Florida Numeric Nutrient Criteria: How the State’s Nutrient Limits Reshape Treatment Plant Sizing Versus Texas or Colorado

Florida numeric nutrient criteria turn nitrogen and phosphorus into day-one sizing inputs for any new plant that discharges to surface water. FDEP sets the nutrient limit from the receiving water, and a growing list of waters falls under the 3 mg/L nitrogen and 1 mg/L phosphorus advanced treatment standard. A Texas or Colorado design can fall short there.

What are Florida's numeric nutrient criteria?

They are FDEP's numeric reading of the state's narrative nutrient standard, which bars nutrient changes that throw aquatic plants or animals out of balance.

Rule 62-302.531, F.A.C. applies them in order, starting with any site-specific number such as a TMDL. Without one, lakes get chlorophyll a criteria with matching nitrogen and phosphorus ranges, and spring vents get 0.35 mg/L nitrate-nitrite. Streams are judged on biology plus regional thresholds from 0.06 mg/L phosphorus and 0.67 mg/L nitrogen in Panhandle West up to 0.49 mg/L phosphorus in West Central.

After approving Florida's rules, EPA withdrew its overlapping federal criteria in a September 25, 2014 notice.

How do the criteria become effluent limits for a new plant?

Through a water quality based effluent limit (WQBEL), and the burden of proof sits with the applicant.

Under Rule 62-620.320(1), F.A.C., the applicant must give FDEP reasonable assurance that the plant will not cause pollution. FDEP's 2013 implementation document for the nutrient standards adds three points that shape a design brief:

• A new or expanded nutrient discharge needs a nutrient WQBEL, and a lake discharge needs modeling at critical conditions.
• A stream discharge above the regional thresholds gets limits as needed to meet the standard.
• Downstream waters count, regardless of distance. If one is impaired, the applicant must show the discharge is not contributing.

So in Florida the receiving water picks the process, and flow only sets the scale.

When does Florida require 3 mg/L nitrogen and 1 mg/L phosphorus?

Mainly when the discharge goes to a water listed for advanced waste treatment (AWT) in section 403.086, Florida Statutes.

Section 403.086(4), F.S. defines AWT as 5 mg/L CBOD5, 5 mg/L suspended solids, 3 mg/L total nitrogen and 1 mg/L total phosphorus on a permitted annual average basis, plus high-level disinfection. Subsection (1)(c) requires it for Tampa Bay, Biscayne Bay and other named waters and their tributaries, the Indian River Lagoon since July 1, 2025, and, by January 1, 2033, waters not attaining nutrient standards or under a nutrient basin management action plan (BMAP). Waters added after July 1, 2023 get 10 years. Section 373.811, F.S. also holds new disposal facilities of 100,000 gpd or more inside an Outstanding Florida Spring BMAP to 3 mg/L nitrogen.

Secondary treatment for a surface water discharge under Rule 62-600.420, F.A.C. is 20 mg/L CBOD5 and TSS as annual averages, with no nutrient limit. Our article on Florida's advanced wastewater treatment mandate covers the trigger waters.

How does Texas regulate nutrients in a discharge permit?

TCEQ screens each new or expanding domestic discharge, mostly for phosphorus, and adds a limit when the screen shows a need.

The standard in 30 TAC §307.4(e) is narrative: nutrients from permitted discharges must not cause excessive growth of aquatic vegetation. Texas numeric nutrient criteria are chlorophyll a values for selected reservoirs.

Under TCEQ's June 2010 implementation procedures, typical phosphorus limits, as a daily average, are 1.0 mg/L below 0.5 MGD, 1.0 to 0.5 mg/L from 0.5 to 3.0 MGD and 0.5 mg/L above that. Nitrogen limits come up only in specific cases, such as nitrate reaching a drinking water supply or seagrass nearby. A watershed rule in 30 TAC Chapter 311 can also set a phosphorus limit or prohibit the discharge. Our post on how TCEQ sets effluent limits covers the rest of the permit.

How does Colorado regulate nutrients in a discharge permit?

Colorado sets technology-based nutrient limits by rule, with exclusions and delays for some existing plants.

Under Regulation 85 (5 CCR 1002-85), a new plant on a new site discharging after May 31, 2012 must meet 0.7 mg/L total phosphorus and 7 mg/L total inorganic nitrogen as rolling annual medians. Existing plants carry 1.0 and 15 mg/L. Total inorganic nitrogen is nitrate, nitrite and ammonia.

What changes in the plant when the nutrient limit tightens?

Almost every unit process changes, along with the footprint, chemicals, solids and operator hours.

