The Role of Environmental Engineers in the Wastewater

Environmental engineers in wastewater management plan, design and permit the systems that collect sewage, treat it and return it safely to a stream, to the ground or to a reuse customer. Within environmental engineering, water treatment means drinking water and wastewater, and the same field also covers stormwater, soil and groundwater cleanup, air and solid waste. On a project, their role is turning flows and loads into a treatment process, meeting the effluent limits in a discharge permit, sealing the plans and helping operators stay in compliance after startup.

What does an environmental engineer do in wastewater treatment?

A wastewater engineer decides how much wastewater a system must handle, how clean it must be when it leaves and which process gets it there at a cost the owner can live with.

The U.S. Bureau of Labor Statistics profile of environmental engineers lists the core duties: design systems that protect the environment, including systems that reclaim water; obtain and maintain plans and permits; and inspect municipal and industrial facilities for compliance. On a wastewater job, that work runs in order:

• Estimate design flows and loads, today and at buildout
• Pick the disposal route: stream discharge, land application or reuse
• Select and size the treatment units, pumps, tanks and controls
• Prepare the permit application and supporting reports
• Review contractor submittals and check the build against the design
• Help operators start the plant, then troubleshoot when effluent drifts

The steps are the same for a replacement wastewater plant project as for a regional facility.

What is wastewater treatment engineering?

It is the design of the process train that removes solids, organic matter, nutrients and pathogens before the water leaves the plant: preliminary, primary and secondary treatment, advanced treatment where the permit needs it, then disinfection.

The EPA Primer for Municipal Wastewater Treatment Systems (2004) lays it out. Screens and grit chambers protect equipment, and primary clarifiers settle solids. Secondary treatment is biological and can remove up to 90 percent of the organic matter. Advanced treatment adds nitrogen and phosphorus control, filtration or membranes. The process options include:

• Conventional activated sludge and oxidation ditches
• Sequencing batch reactors (SBRs), activated sludge run in one tank that fills, treats and draws down
• Membrane bioreactors (MBRs), which can replace the secondary clarifier and sand filters of an activated sludge plant, per EPA's 2007 membrane bioreactor fact sheet
• Lagoons, which the primer says make up more than one-fourth of municipal plants, mostly in smaller communities
• Decentralized onsite and cluster systems for homes and businesses off a central sewer
• Biological nutrient removal for nitrogen and phosphorus limits

The right choice depends on the effluent limits, the site, the flow pattern and who will run the plant. The same fact sheet notes that MBRs usually cost more to build and run, but their effluent suits reuse and tight nutrient limits.

What regulations does a wastewater design have to meet?

The discharge permit sets the effluent limits, and the state's design rules set how the plant must be built to meet them. Federal secondary treatment is the floor.

A point source discharge needs an NPDES permit, and EPA's NPDES permit basics note that the Clean Water Act limits those permits to five years. For municipal plants, the secondary treatment standard in 40 CFR §133.102 caps BOD5 and suspended solids at 30 mg/L (30-day average) and 45 mg/L (7-day average), requires at least 85 percent removal and holds pH between 6.0 and 9.0. Where the receiving water needs more, the permit asks for more.

States with EPA approval issue these permits; EPA's list of authorized state NPDES programs shows Colorado approved in 1975. Texas has run the federal program since September 14, 1998, as the Texas Pollutant Discharge Elimination System (TPDES). Design of domestic wastewater systems falls under TCEQ's wastewater design rules in 30 TAC Chapter 217. 30 TAC §217.6(c) requires plans based on a design that at least meets the permit's requirements and effluent limits, and §217.6(d) requires the owner's summary transmittal letter to carry the design engineer's signature and seal.

Do environmental engineers assess a project's environmental impact?

Yes. They check what the treated water does in the receiving stream, the groundwater under a land application site or a reuse system, and shape the design to limit pollution and habitat harm.

When a federal agency acts on a project, such as deciding a permit application or building a public facility, the National Environmental Policy Act requires it to assess environmental effects and alternatives first. Project engineers often prepare much of its technical content.

What do environmental engineers do after the plant is built?

They help keep it in compliance. Operators run the plant every day; the engineer steps in when numbers drift, flows grow or the permit changes.

