All over the world, humans have used greenhouses to boost the production capacity of fruits, vegetables, flowers and many other consumer products. The challenges associated with greenhouses have been and still are the control of microbial growth and the use of pesticides and biocides to avoid product spoilage.

Challenges in hydroponic greenhouses

Hydroponic production is the major technology used by the industry today. Crops are cultivated soil-free. Nutrient is added directly to the water supply. Nutrient addition to the water supply also generates a favorable environment for mold and bacteria in pipes and other surface areas. Microbial growth must be controlled to mitigate pathogens, hence a number of disinfection methods are required to keep product spoilage, diseases and bacteria at bay. Common methods are organic pesticides, heat, hydrogen peroxide, hypochlorite, UV, and ozone.

Many of these methods and technologies may cause secondary problems and environmental compliance issues related to the greenhouse effluent water, environmental health and safety (EHS) concerns, intense consumables costs, energy demand and extensive maintenance. An overview of various disinfection methods that can be used for greenhouse recirculated water, wastewater and irrigation is presented below.

Water recirculation and reuse in greenhouse has several operational advantages and is associated with significant cost savings. As irrigation water is used to grow crops, a fraction of the volume is not imbibed by the crops. Depending on the type of greenhouse and the type of crops being cultivated, the fraction of excess irrigation water is around 20-40%. New EU regulation stipulates that this volume must be reused in subsequent irrigation cycles. This presents a number of challenges for the grower since circulated water may be subject to microbial contamination. It is also vital to be able to retain the nutrient content. Ozone is an attractive method thanks to its highly potent disinfection capacity and its residue-free characteristics. It is also an excellent approach to treating wastewater containing elevated levels of organic COD and pesticide residues.

Greenhouse water reuse with ozone

As the non-absorbed water volumes are drained from the crops, a recirculation loop pumps the used water back to a collection tank. The annual water demand is typically 3,000-12,000 m3/ha of the greenhouse production area without water circulation, depending on the type of crops. The collected water must be thoroughly disinfected in order to avoid disease from microbes or pests. Ozone opens the possibility for maximizing water reuse rate and minimizing the nutrient consumption. A typical reuse cycle is described in the image below.

Ozone brings oxygen to the plants, increase the yield

When the ozone has disinfected the irrigation water, the residual ozone converts to oxygen, which helps enhance the growth of the plants.

1. Ozone disinfects irrigation water
2. Ozone breaks down into oxygen
3. Extra oxygen increases cultivation volume

99% elimination of pathogens

A properly designed ozone system will eliminate and inactivate bacteria, viruses, fungi, algae, protozoa and odors. Nutrients are not affected.

Ozone – the key advantages

• Strong disinfectant. Ozone’s oxidizing potential is high. It ranks among the top four oxidants. In practise, it’s the second strongest after hydroxyl radicals.
• Fast reduction of COD and BOD. The ozone treatment of unwanted organic residues effectively reduces the organic COD and BOD loads of the water.
• Unaffected nutrients. Nutrients such as ammonium, phosphate, sulphur and potassium remain unaffected.
• Low footprint. Our RENA Vivo systems are designed to fit onto a standard EU-pallet.
• Low energy input. Required power input is normally 1-3 kW.

What does disinfect mean?

Disinfect is to cleanse so as to destroy or prevent the growth of disease carrying microorganisms. Therefor a disinfectant is an agent, such as heat, irradiation or chemical that disinfects by destroying, neutralizing or inhibiting the growth of disease-carrying microorganisms.“The minimum level of effectiveness in a modern-day disinfectant is 100 percent kill of 6 log10 of an organism”