Fixation of nutrient elements in digestate

The main objective is to produce high quality soil amendments and plant fertilizers from digestate by introducing advanced efficient separation technology. To achive this goal, the main foci are: 1) To develop post treatment separation technology to disti nguish between dissolved and suspended organic matter in the digestate and the removal efficiency with respect to phosphorus. 2) To develop post treatment separation technology to remove water dissolved plant nutrients(ammonia and potassium)from the water phase. 3) To optimize the organic fertilizer composition (NPK) and plant nutrient availability in the digestate based fertilizers. Several physical and chemical conditioners have been tested in a screening phase. The ones that show an interesting and suitable behavior for dewatering were the diatomite-bentonite materials (from Republic of Armenia) treated with water glass. The chemical conditioner for enhancing flocculation and a favorable filtration rate was ZETAG 9014 (polymeric cationic polyacryla mide) which is commonly used in the bio-gas plants in Norway. An optimization study of the dewatering process in a laboratory scale was carried out in order to decrease the use of the polymer as much as possible. In parallel, a study of the suspension of ZETAG 9014 in water in a broad range of pH was done from a turbidity and particle size perspective. Several acids and bases have been tested to understand the behavior of the polymer and its changes in the structure with the pH. This aspect is of spec ial interest due to the fact that the polymer contributes to the turbidity of the filtrate in the dewatering process of the ADR. SEM, XRD and spectrophotometric methods have been used to study clinoptilolite and its sorption properties. Studies of ammonium sorption were conducted using Armenian natural zeolite - clinoptilolite and synthetic ammonia solution. Four samples of clinoptilolites were studied, which were activated in different ways (initial, Ca2+ -form, H+ -form and NH4+ -form). In additi on, the influence of particle size on the adsorption properties has been studied. During the last phase of the project, several Norwegian local materials have been tested, with promising results so far.

The proposed project is an interdisciplinary collaboration project between the bio-energy industries, the wastewater treatment industry, bio-energy technology industries, organic fertilizer industry and plant-, soil-, fertiliser-, chemistry- and technolog y researcher from the institute and university sector. The project contributes to fulfil the Norwegian political aim to utilise 30 % of the manure and organic wastes for biogas production, focusing on sustainable use of the digestate from large biogas pla nts in agricultural production. Recyling of plant nutrients in the digestate to agricultural production on large biogas plants is a major challenge because of large volumes with low dry matter content. To reduce the transport of the digestate, the dissol ved and suspended plant nutrients can be removed by introducing advanced efficient separation technology to separate the solid and liquid fractions of the digestate. The aim of the proposed project is to produce high quality organic fertilisers from diges tate by developing post treatment separation technology to distinguish between dissolved and suspended organic matter, developing post treatment technology to remove the dissolved plant nutrients ammonia and potassium, and to optimise the organic fertiliz er composition to obtain optimal plant response and high plant nutrient availability. The main challenges in the project is to use flocculants, a filtration technology and absorbents with a high nutrient removal efficiency and which are acceptable for bei ng used as fertiliser in agricultural production. The project is therefore a success if the separation technology concentrates more than 80 % of nitrogen, phosphorous and potassium (K) in a solid phase of digestate and is easily available for plant uptake and acceptable as fertilizers in agriculture, and if the nutrient concentration in the liquid phase of digestate is reduced to a level acceptable for re-use in biogas production.