Our approach: Sustainable nutrient management

Nutrients such as nitrogen, phosphorus, potassium, calcium and sulphur are essential for the growth of all living things, especially for plants. Therefore, nutrients are the main components of fertilizers and indispensable for global food production. Up to now, nutrients have only partially been managed in a closed cycle. Instead, they are removed from the agroecosystem when the plants are harvested. There is practically no recycling of nutrients via the residues of food production.

Sustainable resource management through nutrient recovery and recycling

The recovery of nutrients is essential for a sustainable economy. Fraunhofer IGB is therefore engaged in the development and implementation of sustainable, cost-efficient technologies and strategies for integrated resource management.

The focus is on the development of novel technologies for the recovery of nutrients from wastewater and organic residues. In recent years, we have characterized wastewater, liquid manure and fermentation residues as well as various other solid or liquid residues, investigated them with regard to the recovery of nutrients and successfully developed patented processes.

In our production processes, the nutrients are precipitated or pelletized in such a way that they can be marketed as a complete and specific product by industrial partners and used in various agricultural sectors. Fertilizers can be produced and marketed both in solid and liquid form. We offer the possibility to develop appropriate product formulations, produce sample quantities and characterize them accordingly.

The industrial production of phosphate fertilizers is based on the use of non-renewable raw phosphates, whose occurrence is constantly decreasing, and the production of nitrogen fertilizers using the Haber-Bosch process requires a very high energy input, especially in the form of natural gas. At the same time, the demand for fertilizers will increase dramatically in the future in order to cover the growing need for plants for food production and for the provision of renewable raw materials for the production of bioenergy or basic chemicals. For these reasons, the prices of industrially produced mineral fertilizers have already risen in recent years and this trend is expected to continue.

Although the raw materials for fertilizer production are becoming increasingly scarce, large quantities of nutrients are simultaneously being lost via the sewage system and further energy consumption. The state of the art in most municipal wastewater treatment plants is the removal of nitrogen compounds such as ammonium (NH₄⁺) and nitrate (NO₃^-) using nitrification and denitrification processes. With high energy consumption, these compounds are converted into gaseous nitrogen that escapes into the air. Phosphate is removed by chemical precipitation by adding aluminium or iron salts. These phosphate salts are landfilled because they are not available to plants or can release iron and aluminium in concentrations that are toxic to plants. It is estimated that about 4.3 million tons of phosphorus are lost worldwide each year in this way [1].

Agriculturally used soils are often over-fertilized with mineral nutrients. Mineral fertilizers applied incorrectly or in excess are washed out of the soil and thus enter the groundwater or surface waters, where the nutrient input leads to undesired eutrophication. The direct use of liquid manure or fermentation residues from biogas production as fertilizer can also be disadvantageous for the soil, as the nutrient composition of nitrogen, phosphorus and potassium (N:P:K) of these organic residues does not meet the respective needs of the plants. Therefore, when using liquid manure or fermentation residues as a fertilizer, a nutrient requirement is calculated which is based on only one nutrient, usually nitrogen. This leads to an overdose of the other nutrients in the soil. The use of uncontrolled amounts of nutrients in organic fertilizers can lead to nutrient oversaturation in the soil, especially in areas with intensive livestock farming, and thus cause environmental damage. In Germany for example, between 2003 and 2005, more than 70 percent of nitrogen and 50 percent of phosphorus inputs into surface waters originated from agriculture [2].

The spreading of liquid manure, fermentation residues from biogas plants and other agricultural waste supplies arable soils with valuable organic components and necessary nutrients. These serve to cover the nutrient requirements of the plants and maintain the fertility of the soil [3]. In areas with intensive livestock farming, however, it is not always possible to spread them on the field, as the soils already have a high nutrient content. For example, a conventional agricultural biogas plant with a capacity of 500 kW_el produces about 100 tons of nitrogen (N) per year through fermentation. A fertilization with 170 kg N/ha would require 588 hectares of land to absorb the amount of nitrogen produced [4]. Therefore, fermentation residues and excess manure from regions with intensive livestock farming must either be removed or stored for a long time.

Furthermore, soil degradation is becoming a serious problem in Europe due to the growing demand for products made from renewable raw materials and bioenergy. In recent years, for example, numerous areas of forest and permanent grassland have been converted into arable land. This has led to a decrease in soil organic matter and, in conjunction with this, to reduced water retention capacity, lower soil fertility and an interruption of nutrient cycles [5].

At present, the loss of soil fertility due to overfertilization with synthetic fertilizers is still more than compensated, but without compensating for the loss of organic matter. In the long term, however, the input of mineral fertilizers will not be sufficient to maintain soil fertility. The decline in soil fertility will have a direct impact on securing food production, especially since soil is not a renewable resource [6].

Fraunhofer IGB is therefore developing technologies for the recovery of nutrients and organic components from wastewater, agricultural waste and food industry residues in order to produce high-quality and compact organic and mineral fertilizers.

[1] Dockhorn, T. (2009). About the economy of phosphorus recovery. Conference proceedings: International Conference on Nutrient Recovery, Vancouver

[2] Mohaupt, V. et al. (2010) Gewässerschutz in der Landwirtschaft, Umweltbundesamt

[3] Stoll, M. S. et al. (2012) Evaluation of Treated Manure as Fertilizer. Proceedings - 8th International Conference ORBIT 2012;Rennes, France 12.-15 Juni 2012

[4] Fuchs, W. and Drosg, B. (2010) Technologiebewertung von Gärrestbehandlungs- und Verwertungskonzepten, pp 10. Universität für Bodenkultur Wien, Wien

[5] Communication from the Commission to the Council, The European Parliament, the European Economic and Social Committee and the Committee of the Regions - Thematic Strategy for Soil Protection. (2006)

[6] Soil. European Commission: Environment http://ec.europa.eu/environment/soil/index_en.htm Access Date: February 10, 2012