In Texas, TCEQ's wastewater operator licensing page says an operator licensed at the required level or higher must run every treatment facility at least five days a week. The engineer diagnoses missed limits, recommends process or equipment changes, trains staff on new equipment and prepares the technical side of renewals and expansions.

How do environmental engineers support water reuse?

They design the added treatment, storage and distribution that make treated wastewater fit for its next use, and they prepare the state authorization.

EPA's water reuse overview describes uses from landscape irrigation to refinery cooling towers to drinking water supply. In Texas, 30 TAC §210.32 sorts uses by exposure. Type I covers places the public may be present, such as residential irrigation, parks and toilet flushing. Type II covers uses where the public would not touch the water, such as cooling tower makeup water and construction dust control. Our guide to Chapter 210 reclaimed water for Texas developers covers the developer side.

Is environmental engineering only about wastewater?

No. The field also covers drinking water treatment, stormwater, soil and groundwater remediation, air and solid and hazardous waste.

The NCEES PE Environmental exam specifications (effective April 2026) show the scope. Water, which covers drinking water, wastewater and stormwater, carries the most questions, 19 to 29 of 80. The rest covers solid and hazardous waste, sustainability, air, site assessment and remediation, and environmental and occupational health. On a wastewater job, the environmental side usually owns the process and the permit, while civil engineers handle hydraulics, piping, the site and the collection system.

Where do environmental engineers work?

Mostly in engineering and consulting firms and in government. BLS counted about 39,100 environmental engineer jobs in 2025.

The largest employers were engineering services (24 percent), state government (20 percent), management, scientific and technical consulting (19 percent), local government (7 percent) and the federal government (6 percent). Consulting engineers on wastewater work serve utilities and municipalities, developers and industrial owners.

Are you ready to call a wastewater engineer?

Yes, if you can answer yes to at least four of these five.

1. Do you know the land use and unit count or square footage at buildout?
2. Do you know whether a city or district sewer can serve the site?
3. Do you know where treated water could go?
4. Do you have a survey or at least parcel boundaries and topography?
5. Do you have a target date for the first occupied building?

A note on limits: this is general education on federal rules and Texas examples as of October 2026. Rules differ by state and permit, and the engineer of record and the agency decide what applies to your project.

Frequently asked questions

What does a wastewater engineer do day to day?

Mostly calculations, drawings, specifications and permit reports, plus coordination with owners, agencies, contractors and operators and site visits during construction.

Do environmental engineers need a PE license?

Not to start. BLS notes that entry-level environmental engineers do not need one, but a Professional Engineer (PE) license lets an engineer oversee other engineers, sign off on projects and serve the public directly.

Is a wastewater engineer the same as a plant operator?

No. Operators run the plant and hold their own licenses, which TCEQ issues in Texas. Engineers design the plant and support operators when performance, flows or permits change.

I'm developing a subdivision in Texas outside city sewer. When should I bring in an environmental engineer, and what will they need first?

As early as you can, ideally before you close on the land. The disposal route drives the permit, the plant size and the land you set aside for treatment. Start with the buildout lot count, any utility that could serve the site and a survey. No engineer can promise the permit outcome.

I'm the public works director for a small Colorado town, and our lagoon keeps missing its ammonia limit in winter. Is that a design problem or an operations problem?

It can be either, so have an engineer review the data before anyone buys equipment. The EPA primer notes that cold winters significantly reduce lagoon performance and that nitrifying bacteria convert ammonia to nitrate. The engineer compares current loads and winter records with the design basis.

Related resources

• The Civil Engineer's Role in the Wastewater Treatment Process
• What Is Water and Wastewater Engineering?
• How TCEQ Sets Effluent Limits: Understanding Receiving Water Quality Standards and Permit Conditions
• Package WWTP vs. Custom-Designed Plant: Which One Fits Your Project?

Planning a wastewater system and not sure who should design and permit it?

MES designs and permits wastewater treatment, collection and reuse systems for developers, utilities and municipalities.

We are headquartered in McKinney, Texas, with offices in Golden, Colorado and San Jose, California, and 525+ projects completed.

Talk to an engineer about your project or call (214) 833-6748.