Results - Discussion

[Analysis - Laboratory]

Initially, we were hoping to yield enough nitrogen to be useful for a farmer to be spread like liquid manure on the fields. However, we could only reach a maximum of 0.3kg/m3 without subsequent concentration or separation of the algae. Therefore we did not reach the needed volume for the average Austrian farmer and continued to search for alternative applications.

We had two ideas:

1. ) Sedimentation - concentration of the Cyanobacteria

The bacteria could be stored in a tank for a relatively short time. Then the bacteria would start to settle on the ground of the basin, leading to a tenfold higher concentration of bacteria (vgl. Measurement Row 3). It would be quite easy to pump the concentrated part of the substrate out of this sedimentation tank. For this only little technical effort would be needed. This sediment could yield 4 to 10kg dry-mass and 1 to 3kg pure nitrogen per cubic meter. One could either harvest once a month and exchange the entire substrate in the course of this procedure, or, even better, one could continuously harvest small amounts and store them, for example in a former liquid manure tank.


The substrate's concentration would be high enough to be brought directly to the fields. The carbon which is fixed in the dry-mass would gradually combine with the nitrogen bound in amino acids, slowly helping to increase the humus layer in the soils.

(solvable) disadvantages:

If a continuous harvest is not possible one would need even greater amounts of substrate and very large sedimentation tanks. If, on top of this, the algae can not be distributed regularly, large and expensive storage facilities would be needed.

As the volume depends on the facilities available, it is unlikely to completely substitute conventional fertilisation. However, we believe that it is quite possible and feasible to upgrade already existing liquid fertilisation systems. The waste heat from the stable could be used to ensure year-round production. As stables are usually too dark for the cyanobacteria to grow at a profitable rate, it would be necessary to use artificial daylight. The most reasonable source of energy are photovoltaic devices, which do not compromise environmental ideals. Moreover, a brighter stable would also be beneficial to the health of the animals.

2. ) Use as irriagtion water in greenhouses - without concentration

In Austria, 420 hectares are farmed below glass or film, 70% of which are vegetables. In Vienna only, 200 hectares are in greenhouses of which again 130 are heated and farmed all year long. Greenhouse cultures need to be irrigated on a daily basis. Depending on the culture and the time of the year 100-300 l/m2 are used for that purpose. The annual need for nitrogen can reach up to 0,06kg/m>2, i.e. 600kg per hectare. A modern Viennese vegetable farm produces fruit vegetables (peppers, tomatoes, cucumbers) on an average area of 2 hectares. The plants are grown on rock wool or coco mats from the middle of January to the middle of November (KD 40-45). The drip irrigation and fertilisation is a close circuit controlled by a computer panel (35% drain, recycling). The concentration of nutrients is comparably low in this water. A tomato bush needs about 250g/m3 pure nitrogen. This would match quite well with the values from our cyanobacteria cultures.

Larger farms collect the rain water in large basins of varying size (up to about 30.000 m3). The rain water makes up between 25% to 60% of the irrigation water, depending on the capacity of the tanks.

Organic farms srill plant their plants in the earth and may only apply natural fertilizers. The demand for irrigation water is much larger, and, depending on the culture and weather, can be between 4-10 litres per square meter and day.

The algae substrate, enriched in nitrogen and biomass, could upgrade the irrigation water and, at the same time, be stocked and grown in the rain water tanks. Those tanks would provide enough air, light and sun. The blue-green algae could continue to grow and contribute to the nutritional value of the water. As a result, the farms might have to use less mineral nitrogen fertiliser.


The nutrition concentration of our algae reactor matches perfectly the irrigation and fertilisation need of greenhouse cultures.

The infrastructure for distributing and stocking the water is already there, the algae reactor can be integrated into an existing system.

The blue-green algae can continue to grow in the collection tanks. If cultures are regularly added and harvested from the tanks they are able to compete against the undesirable green algae.

There is already an existing system to mix the substrate for the cyanobacteria.

The solution for 1m3 of fertiliser with cyanobacteria costs only € 0,09 (January 2009). This is at least as much as the farmer might have to spend on conventional fertilisers.

In large, heated greenhouses there might be enough space for the algae reactor, e.g. just underneath the ceiling. In that case the cyanobacteria can be grown all year long.

A continuing, regular harvest and maintenance of the reactor prompts the cyanobacteria to produce more heterozytes and, thus, more nitrogen. As rain water is always available, this constant harvest can be put into practice.

For organic Farms

The nitrogen in form of Glutamin and the dry-mass of the blue-green algae contribute to the build up of humus.

The nitrogen is fixed organically, therefore slowly available, however, due to the warm and moist conditions of a greenhouse it is more applicable for this kind of farming than in the field.

The indigenous strain D we tested, might contribute greatly to the biological activity in the soil.

(solvable) Disadvantages:

The cynobacteria could plug up the dripping irrigation. In order to prevent this from happening, either a filter or some mechanical device to homogenize the algae will be needed. A system similar to a hand blender would most likely already suffice.

What is of advantage to the organic farmer, namely that the nitrogen is fixed organically, is less advantageous for farming on substrates. In greenhouses, where the plants mainly grow on coco mats, one need enzymes to make the fixed nitrogen available to the plants. Symbiotic bacteria, which digest the dead algae, would be ideal. One could already use these enzymes while the bacteria are still in the tank, or later, in the coco mats. Today many farmers mix so-called effective micro-organisms into the irrigation water to contribute to the plants' health.

The concentration of nutrients depends on the rate of growth. One might have to think of an automatized analysis of this nutrient concentration.

We presented our idea to several experts on greenhouse farming. We got to know Mr Dipl. Ing. FH Gregor Hoffmann from the chamber of agriculture W/NÖ, who works as a gardening advisor. He offered to meet and let us present our idea of algae fertilisation in green houses in more detail. Maybe even launch the first tests. Our idea falls onto fertile ground.

Unfortunately, cyanobacteria are the couch potatoes of the bacteria world, in that they reproduce very slowly. In the lab we are able get the bacteria to double their dry masses in about 5 days. It would be possible to refine our process and obtain a doubling rate of 1-2 days. But even this is slower than what we had hoped for. It is now clear to us that in the next year we will not realize our goal of using cyanobacteria to bind atmospheric Nitrogen.