NR 110.17(1)(1) Applicability. Grit removal facilities are recommended for all sewage plants and are required for plants receiving sewage from combined sewers or from sewer systems receiving substantial amounts of grit. NR 110.17(2)(a)(a) Location. Where practical, grit chambers should precede influent pumps. When installed, grit chambers shall precede all major treatment units. NR 110.17(2)(b)(b) Protection. All grit chambers shall be preceded by a bar rack, coarse screen or comminutor. NR 110.17(2)(c)1.1. Enclosed grit removal areas shall be ventilated. Fresh air shall be introduced continuously at a rate of 12 air changes per hour, or intermittently at a rate of 30 air changes per hour. NR 110.17(2)(c)2.2. All electrical work in enclosed grit removal areas where hazardous gases may accumulate shall meet the requirements of the national electrical code for class 1, group D, division 1 locations. NR 110.17(2)(d)(d) Number of units. Grit removal facilities shall have at least 2 hand-cleaned units, or a mechanically cleaned unit with a bypass. NR 110.17(2)(e)1.1. All facilities not provided with positive velocity control shall include means for grit washing to further separate organic and inorganic materials. NR 110.17(2)(e)2.2. Grit removal facilities located in deep pits shall be provided with mechanical equipment for hoisting or transporting grit to ground level. Impervious, nonslip, working surfaces with adequate drainage shall be provided for grit handling areas. Storage areas for wasted grit shall be provided. NR 110.17(2)(f)(f) Basis of design. Design of grit chambers shall be based on the size and specific gravity of the grit particle to be removed. If this information is not obtained from actual field measurements, then the design shall assume removal of all particles retained on a 65 mesh (0.21 mm) sieve and having a minimum specific gravity of 2.65. The design requirements of sub. (3) are based on these assumptions. NR 110.17(3)(a)2.2. Drains or other means for dewatering each grit unit must be provided. NR 110.17(3)(a)3.3. An adequate supply of water under pressure shall be provided for cleaning grit equipment. NR 110.17(3)(b)(b) Velocity controlled grit chambers. Positive hydraulic control shall be provided to maintain a channel velocity of 30 centimeters per second (one foot per second) through the expected flow range. Positive hydraulic control shall be provided by one of the following: NR 110.17(3)(c)1.1. Air rates should be in the range of 4.6 to 12.4 liters per second per meter (3 to 8 cubic feet per minute per foot) of tank length. NR 110.17(3)(c)2.2. The detention time at the maximum design flow rate should not exceed 3 minutes. NR 110.17(3)(c)3.3. Inlets and outlets shall be designed to prevent short circuiting. NR 110.17(3)(c)4.4. The design of the grit chamber shall be such to avoid producing dead spaces. NR 110.17(3)(d)1.1. Inlets shall be designed to distribute flow evenly across the tank. NR 110.17(3)(d)3.3. An additional depth of 15 to 25 centimeters (6 to 10 inches) shall be provided for raking mechanisms. NR 110.17(3)(d)4.4. Surface area of the sedimentation tank shall be designed not to exceed a surface settling rate of 1,900 cubic meters per day per square meter (46,000 gallons per day per square foot). NR 110.17 HistoryHistory: Cr. Register, November, 1974, No. 227, eff. 12-1-74; r. and recr. Register, February, 1983, No. 326, eff. 3-1-83. NR 110.18(1)(a)1.1. Multiple settling tanks shall be provided at all sewage treatment plants with an average design flow which exceeds 1,890 cubic meters per day (0.5 million gallons per day). NR 110.18(1)(a)2.2. Control appurtenances such as valves, gates, splitter boxes, and flow measuring devices, shall be provided to divide inflow equally to each settling tank. NR 110.18(1)(b)1.1. All settling tanks shall be provided with easy access for maintenance. NR 110.18(1)(b)2.2. Each settling tank shall be capable of being independently dewatered and isolated for servicing. Provisions shall be made to protect empty settling tanks from the hydrostatic uplift due to high groundwater. NR 110.18(1)(c)(c) Safety. Operator safety shall be considered in the design of settling tanks. Safety features such as machinery covers, life lines, stairways, walkways, handrails and slip-resistant surfaces shall be provided if appropriate. NR 110.18(1)(d)(d) Electrical controls. Electrical fixtures and controls in enclosed settling tanks shall meet the requirements of the national electrical code for class 1, group D, division 1 locations. The fixtures and controls shall be located to provide convenient and safe access for operation and maintenance. NR 110.18(1)(e)(e) Imhoff tanks. Imhoff tanks will not be approved by the department. NR 110.18(2)(a)1.1. Settling tank inlets shall be designed to dissipate the inlet velocity, to distribute the flow equally and to prevent short-circuiting. Either channel shall be designed to maintain a velocity of at least 30 centimeters per second (one foot per second) at one-half of average design flow or some other means of preventing solid deposition shall be used. Corner pockets and dead ends shall be eliminated and corner fillets or channeling used where necessary. Elimination or removal of floating materials in inlet structures having submerged ports shall be required. NR 110.18(2)(a)2.2. Inlet velocities in rectangular settling tanks may not exceed 15 centimeters per second (0.5 foot per second). NR 110.18(2)(a)3.3. Inlet velocities in center feed circular settling tanks may not exceed 91 centimeters per second (3 feet per second). NR 110.18(2)(b)1.1. The side water depth of mechanically cleaned settling tanks shall be as shallow as practical but not less than 2.1 meters (7 feet). Final clarifiers for activated sludge may not be less than 3 meters (10 feet) in depth. Final clarifier for fixed film treatment systems may not be less