NR 110.21(7)(b)1.1. If motor driven return sludge pumps are used, the maximum return sludge capacity shall be met with the largest pump out of service. A positive head shall be provided on pump suctions. Pumps shall also have at least 7.6 centimeter (3-inch) suction and discharge openings. NR 110.21(7)(b)2.2. If air lifts are used for returning sludge from each settling tank hopper, no standby unit will be required provided the design of the air lifts allows rapid and easy cleaning. Air lift pumps shall be designed to provide positive control of the return sludge rate. NR 110.21(7)(c)(c) Return sludge piping. Suction piping and discharge piping for returning activated sludge shall be at least 10 centimeters (4 inches) in diameter and must be designed to maintain a velocity of not less than 60 centimeters per second (2 feet per second) at normal return sludge rates. Suitable devices for observing, sampling and controlling return activated sludge flow from each settling tank shall be provided. NR 110.21(7)(e)(e) Waste sludge pumps. Variable speed or multiple constant speed waste sludge pumps shall be provided. The maximum sludge pumping rate shall be at least 200% of the anticipated volumetric sludge production rate. Devices for measuring waste activated sludge flow rates shall be provided. NR 110.21 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. (4) (b), (d) 5., (5) (b) 2., 3., (c) 2., (6) (a) 2., (b) 1. and Table 5 (title) Register July 2010 No. 655, eff. 8-1-10. NR 110.22NR 110.22 Physical-chemical treatment. NR 110.22(1)(1) Applicability. Physical-chemical treatment processes may be used where appropriate to achieve the required effluent limits. NR 110.22(2)(2) Design report. A design report shall be submitted in accordance with s. NR 110.05 (1). The report shall detail any lab testing, pilot plant studies or operating experience used to design the physical-chemical process. NR 110.22(3)(a)(a) Chemical selection. Selection of chemicals used in chemical treatment shall be based on the characteristics of the wastewater and constituents to be removed. NR 110.22(3)(b)1.1. Design of chemical treatment processes shall be based on laboratory testing, pilot plant studies or practical operating experience. NR 110.22(3)(b)2.2. Design of chemical treatment equipment, reactors, and appurtenances shall consider: NR 110.22(3)(b)2.f.f. The velocity of waste streams in flow conduits to minimize destruction of floc. NR 110.22(3)(c)1.1. Addition of lime or the salts of aluminum or iron may be used for the chemical precipitation of soluble phosphorus. NR 110.22(3)(c)2.2. The addition of polyelectrolytes to aid in the settling of phosphate precipitates should be considered. NR 110.22(3)(c)3.3. Chemicals shall be mixed rapidly and thoroughly with the wastewater. NR 110.22(4)(a)1.1. Eye-wash fountains and safety showers using potable water shall be provided in the laboratory and on each floor level or work location where hazardous chemicals are stored, mixed or slaked, pumped, metered or unloaded. These fountains and showers shall be less than 7.6 meters (25 feet) from points of exposure to hazardous chemicals and shall be fully usable during all weather conditions. NR 110.22(4)(a)2.2. Eye-wash fountains shall be supplied with water with a temperature not exceeding 38°C (100°F). This supply shall be separate from the hot water supply and be able to provide 15 to 30 minutes of continuous irrigation of the eyes. NR 110.22(4)(a)3.3. Safety showers shall be capable of discharging 1.9 to 3.2 liters per second (30 to 50 gallons per minute) of water with a temperature not exceeding 38°C (100°F) temperature, and at pressures of 1.41 to 3.52 kilograms force per square centimeter (20 to 50 pounds per square inch).