Evaluation of Environmental Impact for Tofu Production on the Basis of Cumulative CO₂ Emission Unit

Abstract

A life cycle inventory analysis was conducted based on the material balance between the low materials and the products and as well as for the utilities including electricity, gas, fuel oils and water in a "tofu" production factory and the value of cumulative CO₂ emission unit with respect to unit ton of the produced tofu was evaluated. Then the effects of the treatment methods of the bean curd refuse, including burning, drying for feed, carbonization and composting on the cumulative CO₂ emission unit for the product tofu were evaluated. Furthermore, the effect of recovery of energy from the bean curd refuse via methane fermentation with a fuel cell power generator on the cumulative CO₂ emission unit for the tofu was also evaluated. It was found that the value of the cumulative CO₂ emission unit for the product tofu is 918.0 [kg-CO₂/t]. The increase of the cumulative CO₂ emission unit due to the treatment of the bean curd refuse is in order as; carbonization>burning>drying by waste heat>composting. The combustion of bean curd refuse with a high water content needs subsidiary fuel such as heavy oil and increases the cumulative CO₂ emission unit as well as drying. It is also found that the recovered energy using a fuel cell associated with methane fermentation of bean curd refuse amounts to a value more than 90 % of the spent total electric power and greatly helps to save the cumulative CO₂ emission unit.