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Summary The closing of material loops is a critical challenge in industrial ecology. It relies mainly on the utilization of recovered materials/parts/products in the original and principal production system while their original function is retained at the highest level possible. In this study, advanced loop‐closing systems for the recycling of end‐of‐life vehicles and electric household appliances are first designed in “Hyogo Eco‐town.” Second, a methodology for evaluating the eco‐efficiency of these systems is developed. Finally, the eco‐efficiency of the designed advanced loop‐closing strategies for the two products is evaluated, based on the results of materials flow analysis and life‐cycle assessment. The results show that, compared with conventional recycling systems, when an industrial complex and an advanced loop‐closing system for end‐of‐life vehicles are established, the total economic value increases by 114% and the eco‐efficiency in terms of the amount of direct material input is improved by 57%. This system permits the utilization of the by‐products, wastes, and recovered materials that originate from other industrial sectors as input to production activities. In the case of end‐of‐life electric household appliances, an advanced loop‐closing strategy to lengthen the product life with parts reuse improves the eco‐efficiency in terms of carbon dioxide (CO2) emissions by 4% compared with the conventional replacement of the appliance with a new product along with the material recycling option.

Ammonia has been proposed as a promising energy carrier and is expected to play a resilient and sustainable role in future energy scenarios. Energy systems critically impact biogeological carbon and nitrogen cycles. Thus, carbon and nitrogen footprints are two important indicators of sustainability for energy systems. In the present study, we explored the optimal supply pathway and identified impact hotspots by investigating the carbon footprint associated with greenhouse gas emissions and the nitrogen footprint associated with reactive nitrogen emissions from the ammonia energy system. Four scenarios (Japan to Japan, JP–JP; Australia to Japan, AU–JP; Chile to Japan, CL–JP; Saudi Arabia to Japan, SA–JP) were modeled based on international relations and energy distribution between these countries. Compared with the Japan electricity mix, it is a win–win situation under scenario JP–JP from the perspective of carbon and nitrogen footprints, while trade-offs were identified under the scenarios AU–JP and CL–JP. SA–JP performed worse in both carbon and nitrogen footprints. Improvement of key processes is critical to mitigate greenhouse gas and reactive nitrogen emissions. When the efficiency of partial oxidation increased by 25% in SA–JP, the carbon and nitrogen footprint decreased by 17% and 8%, respectively. This evaluation relayed information on the sustainable use of ammonia as an energy carrier by examining the relative impacts on both carbon and nitrogen footprints.

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