---identifier: "/us/cfr/t40/s133.102"source: "ecfr"legal_status: "authoritative_unofficial"title: "40 CFR § 133.102 - Secondary treatment."title_number: 40title_name: "Protection of Environment"section_number: "133.102"section_name: "Secondary treatment."chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"subchapter_number: "D"subchapter_name: "WATER PROGRAMS"part_number: "133"part_name: "SECONDARY TREATMENT REGULATION"positive_law: falsecurrency: "2026-04-05"last_updated: "2026-04-05"format_version: "1.1.0"generator: "[email protected]"authority: "Secs. 301(b)(1)(B), 304(d)(1), 304(d)(4), 308, and 501 of the Federal Water Pollution Control Act as amended by the Federal Water Pollution Control Act Amendments of 1972, the Clean Water Act of 1977, and the Municipal Wastewater Treatment Construction Grant Amendments of 1981; 33 U.S.C. 1311(b)(1)(B), 1314(d) (1) and (4), 1318, and 1361; 86 Stat. 816, Pub. L. 92-500; 91 Stat. 1567, Pub. L. 95-217; 95 Stat. 1623, Pub. L. 97-117."regulatory_source: "49 FR 37006, Sept. 20, 1984, unless otherwise noted."cfr_part: "133"---
Identifier
/us/cfr/t40/s133.102
Currency
2026-04-05
Positive Law
No
Updated
2026-04-05
Chapter
Environmental Protection Agency
Authority
Secs. 301(b)(1)(B), 304(d)(1), 304(d)(4), 308, and 501 of the Federal Water Pollution Control Act as amended by the Federal Water Pollution Control Act Amendments of 1972, the Clean Water Act of 1977,... Secs. 301(b)(1)(B), 304(d)(1), 304(d)(4), 308, and 501 of the Federal Water Pollution Control Act as amended by the Federal Water Pollution Control Act Amendments of 1972, the Clean Water Act of 1977, and the Municipal Wastewater Treatment Construction Grant Amendments of 1981; 33 U.S.C. 1311(b)(1)(B), 1314(d) (1) and (4), 1318, and 1361; 86 Stat. 816, Pub. L. 92-500; 91 Stat. 1567, Pub. L. 95-217; 95 Stat. 1623, Pub. L. 97-117.
# 133.102 Secondary treatment.The following paragraphs describe the minimum level of effluent quality attainable by secondary treatment in terms of the parameters—BOD<sub>5</sub>, SS and pH. All requirements for each parameter shall be achieved except as provided for in §§ 133.103 and 133.105.(a) *BOD*<sub>5</sub>.(1) The 30-day average shall not exceed 30 mg/l.(2) The 7-day average shall not exceed 45 mg/l.(3) The 30-day average percent removal shall not be less than 85 percent.(4) At the option of the NPDES permitting authority, in lieu of the parameter BOD<sub>5</sub> and the levels of the effluent quality specified in paragraphs (a)(1), (a)(2) and (a)(3), the parameter CBOD<sub>5</sub> may be substituted with the following levels of the CBOD<sub>5</sub> effluent quality provided:(i) The 30-day average shall not exceed 25 mg/l.(ii) The 7-day average shall not exceed 40 mg/l.(iii) The 30-day average percent removal shall not be less than 85 percent.(b) *SS.* (1) The 30-day average shall not exceed 30 mg/l.(2) The 7-day average shall not exceed 45 mg/l.(3) The 30-day average percent removal shall not be less than 85 percent.(c) *pH.* The effluent values for pH shall be maintained within the limits of 6.0 to 9.0 unless the publicly owned treatment works demonstrates that: (1) Inorganic chemicals are not added to the waste stream as part of the treatment process; and (2) contributions from industrial sources do not cause the pH of the effluent to be less than 6.0 or greater than 9.0.[49 FR 37006, Sept. 20, 1984; 49 FR 40405, Oct. 16, 1984]