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Transformation of biogas digestates to a fertilizer which reduce N2O emissions.

Alternative title: Transformering av biogass digestater til gjødsler som reduserer N2O emisjon.

Awarded: NOK 6.6 mill.

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Project Period:

2022 - 2025

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NMBU Nitrogen group, together with Norway's largest wastewater treatment plant, Veas, has developed and a promising technological platform that addresses the emissions of greenhouse gas nitrous oxide (N2O) from soil. These emissions constitute 1/3 of the total climate forcing of food production and must be reduced if we are to achieve the goals set in the Paris Agreement. The idea is simple: agricultural soil is supplied with large amounts of organic material in the form of plant residues, livestock manure, and sludge from treatment plants. An increasing proportion of this material flow now goes via biogas plants before the residual product is returned to soil as a fertilizer. This gives us a unique opportunity to cultivate large amounts of nitrous oxide reducing bacteria in the bio-residue, utilizing it as a growth substrate and vector for these organisms. We have searched for "wild" N2O-reducing bacteria in soil and bio-residue by first enriching them under special conditions, identifying them using genetic methods, and finally isolating individual organisms. The work has been successful and has resulted in several isolated organisms shown to have very beneficial properties; they grow well in bio-residue and at the same time survive in bio-fertilized soil where they virtually eliminate N2O emissions! This development project will expand upon our recent work and aims to develop robust routines for the production of nitrous oxide reducing fertilizers and increase the technology readiness level (TRL) by implementing the technology at the Veas WWTP. We will also verify that the concept is transferrable to biogas plants that treat other types of organic waste, allowing them to offer the farmer a fertilizer product that significantly reduces N2O emissions.

Nitrous oxide (N2O) emissions from soils make up ~1/3 of the climate forcing from food production and mitigation beyond that achieved by good nitrogen management practices is needed if we are to limit global warming to 2 °C as set in the Paris Agreement. Recent cutting-edge research conducted by the NMBU-Nitrogen group in collaboration with VEAS has addressed this issue by developing a technology that utilizes the residue (digestate) from biogas production, used as organic fertilizers in agriculture, as growth substrate and vector for specially selected nitrous oxide reducing bacteria (NRB) to agricultural soil. The novelties of this technology are the simplicity of NRB cultivation in digestates, and the low marginal costs of integrating this technology in the existing material pipeline of organic wastes to the soil. This makes the technology a feasible and cost-effective approach to achieving substantial reductions of N2O emissions from soils. This project will pave the way for the implementation of the technology within the VEAS plants existing biogas production line by increasing the TRL from 3-4 to 5-6. An implementation will require upscaling, which is far from trivial, and the project aims to: increase the robustness of the technology in terms of NRB-survivability (shelf life), and to validate the technology in several different soil types. The potential of the invention will increase with time as an increasing amount of agricultural waste (manure, food waste, and crop residues) is used for biogas production. The currently isolated NRBs have only been tested in municipal wastewater sludge digestate, but we expect that these bacteria can grow in digestates from animal manure and urban wastes. This cannot be taken for granted, however, and will need to be tested: a continuation of our search for suitable NRB’s is now a relatively simple task since the pioneering work on enrichment, meta-omics, and isolation is already done.

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