Advancing Direct Potable Reuse Through Oxidation Science and Engineering

As water scarcity accelerates across the Western U.S., Mexico, and arid urban centers globally, Direct Potable Reuse (DPR) is gaining momentum as a viable long-term water supply strategy. Unlike Indirect Potable Reuse (IPR), which relies on environmental buffers, DPR integrates high-barrier treatment technologies to deliver purified water directly into the drinking water distribution system.

At Pinnacle Ozone Solutions, we specialize in ozone-based advanced oxidation systems, critical components in DPR treatment trains. Through precise chemistry, mass transfer optimization, and system reliability, we enable utilities and engineers to meet the technical and regulatory demands of DPR with confidence.

What Is DPR and Why Is Oxidation So Critical?

DPR treatment trains typically include:

• Microfiltration (MF) or Ultrafiltration (UF)
• Reverse Osmosis (RO)
• Advanced Oxidation Processes (AOPs)
• Biologically Active Carbon (BAC) or GAC
• Monitoring and pathogen log removal controls

In this framework, ozone is used either alone or in combination with hydrogen peroxide (H₂O₂) to form hydroxyl radicals (·OH), highly reactive oxidants capable of destroying trace organics, pathogens, and chemical by-products that survive membrane filtration.

“Ozone is essential in advanced reuse applications for the destruction of low molecular weight organics, pharmaceutical residues, and nitrosamines.” — Rice & Browning (1981); von Gunten (2003)

Oxidation Chemistry: How Ozone Enables AOP Performance

Ozone is a selective oxidant, but under the right conditions it decomposes to form hydroxyl radicals:

O₃ + OH^– → HO₂^– → O₂^–· → O₃^–· → ·OH + O₂

Hydroxyl radicals:

• React with rate constants between 10⁶ and 10⁹ M^-1s^-1
• Destroy contaminants like NDMA, geosmin, MIB, pesticides, and personal care products
• Mineralize organic carbon into CO₂ and water

Source: Hoigné & Bader (1983); von Gunten (2003); Westerhoff et al. (2009)

This radical chemistry underpins most DPR AOPs, especially ozone + H₂O₂ (peroxone) systems. These combinations deliver high oxidation potential without persistent residuals or chlorine-based by-products.

Regulatory Drivers: DPR Requires Verified Oxidation Barriers

States like California, Texas, Arizona, and Colorado are moving toward formal DPR permitting. Frameworks require treatment trains to achieve:

• 12-log virus, 10-log Giardia, and 10-log Cryptosporidium removal/inactivation
• NDMA < 10 ng/L, TOC < 0.5 mg/L, and pathogen risk < 10^–⁴/year
• Demonstrated AOP efficiency for unregulated contaminants of emerging concern (CECs)

Sources: SWRCB (2023), USEPA DPR Literature Review (2012), TCEQ Draft Rules (2021)

Ozone-based AOPs are validated to provide >90% removal of NDMA, with oxidation of a broad spectrum of CECs, including:

• 1,4-dioxane
• Carbamazepine
• Sulfamethoxazole
• Bisphenol A
• Tris(2-chloroethyl) phosphate (TCEP)

Pinnacle’s Role in DPR: Engineering the Oxidation Barrier

At Pinnacle, we don’t just generate ozone, we engineer oxidation performance into the heart of DPR systems.

Our technical contributions include:

• High-dose ozone injection systems for rapid oxidation under variable TOC and bromide conditions
• Integrated ozone + peroxide systems with precision molar ratio control
• Dynamic feedback controls based on TOC load, UVT, and pH
• CFD-modeled contactor designs for uniform flow, retention time, and residual control
• BAC integration support, with ozone pre-treatment to reduce biofouling and increase biodegradability

“Ozone pretreatment significantly enhances BAC filter performance by increasing the biodegradable fraction of organic matter.” — Tchobanoglous et al. (2014), Direct Potable Reuse: Benefits for Public Water Supplies

System Design Challenges: Bromate and Scavengers

Key technical design considerations for ozone in DPR include:

• Bromate Formation

  Bromide oxidation is pH- and dose-sensitive. Pinnacle mitigates risk through pH control, ammonia pre-dosing, and contactor design.

  Source: von Gunten & Oliveras (1998)

• Hydroxyl Radical Scavenging

  Carbonate, bicarbonate, and natural organic matter (NOM) compete with contaminants for radicals. Pinnacle systems monitor ORP and adjust peroxide ratios accordingly.

  Source: Haag & Hoigné (1985)

Demonstration and Deployment

Our work with the Colorado project exemplifies Pinnacle’s approach:

• Scalable ozone + AOP system for direct reuse
• Continuous online monitoring of ozone dose, H₂O₂ ratio, pH, and TOC
• Designed for >95% NDMA removal and full regulatory compliance
• Data collected to support future state rulemaking and public acceptance

This facility will serve as a national reference for ozone-based DPR treatment performance.

Conclusion

Direct Potable Reuse demands systems that are proven, adaptable, and traceable. At Pinnacle Ozone Solutions, we combine oxidation science, regulatory awareness, and precision engineering to deliver ozone systems that meet the exacting standards of DPR, today and into the future.

Technical References

• von Gunten, U. (2003). Ozonation of drinking water: Part I. Oxidation kinetics and product formation. Water Research.
• Hoigné, J. & Bader, H. (1983). Rate constants of reactions of ozone with organic and inorganic compounds. Ozone: Science & Engineering.
• Westerhoff, P. et al. (2009). Oxidation of CECs in AOPs: Kinetics and by-products. Journal AWWA.
• Tchobanoglous, G., et al. (2014). Direct Potable Reuse: Benefits for Public Water Supplies. WateReuse Research Foundation.
• Rice, R.G. & Browning, M.E. (1981). Ozone for Industrial Water and Wastewater Treatment.
• von Gunten, U., & Oliveras, Y. (1998). Advanced oxidation of bromide-containing waters. Environmental Science & Technology.
• Haag, W.R., & Hoigné, J. (1985). Ozonation of humic substances in natural waters. Environmental Science & Technology.
• SWRCB. (2023). Direct Potable Reuse Treatment Requirements. California State Water Board.
• USEPA. (2012). DPR Literature Review for Chemical and Pathogen Control. Office of Water.