Natural Resources Institute Finland (Luke), Production Systems, Latokartanonkaari 9, FI-00791 Helsinki, Finland.
Åbo Akademi University, Faculty of Science and Engineering, Laboratory of Process and Systems Engineering, Henrikinkatu 2, 20500 Turku, Finland.
Waste Manag. 2022 Jul 15;149:105-113. doi: 10.1016/j.wasman.2022.06.013. Epub 2022 Jun 18.
Nutrients can be circulated back to agriculture from waste streams through anaerobic digestion and digestate processing. Digestate processing, however, is making slow progress as circulated nutrient products have not been cost competitive compared to fossil fertilizers and not designed from the farmer's perspective to truly match with the regional nutrient need. In this study, the aim is to assess apply mathematical optimization to the design of a cost-optimal processing route for a biogas plant's digestate to produce fertilizer products based on specified regional needs. Another aim is to analyze whether such a cost-optimal solution can fully exploit the nutrient recycling potential, that is, the efficiency of such a solution in returning nutrients to agriculture. The results indicate that mathematical optimization allows the design of a cost-optimal digestate production routes based on the region's nutrient need and characteristics. The true cost optimum was found for a design combining three processing technologies and producing four nutrient products, which when mixed, would fulfil farmer's fertilization needs. However, there seems to be a conflict between an optimal economic design and a full exploitation of recycling potential as only 25% of the digestate's phosphorus was utilized within the case region. This is because only 29% of the digestate mass was used and processed as fertilizer, as the concentration of required nutrients was deemed too low for economic use. The proposed mathematical model could be implemented as tool to assist in biogas plant investment decisions.
养分可以通过厌氧消化和消化物处理从废物流回农业。然而，消化物处理进展缓慢，因为循环养分产品在成本上没有竞争力，与化石肥料相比，而且从农民的角度来看，也没有设计成真正与区域养分需求相匹配。在这项研究中，目的是评估应用数学优化来设计基于特定区域需求的沼气厂消化物生产肥料产品的成本最优处理路线。另一个目的是分析这样的成本最优解决方案是否可以充分利用养分回收潜力，即该解决方案将养分返回农业的效率。结果表明，数学优化允许根据区域养分需求和特性设计成本最优的消化物生产路线。发现了真正的成本最优解，设计方案结合了三种加工技术，生产四种养分产品，混合后可以满足农民的施肥需求。然而，在最优经济设计和充分利用回收潜力之间似乎存在冲突，因为只有 25%的磷被消化物在案例地区回收利用。这是因为只有 29%的消化物被用作肥料，因为所需养分的浓度被认为太低，不适合经济使用。所提出的数学模型可以作为一种工具来协助沼气厂投资决策。
