Short Description of Technology – GENERAL

The proposed innovative technologies focus on nutrient recovery from liquid waste materials and biomass wastes through several innovative processes. The technology proposed by ARI involves 1) microbial immobilization of nitrogen (N) during the co-composting process of liquid waste materials (digestate from biogas plants and hydroponic waste solutions) with dry green waste. 2) UNITO and NIBIO focus on technologies for N and phosphorus (P) recovery via struvite precipitation and 3) ammonium stripping, which involves the evaporation of ammonia gas from liquid anaerobic digestate under low temperature and low vacuum conditions and its recovery as ammonium sulphate and ammonium water. These approaches may significantly reduce greenhouse gas (GHG) and ammonia emissions and N, P-pollution associated with organic waste.

• Nutrient recovery from liquid waste materials through microbial immobilization in compost

Short description of technology

Microbial N-immobilization during the co-composting of liquid and green waste has not been attempted yet on an industrial scale and has significant potential to prevent N-loss by immobilizing it in an organic form or stabilizing it in the compost matrix. The proposed technology developed by ARI focuses on nutrient recovery from liquid waste materials, such as digestate from biogas plants and hydroponic waste solutions, through microbial immobilization during composting. This process co-composts liquid waste, which in the case of digestate is stored in drying lagoons and it is characterized by high ammonia volatilization rates, with dry green waste, which would otherwise be hardly composted due to its high carbon-to-nitrogen ratio.

Innovative features

Convergence of these two waste streams has not been attempted yet on an industrial scale. By soaking green waste in liquid digestate, the technology could solve problems in the composting of dry and high C/N ratio materials and at the same time prevent N loss by immobilizing it in an organic form or stabilizing it the compost matrix.

 

Type of contribution

This technology reduces N losses from liquid waste streams and gives the opportunity for the use of this N by plants through the production of an N rich compost. Additionally, it lowers the release of ammonia in the atmosphere, which contributes to the production of aerosols (GHG) and may cause health problems to humans and animals.

Benefits for farmers, industry, and environment

Farmers benefit from improved soil fertility, productivity and health by acquiring stable, high N content organic fertilizers. Convergence with digestate waste streams enables composting units to better manage green waste. Environmentally, technology enables better nitrogen exploitation by reducing N losses, lowers ammonia and greenhouse gas emissions, and promotes the recycling of organic waste materials, supporting a circular economy in agriculture.

• Recovery of N and P from biogestates following pretreatments

 

Short Description of the technology

UNITO and NIBIO are developing a technology for recovering nitrogen (N) and phosphorus (P) from biomass waste, while improving the nutrient balance in the resulting organic fertilizer products. The innovation aims to improve the anaerobic digestion process, which converts cattle manure and slurry into biogas, a green energy source, and digestate, a byproduct rich in plant nutrients. UNITO and NIBIO focus on the precipitation of struvite, a mineral with composition NH₄MgPO₄·6H₂O that can be used as slow-release fertilizer, from the digestate liquid fraction. When the digestate is separated into solid and liquid fractions, N tends to concentrate in the liquid and P to accumulate in the solid, leading to an unbalance N:P ratio in the final products. This technology involves pre-treating cattle manure and slurry before anaerobic digestion to solubilize P and promote its recovery from the digestate liquid fraction in form of struvite.

Innovative Features

Various pre-treatments can be applied on the starting substrate before anaerobic digestion, to enhance biogas production. The innovation proposed by this technology is the combination of a physical process, called hydrodynamic cavitation, with the application of enzymes targeting organic matter degradation and P hydrolysis. Hydrodynamic cavitation is a physical process where the substrate is passed through a narrow channel or rotated, creating bubbles that implode generating high temperature and pressure, which can break cells and degrade organic matter. For the enzymatic pre-treatments, we selected a commercial blend of cellulase, hemicellulases and protease (called USC4), along with alkaline phosphatase catalyzing phosphate hydrolysis, and phytase targeting the hydrolysis of inositol hexaphosphates, organic forms of P produced by plants and microorganisms. NIBIO is using a chemical approach to solubilize P, such as formic acid. The combination of different pre-treatments has a double purpose: enhancing the degradation of organic matter to increase energy production during anaerobic digestion, and solubilizing phosphorus to facilitate its recovery through struvite precipitation from the digestate liquid fraction.

