Plant yield can be optimised by increasing the amount of carbon dioxide present in the atmosphere. Enter the industrial gas company...

A key component in photosynthesis, carbon dioxide is essential to the growth and vitality of a plant.

Using energy from sunlight plus water, the gas is converted into sugar and oxygen. This sugar is processed in the plant to make building material, used to make the plant grow.

Studies have shown that if CO2 levels are increased in the atmosphere, plants grow at a much faster pace, with accelerated rooting and shooting, and often improve in quality, in terms of the amount of flowers they produce and their enhanced defences against fungal attack.

The concentration of CO2 in the ambient air is currently around 385ppm. In a standard greenhouse, this amount decreases substantially due to plant respiration, particularly when there is a great deal of exposure to light.

If the level of CO2 falls below 385ppm, photosynthesis is no longer taking place at a maximum reaction, and plant growth slows, resulting in reduced quality and yield.

Using extra CO2
One option to boost the amount of CO2 in the atmosphere of the greenhouse, is to manually put more in, therefore bringing photosynthesis back up to optimum levels.

This is not a new technology, but one which, as the world’s focus increasingly moves towards environmentally friendly processes and technologies, is being pushed by gas companies, as one use for the CO2 which would otherwise be released into the atmosphere.

Rudolf Berghoff, of Linde Gas, told gasworld, “At Linde, the majority of our greenhouse customers which are using CO2, are based in the Netherlands, because the density of greenhouses in that area is very high.”

“Most of the CO2 is coming from industrial processes where it is filtered and purified. If we weren’t doing that, it would be directly released into the atmosphere.”

In the Netherlands, an old oil pipeline running from Rotterdam to Amsterdam is used to transport CO2 from refineries, to greenhouses on the network.

Berghoff added, “We supply the customers via this pipeline; we pump the CO2 at one end into the pipeline, we can also use the pipeline as a buffer tank and then there are several dozen of these customers connected to this pipeline.”

“If they are not connected to this pipeline then they are supplied with liquid CO2, so they have a gas tank outside their company, we fill the tank with liquid CO2, reducing the volume by around 550 times, so more can be stored, and then we give this to the customer and he can put it into his greenhouse by automated control.”

Levels are closely monitored to ensure that the plants are getting just the right amount of extra CO2 from the atmosphere.

Mark Ewig, Global Strategic Marketing for Food & Beverage at Linde explains, “There is a monitoring device physically in the greenhouses, and users try to have a set point of around 400–1100 parts per million of CO2 as a target. As the plants grow, they absorb the CO2 from the greenhouse atmosphere. The monitoring device measures the depletion and sends a signal to add more CO2 into the greenhouse.”

This is an effective technology - the only other option plant growers have, is to put more fresh air into the greenhouses, but this is problematic, as Berghoff explains, “When plant growers bring in fresh air, especially in winter times when the weather is not warm enough, they have high losses of energy, because the plants need a certain temperature to grow, and if you constantly add fresh air then you lose more energy.”

Green technology
Ewig acknowledges that from a marketing point of view, this technology is nothing ‘new’ as such, but adds, “Stronger, healthier plants, coupled with the sustainability drives that we’re seeing in the market place, have increased the demand for the CO2 we’re supplying. You’ve got a full circle – you’re taking CO2 that would go into the atmosphere and actually putting it to good use – a real green application.”

“Additionally, the whole point of this process is to improve food supply across the world, which is very positive.”
This is not a technology which is widely used across the globe however, Berghoff explains, “We do have it in other countries as well, but it is just a few who really use it because in many countries the greenhouses are not as technical.”

However, Ewig sees increased potential for the technology to become more widespread, especially given its green credentials, he said, “I have definitely seen renewed interest in this project because of potential credits and sustainability drives. In the US for example, we’re starting to see a renewed interest, as well as in South America.”

Berghoff said that Linde is currently installing more filters and liquefiers to capture CO2 from industrial processes, in order to have a constant supply for greenhouses.

Ewig adds, “Typically it’s regional issues – a lot of times there are supply problems and deficits, and in the Netherlands especially, in summertime the demand is fairly great for greenhouses, as well as for beverages and all the other uses. We’re looking at sources to be more regionalised so that we can handle the demand.”

Ewig and Berghoff do not consider that this will ever be a huge growth driver for the industrial gas industry, but with the world focused on green technologies, and the media looking to energy intensive industries like ours to be making substantial steps towards greener processes, it’s certainly a start.

This technology is transformed into a new Linde application called “SeeGrow”. Here, CO2 enriched mobile greenhouses are used to solve the poor grass growth in modern football stadiums.