Can I use electrolysis for nutrient solution in a hydroponic system for increasing the dissolved oxygen levels?

Q:

Can I use electrolysis for nutrient solution in a hydroponic system for increasing the dissolved oxygen levels? If I use electrolysis in my nutrient solution will it have any adverse effect on the nutrients?

A:

Electrolysis can be used to produce oxygen in a liquid – this is a well-known process often termed the “decomposition” or “splitting” of water. During the electrolysis process an electrical current of the correct voltage is applied across a positive anode and a negative cathode which are placed into the water.

The electric potential through the water causes hydrogen gas to be produced at the cathode and oxygen gas at the anode. During this reaction, twice as many moles of hydrogen as oxygen are produced. Basic electrolysis experiments such as this are often used as science experiment for young students as the oxygen generated is usually quite visible as cloudy bubbles around the anode. This is also an industrial process, used to generate hydrogen gas and to a lesser extent, oxygen that can be collected from the surface of the liquid. While this may seem as a great way to generate oxygen and boost dissolved oxygen (DO) levels in a nutrient solution, there are a few drawbacks if you want to set up your own electrolysis system for this purpose. Firstly, the electrodes need to be of the correct, non-reactive material (such as titanium) as other metals will corrode and dissolve under electrolysis which could be rather toxic in a nutrient solution.

Secondly, the correct voltage for the solution must be applied as the current flowing and duration will determine the amount of gases produced.

And thirdly, there could be much more complex reactions which occur with the ions dissolved in the nutrient solution. It may seem more sensible to only apply the electrolysis to pure (RO) water and then add this to the hydroponic system to boost DO levels.

However, pure water does not conduct an electric current well, so oxygen won’t be produced.

For electrolysis to proceed at a good pace, salts or acids need to be added to the water to conduct the current (industrially, inexpensive sodium chloride may be used as what happens to this salt solution during the process is not important when the main objective is to simply collect hydrogen). In a hydroponic solution there are nutrient ions that will allow electrolysis to occur and generate H2 and O2 gases, however, these nutrient ions may then undergo redox reactions at an electrode themselves producing new solutes and gases. These may then react together to produce other materials. These side reactions could be quite complex and not well understood as nutrient solutions contain not only the ions derived from fertilizers salts but potentially many others from water supplies, supplements and boosters, acids, leached from substrates, as impurities in fertilizers and other sources.

The oxygen that is generated in solution is not all necessarily going be available for plant use either — larger bubbles will quickly disperse, nanobubbles of O2 gas are formed and will stay longer in solution, however, passing through pumps, irrigation equipment, substrates may cause the loss of some of these, and some of the oxygen and hydrogen may even reconvert back to water.

For these reasons simply measuring the DO levels in the solution around the electrodes during electrolysis is not necessarily a good indication of the O2 levels available directly around the root surface where they are of most importance.

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Written by Lynette Morgan
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Dr. Lynette Morgan holds a B. Hort. Tech. degree and a PhD in hydroponic greenhouse production from Massey University, New Zealand. A partner with SUNTEC International Hydroponic Consultants, Lynette is involved in remote and on-site consultancy services for new and existing commercial greenhouse growers worldwide as well as research trials and product development for manufacturers of hydroponic products. Lynette has authored five hydroponic technical books and is working on her sixth.

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