Pilot plant to convert AD waste into high-quality fertilizers

The pilot plant will take in digestate and process it via chemical hydrolysis, followed by a high-efficiency organic fertilizer granulation process.

The Basque Institute for Agricultural Research and Development, Neiker-Tecnalia, and the Guipuzkoa-based company Ekonek will be building a pilot plant to treat organic waste for producing organic fertilizers. The facility will enable the organic material resulting from biogas plants to be effectively put to use. The plant will be located on Neiker-Tecnalia’s agricultural land in Arkaute (Álava, Basque Country) in northern Spain. The budget of EUR 1.5 million ($1.96 million) will be provided by the European Union within the framework of a CIP-Ecoinnovation project, and four organisations will be participating in the initiative: Neiker-Tecnalia, Ekonek Innovation in Product Upgrading, Blue Agro, and the Dutch company Colsen.

The project sets out to make use of the organic matter resulting from biogas plants (biogas residue into organic fertilizer) following the anaerobic digestion process, which consists of subjecting the matter to a decomposition process in oxygen-free conditions. Biogas is obtained from this decomposition and the matter resulting from the process is called digestate. Neiker-Tecnalia is planning to made use of this product, frequently regarded as waste, to turn it into high quality organic fertilizer that is up to ten times more productive than conventional types. It will be possible to use it on high added value crops, like sports lawns, ornamental crops and particularly delicate agricultural crops.

Neiker-Tecnalia is hoping that this pilot plant will come up with solutions for the agricultural sector that will be environmentally friendly and at the same time be economically viable. The advantages of the fertilizer that will be obtained are based on the fact that it is an organic product in the form of microgranules that requires much lower doses than traditional fertilizers and releases its nutrients slowly, which means a reduced impact on the environment.

The process to obtain bio-fertilizer basically consists of subjecting the digestate to a process known as chemical hydrolysis followed by a high-efficiency granulation process. It is about adding to the digestate, which is in a liquid or semi-liquid state, a number of reagents that cause the fibres to dissolve so that it can then be turned into microgranules. Obtaining a product in the form of small granules means significant advantages for transporting and storing purposes, and for the practical aspects when using it.

One of the main tasks of the Neiker-Tecnalia researchers will be to ensure that the resulting microgranules have optimum chemical and agronomic characteristics. In this respect, it is particularly important to obtain fertilizer with a balanced level of NPK; i.e., of nitrogen, phosphorus and potassium. The experts reckon that the facility will be able to treat about 28,000 metric tons of digestate per year, which will produce about 9,200 metric tons of fertilizer.

The bio-fertilizer obtained will be produced by reusing organic waste which until now has not been put to any use. Much lower doses will be needed compared with traditional organic fertilizers due to the fact that its end formulation will be determined in a customized way according to the target crop and soil; the fertilizing elements will be released progressively, and this will enable the fertilizer to be much more effective. This will mean that it will be better used and, therefore, at a lower cost, since it will allow the same area of land to be fertilized with a smaller amount of the product than when ordinary fertilizers are used.

The company Ekonek, in collaboration with Neiker-Tecnalia, will be in charge of building the pilot plant on the agricultural experimentation land belonging to the research and development center in the Alavese town of Arkaute. The Dutch firm Colsen will be providing the material produced by various biogas plants after the anaerobic digestion process of the organic products has taken place. Neiker-Tecnalia and Blue Agro will together be designing the final, ideal formulation of the fertilizer. The research and develoment center will be doing research on the product and adapting it from the point of view of its agronomic performance, and Blue Agro will be handling its commercial viability.