Fraunhofer Institute for Interfacial Engineering and Biotechnology IGBLarge quantities of organic waste are generated in the agricultural production of food or feed for livestock. These can be used sensibly as biomass for bioenergy production, but also for the recovery of important nutrients. The Fraunhofer IGB is developing the corresponding biotechnological processes.
Nutrient management.
Nutrients from food and animal feed industry
Processing of organic residues
Enzymatical and chemcial recovery of phosphorus
The Fraunhofer IGB is developing biocatalytic processes for the mineralization of organic phosphates contained in agricultural residues. In this way, they can be recovered as high-quality fertilizer.
Stabilization trough drying, torrefaction or carbonization
In the production, preparation and processing of solids, drying is usually an essential process step. Drying processes are used, for example, to stabilize the shape of granulates, pellets or powders.
Torrefaction aims to increase the mass-related energy density and thus the calorific value of the raw material. It also increases the transport and storage capability of the raw material.
In hydrothermal carbonisation, the biomass from agricultural waste is converted into fuels and thus made usable for bioenergy production independent of location.
Recovery of nutrients from process water
Phosphorus recovery
Phosphorus is a nutrient that is highly sought after as a fertilizer in agriculture. On the basis of the processes developed at the Fraunhofer IGB, phosphorus can be recovered from agricultural residues and reused as fertilizer.
Nitrogen recovery
Like phosphorus, nitrogen is a nutrient that can be recovered from agricultural waste and used as fertiliser.
Tabbed contents
Recovery of organic phosphorus
Recovery of organic phosphorus for enhanced phosphate precipitation
Phosphorus is found in many organic residues as both inorganic and organic compounds. These phosphorus compounds may be very stable in nature. The phosphorus dosage can therefore hardly be controlled by direct application of manure or fermentation residues. This frequently results in an over-application of phosphorus on soil, which has negative environmental and economic consequences. The natural biological decomposition process converts these organic compounds into inorganic plantavailable ions (NO3–, NH4+, PO43–). However, this process can take several months or years, as it depends on the specific local conditions such as humidity, temperature, precipitation, the activity of microorganisms, etc. At the Fraunhofer IGB, we have developed analytical methods for the characterization of organic residues in regard to their phosphorus content. Moreover, we are developing biocatalytic processes for the mineralization of organic phosphorus in agricultural residues and its recovery as a valuable fertilizer.
Drying
Drying
Drying processes play an important role in the production of fertilizers or pesticides. They facilitate the transport and storage of extracted nutrients and active ingredients, for example in the form of powders. Drying thus also forms the basis for the production of fertilizer pellets.
Drying of organic residues and cyanobacteria with superheated steam dryer
In the EcoBug project, the drying of the digested manure and cyanobacteria was carried out with a novel superheated steam dryer (SHSD). This dryer offers significant advantages in comparison with common hot air dryers.
Due to the superior heat transfer of steam, higher drying rates are achievable with SHSD at the same temperature. This leads to a lower specific energy consumption of
0.75–0.90 kW·h/kg water removed for SHSD compared to 1.10–1.70 kW·h/kg water removed in a comparable hot air dryer[1].
Moreover, higher thermal conductivity and heat capacity of superheated steam compared with hot air results in enhanced heat transfer to microorganisms, enabling pasteurization and/or sterilization. As superheated steam is recirculated and reheated in a closed loop, an excess of evaporated water develops which is carried off along with NH3 and volatile organic carbon (VOC) from SHSD. In our approach VOCs and NH3 are condensed out with the excess steam enabling condensable valuable organic substances including volatile fatty acids (VFA) and NH3 to be recovered. This eliminates the environmental problem of VOC and NH3 emissions in conventional hot air dryers.
Literature
[1] Desai, D. K. et al. (2009) Superheated Steam Drying of Brewer’s Spent Grain in a Rotary Drum, Advanced Powder Technology, Vol. 20, Issue 3, pp. 240-244