NR 110.20(2)(a)(a) Design report. A design report for rotating biological contactors shall be submitted in accordance with s. NR 110.15 (1). NR 110.20(2)(b)(b) Design parameters. The design of rotating biological contactors shall consider: NR 110.20(3)(a)(a) Primary treatment. Rotating biological contactors shall be preceded by primary treatment. 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)(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)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 110.21(1)(1) Applicability. The activated sludge process, and its various modifications, may be used where sewage is amenable to biological treatment. NR 110.21(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.