NR 110.20(2)(b)5.5. Percent influent biochemical oxygen demand which is soluble.
NR 110.20(3)(3)Design features.
NR 110.20(3)(a)(a) Primary treatment. Rotating biological contactors shall be preceded by primary treatment.
NR 110.20(3)(b)(b) Contact tanks.
NR 110.20(3)(b)1.1. Contact tanks shall be sized to maintain a maximum hydraulic detention time of 100 minutes.
NR 110.20(3)(b)2.2. Tanks shall contain positive liquid level control so that the rotating biological contactors will remain approximately 40% submerged.
NR 110.20(3)(b)3.3. Contact tanks and rotating shafts shall be enclosed. The enclosure shall be ventilated.
NR 110.20(3)(b)4.4. Removable baffles shall be provided between contact stages.
NR 110.20(3)(c)(c) Equalization. Equalization facilities shall be provided ahead of rotating biological contactors if the ratio of maximum hourly design flow to average design flow exceeds 2.5:1.
NR 110.20(3)(d)(d) High density media. High density shafts may not be used in the first 2 stages of any rotating biological treatment unit or system.
NR 110.20(3)(e)(e) Rotational speed.
NR 110.20(3)(e)1.1. Contactors shall be equipped with drive units which will allow variable rotational speed.
NR 110.20(3)(e)2.2. Maximum rotational speed shall be limited to a peripheral velocity of 49 centimeters per second (1.6 feet per second).
NR 110.20(3)(f)(f) Load monitoring. Each rotating biological shaft shall be equipped with a load monitoring device.
NR 110.20 HistoryHistory: Cr. Register, November, 1974, No. 227, eff. 12-1-74; r. and recr. Register, February, 1983, No. 326, eff. 3-1-83.
NR 110.21NR 110.21Activated sludge.
NR 110.21(1)(1)Applicability. The activated sludge process, and its various modifications, may be used where sewage is amenable to biological treatment.
NR 110.21(2)(2)Design report. A design report shall be submitted in accordance with s. NR 110.15 (1).
NR 110.21(3)(3)Design considerations.
NR 110.21(3)(a)(a) Process selection. The choice of activated sludge process will be influenced by the degree of treatment needed to achieve the required effluent limits, the proposed treatment facility size, and the characteristics of the waste to be treated.
NR 110.21(3)(b)(b) Winter protection. Activated sludge processes and aeration equipment which are subject to freezing or icing shall be designed to minimize the degree of freezing and icing.
NR 110.21(3)(c)(c) Pretreatment. Where primary settling tanks are not used, effective removal of grit, debris, excessive oil or grease, and comminution or screening of solids shall be provided prior to the activated sludge process.
NR 110.21(3)(d)(d) Measuring devices. Devices shall be installed for measuring and displaying flow rates of raw sewage or primary effluent, return sludge, and air to the aeration facilities. It is recommended that these devices totalize and record, as well as indicate, flows if the average design flow for the treatment plant is greater than 5,680 cubic meters per day (1.5 million gallons per day).
NR 110.21(3)(e)(e) Equalization. Equalization chambers shall be provided when large daily fluctuations of influent flow or organic loading are expected to occur.
NR 110.21(4)(4)Aeration tanks.
NR 110.21(4)(a)(a) Process design. The size of aeration units for any particular adaptation of the activated sludge process shall be determined by pilot plant studies, or calculations based mainly on food to microorganism (F/M) ratio and mixed liquor suspended solids (MLSS) levels. Other factors such as size of treatment plant, diurnal load variations and degree of treatment required shall also be considered. In addition, temperature, pH bicarbonate hardness, and reactor dissolved oxygen shall be considered when designing for nitrification. The calculations used to determine the aeration capacity shall be included in the design report required by s. NR 110.15 (1). Designs based on mixed liquor suspended solids levels greater than 5,000 milligrams per liter will not be approved unless adequate data is submitted showing the aeration and settling systems are capable of supporting such levels.
NR 110.21(4)(b)(b) Permissible loadings. In lieu of the design calculation requirements of par. (a), the parameters shown in Table 5 may be used to design aeration tank capacities. The volumetric loadings in Table 5 shall be based on the organic load influent to the aeration tank at the average design BOD5 loading rate.
Table 5
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