Abstract
This paper investigates the application of direct ozonation and ozone-hydrogen peroxide (PEROXONE) Advanced Oxidation Processes (AOP) for degrading geosmin, a common taste and odor compound found in surface water. Controlled laboratory trials were performed on representative source water to quantify ozone demand and decay kinetics, assess bromate formation risk, and evaluate geosmin oxidation performance at varying transferred ozone doses (TOD). Results demonstrate that both ozone and AOP are highly effective at removing geosmin, with PEROXONE showing enhanced oxidation efficiency at higher contaminant concentrations. The data support ozone-based strategies for robust taste and odor control in water treatment.
Introduction
Geosmin, produced by actinomycetes and blue-green algae, imparts earthy-musty tastes to water at concentrations as low as 5 ng/L. Due to its low sensory threshold and persistence, conventional treatment methods may be inadequate for effective removal during episodic blooms. Ozonation, with or without peroxide enhancement, offers a highly reactive oxidative pathway that can degrade geosmin’s molecular structure through hydroxyl radical (*OH) mechanisms.
This study aimed to evaluate:
- Ozone demand and decay profiles of raw surface water.
- Geosmin degradation across different TOD values.
- Comparative performance of direct ozonation and PEROXONE AOP.
- Bromate formation potential under varying oxidative conditions.
Materials and Methods
Raw Water Characterization
Source water was analyzed using Standard Methods. Key quality parameters are summarized in Table 1.
Table 1. Raw Water Characterization Results
| Parameter | Value |
| pH | 6.65 |
| Alkalinity (mg/L as CaCO3) | 26 |
| TDS (ppm) | 139 |
| NPOC (mg/L) | 2.58 |
| Iron, Total (mg/L) | 0.68 |
| Manganese (mg/L) | 0.023 |
| Bromide (µg/L) | <4.7 |
| Bromate (µg/L) | <1.0 |
Ozone Demand and Decay Testing
High-concentration ozone stock solutions were dosed into 0.5 L water aliquots at target TODs of 1.5, 2.46, and 5.0 mg/L. Ozone residuals were tracked over time using the indigo colorimetric method. pH was stabilized at 7.0 ±0.04 prior to ozonation.
Table 2. Ozone Demand and Half-Life Results
| TOD (mg/L) | Ozone Demand (mg/L) | Half-Life (min) |
| 1.50 | 0.92 | 1.11 |
| 2.46 | 0.95 | 1.17 |
| 5.00 | 1.06 | 4.77 |
Geosmin Oxidation: Ozone vs. PEROXONE
Water samples were spiked with geosmin to concentrations ranging from 72 ng/L to over 1,000 ng/L and treated with either ozone alone or in combination with hydrogen peroxide (H₂O₂) at a 0.4:1 mass ratio (H₂O₂:O₃). Analytical geosmin concentrations were measured before and after treatment.
Results and Discussion
Geosmin Oxidation Performance
Table 3. Summary of Geosmin Oxidation Results
| Initial Geosmin (ng/L) | TOD (mg/L) | Residual Geosmin (ng/L) | Process |
| 72 | 1.50 | <1 | O3 |
| 277 | 2.50 | 19 | O3 |
| 457 | 2.56 | 68 | O3 |
| 486 | 3.51 | 16 | O3 |
| 453 | 4.99 | 6 | O3 |
| 943 | 3.07 | 222 | O3 |
| 943 | 4.08 | 136 | O3 |
| 943 | 5.13 | 65 | O3 |
| 1068 | 5.00 | 104 | AOP |
- Low Dose Results: Ozone alone reduced geosmin from 72 ng/L to <1 ng/L at just 1.5 mg/L TOD.
- Moderate Spikes (~450 ng/L): ≥95% removal achieved at TOD ≥3.5 mg/L.
- High Spikes (~943–1068 ng/L): Ozone removed 93% of geosmin; PEROXONE improved removal by up to 9.8%.
AOP Effectiveness
PEROXONE provided a measurable enhancement over ozone alone:
- At 277 ng/L: 1.9% better removal
- At 1,068 ng/L: 9.8% better removal
These gains suggest PEROXONE is most beneficial when treating elevated contaminant loads or in high NPOC conditions.
Bromate Formation Risk
Bromate was below 2.5 µg/L in nearly all tests. One exception (5.0 mg/L TOD at low geosmin concentration) yielded 8.1 µg/L, indicating the importance of bromide monitoring at high ozone doses.
Conclusion
This study demonstrates that both ozone and PEROXONE are highly effective for degrading geosmin in surface water, with PEROXONE offering increased performance in high-contaminant scenarios.
Key findings:
- Direct ozonation removed >95% geosmin at TOD ≥3.5 mg/L.
- PEROXONE improved geosmin removal by 1.9–9.8% depending on concentration.
- Bromate formation remained below regulatory concern except at elevated ozone exposure.
These results support ozone-based strategies, including AOP when necessary, for robust and flexible taste and odor control in drinking water treatment applications.
