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The purpose of the paper is to determine the environmentally safe and economically feasible technology of biofertilizer production from the digestate including dewatering process. Methodological basis is based on the systematic approach to the determination of factors effected on the distribution of nutrients and pollutants between liquidand solid fractions after digestate separation. We studied modern technologies aimed at dewatering the digestateand reduction of its volume, showed their effectiveness. These technologies allow expanding the opportunities forcommercialization of the digestate, increasing the cost of its transportation and application to the soil instead ofcomplex fertilizers, using some valuable products. The results of the study showed that the ecological quality ofthe digestate is the highest as well as co-digested thermally pre-treated feedstock is used for solid-liquid separationin centrifuge with polymer addition as post-treatment approach to the flocculation. In order to increase efficiencyof biofertilizer application the technological scheme of production process of granular fertilizers from digestatewas proposed. Special feature of this scheme is in the use of phosphogypsum binder for the production of organomineral fertilizer that contributes phosphogypsum recycling in the waste management system.

The study aims to define the potential and technological aspects of the digestate treatment for its application as a biofertilizer. Life cycle assessment methodology was used in terms of digestate quality management. The potential of nutrients, organic carbon, and useful microelements in the digestate allows for its consideration as a mineral fertilizer substitute and soil improver. The valorization of digestate as fertilizer requires quality management and quality control. Based on the research focus, the successful soil application of digestate post-treatment technologies was analyzed. Among the different commercial options for digestate treatment and nutrient recovery, the most relevant are drying, struvite precipitation, stripping, evaporation, and membranes technology. Comparing the physical and chemical properties of the whole digestate, separated liquid, and solid liquor fractions showed that in the case of soil application of granular fertilizer, nutrients from the digestate are released more slowly than digestate application without granulation. However, realizing this potential in an economically feasible way requires improving the quality of digestate products through appropriate technologies and quality control of digestate products. To support the manufacture of quality digestate across Europe, the European Compost Network developed a concept for a pan-European quality assurance scheme.

In this paper, we performed technology assessment and systems analysis of primary digestate processing techniques to provide a comprehensive analysis of their environmental and cost performance. We compiled more than 100 observations from large-scale biogas plants and considered digestate based on manure, crops and agro-wastes, and food waste under the geographical contexts of Sweden and Belgium. Centrifuge, screw press, and rotary drum were identified as suitable primary processing techniques. We analyzed the climate impact, energy use, and operational cost of digestate management under these scenarios: no processing, partial processing (solid-liquid separation) and full processing (solid-liquid separation followed by ammonia stripping). As expected, the suitable digestate processing varied with the context, transport was often the most critical cost factor, and emissions from storage reduced the climate savings from the use of biofertilizers. However, treating liquid fraction became a main contributor to cost and climate impact under the Belgian conditions. Consequently, the possibility for local application of liquid fraction as biofertilizer could prevent costs and impacts associated with its further treatment. The main novelty of this work is in its integrative and comprehensive approach toward the choices and impacts of primary processing of digestate. We tried to bridge many individual case studies, drew from experiences of biogas plants in different geographical contexts, assessed suitable processing techniques for different digestate types, and analyzed the environmental impacts and cost of digestate management from a life cycle perspective. We believe that such integrated approaches would help decision-making for increased sustainability of the biogas sector.