VSEP Industries

Gypsum Stack Wastewater

Gypsum Stack Wastewater Treatment Solution

A Proven RO Technology for Phosphogypsum & TENORM Wastewaters

Safely Treat Acidic Gypsum Stack Wastewater with Proven VSEP® RO Technology.
92% volume reduction. No scaling. No fouling. Field tested in Florida.

Gypsum Stack Wastewater Is One of the Hardest Industrial Effluents to Treat

Phosphogypsum (gypsum stack) wastewater is generated during phosphate fertilizer production and is among the most chemically complex and risk‑laden industrial wastewaters in the United States.

Approximately 70% of U.S. phosphate ore is mined and processed in central Florida, where sulfuric acid is used to convert calcium phosphate into phosphoric acid, a building block for fertilizers. This process produces five tons of acidic gypsum wastewater for every ton of phosphoric acid.

Over 265 billion gallons of acidic gypsum stack water are currently stored in Florida alone, with 7 billion gallons generated annually.

This wastewater is stored indefinitely in large above‑ground gypsum stacks—hydraulic containment systems with earthen berms and increasing structural and environmental risk as they age.

What Makes Gypsum Stack Water So Difficult to Treat?

Gypsum stack wastewater combines multiple treatment challenges in a single effluent:

  • Low pH: typically pH 2–4
  • High dissolved solids (TDS > 8,000 mg/L)
  • High sulfate, fluoride, phosphate, ammonium
  • Super‑saturated gypsum and calcium
  • Heavy metals and radionuclides
    • Uranium (5–10 mg/L)
    • Radium‑226 / Radium‑228 (5–50 pCi/L)
    • Also has radon and polonium
  • Classified as TENORM (Technology‑Enhanced Naturally Occurring Radioactive Material)

Why Conventional Treatment Options Fails

Treatment Method Failure Mechanism
Spiral RO Rapid scaling, fouling, plugging
Lime neutralization Massive sludge generation
Evaporation Energy infeasible (647+ TWh required)
Long‑term storage Structural failure risk

647 TWh of energy is three times the amount of energy the entire State of Florida consumes. If gypsum stack wastewater were easy to treat, it would not still be accumulating.

Environmental Risk: Lessons From Piney Point

The Piney Point gypsum stack disaster in 2021 demonstrated the real‑world risk of indefinite storage.

  • 215 million gallons was discharged into tidal waters of Tampa Bay
  • Pumped into the bay at a rate of 22,000 gpm in an emergency release
  • Resulted in:
    • Severe red tide blooms
    • Massive fish kills
    • Ecosystem disruption
    • Public and regulatory backlash

After a liner failure and leak at the base of the Piney Point gypsum stack risked a more catastrophic failure, the Florida Department of Environmental Protection approved an emergency release. The alternative could have been release of hundreds of millions of gallons at once, flooded residential neighborhoods, and compromising of adjacent gypsum stacks

A Proven Solution: VSEP® RO for Gypsum Stack Wastewater

Field‑Tested Under Florida Conditions

In 2005, the Florida Institute of Phosphate Research (FIPR) funded a pilot study at Piney Point to evaluate VSEP® (Vibratory Shear Enhanced Processing) Reverse Osmosis for gypsum stack wastewater. FIPR is a State funded industry organization.

This study was conducted years before the Piney Point emergency release, with the explicit goal of evaluating scaling resistance and long‑term operability.

Results: 92% Overall Recovery, No Scaling, Ultrapure Water Produced

Two‑stage VSEP® RO + Spiral RO polishing

Parameter (mg/L) Gyp Stack Feed VSEP® Permeate Spiral RO 1 Spiral RO 2
Fluoride 66 37 23 4.6
Ammonia 370 30 1.4 0.1
Nitrogen 450 16 2.0 0.3
Phosphorus 1,030 13 0.4 0.0
TDS 8,260 120 40 13

Key performance outcomes:

  • 65% recovery in Stage 1
  • 75% recovery in Stage 2
  • 92% total volume reduction
  • No membrane scaling or fouling
  • Stable flux: Stage 1 – 30 GFD (50 LMH)), Stage 2 – 12 GFD (20 LMH)

Aluminum and magnesium were reduced by 99.99%, indicating high rejection of similar metals and radionuclides such as uranium.

Image showing samples from Gypsum Stack Wastewater Treatment with VSEP system.

There was only slight turbidity in the initial wastewater shown in the middle. The final VSEP® concentrate measuring about 10% total solids has large amounts of precipitated solids settled on the bottom of the jar on the right. Additionally, there are lots of precipitated small colloids that do not settle causing turbidity in the final concentrate.

 

The FIPR Report has been archived and is no longer available online. However, New Logic’s report summarizing the work at Piney Point can be found here: https://www.vsep.com/pdf/VSEP_Pond_Water_Report_1.pdf

Why VSEP® Works Where Spiral RO Cannot

The Fundamental Difference: Vibratory Shear at the Membrane Surface

Spiral RO systems rely on laminar crossflow, which:

  • Is insufficient to prevent concentration polarization
  • Allows solids concentrations of 10–20× at the membrane surface
  • Does not provide enough agitation at the membrane to prevent scaling
  • Cannot tolerate supersaturated gypsum solutions

VSEP® Technology Advantage

VSEP® uses torsional membrane oscillation:

  • 50 Hz vibratory shear
  • Prevents concentration polarization
  • Disrupts crystallization at the membrane surface due to high agitation
  • Allows precipitation in the bulk flow as the shear decays away from the membrane

Precipitation occurs away from the membrane, Membrane remains clean, System behaves like a controlled membrane crystallizer

This makes VSEP® uniquely suited for supersaturated gypsum, acidic, high‑hardness wastewater with no pretreatment. VSEP® is often used instead of or in front of crystallizers or evaporators due to its low energy costs.

Why This Matters for Final Gypsum Stack Remediation

Gypsum stacks cannot store wastewater indefinitely. When final closure or discharge is required:

  • Massive volumes must be processed
  • Conventional RO will fail
  • Sludge‑based treatment becomes unmanageable
  • There is insufficient power in Florida to evaporate all the water

VSEP® RO provides a technically proven path to:

  • High volume reduction
  • Discharge‑quality water
  • Minimal chemical usage
  • Controlled solids handling

This system was reviewed by the State of Forida and the Florida Institute of Phosphate Research (FIPR)

Get a Site‑Specific Cost Analysis

Every gypsum stack is chemically unique. All of our projects are treated confidentially. New Logic can provide an accurate performance and cost evaluation for your specific project.

Work directly with an experienced VSEP engineer to model your treatment system:

info@vsep.com
+1‑775‑783‑7600

Learn More

Related Applications where VSEP® excels:

  • Phosphogypsum water treatment
  • TENORM wastewater treatment
  • RO Filtration for Acidic wastewater
  • Phosphate industry wastewater
  • Ammonium nitrate effluent treatment

The information generated on this page was supplied by Greg Johnson, CEO of New Logic since 2000, who participated in the Piney Point pilot study.

 

VSEP® has been used globally since 1987 for many difficult industrial filtration applications, including acid purification, landfill leachate, mining effluents, oil and gas wastewater, and PFAS‑impacted streams.