Washing and fruit/vegetable with ozonized water and packaging in modified atmosphere for better conservation in cooling cells are technologies that are rapidly gaining popularity.
Filtration and Ozone Application – Fruit and Vegetables
The first- and fourth-range fruit and vegetable products industry requires not only careful selection of raw materials, but also the use of sustainable techniques to reduce losses and improve the quality of the products marketed.
The most important index for product quality is the bacterial load, which can be substantially reduced during the washing phase.
Washing the product with good-quality water is the first step in reducing the bacterial load and avoiding excessive use of chemicals.
The use of chlorine as a sanitizing agent was very common in the past, but its use can lead to the production of toxic substances as reaction by-products. In addition, in some cases chlorine is not sufficiently effective.
Another common problem with chlorine and similar substances is the possible residue left by the chemical compounds used to sanitize distribution lines. This residue could end up on the final products.
Washing the product with ozone dissolved in water, combined with suitable physical filtration treatments, can be a response to these issues.
Ozone guarantees rapid water sanitization, removing pathogens contained in the water and on the surface of the product.
At the same time, ozone reduces BOD and COD values, does not form harmful products and avoids the addition of chemicals or chlorine to sanitize the water.
Sepra is able to offer multiple technological solutions, customized to customer needs, for the treatment of process water on fruit and vegetable washing lines, combining ozone generation and water dissolution systems with filtration plants, such as sand filters or membrane ultrafiltration.
Secondly, it is possible to extend the shelf life of products with an ozone generation system inside cold rooms, creating an ozone-enriched atmosphere in a confined environment.
The system is normally combined with dedicated instrumentation that monitors the ozone concentration inside the room and adjusts it according to the different production phases.
The two solutions can be used independently or in combination.
Washing with Ozonated Water
The system can be connected directly to the fruit and vegetable washing machine, on the water recirculation line, which must be pre-filtered at the same time to ensure maximum effectiveness. The system consists of a suitably sized ozone generator, see GEO series, combined with a water/ozone mixing system and subsequent degassing of the excess gas present, see GEOmix series.
In this way, it is possible to produce gas-free ozonated water, which is used directly on the fruit and vegetable product at the end of the washing line, with no impact on operators. The generator is powered by compressed air; air availability at P=8 bar is required. If it is not available, a silent centrifugal compressor, ideal for continuous operation, can be supplied. The ozone generators are water-cooled to ensure component durability and constant ozone production over time.
Filtration is carried out using techniques suited to the type of water and product: a simple sand filtration system or a membrane ultrafiltration plant may be used.
Ozone in Cold Rooms
In the gas phase, ozone acts on the outer surface and is able to reach areas that are difficult for water to access. Compared with treatment using ozonated water, in a closed cold room it is possible to control the ozone concentration present in the environment, on the surface of the product.
In confined environments, ozone concentrations can be reached that are so high they would be impossible to achieve when dissolved in an aqueous solution.
The air treatment system consists of an ozone generator located outside the cold room and a probe inside the room, which sends the signal to the measuring instruments. The measuring instruments, positioned outside the cold room, detect the amount of ozone present in the air inside the confined environment.
The achievable results are numerous:
- Removal of ethylene, in climacteric fruits, which is responsible for early ripening, allowing ripening to be delayed and appearance to be improved, in terms of texture and color;
- Rapid sanitization of the entire external surface of the product: removal of bacteria, viruses, fungi and molds;
- Avoids the addition of chemicals to sanitize the product;
- Achievement of high ozone concentrations compared with water treatment.
The system is complete with a single control PLC, which, by reading the measuring instrument, regulates the ozone generator’s production in order to guarantee a controlled concentration during the different hours of the day and night.
The ozone introduced is distributed evenly thanks to internal fans in each cold room.
This solution should preferably be used for cold rooms in steady-state conditions, with occasional and scheduled openings.
Some Concrete Data – Removal of Bacterial Load from Well Water
Below are some data collected in a first-range salad washing plant using recirculated well water.
A complete analysis of this water had detected the presence of microorganisms, shown in the following table, while from a chemical-physical point of view the water fell within the parameters established by current legislation.
An ozonated water generator, type GEOmix, was therefore installed, combined with sand filtration and recirculating to the collection tank. The figure shows the ozone generator in gray, the mixing system, consisting of tank, pump, valves and instrumentation, and the concrete structure on which the entire system rests, which is the water collection tank. The GEOmix 50 system draws water from the collection tank, mixes it with ozone and returns it to the tank. The generator was switched on for approximately 10 hours a day. After 4 days, the microbiological analyses of the water in the collection sump were repeated and a significant reduction in bacterial load was confirmed, as shown in the following table.
Water sample before ozone treatment
Water sample after 4 days of ozone treatment – GEOmix, consisting of a 50 g/h ozone generator
Examples of Ozone Generation Systems Integrated with Vegetable Washing Machines
This system makes it possible to continuously wash fruit and vegetables in crates with an ozone water treatment system. The washing capacity is approximately 800 crates per hour.
The fruit and vegetable crates enter the head rollers, where water jets are present for an initial wash.
The crates then enter the steel tunnel, where they are washed.
The water in the tank is constantly recirculated, filtered through a filtration system to remove contaminants and treated with ozone.
The clean water is reintroduced into the tank through nozzles so that it is sprayed onto the fruit and vegetable products.
All products can be washed daily with quality water, filtered and sanitized, extending their shelf life and reducing the waste of drinking water.
- Installed power: approximately 12 kW
- Overall dimensions: approximately 13,000 x 2,200 x 1,800 mm (height)
- Tunnel dimensions: approximately 6,000 x 2,200 x 1,800 mm (height)
Here are some examples of vegetable crates:
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