40 CFR § 437.21 - Effluent limitations attainable by the application of the best practicable control technology currently available (BPT).

---
identifier: "/us/cfr/t40/s437.21"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 437.21 - Effluent limitations attainable by the application of the best practicable control technology currently available (BPT)."
title_number: 40
title_name: "Protection of Environment"
section_number: "437.21"
section_name: "Effluent limitations attainable by the application of the best practicable control technology currently available (BPT)."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "N"
subchapter_name: "EFFLUENT GUIDELINES AND STANDARDS"
part_number: "437"
part_name: "THE CENTRALIZED WASTE TREATMENT POINT SOURCE CATEGORY"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "33 U.S.C. 1311, 1314, 1316, 1317, 1318, 1342, and 1361."
regulatory_source: "65 FR 81300, Dec. 22, 2000, unless otherwise noted."
cfr_part: "437"
---


# 437.21 Effluent limitations attainable by the application of the best practicable control technology currently available (BPT).

Except as provided in 40 CFR 125.30 through 125.32 or § 437.20(b), any existing point source subject to this subpart must achieve the following effluent limitations representing the application of BPT:

BPT Limitations

| Regulatedparameter | Maximum daily | Maximum monthly avg. |
| --- | --- | --- |
|  |  |  |
| O&G | 127 | 38.0 |
| pH | () | () |
| TSS | 74.1 | 30.6 |
|  |  |  |
| Arsenic | 2.95 | 1.33 |
| Cadmium | 0.0172 | 0.0102 |
| Chromium | 0.746 | 0.323 |
| Cobalt | 56.4 | 18.8 |
| Copper | 0.500 | 0.242 |
| Lead | 0.350 | 0.160 |
| Mercury | 0.0172 | 0.00647 |
| Tin | 0.335 | 0.165 |
| Zinc | 8.26 | 4.50 |
|  |  |  |
| Bis(2-ethylhexyl) phthalate | 0.215 | 0.101 |
| Butylbenzyl phthalate | 0.188 | 0.0887 |
| Carbazole | 0.598 | 0.276 |
| n-Decane | 0.948 | 0.437 |
| Fluoranthene | 0.0537 | 0.0268 |
| n-Octadecane | 0.589 | 0.302 |
| mg/L (ppm). |  |  |
| Within the range 6 to 9. |  |  |

[65 FR 81300, Dec. 22, 2000, as amended at 68 FR 71023, Dec. 22, 2003]