Abstract
A circular biobased economy must be able to sustainably manage multiple resources simultaneously. Nutrient (nitrogen, phosphorus, and potassium) recycling and renewable energy production (biogas) can be compatible practices but require substantial transport of heavy organic waste. We combine a spatial optimization model and Life Cycle Assessment (LCA) to explore how Sweden could maximize its use of excreta resources. We use 10×10 km2 resolution data on the location of animal and human excreta and crop demand and model both optimal biogas plant locations and transport of nutrients to and from these plants. Each type of biogas plant (given 4 realistic mixes of excreta) is then evaluated for global warming potential, primary energy use and financial resource costs. Moving excreta through biogas plants, as opposed to simply reapplying on fields, to meet crop nutrient demands comes at a similar cost but the climate and primary energy savings are substantial. As much as 91% of phosphorus and 44% of nitrogen crop demand could be met via optimally transported excreta and the country would avoid about 1 450 kt of CO2-eq, save 3.6 TWh (13 000 tera-joules) of primary energy, and save 90 million euros per year. Substituting mineral fertilizers with recycled nutrients results in savings across all indicators, but the added energy and avoided greenhouse gas emissions associated with biogas production make a large difference in the attractiveness of nutrient recycling. Although the numeric values are theoretical, our results indicate that carefully coordinated and supported biogas production could help maximize multi-resource benefits.
Highlights
The UNs Sustainable Development Goals (SDGs) related to global food security, clean water and healthy aquatic ecosystems all demand that we change the way we manage natural resources, including nutri ents (Kanter and Brownlie, 2019), in modern society (Randers et al, 2019)
A large proportion of crop nutrient demand could be ful filled by recycling manure and sludge in Sweden, without transportation it is impossible to properly utilize this potential
The total supply of P was equivalent to 113% and the supply of K 142% of crop nutrient demand
Summary
The UNs Sustainable Development Goals (SDGs) related to global food security, clean water and healthy aquatic ecosystems all demand that we change the way we manage natural resources, including nutri ents (Kanter and Brownlie, 2019), in modern society (Randers et al, 2019). Each natural resource has its own particularities and implications for SDGs, three types of changes are often examined: 1) increased resource substitution, 2) increased efficiency, and 3) increased recycling as ways to decrease resource depletion and pollution. Nitrogen (N) and phosphorus (P) in particular require a redesign of waste management as losses to the environment have caused atmo spheric (N) and aquatic (N and P) pollution, while production of mineral fertilizers to supply these essential plant nutrients deplete fossil resources (Ibisch et al, 2016; Steffen et al, 2015). One major challenge is the distance between food and feed production and con sumption resulting in spatial concentrations of excreta and long trans port distances to fields where the nutrients are mostly needed Valuing more ben efits from reuse, such as energy production or mitigated pollution, could be a way of addressing this profitability gap
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