Keep it Clean: Disinfecting Hydroponic Water

Practiced around the world, hydroponics is especially advantageous where climates restrict plant growth, where low-quality soil won’t support large-scale production, and in countries where once fertile soil has been over-farmed. The availability of fresh water is also an important variable as clean, recycled water is a valuable resource. Hydroponics reduces consumption of fresh water from our already endangered water supply—a recent report states agriculture uses 70 per cent of available fresh water, while industry uses about 25 per cent and residential uses five per cent worldwide. The benefits of recycled hydroponic water for small and large operations include cost savings and higher crop yields.

To reduce the risk of recycled water spreading bacteria, viruses, and other waterborne diseases to crops, it’s important to disinfect the water before it is recycled through the system. There are several ways to disinfect your hydroponic water, but in this article, we’ll examine the benefits and challenges of the top three: heat pasteurization, ozonation, and UV disinfection.

Heat Pasteurization

With pasteurization, water is heated and then cooled to kill bacteria and viruses. Developed in the 1860s, heat pasteurization is one of the most popular ways to disinfect hydroponic systems due to its simple design and ability to terminate the most heat-resistant pathogens. Different temperatures and contact times are needed depending on the source of recycled water and what it’s being used for. Due to potentially high costs of heating and cooling recycled water, this method is best used by smaller operations.

Benefits

• Water does not need to be pre-filtered.
• Minimal biological and mineral fouling.

Challenges

• Expensive for large operations.
• Over time, high mineral content in the water leads to the buildup of deposits on the heat exchangers of the pasteurization system, which will decrease efficiency and increase maintenance costs.

Ozonation

Ozone (O3) is basically just oxygen with three molecules. A natural gas, ozone is created when the air in the grow room is bombarded with ultraviolet radiation from the sun. It can also be created artificially through an ozone production system by using a high-voltage corona discharge. Ozone is an intense, thorough, and environmentally friendly way to effectively destroy bacteria, fungi, and other waterborne diseases. It’s the strongest available water disinfectant on the market.

Benefits

• Microorganisms can never become resistant to ozone.
• Ozone reacts quickly and has no residual capacity.
• Controlled ozone in the growroom can also kill spiders and mites.
• Leads to savings on fertilizer.

Challenges

• More expensive to operate than heat pasteurization.
• Ozone is a strong oxidizer and thus highly corrosive.

UV Disinfection

With this disinfectant method, recycled water is passed through a radiation chamber that holds one or two high-pressure UV lamps. In recent years, more growers have turned to UV radiation as an alternative to chlorination, largely out of concern for the environment. Ultraviolet disinfection has a unique effect on microorganisms. It does not necessarily kill the target but rather alters its DNA strands so that the microorganism is incapable of reproducing. A bug that can’t reproduce quickly dies.

Benefits

• UV disinfection is cost-effective.
• If the UV dose is too low, inadequately disinfected water is automatically returned to the system.
• No toxic chemicals are used, and no byproducts are left behind.

Challenges

• UV light is only able to remove microorganisms and does not remove any other contaminants like heavy metals, salts, chlorine, or man-made contaminants.
• UV light is also only effective if the water being treated is clear.

While hydroponics is trending upward for both commercial and hobby growers, it’s important to note that variables must be strictly controlled to ensure the correct hydroponic balance is not disturbed once it is achieved. Without soil as a buffer, any failure in the hydroponic system can result in rapid plant death. To ensure maximum quality and yield, no matter what hydroponic system you use, water samples should be taken regularly and discussed with a professional.