Q.01

What is industrial wastewater pretreatment?

Industrial wastewater pretreatment is treatment an industrial or other non-domestic facility gives its own wastewater before that wastewater goes into a municipal sewer and treatment plant. It is not treatment before discharge straight to a river or other surface water. Under US federal law (40 CFR 403.3(s)), pretreatment means "the reduction of the amount of pollutants, the elimination of pollutants, or the alteration of the nature of pollutant properties in wastewater prior to or in lieu of discharging or otherwise introducing such pollutants into a POTW" (a publicly owned treatment works).

Approach: I checked the US EPA effluent guidelines register and Turkey's Water Pollution Control Regulation No. 7221. Neither holds the US General Pretreatment Regulations (40 CFR Part 403), so I took the definitions from eCFR and the program description from EPA.

What the rule says (US, 40 CFR Part 403) (eCFR §403.3)

  • How it can be done: the reduction or change "may be obtained by physical, chemical or biological processes, process changes or by other means", except as § 403.6(d) prohibits. Suitable pretreatment technology includes equalization tanks to protect against surges or slug loadings.

  • Mixed waste streams: where regulated process wastewater is mixed in an equalization facility with unregulated wastewater, or with wastewater from another regulated process, the effluent "must meet an adjusted pretreatment limit" calculated under § 403.6(e).

  • Who it applies to: an Industrial User is a source of Indirect Discharge. That means introducing pollutants into a POTW from any non-domestic source regulated under section 307(b), (c) or (d) of the Clean Water Act.

  • Why it is needed: to prevent two things:

    • Interference: a discharge that disrupts the treatment plant, its processes or its sludge use or disposal, and so causes a permit violation.
    • Pass Through: pollutants that leave the POTW into waters of the United States and cause a violation of the POTW's NPDES permit.

  • Two kinds of obligation: National Pretreatment Standards are EPA discharge limits under CWA section 307(b) and (c), including the prohibitions in § 403.5. Pretreatment requirements are any other substantive or procedural requirements imposed on an Industrial User.

  • Significant Industrial Users are subject to closer control. They include:

    • all users subject to Categorical Pretreatment Standards;
    • any other user that discharges an average of 25,000 gallons per day or more of process wastewater;
    • any user contributing 5 percent or more of the treatment plant's average dry-weather hydraulic or organic capacity;
    • any user the Control Authority designates.

    A categorical user that never discharges more than 100 gallons per day of categorical wastewater may instead be classed as a Non-Significant Categorical Industrial User, if certain conditions are met.

How the program works (EPA, National Pretreatment Program)

  • EPA describes it as a part of the NPDES program. It aims to "protect POTW infrastructure" and to "reduce conventional and toxic pollutant levels discharged by industries and other nondomestic wastewater sources into municipal sewer systems."
  • There are three layers of standards: general and specific prohibitions, Categorical Pretreatment Standards for particular industries, and local limits.
  • EPA and authorized states approve municipalities to issue permits, administer and enforce discharges to their POTWs. Under § 403.3(f), the municipality is the Control Authority once its program has been approved; until then, the approving authority is.

Where industry-specific limits sit: the industry-specific categorical limits are in the effluent guidelines Parts for each point-source category. When I searched for pretreatment standards for existing sources, the categories that came up were Pulp, Paper and Paperboard (Part 430) [1], Metal Finishing (Part 433) [2], Steam Electric Power Generating (Part 423) [3], Iron and Steel Manufacturing (Part 420) [4] and OCPSF (Part 414) [5].

Other jurisdictions: Turkey's Regulation No. 7221 states that wastewater sources "zorundadırlar" (are obliged) to install treatment facilities or systems, on their own or shared, and to treat their wastewater to meet discharge standards [6]. It also sets sector-specific tables, such as Table 5.15 for the food industry [7]. I did not find a definition of "pretreatment" in it.

If you have a particular jurisdiction or industry in mind, I can pull the categorical standards or local-limit rules that apply to it.

Q.02

How do categorical standards and local limits apply?

Categorical standards and local limits are two separate layers, and an industrial user discharging to a POTW has to meet both. Under 40 CFR Part 403, every user must also meet a third layer, the general and specific prohibitions. Categorical standards are national, industry-specific limits that apply "in addition to" the rest of Part 403. Local limits are set by the POTW and carry the same legal force as national Pretreatment Standards.

Approach: I read the US EPA effluent guidelines Parts in the datasets for how categorical standards are written, using Metal Finishing (Part 433) as the example. The General Pretreatment Regulations themselves (40 CFR 403.5 and 403.6) are not in the datasets, so I took them from eCFR.

