大学キャンパスにおける有機性廃棄物の学内循環システムの導入可能性検討：北海道大学をケーススタディとして

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Background Aim and Scope. Hokkaido University is one of the largest general business institutions in Hokkaido Prefecture, and is now socially required to reduce its greenhouse gas (GHG) emission such as CO₂ and N₂O on campus. The campus can be regarded as a miniature town, and several trial experiments and measures have been applied to the campus to reduce environmental burdens including GHG emission. Such activities are called “Sustainable campus activities”, and have been implemented in many universities all over the world recently. Hokkaido University is now trying to establish a recycling system of organic wastes on campus. This study aims to examine the possibility of introducing the recycling system, by assessing the effects in terms of GHG reduction and economic effects.
Material and Methods. To figure out the current status of organic wastes on campus, we came in for an interview to officers in Hokkaido University and the CO-OP. The current organic waste management on campus was clarified by the interview. For a comparative study to the current system of organic waste treatment, two new recycling systems of organic wastes were assumed in this study. One of the new systems is that in which all the leftover food from the university cafeterias and hospitals is assumed to be composted and all the dead and pruned branches are assumed to be chopped and sheeted on trails on campus (Scenario 1). In the other new scenario (Scenario 2), all the dead and pruned branches are assumed to be chopped and be utilized for fuel of wooden chip stoves as alternatives of part of the oil stoves on campus, while the leftover food is assumed to be treated in the same way as in Scenario 1. The Life Cycle Assessment was applied to the current system and the two new scenarios to examine the most adequate recycling system of organic wastes on campus, by comparing the GHG reduction as the representative of the environmental effects. Similar assessment was also performed to examine the economic effects of introducing the new recycling systems.
Results and Discussion. The effect of GHG reduction on campus by Scenario 1 and 2 was estimated to be 63 t-CO₂/year and 161 t-CO₂/year, respectively, compared to the current recycling system. This means that both of the scenarios can contribute to reduce GHG reduction on campus, and the effect is especially prominent in Scenario 2 by replacing partly oil stoves with wood chip stoves. The initial cost, running cost, and income by establishing Scenario 1 was estimated to be 37,210,900 yen, 934,000 yen/year, and 2,150,000 yen/year, respectively. Similarly, the costs and income for Scenario 2 was estimated to be 61,210,900 yen, 934,000 yen/year, and 4,911,200 yen/year, respectively. This means that the initial and running costs can be paid off in 31 years and 15 years for Scenario 1 and 2, respectively.
Conclusions. While this study demonstrates that the two new recycling systems of organic wastes are both effective in GHG reduction on campus, the economic effect of introducing the new systems is still controversial. If we assume that the general durable years of the facilities introduced in the new systems are 20 years or around, Scenario 2 is considered to be worth being introduced with regard to both environmental and economic effects. Moreover, Scenario 2 will be economically more effective in future because oil prices are supposed to keep rising. The new recycling systems can also lead to more job opportunities on campus. Such results are considered to be of some help for local municipalities in Hokkaido Prefecture in a cold district and with a large amount of biomass to design future policy making for balancing environmental conservation and regional vitalization.