抄録
An environmental life cycle assessment (LCA) was applied to the treatment of inorganic waste water from a research institute by coagulation and flocculation. Three types of waste water was classified and treated in 2002. Global warming potential (GWP) resulting from their treatment was 782kg CO2-eq/m3 for waste water including fluoride, 150kg for the one including heavy metals and 19kg for scrubber waste water. They are greatly different from each other and also far larger than those for municipal waste water treatment that is around 0.2-2kg CO2-eq/m3.
In order to understand the implications of these data, a relationship between the water quality and GWP from treatment of the water was derived from the records of this facility. The result indicated that most of the GWP exhaustion can be contributed to the reinforced reagents addition and resultant sludge production owing to the high concentration of fluoride, mercury and arsenic, besides some disadvantage by treating a little quantity, around five to thirty m3 per week. In particular, treating fluoride produces a large amount of sludge, whose combustion produces a large amount of carbon dioxide.
Reagents production contributes most to global warming in treating waste water including heavy metals, while sludge treatment contributed most in treating fluoride or scrubber waste water. This difference was explained from the concentrations of three chemicals above using the relationship obtained here.
