Ozone for greenhouse water: what its maker says to measure before you buy

A supplier says ozone will look after your irrigation water and the lines that carry it. The quote is real money, and nobody in the building has run a system. For a propagation lab the question is sharper still, because the two pieces of kit that carry sterility, the autoclave and the laminar flow hood, are already paid for, and anything new has to earn its place beside them.

On 14 October Hortidaily published an interview with Ángel Manuel Sereno Marchante, president and chief executive of Cosemar Ozono, a Spanish maker of ozone systems, under the headline that ozone is gaining ground in greenhouses but requires technical expertise. It is one company's account of its own field. It is also more useful than most supplier interviews, because so much of it is about what has to be measured and what can go wrong.

The report

What he says ozone is for

Sereno describes two uses for the gas, which is generated on site and mixed into the water. The first is sanitary: reducing the microbial load and keeping biofilm under control in tanks, pipes and irrigation components, where it can harbour pathogens and cause blockages that spoil irrigation uniformity.

The second he calls physiological: ozonated water acting on roots and leaves as an elicitor, a signal that switches on antioxidant and defence responses. He points to studies that observed changes in enzymes such as catalase, superoxide dismutase and glutathione reductase, and says these responses depend on the crop, the concentration and the frequency, and should not be presented as an automatic effect.

He says the company moved into intensive horticulture more than fifteen years ago, running trials for growers in El Ejido, Almería, and that growers now want advice, protocols adapted to their crops and ongoing technical support rather than just a generator.

What he says to measure

This is the part a buyer should read twice, because it is a supplier naming its own system's requirements. For the treatment to work, Sereno says, you need to know the water's flow rate, pH, temperature and composition, particularly its organic matter content and oxidant demand, and you need to monitor dissolved ozone, contact time and the residual that reaches the roots.

Redox potential is a useful monitoring tool, he says, but it does not replace direct ozone measurement or microbiological testing. The key is calibration, because excessive exposure can damage the roots, alter the nutrient solution or harm beneficial microorganisms.

In recirculating hydroponics he warns that the gas can react with parts of the nutrient solution, including certain chelates and micronutrients, so the treatment point has to be chosen with care: before fertilisers are added, or on the return flow in a dedicated circuit.

What growers report, and what that proves

Among Cosemar Ozono's grower customers in Almería, the interview reports improved root development and greater vigour in crops such as cucumber and watermelon, and better performance against nematodes, Fusarium and Pythium. Sereno himself separates general crop improvement from demonstrated control of a specific pathogen, and says cleaner irrigation water addresses a source of risk without eliminating an infection already in the soil or the plant.

That is the right way to read it. These are field observations relayed by the supplier, with no trial design, plant counts or controls published alongside them. They are a reason to ask for references, not evidence that ozone controls any disease.

The same caution applies to fertiliser. He says ozone is not a replacement for fertilisers, and that any reduction in fertilisation should be gradual and checked against analyses, monitoring and harvest records.

Where it would sit next to what a lab already runs

Greenhouse water treatment and lab sterility are different jobs. Nothing in the interview concerns media in vessels, the inside of a sealed jar or the air over a flow hood work surface. Media sterilisation is the autoclave's job, and clean air at the bench is the hood's. Ozone, on this account, is a candidate for the water upstream: incoming or recirculated irrigation water, tanks and lines in a nursery or a hardening-off area, not the culture room.

So the comparison to make is narrow. What does your current water treatment cost to run per cubic metre, and what does it fail at? If an ozone system cannot be priced against that, it is not yet a proposal.

The interview's other constraint is people. Sereno says installing a piece of equipment is not enough: someone has to interpret water quality data, adjust the treatment, verify that it works, and know when to adjust it or stop it. In a small operation that named person, and cover for when they are away, is often the real cost.

Before you sign

Six things to get in writing

Rated output and flow, and the dissolved ozone and contact time the supplier will hold at your point of use, in water like yours.

Where the ozone is injected, and how the residual that reaches the roots is kept below a level that harms them or the beneficial microorganisms in the system.

For a recirculating system, what the treatment does to your nutrient solution, including chelates and micronutrients, and where in the circuit it goes.

The monitoring package, with direct ozone measurement rather than redox alone, and whether it is in the quoted price.

The legal status of the proposed use in your country, the safety documentation, and the controls for inhalation exposure, phytotoxicity and by-products.

Two reference sites at your scale that you may contact directly, and the records they keep.

The rules, and the call

On regulation, the interview notes that ozone generated from oxygen is approved in the European Union as an active substance for product types 2, 4, 5 and 11, and Sereno warns that this should not be confused with authorisation of a specific biocidal product or its uses: water or facility disinfection and direct crop protection may face different requirements. A grower, he says, must demand documentation on the legal status of the proposed use.

On this account ozone is worth a quote, and the quote is worth testing hard. The supplier's own list of what must be measured is long, and every item on it is a question a lab can put to any seller. If you have a water problem you can describe in numbers, a flow rate, a cost per cubic metre or a recurring failure you have logged, take the quote and ask the six questions. If not, price your current routine first.

Keep the records either way. Water treatment runs, sanitation rounds and contamination counts written down at the time are the evidence you hold a supplier's claims against, whoever's system you choose.