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by Dr. Lynette Morgan
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 E
lectrolysis 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 a 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 like 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
that 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 H 2 and
O 2 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 O 2 gas are formed and will stay longer in solution,
however, passing through pumps, irrigation equip-
ment, 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 O 2 levels
available directly around the root surface where they
are of most importance.
Dr. Lynette Morgan
LM 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 authored five hydroponic technical books.
Visit suntec.co.nz for more information.
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Maximum Yield