1. The base layer applies to every user (40 CFR 403.5)

  • General prohibition, § 403.5(a)(1): "A User may not introduce into a POTW any pollutant(s) which cause Pass Through or Interference." This applies "whether or not the User is subject to other National Pretreatment Standards or any national, State, or local Pretreatment Requirements."
  • Specific prohibitions, § 403.5(b): these pollutants "shall not be introduced into a POTW":
    • fire or explosion hazards, including a closed-cup flashpoint below 140 °F / 60 °C;
    • corrosive discharges, and "in no case" pH lower than 5.0 unless the works is designed for it;
    • solids or viscous material that obstructs flow;
    • pollutants released at a rate or concentration that causes Interference;
    • heat that inhibits biology, and in no case a temperature at the plant above 40 °C (104 °F) unless alternate limits are approved;
    • certain oils;
    • toxic gases or fumes;
    • trucked or hauled pollutants, except at points the POTW designates.

2. Categorical standards apply by industry (40 CFR 403.6)

  • Where they are set: in separate regulations under Subchapter N, one per industrial subcategory. "Unless specifically noted otherwise," they "shall be in addition to" all other Part 403 standards and requirements.
  • Two sets of limits: each category Part has pretreatment standards for existing sources (PSES) and for new sources (PSNS). For example:
    • § 433.15 requires an existing metal finisher discharging to a POTW to "comply with 40 CFR part 403 and achieve" the PSES table (for example cadmium 0.69 mg/l maximum for any 1 day and 0.26 mg/l monthly average), "except as provided in 40 CFR 403.7 and 403.13".
    • § 433.17 sets tighter PSNS for new sources (cadmium 0.11 / 0.07 mg/l) [2].
    • Part 433 also sets which facilities it covers (six core operations), and lists other category Parts that apply in its place [2].
  • Confirming your category, § 403.6(a): a user or POTW "may" ask EPA or the State Director for written certification of the applicable subcategory. An existing user adding or changing a process "must" request it before discharging from that process, and a New Source "must" request it before starting to discharge.
  • Compliance deadlines, § 403.6(b):
    • Existing sources: within 3 years of the standard's effective date, unless the category Part sets a shorter time.
    • New Sources: they "shall" have control equipment installed and started up before discharging. They "must" meet all standards within the shortest feasible time, not exceeding 90 days.
  • Where the limits apply, § 403.6(c):
    • Limits apply "to the effluent of the process regulated by the Standard, or as otherwise specified by the standard."
    • The Control Authority may convert production-based limits into mass-per-day or concentration limits.
    • It also has discretion to grant equivalent mass limits in place of concentration limits. To qualify, the user must use water conservation, already achieve compliance without dilution, monitor flow continuously, and have a consistent compliance record. The user must then notify the Control Authority if production is expected to vary by more than 20 percent from baseline.
  • No dilution, § 403.6(d): no user "shall ever increase the use of process water, or in any other way attempt to dilute a Discharge" as a substitute for treatment. Part 433 repeats this ban [2].
  • Mixed streams, § 403.6(e): where regulated process water is mixed with other wastewater before treatment, the combined wastestream formula gives alternative limits for the mixed effluent.
    • The user "may" monitor either the segregated process stream (applying the categorical standard) or the combined stream (applying the formula limit).
    • It may change monitoring points only with Control Authority approval.
    • An alternative limit "may not be used" if it falls below the analytical detection limit.

3. Local limits are set by the POTW (§ 403.5(c)-(d))

  • Who must set them:

    • A POTW with an approved pretreatment program "shall develop and enforce specific limits to implement the prohibitions" in § 403.5(a)(1) and (b), and "shall continue to develop these limits as necessary."
    • Other POTWs "shall" set limits where user discharges cause Interference or Pass Through that is likely to recur.

  • Process: limits "shall not be developed and enforced without individual notice" to those who asked for notice and an opportunity to respond.

  • Best Management Practices: POTWs "may" use BMPs, which count as local limits.

  • Legal status, § 403.5(d): local limits "shall be deemed Pretreatment Standards for the purposes of section 307(d) of the Act." That means they are federally enforceable, just like categorical standards.

  • Why they matter to you: under § 403.5(a)(2), if you are accused of causing Pass Through or Interference, you have an affirmative defence if you did not know your discharge would cause it, and either:

    • you were complying with a local limit for that pollutant at the time; or
    • no local limit existed and your discharge had not changed substantially from when the POTW was regularly in compliance.

    This defence covers the general prohibition and specific prohibitions (b)(3) to (b)(7).

How they combine in practice

  1. A user subject to a category Part (for example Part 433) must meet its PSES or PSNS at the regulated process effluent. Those limits may be adjusted for production, mass equivalents or mixed streams.
  2. The same user must also meet the POTW's local limits and the § 403.5 prohibitions. All of these are Pretreatment Standards, and none replaces another. For any one pollutant, the tighter applicable limit is the one that decides compliance.
  3. A user outside any category Part still has to meet the prohibitions and local limits.

If you name the industry or the POTW, I can pull the PSES or PSNS tables for that category Part.

Q.03