Although regulating water temperature has not traditionally been included in pre-treatment processes, it remains crucial to the irrigation cycle. Cold water has the ability to hold more dissolved oxygen compared to warm water, an essential component for irrigation. In contrast, warmer water often provides a favorable environment for the reproduction of microorganisms. However, water that is too cold can cause shock to plants. As a result, in greenhouses it is preferable to use ambient water maintained at a temperature of 15-20 degrees Celsius. Management of this factor is accomplished through a heat exchanger linked to the facility's central heating or cooling system.
Pre-Treatment of irrigation water in greenhouses
Irrigation water Pre-treatment
For the pre-treatment of greenhouse irrigation water, there are four characteristics of the source water that must be controlled, each with their own specially developed purification methods. In practice, technology serves more purposes and complements or complements each other when pre-treating irrigation water. The four pre-treatment control points are: PH control, micro-organisms, particles and water hardness.
PH-control for irrigation water
Controlling the PH of the incoming water is very important to prevent algae, pathogens, etc. This is especially necessary when water is stored in a tank or basin before entering the greenhouse irrigation system. The PH pre-check is done in a shunt system, where the water circulates continuously and acid or lye is dosed to the water to ensure a stable PH level.
Removing Micro-Organisms before irrigation
Microorganisms are certainly undesirable for harmless and consistent irrigation water. To deal with microorganisms in incoming water, there are two options. The first is UV treatment. Water is pressurized and comes into direct contact with UV light, which kills the microorganisms. UV disinfection systems, whether high-pressure UV or medium-pressure UV units, are a proven technology that serves its purpose.
The second option to remove microorganisms from irrigation water is Ultra-Filtration, our preferred system. Unlike UV systems that kill microorganisms, ultrafiltration in the pre-treatment of irrigation water removes them completely. The advantage of this is that no 'residues' of micro-organisms are left behind that can serve as food for new, living organisms. Another advantage is the operational and maintenance costs, because UV systems have high energy consumption and UV lamps are expensive.
Making irrigation water free of particles and sediments
Particles and sediments can be filtered out. The most commonly used technology for this is a Paper-Belt Filter. The paper belt filter is a simple, maintenance-free filter without backwashing water. Three types of belt filters are used in greenhouses: flat bed, deep bed and hydrostatic filters. The type is chosen based on the application, capacity and degree of contamination. The filter paper chosen determines the particle size that the belt filter will remove.
Water softener as irrigation water pre-treatment
A water softener is used to reduce the calcium content. On turnkey projects we install these before filling tanks and systems, because water hardness can have a direct influence on the lifespan of pumps, pipes and valves. Also for irrigation purposes, depending on the water source conditions, a water softener can prevent problems in the long term and make fertilization more efficient.
Pre-treatment with Reverse Osmosis (RO)
The most rigorous pre-treatment method for incoming irrigation water is Reverse Osmosis. This removes all micro-organisms, particles and minerals from irrigation water. It also removes good minerals, making fertilisation a more precise, but costly endeavour.
Learn more about pre-treatment of irrigation water?
Learn more about pre-treatment of irrigation water?
Sources of Irrigation Water
City water for greenhouse irrigation
Using city water, also known as tap water, is generally the most stable and reliable source of irrigation water in many cases. It undergoes pre-treatment at the source, which has both advantages and disadvantages. If the water has a high calcium content, it is wise to consider a water softener. In addition, the temperature of city water is usually already at the desired ambient level. However, it is important to note that city water is usually the most expensive option available.
Surface water as source
There are three types of surface water: perennial, ephemeral and man-made. Perennial water is consistent, but ephemeral and man-made species, which occur in different locations, are not always reliable. For greenhouse irrigation, a reliable source all year round is crucial because quality and quantity can vary, making pre-treatment more complex due to the possible presence and fluctuation of microorganisms and minerals.
Using well water for greenhouse irrigation
Well water can serve as a reliable source of irrigation because it is often consistently available and can be rich in minerals beneficial to plant growth. However, it is critical to regularly test source water for contaminants and adjust pretreatment accordingly to ensure it meets the quality standards necessary for irrigation. In addition, water availability and quality can vary depending on the depth and location of the well, requiring careful consideration and possibly additional water sources during periods of high demand or low supply.
Rainwater serves as an excellent irrigation source and can be collected and reused directly from the greenhouse structure. However, its availability is inconsistent, necessitating supplementation or backup from other sources.