Case Study

Eliminating Microbiological Contamination in Ozone Fruit Wash Water

South Africa

May 2025

May 2025

Background

The facility employs Arc Aqua ozone washers to sanitize fruit surfaces prior to their entry into high-care zones. While initial expectations were that ozone paired with standard filtration would suffice to meet hygiene standards, consistent microbial contamination—including E. coli, coliforms, and total bacteria—persisted, along with issues such as organic residue and biofilm formation.

Challenges Identified:

  • Incomplete removal of organic residues

  • Persistent microbial contamination

  • Formation of biofilms in wash systems

  • Unsustainable water loss in early-stage solutions

    Filtration System Overview

To tackle physical contaminants, a filtration system was deployed with the following stages:

  1. Settler: Removed sand, soil, and large debris

  2. Carbon Filter: Targeted organic compound adsorption

  3. Sand Filter: Reduced suspended solids

  4. Bag Filters (25 micron): Captured fine particles

  5. Treatment Tank: Recirculated treated water to the wash system

  6. UV Lamps: Provided baseline disinfection

  7. Waboost Ozone Ultrafine Bubble Generator: Trail focus

  8. Ultrafiltration: Future investigation


    Filtration Performance:

Parameter Removal Efficiency

Suspended Solids 98%

Organic Matter 76%

Chemical Oxygen Demand 57%

Microbiological Contamination 0%

Despite effective physical filtration, microbiological testing confirmed the need for advanced disinfection

Disinfection Trials Overview

Objectives:

• Achieve full microbial elimination

• Enable water recycling within a closed-loop system

• Avoid harmful residues or negative fruit impact

• Suppress biofilm formation and regrowth


Summary of Treatment Methods Trialed

1. Total Loss System

Effective but water-intensive (~6,000 L/hr); unsustainable.

2. Sodium Hypochlorite

Reduced bacteria but raised concerns over chemical residues and by-products.

3. Hydrogen Peroxide

Good microbial results, but high operational cost.

4. Peracetic Acid

Effective, but introduced strong odor issues and risk of surface residue.

5. Chlorine Dioxide

Strong microbial action; corrosion risks to stainless steel infrastructure.

6. Ozone Injection — Ultrafine Bubbles

Delivered complete microbial and biofilm control with zero chemical residue.

Low-cost, chemical-free, compatible with closed-loop systems, and highly sustainable.

7. Reverse Osmosis (RO)

Excellent microbial removal, but overengineered, expensive, and prone to fouling.

8. "Long Water Loop" Simulation

Promising model based on reuse via central water treatment plant (includes ozone + filtration).


Summary and Recommendation

The eight treatment methods varied significantly in microbial efficacy, operational sustainability,

chemical impact, and cost. While chemical agents such as chlorine dioxide, peracetic acid, and peroxide

showed good microbial suppression, they introduced undesirable risks—chemical residues, odors,

corrosion, and high operating expenses.

Mechanical options like ultrafiltration and reverse osmosis provide robust microbial reduction but at high capital and maintenance costs and are sensitive to fouling. Total-loss water systems, while effective, conflicted with the company's sustainability goals.


Ozone injection, particularly via nano-bubble generation, stood out as the most balanced and

effective strategy. It provided:

• Complete microbial and biofilm control

• No chemical residues

• Minimal impact on fruit quality

• Reduced need for chemical procurement and storage

• Low operating cost and no water loss

Ozone is a powerful oxidizer with unique advantages:

• It naturally breaks down into oxygen, leaving no harmful residues

• Effective against a wide spectrum of pathogens including bacteria, viruses, and spores

• Penetrates biofilms where other agents fail

• Compatible with closed-loop water systems

• Requires minimal infrastructure modification

• Cost per liter of treated water is the lowest among all methods trialed


With growing regulatory and environmental pressure to reduce water waste and chemical use in food

processing, ozone-based disinfection emerges as the most future-proof strategy for microbial

control. It aligns sustainability goals, ensures food safety, and reduces long-term operational costs.

Finally, an approach where the water comes back to the upgraded factory water treatment plant equipped

with the below, should deliver the best quality water.

- Bag filtration

- Carbon filtration

- Glass media filtration

- Cartridge filtration

- Chlorine Dioxide filtration

- Ozonation

- UV disinfection

Why Ozone is the Best Solution

Among all disinfection options tested, ozonation—specifically via nano-bubble injection merged as

the most effective, practical, and scalable method. It provides:

- Complete microbial and biofilm elimination

- No chemical additives or harmful by-products

- Enhanced penetration into biofilms

- No impact on fruit quality

- Lowest cost per liter of water treated

- Perfect compatibility with closed-loop water systems

- Minimal infrastructure upgrades required


Scientific Basis for Ozone Superiority

- Ozone is one of the most powerful oxidizers available, 50% stronger than chlorine.

- It reacts quickly with a broad spectrum of pathogens (bacteria, viruses, spores).

- It breaks down into oxygen, leaving no residual toxicity.



Recommended Future Strategy

For best-in-class water recycling and disinfection, it is recommended that the facility adopts a "Long

Water Loop" model—returning wash water to the upgraded factory treatment plant. When paired with

ozone as the primary disinfectant, this approach guarantees:

Food safety through complete microbial control

Compliance with sustainability targets

Cost reduction through minimized chemical use

Extended equipment lifespan via chemical-free treatment


Ideal system components:

• Multi-stage filtration (sand, carbon, bag, cartridge, glass media)

• UV disinfection

• Centralized ozonation

• Optional chlorine dioxide dosing for periodic sanitation

Conclusion
Ozone-based disinfection, particularly using ultrafine bubbles delivery, is not just the most effective method tested—it is the only one that delivers scientific rigor, economic sense, operational sustainability, and food safety compliance in a single, unified solution. As regulatory demands for reduced water use and chemical residues grow, ozone stands out as the future-proof standard for produce washing operations.

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Let’s Talk About Your Ideas — On Us

We’d love to learn more about your goals and how we can support your vision