EPA's Nutrient Control Design Manual says standards near 3 mg/L total nitrogen and very low phosphorus moved plants past biological nutrient removal (BNR), typically to BNR, chemical addition and effluent filtration together. A 4-stage Bardenpho process adds a second anoxic zone and a reaeration zone, has a larger footprint than an MLE process and can take methanol. At 3 mg/L or less, resistant dissolved organic nitrogen, typically 0.5 to 1.5 mg/L, can limit removal.

For phosphorus, the manual cites metal salt addition in secondary treatment, aimed at 0.5 to 1.0 mg/L phosphorus, which may raise overall plant sludge production by 5 to 25 percent.

Rule 62-699.310, F.A.C. puts any plant with nitrogen or phosphorus permit limits in Category I. From 0.05 up to 0.1 MGD, that means a Class C or higher operator 3 hours a day, 5 days a week, plus a visit each weekend day. An extended aeration plant without nutrient limits, from 25,000 gpd up to 0.25 MGD, needs half an hour a day.

Averaging matters. Florida's AWT numbers are annual averages, a TCEQ daily average is a calendar-month average under 30 TAC §305.2, and Colorado uses rolling annual medians, each with a different design margin. The EPA manual adds that flow and load peaks can hurt biological phosphorus removal, which equalization tanks smooth out.

Can reuse or land application get around the nutrient limits?

Sometimes, but Florida is moving nutrient limits onto reuse too.

FDEP's implementation document names land application as an option when a discharger cannot protect a downstream lake. Under section 403.064(16), F.S., a utility seeking a new or expanded surface water discharge must also show an approvable plan to end nonbeneficial discharge, with some exemptions. But by July 1, 2034, section 403.086 holds reclaimed water used for irrigation or other land application inside a nutrient BMAP area to the AWT nitrogen and phosphorus numbers, where the plan finds that the reuse contributes to the impairment. A later finding gets 10 years.

Is your Florida project ready for a plant sizing decision?

Run this check before anyone fixes a footprint. If any answer is no, the plant size is still a guess.

1. Do you know the receiving water and its type: stream, lake, spring or estuary?
2. Have you checked whether it, or any water downstream, is impaired for nutrients or under a TMDL or BMAP?
3. Is it one of the section 403.086 AWT waters or a tributary to one?
4. Do you have target nitrogen and phosphorus numbers, with their averaging period, before choosing a process?
5. Have you compared discharge with reuse and land application?
6. Does the site plan hold room for anoxic volume, equalization, chemical storage, filtration and extra solids?
7. Have you planned operator hours for a Category I plant?

Ask your engineer what sets your nutrient number and which unit process carries your margin.

This article is general education on public rules as of October 2026. Actual limits come from the permit for a specific discharge, and process selection needs site data and an engineer's review.

Frequently asked questions

Does every new Florida plant need advanced waste treatment?

No. Secondary treatment is the baseline, and AWT applies by statute to the listed waters. Elsewhere the nutrient limit comes from the WQBEL for that receiving water.

Is Colorado's 7 mg/L nitrogen limit close to Florida's 3 mg/L?

Not really. Colorado's is total inorganic nitrogen as a rolling annual median. Florida's is total nitrogen, organic nitrogen included, as an annual average.

I'm a Texas developer with a small package plant permitted in Central Texas under a 1.0 mg/L phosphorus limit. Can we reuse that design in Florida?

Check the process first. A plant built for a phosphorus limit alone may have no anoxic zone. Then test it against the receiving water's nutrient number. On an AWT water, plan for 3 mg/L nitrogen and 1 mg/L phosphorus.

I run a small Colorado civil firm preparing our first Florida surface water discharge permit. What will FDEP expect on nutrients?

Expect to show reasonable assurance under Rule 62-620.320, typically through a preliminary design report and plans, plus a nutrient WQBEL, modeling where a lake is involved and a look at downstream waters.

I manage a Florida HOA whose package plant discharges to a lake just listed as impaired for nutrients. Will our limits change?

Probably, at renewal. Revised nutrient WQBELs generally come through renewal, with compliance schedules to give you time. Section 403.086 also requires AWT for a water found impaired after July 1, 2023, within 10 years of that finding.

Related resources

• FDEP Permitting for Wastewater Systems in Florida: A Practical Guide for Developers
• Water Reuse in Florida: How the State's Progressive Rules Are Shaping Infrastructure Design
• Colorado Water Quality Control Commission Basin Specific Standards: Why the Same Discharge Limit Does Not Apply Statewide
• Flow Rate Projections: How to Size a Wastewater Treatment Plant for Your Development Without Over-Building

Sizing a Florida plant around a nutrient limit?

Send us the site location, the expected flow and your disposal plan. We will tell you which nutrient rules apply and what they mean for the process and the footprint.

Modern Engineering Solutions, McKinney, Texas, with offices in Golden, Colorado and San Jose, California. Licensed in Florida, Texas and Colorado. 525+ projects completed.

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