40 CFR § 439.52 - Effluent limitations attainable by the application of the best practicable control technology currently available (BPT).
(c) The maximum monthly average limitation for COD, expressed as mass loading (lbs, kg) per day, must reflect not less than 74 percent reduction in the long-term average daily COD load of the raw (untreated) process wastewater, multiplied by a variability factor of 2.2. No facility shall be required to attain a limitation for COD that is less than the equivalent of 220 mg/L.
(d) The long-term average daily BOD5 or COD mass loading of the raw process wastewater (i.e., the base number to which the percent reduction is applied) is defined as the average daily BOD5 or COD load during any calendar month, over 12 consecutive months within the most recent 36 months.
(1) To assure equity in the determination of NPDES permit limitations regulating discharges subject to this subpart, calculation of the long-term average daily BOD5 or COD load in the influent to the wastewater treatment system must exclude any portion of the load associated with solvents, except for residual amounts of solvents remaining after the practices of recovery and/or separate disposal or reuse. Residual amounts of these substances may be included in the calculation of the average influent BOD5 or COD loading.
(2) The practices of recovery, and/or separate disposal or reuse include: recovery of solvents from wastestreams; and incineration of concentrated solvent wastestreams (including tar still bottoms). This regulation does not prohibit the inclusion of such wastes in raw waste loads in fact, nor does it mandate any specific practice, but rather describes the rationale for determining NPDES permit limitations. The effluent limitation for BOD5 or COD may be achieved by any of several, or a combination, of these practices.
(e) The pH must be within the range 6.0 to 9.0.
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