This technology will not only enable the recovery of P and N in the form of a marketable product but will also contribute to balance the nutrient composition in both the liquid and solid fractions of the digestate. Currently, the two fractions exhibit an imbalanced N:P ratio, with excess nitrogen in the liquid and phosphorus surplus in the solid. Through pre-treatment processes, phosphorus can be transferred from the solid to the liquid fraction, thereby adjusting the N:P ratio in both products and enhancing their effectiveness as organic fertilizers.

Type of Contribution

On the one hand, the combination of physical and enzymatic processes for the livestock waste pre-treatment resulted being efficient in solubilizing P and moving it from the solid to the liquid fraction of digestate. Hydrodynamic cavitation, along with USC4 and phytase, allowed an increase of 29% total P and 42% soluble P in the digestate liquid fraction as compared to the untreated material. On the other hand, struvite precipitation enabled recovering 66% ammonium, 92% phosphate and 99% magnesium from the digestate liquid fraction. The nutrients were collected in the form of a stable mineral that can be used as slow-release fertilizer, able to delay the release of P in aqueous solution in comparison with most common mineral fertilizers.

Not only does this technology allows to recycle nutrients from a liquid biomass waste, but it also promotes the correction of the nutrient balance in the digestate solid fraction, generally used as soil amendment. Solubilizing and moving P to the liquid fraction is an efficient method to decrease the P content in the solid fraction and make this waste material more suitable for the application in soil, reducing the need for the addition of mineral N fertilizers. This work will hence contribute to recycling nitrogen and phosphorous from widely available organic waste, and to reducing the losses of these nutrients in the environment.

Benefits for farmers, the industry, and the environment

This technology aims at producing organic fertilizers from the liquid and solid fractions of anaerobic digestate with an N:P ratio optimized to match the needs of the crop. The excess nutrients will be separated and made usable to produce struvite, a high-quality mineral fertilizer. The objectives of the project are both to recover nutrients from an abundant waste stream, and to optimize nutrient plant uptake minimizing N and P losses in soil and via volatilization. This work will hence be beneficial for both industrial partners and farmers and will contribute to environmental preservation.

• Recovery of N from biogestates via ammonium stripping

 

Short Description of the technology

NIBIO is developing a technology for recovering nitrogen (N) from biomass waste, while improving the nutrient balance in the resulting organic fertilizer products. The innovation aims to improve the anaerobic digestion process, which converts cattle manure and slurry into biogas, a green energy source, and digestate, a byproduct rich in plant nutrients. UNITO and NIBIO focus on the precipitation of struvite, a mineral with composition NH₄MgPO₄·6H₂O that can be used as slow-release fertilizer, from the digestate liquid fraction. When the digestate is separated into solid and liquid fractions, N tends to concentrate in the liquid and P to accumulate in the solid, leading to an unbalance N:P ratio in the final products. This technology involves pre-treating cattle manure and slurry before anaerobic digestion to solubilize P and promote its recovery from the digestate liquid fraction in form of struvite.

Innovative Features

UNITO’s and NIBIO’s work focuses on improving the N:P ratio and enhancing the recovery of N and P from liquid organic waste products through various pre-treatments: enzymatic (using phytase, phosphatase, and USC4, a mixture of cellulase, hemicelluloses, and pectinases), physical (hydrodynamic cavitation), and chemical (formic acid) to solubilize P, facilitating its recovery as struvite. Meanwhile, low-temperature vacuum ammonium stripping can be used to refine fertilization (ammonium sulphate), pH adjustment and scrubbing products (ammonium water) at the local farm level.

Type of Contribution

The co-composting of liquid and green organic waste, struvite precipitation, and ammonium stripping technologies contribute by broadening knowledge of the utilization of N and P-recovery technologies, reducing pollution and GHG emissions from liquid waste streams in agriculture, and producing N-rich compost, fertilizers, and pH-regulator products.

Benefits for farmers, the industry, and the environment

These innovative technologies for N and P recovery will benefit farmers, greenhouse growers, waste treatment facilities, and regulators with new data on potential N and P reductions and the recovery of nutrient-rich fractions as fertilization and pH-regulator products from liquid organic waste. Implementation of these technologies may lead to higher recovery of N and P, thereby reducing environmental pollution. Integration of these technologies will improve the circularity of agriculture and reduce reliance on synthetic fertilizers.