Case Study
Eliminating Microbiological Contamination in Ozone Fruit Wash Water
South Africa
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:
Settler: Removed sand, soil, and large debris
Carbon Filter: Targeted organic compound adsorption
Sand Filter: Reduced suspended solids
Bag Filters (25 micron): Captured fine particles
Treatment Tank: Recirculated treated water to the wash system
UV Lamps: Provided baseline disinfection
Waboost Ozone Ultrafine Bubble Generator: Trail focus
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.