Ozone Use in Storage
- O₃ is used extensively in the US apple storage sector.
- Nearly a third of the CA rooms in Washington now include ozone technology.
— David McGrath, 2019, VP Guardian Ozone
Why Use Ozone?
The South African industry is continuously looking for innovative, smarter ways to reduce decay and extend storage life.
Ozone can be used for:
- Reducing harmful airborne bacteria, moulds, and fungal spores
- Phytosanitary control
- Reducing ethylene levels
Postharvest Diseases to Avoid
- Blue Mould
- Grey Mould
- Mucurrot
- Rhizopus Mould
- Bulls Eye Rot
Ozone Basics
- Highly reactive form of oxygen gas
- Very potent oxidizer (1.5× oxidizing potential of chlorine)
- Quickly breaks down to O₂ after reacting with organic matter (no residue)
- Produced by corona discharger and UV-type ozone generators
Comparison of Common Chemical Disinfectants
- Based on Standard Hydrogen Electrode (SHE)
- Ozone is among the most powerful oxidizers
Ozone Destroys Fungi and Moulds
- Reduces fungal spore production
- Penicillium (green and blue mould)
- Botrytis cinerea (grey mould)
- Reduces mould nesting (spoilage benefit)
- Pathogenic bacteria decontamination (e.g., Listeria monocytogenes: 260 deaths annually in the USA)
Ethylene in Postharvest Storage
Ethylene has been shown to substantially increase:
- Respiration
- Water loss and thus weight loss
- Accelerated ripening, aging, and decay
- Reduction in nutrient content
- Taste & aroma changes, off flavours
- Ethylene produces more ethylene
Ozone Reduces Ethylene Build-Up
- Ozone is highly effective at reducing ethylene build-up.
- Ethylene gas is readily oxidized to water, oxygen, and carbon dioxide.
Example: Ethylene Reduction with Ozone in Cold Storage
- Ethylene levels in ozonized (0.4 μL/L) and non-ozonized apple and pear cold storage rooms (Skog & Chu, 2001).
- Ozone treatment reduces ethylene concentration over storage time.
Gaseous Ozone Applications / Postharvest Treatment
- Control diseases
- Retard the production of spores
- Prevent nesting
- Ethylene control
- Sanitation (bins & cold room pre-storage)
- Pest control
- Pesticide removal
Ozone Concentrations Need to Be Managed
- Human exposure limit for an 8-hour period: 100 ppb (0.1 ppm)
- Human exposure limit in indoor medical facilities: 50 ppb
- Typical treatment level for apples and pears: 30–70 ppb
- Berries: up to 600 ppb
Source: Federal Occupational Safety and Health Administration (OSHA) and National Institute for Occupational Safety and Health (NIOSH)
Ozone Generation System for CA
- Ozone dual sampling
- Ozone generation
- Ozone injection behind fans (interlock fans on)
- Example: Ozone system set up for 6 CA rooms (60 mg per hr)
- Typical capital cost over 6 × 1000 bin rooms: ~R175 per bin
Ozone Control and Safety
- Ozone monitoring
- Dual independent analysers with logic
- Technology: UV photometric absorption
- Traceable calibration on annual basis
- Faults and fail-safes:
- Ozone level above or below setpoint for too long
- Ozone analyser fault
- Adjustable flow meters for each room to set maximum mass flow
- Interlocks on cooling fans (no ozone injection if fans are off)
Flume Water Treatment with Ozone
- Ozone can be used for flume water treatment.
- Example: PAA vs. ozone-treated flume water after a full day of operation.
Quantifying the Benefits of Ozone
- Export industry: goal is to continuously strive for better market access and sustainability
- Limit export rejections (huge numbers; food for thought)
- Tool for lowering risk of loss
- Developing interest for insect infestation control
Questions?
Contact: AndrewB@GasAtSite.com