Reduction of Discharge Water by Heating the Nutrient Solution During the Winter Period
Why?
Necrosis virus is becoming an increasing problem in lettuce cultivation, both in soil-grown and hydroponic systems. The virus is spread by the fungus Olpidium virulentus, which can be present in irrigation and nutrient water. By preventively heating the nutrient solution to 18–20°C, this study investigates whether the development of the fungus and the symptoms of the necrosis virus can be reduced. The aim of this measure is to improve water quality and reduce reinfection in recirculating hydroponic systems.
What
How
Cost
Benefits
Attention
Description & visualization of technique
This measure consists of the controlled heating of the nutrient solution within a hydroponic system. The water is continuously maintained at a temperature between 18 and 20°C using heating units and circulation pumps. O. virulentus is mainly observed during colder periods, which is why research is being carried out to determine whether heating the nutrient solution can influence the reproduction of this fungus and thereby reduce the spread of the virus.
Construction (materials, technical sheet / cross-sections)
The installation usually consists of:
- A heating element or heat exchanger connected to the water buffer
- Temperature sensors and automatic control systems
- A circulation pump to ensure a uniform water temperature
- Application in a recirculating nutrient water system
Maintenance
Daily monitoring of the water temperature is strongly recommended, together with regular monitoring of the oxygen level and microbiological load of the water. In addition, it is important to apply this measure preventively, before the first virus symptoms appear. However, further research is still needed to confirm the effect of water heating on suppressing the development of O. virulentus.
Indicative prices for construction and other costs
The cost of this measure depends on the size of the hydroponic system and the type of heating installation used. Prices can start from approximately €10.000 and increase significantly for systems with larger flow rates. The main investments are related to energy consumption, installation of heating elements, and monitoring and regulation of the water temperature. Both installation costs and recurring operational costs can vary depending on the scale of the system and the level of automation.
Relevant subsidy channels
For innovative investments in water treatment and water recirculation in greenhouse horticulture, growers may be eligible for VLIF support (Flemish Agricultural Investment Fund). Depending on the type of investment and its innovative value, the subsidy rate may cover approximately 40 to 50% of the eligible investment costs.
Economic benefits
This measure can provide several benefits. Economically, a more stable water quality can help reduce yield losses caused by necrosis symptoms, lower plant losses, and improve product quality.
In addition, this technique also offers benefits in terms of ecosystem services and sustainability. Better control of waterborne pathogens can reduce the need for chemical plant protection products. Furthermore, the measure promotes more sustainable water use in closed cultivation systems and supports integrated strategies for disease management and biodiversity.
Sources for information & guidance
There are several important points to consider when applying this measure. Heating the nutrient solution is expected to work mainly as a preventive measure and may be less suitable as a curative treatment once symptoms are already present. Continuous monitoring of the water temperature is necessary to guarantee stable system performance. In addition, higher water temperatures can influence the oxygen content of the water, which should therefore also be monitored regularly.
For optimal disease management, it is recommended to combine this technique with other water treatment methods and, if possible, with resistant varieties. Within ACLIMA, a positive effect of this treatment on the symptoms of lettuce ring necrosis has not yet been demonstrated. Further research is needed before heating the water can potentially be applied as a preventive measure.
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