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SUCCESSFUL LETTUCE GROWING IN DEEP WATER CULTURE WITH PURE OXYGEN

THE FUTURE HAS BEGUN

The company B-Four Agro grows lettuce using the hydroponic method. The heads of lettuce, which grow in covered deep water cultures, find the ideal conditions here for quick and healthy growth. The efficient use of space, combined with a low consumption of resources, protects not only the environment but also enables the growing of lettuce at very low cost. An important component of the active hydroponic system is the sufficient supply of oxygen to the plants. This is ensured in the greenhouses of the Dutch company with an oxygen generator from Inmatec.

The world’s growing population is increasing the demand for food. Ensuring a sufficient food supply for the future while conserving the environment and natural resources needs new approaches in food production. The company B-Four Agro from the Dutch town of Warmenhuizen is a specialist of many years’ experience in the field of lettuce growing and is now breaking new ground with a deep water culture system constructed in 2019. The goal is the sustainable production of lettuce in industrial scale hydroponics. The concept is unique: almost all resources used are generated in the system and recycled in a closed circuit.

Cultivation begins with a small mesh pot filled with a substrate (vermiculite) and a lettuce seed. The mesh pots are first placed on trays with pre-made cut-outs and then briefly immersed in a water bath so that the substrate can become fully saturated. The substrate will later also store the nutrients and oxygen released in the deep water culture and provide the plants with support and stability. Finally, the trays of 100 pots each are conveyed to a 10-storey vertical farm on a conveyor belt. The seeds grow into seedlings here under LED lighting and automatic water misting. After 10 days, the young plants are moved to new trays by a gripper. The polystyrene rafts hold 20 young plants each and offer them enough space for their future growth. The floating platforms are finally placed in a pond. In this way, a total of 190,000 lettuce plants slowly move along in a 50 cm-deep water pond from one end of the approx. 3 hectare greenhouse to the other. On their way, which will take about 6 weeks, the plants slowly form long roots that reach deep into the water. Here they absorb the dissolved plant nutrients essential for their growth, including phosphorus, potassium, magnesium, sulphur, calcium, copper and zinc.

In addition to the total of 14 micro-nutrients and trace elements, oxygen is essential for the growth and health of the plants. The root system hanging in the nutrient solution needs a sufficient quantity of oxygen. Thus an oxygen saturation of at least 9 mg/l at a water temperature of 20 degrees Celsius is required. If the oxygen content is below that, the roots will rot and the plant will die. The water matched to the plants’ needs is prepared in a large plant room. A water treatment plant takes the plant nutrients, which are located in large containers in a multi-level rack, and mixes them into the water in the necessary dose. The oxygen is generated directly on site in an environmentally friendly way by a POC 8000 OnTouch Connect oxygen generator.

The generator is equipped with Pressure Swing Adsorption (PSA) technology and enables the production of oxygen with a purity of up to 95%. To this end, ambient air is guided into a valve block at the required pressure via an air compressor. This automatically ensures that the compressed air is guided alternately into two adsorption vessels filled with a zeolithic molecular sieve. These vessels switch successively from filter mode to regeneration mode. Water vapour, nitrogen, noble gases and carbon dioxide contained in the air are adsorbed in the sieve in one vessel, while the sieve regenerates in the second vessel through the action of compressed air. The oxygen obtained at B-Four Agro is passed to a 500-litre product container. Thus 8.4 m3 of oxygen with a purity of 93% are available per hour to enrich the water with oxygen. The water enriched with nutrients and oxygen is pumped through the active hydroponics system at a rate of 400 m3 per hour.

Sustainability and the protection of natural resources played an important role in the development of the new hydroponic system. The majority of the resources used in the deep water culture are generated at B-Four Agro itself. For example, rainwater is collected from the roofs of the greenhouses and stored in large holding ponds. The light provided in the halls by LED lighting is generated by more than 1,000 solar collectors on the roof of the company building. Carbon dioxide (CO2), which is also needed for photosynthesis and the formation of plant cells, is also obtained internally. The subsidiary B4 Energy produces over 2 million m3 of gas per year on site from the lettuce waste; this is supplied to almost 1,500 households in the region for energy production. The CO2 generated in the biogas plant is returned to the greenhouses to support plant growth. The water that was already used in the deep water culture is also enriched and treated again with the nutrients and oxygen removed by the plants. This creates a closed circuit that minimises and optimises the consumption of natural resources.

The new deep water culture in Warmenhuizen sets new standards in matters of environmental protection and efficiency. The experiences that B-Four Agro has had in hydroponics since 2009 have been used in the new system. This now allows the production of lettuce on an industrial scale with minimal use of space and efficient use of resources. The varieties grown, such as Lolo Bionda, Lolo Rossa, green oakleaf lettuce or Salanova lettuce, are marketed to the wholesale trade. The hydroponic growing of a head of salad consumes 90% less water than conventional agricultural cultivation in soil. While an average of 4 kg of lettuce per square metre can be obtained in soil, over 40 kg can be achieved with deep water culture. Growing in water is also much less elaborate. The plants do not have to be watered. As there are no root pests, no insecticides or pesticides have to be used. The fully automated operation is low-maintenance and requires few personnel.

“Hydroponic systems are a forward-looking and sustainable option for food production. Their key disadvantage, however, is the inherent lack of oxygen. The active addition of and enrichment with oxygen is vital to the plants’ survival. By generating oxygen on site with an oxygen generator from Inmatec, we can kill two birds with one stone. On the one hand, we can specifically control the optimal oxygen saturation of the water with the addition of pure oxygen. On the other, the on-site generation of oxygen supports our sustainable approach, as lorry journeys to deliver oxygen are rendered unnecessary. The integration of the user-friendly generator into our water treatment system also went swimmingly,” said Bart Bak, Managing Director of B-Four Agro B.V.

Inmatec POC 8000 OnTouch Connect oxygen generator

Details

  • Gewerbestraße 72, 82211 Herrsching am Ammersee, Germany
  • Markus Berninger