Wastewater pretreatment

A waste water manhole cover with the imprinted words "sewer 1925"

Pretreatment is the treatment of wastewater by commercial facilities and other non-domestic wastewater sources to remove harmful pollutants before the wastewater is discharged to a municipal sewer system. It prevents the introduction of pollutants to public systems that may pass through public treatment to rivers, lakes, and streams. Pretreatment also prevents discharges to publicly owned treatment facilities of pollutants that would interfere with facilities' operations, including their use and disposal of biosolids.

The U.S. Environmental Protection Agency has delegated MPCA the authority to approve pretreatment programs at the local level and oversee statewide pretreatment activities. The Code of Federal Regulation in title 40 Part 403 defines implementation of pretreatment programs and describes the responsibility of the EPA, states, public treatment facilities, and industrial users in protecting infrastructure, workers, and the environment. The communities approved to implement pretreatment programs issue industrial user permits, conduct inspections of industrial and commercial sources, sample industrial discharges, and enforce regulations.

Municipal pretreatment

All publicly owned treatment works (POTWs) are responsible to control their industrial users to prevent interference and pass-through.

Interference — a discharge from an industrial user that, alone or in conjunction with other sources a) inhibits or disrupts a POTW plant, its treatment processes or operations, or its sludge processes, use, or disposal, and b) therefore causes a violation — including increasing a violation's magnitude or duration — of any permit or rule that controls release of pollutants from the POTW.

Pass-through — a POTW has a violation of its limits caused by an industrial users discharge that passes through the public facility without being adequately treated. The pollutant limit violated must be a pollutant discharged by the industrial user, but it's not necessary to demonstrate impact on the POTW operation.

Industrial users — non-domestic sources of wastewater with discharges large enough to potentially affect a POTW

Significant industrial users (SIUs) are industrial users:

  • That discharge an average of 25,000 gallons per day or more of process wastewater to their receiving POTW
  • With discharges that make up 5% or more of their receiving POTWs' capacity
  • Designated by the MPCA or receiving POTW as significant, based on potential to affect the POTW or violate pretreatment standards

Publicly owned treatment facilities in Minnesota without formally delegated pretreatment programs must notify the MPCA, using the form provided, of any significant industrial user within 30 days of identifying them as significant. The MPCA may also request additional information.

Enforcing pretreatment standards

The POTW must monitor SIUs for pollutants of concern, or require the SIU to self-monitor. Monitoring must be representative of the SIU discharge. The POTW must report annually on the pretreatment annual report form provided.

POTWS are required to inspect its SIUs at least once per year. The EPA provides guidance:

Delegated POTWs have additional and more detailed responsibilities. A delegated POTW pretreatment program requires substantial program development and a formal delegation process.

Developing local limits

Delegated POTWs must control SIUs individually and not impose limits on them that may allow violations of the general or specific prohibitions. The POTW generally should impose required local limits (limits imposed by POTW to prevent interference or pass-through) for all SIUs, and is required to when interference or pass-through has occurred and may reoccur. A POTW also must evaluate local limits if an SIU causes interference or pass-through without violating a local limit. In addition to required local limits, a POTW may set other local limits not required by pretreatment rules. The MPCA can enforce required local limits, but cannot enforce the non-required limits.

Industrial categorical requirements

Delegated POTWs must enforce national categorical pretreatment standards for industrial users in their systems. Elsewhere, MPCA enforces the same standards through the permits it issues. The categorical pretreatment standards apply to the specific categories of industrial users found in Minnesota Rule 7049.0310 and the Code of Federal Regulations 40 CFR parts 405 through 471. Any industry listed in these categories must have a Minnesota permit; if the industry discharges to a POTW, a State Disposal System (SDS) permit is required. The following application forms must be completed and sent to the MPCA with the appropriate permit application fee.

Industrial facilities that are subject to 40 CFR part 433 metal finishing rules may be eligible to apply for the General Metal Finishing permit MNG120000. Please contact the State Pretreatment Coordinator to determine eligibility for this permit.

Dental rule

The EPA has introduced new pretreatment standards — effective July 14, 2017 — to reduce mercury discharges from dental offices into public wastewater treatment facilities.

What does the rule require of dental offices?

Dental offices that do not place or remove amalgam but do discharge to POTWs need only submit a one-time certification to the control authority. (Your control authority is either your local wastewater utility, if it has an approved pretreatment program, or the MPCA.) Dental offices that place or remove amalgam must operate and maintain an amalgam separator and must not discharge scrap amalgam or use certain kinds of line cleaners. They must also submit a one-time compliance report. One form can be used to submit either the certification or the compliance report:

Microsoft Office document icon One-time dental certification/compliance report (wq-wwtp7-49a)

Determine if your POTW is a delegated control authority: PDF icon Communities served by a delegated POTW (wq-wwtp7-49b)

If it is, contact your municipality for information on submitting the compliance form. If your community is not listed, the MPCA is your control authority. Send your completed form to: Minnesota Pollution Control Agency, Attention: WQ Submittal Center, 520 Lafayette Road North, St. Paul, MN 55155-4194

  • Existing dental dischargers (dental offices that were in operation before July 14, 2017) must comply with the rule by July 14, 2020, and submit a one-time compliance report no later than October 12, 2020, or 90 days after a transfer of ownership. 
  • Dental offices that begin operating on or after July 14, 2017 must be in compliance immediately, and submit a one-time compliance report no later than 90 days after the introduction of wastewater to a POTW.
  • Existing amalgam separators may be operated for their lifetime or ten years, whichever comes first. When a separator needs replacement, or the ten-year period has ended and the separator does not meet the standard, a dental office must replace it with one that meets the rule requirements and file a one-time compliance report within 90 days of installation.
  • Frequently asked questions on the dental office category rule (U.S. EPA)


Jaramie Logelin, 218-302-6640