Pretreatment is the reduction of the amount of pollutants, the elimination of pollutants, or the alteration of the nature of pollutant properties in wastewater before or in lieu of discharging such pollutants into a Publicly-Owned Treatment Works (POTW). Since the mid-1980s, Missouri requires cities to have a state-approved pretreatment program when certain industries connect to the POTW. This pretreatment program requires industries to meet numeric limits on pollutants and to employ best management practices to control pollutants that discharge into city sewers. 

In 1972, Congress passed the Federal Water Pollution Control Act, also known as the Clean Water Act (CWA) to restore and maintain the integrity of the nation’s water. The goals of the CWA are to eliminate the introduction of pollutants into the nation’s waters and to achieve fishable and swimmable water quality levels. The CWA’s National Pollutant Discharge Elimination System (NPDES) Permit Program generally requires direct discharges to obtain a NPDES permit. The Congress again revised the CWA in 1977 creating Section 307 (b) which established a program, the National Pretreatment Program, to address indirect discharges for industries that discharge to a POTW. The National Pretreatment Program under 40 C.F.R. Part 403 requires Significant Industrial Users to obtain an industrial user permit to discharge wastewater to the POTW. The pretreatment component of the POTW’s or municipal NPDES permit is part of the National Pretreatment Program. 

Pretreatment standards protect the POTW from interference with the operation of the facility, prevent violations of the NPDES permit, protect the receiving waters, and improve opportunities to recycle the sewage sludge. Industrial processes may produce wastewater with pollutants not treated by the biological treatment systems used for conventional pollutants at a POTW.  Alternatively, an industry may discharge conventional pollutants that are treatable, but are more concentrated or are a large volume.

In June 2017, EPA finalized technology-based pretreatment standards under the Clean Water Act to reduce discharges of mercury and other metals from dental offices into POTWs. Visit the dental amalgam rule page to learn more.

Public Notices/ Public Comments

There are no currently active Wastewater Pretreatment Public Notices/ Public Comments.


POTWs with Approved Pretreatment Programs

In cities with an approved pretreatment program, the POTW is the regulating authority for all industrial users contributing wastewater to the POTW. An industrial user permit is a mechanism for controlling the discharge in terms of specific limitations, monitoring frequencies, monitoring locations, and best management practices. An industrial user permit describes, at a minimum, the duration of the permit, a statement of conditions for transferability, the effluent limits, monitoring and reporting requirements, and a statement of applicable civil and criminal penalties and any compliance schedule.

Industrial user permits allow the POTW to measure the performance of the user against the pretreatment standards to determine noncompliance. The requirements reflect the most stringent of the applicable federal, state and local pretreatment standards. Federal pretreatment standards for categories of industries are in the federal regulations at 40 C.F.R. Parts 405 through 471. State of Missouri pretreatment standards are the general and specific prohibitions in the state’s General Pretreatment Regulation at 10 C.F.R. §20-6.100. Local control authorities (cities/POTWs) are required to develop local limits, or demonstrate that local limits are not necessary. The POTW calculates these local limits as part of the initial pretreatment program submission, and thereafter the POTW reviews them after 1) each NPDES permit renewal, 2) treatment plant conditions change, or 3) significant changes in the POTW’s industrial user base.

Industrial users provide information in their permit applications about their processes, raw materials and flows of pollutant. The public has access to the industrial user permit, application information, and monitoring results. Provisions are made, however, to protect the confidentiality of business proprietary information excluding the effluent data. Cities will monitor the industrial user and require the industrial user to self-monitor to ensure continued compliance.

POTWs without Approved Pretreatment Programs 

The State of Missouri is the control authority in partnership with the local authorities for those industrial users in cities that do not have a state-approved pretreatment program. Currently, the State of Missouri regulates 34 industrial users that are located in cities that do not have approved pretreatment programs. In accordance with Subsection 644.026(13), RSMo, the State of Missouri cannot issue an industrial user permit to users that discharge to a POTW with a state-issued permit; yet components of the National Pretreatment Program regulations at 40 CFR 403 still apply to all industries. For industrial users subject to the categorical standards in 40 CFR Parts 405-471, the state will require compliance (in writing) with federal and state pretreatment standards, inspect and monitor the industries, and report compliance to EPA Region 7. When conditions develop where the POTW is the best control authority over industrial users to protect the POTW, the State of Missouri will require that the city/POTW develop a pretreatment program as a NPDES permit condition.

The department regulates industrial users by authorizing discharge in accordance with 10 CSR 20-6.100(12). Initially, the department’s Industrial Waste Survey Form (available upon request) will help identify the applicability of the categorical standards or any pretreatment requirements specific to the industrial user. After form review, once the department identifies an industrial facility as a categorical industrial user that discharges process wastewater to a POTW without an approved pretreatment program, the department will notify the industry in writing and provide documentation that summarizes the industry’s obligations as a categorical industrial user. The department first requests a Baseline Monitoring Report (BMR; available as a form from the department) per 40 C.F.R. §403.12(b), and subsequently, a 90-day Compliance Report per 40 C.F.R. §403.12(d) after BMR review and approval and authorizing discharge. Subsequent requirements are Periodic Reports on Continued Compliance, annual department discharge monitoring and pretreatment inspection. The Periodic Reports on Continued Compliance [40 C.F.R. §403.12(e)] are due twice per year, once for January through June and once for the July through December reporting periods.




The National Pretreatment Program is a cooperative effort among the federal, state and local regulatory environmental agencies established to protect water quality. Through an agreement with the U.S. Environmental Protection Agency (EPA) on June 3, 1981, the Missouri Department of Natural Resources (department) became the approval authority for delegating control authority to cities or sewer districts and their POTWs. Missouri state law authorizes control authorities (cities/POTWs) to issue and enforce pretreatment permits. Missouri’s General Pretreatment Regulation, 10 CSR 20-6.100 effective Oct. 30, 2012, has incorporated the federal general pretreatment regulation 40 C.F.R. Part 403 and those federal categorical standards in 40 C.F.R. Parts 405-471 that have pretreatment requirements.

General pretreatment regulations require all POTWs with design flows greater than 5 million gallons per day and receiving industrial discharges that are subject to federal limitations or that pass through or interfere with the operation of the POTW to develop and implement an approved pretreatment program. At the discretion of the department, smaller POTWs can also be required to develop programs. The State of Missouri as approval authority will review and approve a city’s pretreatment program submission.

The legal authority of the local control authority (city/POTW) to administer a permit program is derived from state law and local ordinance. The control authority collects data on industrial user discharge, determines which industries need regulation, and pass ordinances.  Local authorities incorporate pollutant limits and best management practices within their industrial user permit process. These same authorities are responsible for the staffing and funding of their local pretreatment programs. There are currently 47 approved and active pretreatment programs in the state. A program may become inactive over time due to changes in the industrial base; and the state will place that program in an inactive status until conditions under which the program was established return.