than 2.1 meters (7 feet). NR 110.18(2)(b)2.2. The tops of troughs, beams, and similar construction features which are submerged shall have a minimum slope of 1.4 vertical to one horizontal. A slope of one to one shall be provided on the underside of such features to prevent the accumulation of scum and solids. NR 110.18(2)(c)1.1. Scum baffles shall be provided ahead of outlet weirs on all primary and final settling tanks. NR 110.18(2)(c)2.2. Sludge hoppers shall have a minimum side wall slope of 1.7 vertical to one horizontal. Hopper wall surfaces should be made smooth with rounded corners to aid in sludge removal. The department will not approve increasing the depth of sludge hoppers for the purpose of sludge thickening in settling tanks. NR 110.18(2)(c)3.3. Each sludge hopper shall have an individually valved sludge withdrawal line at least 15 centimeters (6 inches) in diameter. Head available for withdrawal of sludge shall be at least 76 centimeters (30 inches), or greater as necessary, to maintain a velocity of 91 centimeters per second (3 feet per second) in the withdrawal pipe. NR 110.18(2)(c)4.4. A sludge well or other appropriate equipment shall be provided for viewing and sampling sludge. NR 110.18(2)(c)6.6. The department may approve the use of glass lined pipe for sludge. Glass lined pipe may not be less than 10 centimeters (4 inches) in diameter. NR 110.18(2)(c)7.7. Suitable mechanical sludge and scum collection equipment shall be provided in all settling tanks. Provisions for separate scum washing shall be made for treatment facilities which do not have primary settling facilities. NR 110.18(2)(d)1.1. Operating design parameters for settling facilities may not exceed the values given in Table 3. The surface settling rate for primary settling tanks shall be calculated with all flows received at the settling tank. The surface settling rate for final settling tanks shall be based on influent flow. The maximum hour solids loading shall be computed based on the maximum day design flow plus the maximum design return sludge rate requirement and the design mixed liquor suspended solids (MLSS) under aeration. Table 3
NR 110.18(2)(d)2.2. For treatment plants with an average design flow greater than 3,785 cubic meters per day (one million gallons per day), the department may approve an overflow rate of 188 cubic meters per meter per day (15,000 gallons per foot per day). NR 110.18(2)(d)3.3. The design parameters shown in Table 3 may be waived by the department if the settling tank design is based on settling tests of wastes currently received at the existing treatment facility, or if the effluent from the sewage treatment facility is to be disposed on land. NR 110.18 HistoryHistory: Cr. Register, November, 1974, No. 227, eff. 12-1-74; r. and recr. Register, February, 1983, No. 326, eff. 3-1-83; CR 09-123: am. (2) (d) Register July 2010 No. 655, eff. 8-1-10. NR 110.19(1)(a)(a) Surface water discharge. New trickling filters shall be used in conjunction with other treatment units which, in combination, will produce an acceptable level of treatment as defined in s. NR 110.15 (2) (a). Existing trickling filters may be used as a treatment unit in plant expansion if the effluent quality requirements of s. NR 110.15 (2) (a) are met. NR 110.19(1)(b)(b) Land disposal. Trickling filter treatment systems are an acceptable means of treatment prior to land disposal of effluent. NR 110.19(2)(2) Design report. A design report must be submitted in accordance with s. NR 110.15 (1). The report shall show the empirical equations and the assumptions used for designing the trickling filter and the additional treatment units. NR 110.19(3)(a)(a) Recirculation. Recirculation shall be provided for intermediate and high-rate filters to increase treatment efficiency and to provide wetting of the biological growth. The recirculation rate shall be variable. The recirculation rate to average influent flow ratio should not exceed 4:1. NR 110.19(3)(b)(b) Dosing cycle. The interval between dosing cycles may not exceed one hour. NR 110.19(3)(c)(c) Flooding. Filter structures should be designed to allow flooding of the filter. NR 110.19(3)(d)(d) Primary treatment. Trickling filters shall be preceded by primary treatment facilities. NR 110.19(4)(4) Design loading. Hydraulic and organic loadings to trickling filters may not exceed the values given in Table 4. Higher loadings may be approved if justified by pilot studies or if manufactured media is used. Higher loadings may also be used if the trickling filter is intended to act only as a roughing or polishing treatment unit. Table 4
NR 110.19(5)(a)1.1. Sewage shall be distributed over the filter by rotary distributors or other suitable devices which will permit uniform distribution to the filter surface area. NR 110.19(5)(a)2.2. Sewage shall be applied to the filters by siphons, pumps or by gravity discharge from preceding treatment units when suitable flow characteristics have been developed. The dosing rate shall be large enough to insure rotation of the distributor arms. NR 110.19(5)(a)3.3. A minimum clearance of 15 centimeters (6 inches) between media and distributor arms shall be provided. NR 110.19(5)(b)1.1. An underdrainage system which covers the entire floor of the filter shall be provided. Inlet openings into the underdrains shall have an unsubmerged gross combined area equal to at least 15% of the surface area of the filter. NR 110.19(5)(b)2.2. The underdrains shall have a minimum slope of 1%. Effluent channels shall be designed to produce a minimum velocity of 60 centimeters per second (2 feet per second) at the average design flow of application to the filter including recirculated flows.
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Department of Natural Resources (NR)
Chs. NR 100-199; Environmental Protection – General
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