic and Organic Loadings for Nitrification in Trickling Filters Trickling Filter Configuration Loadings Rock or Slag Media Filters Hydraulic Loading Less than or equal to 4 million gallons per acre per day, or less than or equal to 4 cubic meters per square meter per day Organic Loading Less than or equal to 25 pounds BOD5 per day per 1000 cubic feet, or less than or equal to 0.4 kilograms BOD5 per day per cubic meter Deep Manufactured Media Filters Hydraulic Loading Less than or equal to 25 million gallons per acre per day, or less than or equal to 25 cubic meters per square meter per day Organic Loading Less than or equal to 100 pounds BOD5 per day per 1000 cubic feet, or less than or equal to 1.6 kilograms BOD5 per day per cubic meter TABLE R317-3-7.2(B)(1)(c) Permissible Aeration Tank Capacities and Loadings Process Hydraulic Solids Aeration Food:Mass Mixed Retention Retention Tank (F:M) Liquor Time Time Loading, Ratio, Suspended (HRT), (SRT), pounds of pounds of Solids (1) hours days BOD5 per BOD5 per (MLSS) day per day per milligrams 1000 pound of per liter cubic MLVSS (2) feet Conven- 4-8 4-8 20-40 0.2-0.4 1,500- tional 4,000 Step Aeration Complete Mix Contact 1-3 (4) 3-10 50 (3) 0.2-0.6 2,000- Stabili- 3-6 (5) 4,000 zation Extended Aeration, or 24 30 10-12 0.05- 2,000- Oxidation 0.1 4,000 Ditch Notes: (1) Mixed Liquor Suspended Solids (MLSS) values are dependent upon the surface area provided for sedimentation and the rate of sludge return as well as the aeration process. (2) Mixed Liquor Volatile Suspended Solids (MLVSS) (3) Total Aeration capacity, includes both contact and reaeration capacities. Normally, the contact zone equals 30 to 35 percent of the total aeration capacity. (4) Contact zone (5) Reaeration zone TABLE R317-3-7.2(B)(6)(a)(1). Return Sludge Rate Process QR / Q, Percent Standard Rate 15-75 Carbonaceous stage of separate stage nitrification 15-75 Step Aeration 15-75 Contact stabilization 50-150 Extended aeration 50-150 Nitrification stage of separate stage nitrification 50-200 TABLE R317-3-9.3(A)(1)(a). Gravity Thickening Type Solids Loading Rate, Percent solids pounds per day per in thickened square foot (kilograms sludge per square meter per day) Primary sludge 20-30 (98-146) 8-10 Trickling filter sludge 8-10 (39-49) 7-9 Activated sludge 4-8 (20-49) 2.5-3 Combined primary and trickling filter sludges 10-12 (49-59) 7-9 Combined primary and activated sludges 6-10 (29-49) 3-6 TABLE R317-3-9.4(A)(4)(a). Sludge Volume Generated Type of Plant cubic feet per Population Equivalent (P.E.) or cubic meters per Population Equivalent (P.E.) Trickling Filter 5 (0.14) Activated Sludge 6 (0.17) TABLE R317-3-10.3(G)(3)(a). Circle of Influence Nameplate Horsepower Radius, Feet 5 35 10-25 50 40-60 50-100 75 60-100 100 100 TABLE R317-3-12.2(E)(2). Media Depths and Size Media Material Single Media Multi-Media Two Three Anthracite: Minimum Depth, inches 20 20 Effective Size, millimeters 1-2 1-2 Sand: Minimum Depth, inches 48 12 10 Effective Size, millimeters 1-4 0.5-1 0.6-0.8 Garnet or Similar Material: Minimum Depth, inches 2 Effective Size, millimeters 0.3-0.6 Uniformity Coefficient shall be less than or equal to 1.7