Kiyohiko Nakasaki*, Atsushi Watanabe*, Kenichiro Ssuehara*, Hiroshi Kubota**

*Department of Chemical Engineering, Faculty of Engineering, Shizuoka University
**Hamamatsu Polytechnic College
(3-5-1, Shirokita, Hamamastu, Shizuoka 432 Japan)

Abstract

Effects of seeding on the thermophilic composting of organic waste were examined by measuring the changes in CO2 evolution rate, conversion of carbon, pH value, and microbial succession in the composting reaction using a commercial dog's food as raw material. Time courses of the above values for six experimental runs inoculated with different seeding materials which contain different kinds and concentration of microorganisms were grouped into two substantially different patterns. One was of a successful composting, in which the CO2 evolution rate and conversion of carbon were large and the pH value gradually increased to around 8.5 with the progress of reaction. The other was of unsuccessful composting, where the pH value dropped from the initial level of 7 to a low level of 5 at the early stage of reaction and never rose up. The organic matter decomposition was discontinued at a low level of carbon conversion because of inhibitory effect on the microbial growth at the low pH level. In such case, however, the organic matter decomposition could be promoted by adjusting the initial pH value at the higher level in order to avoid the pH value dropping to the low level. The analysis of microbial succession indicated that the kind of microorganisms on seeding was more important than the total number of microorganisms for successful composting.

Key words: waste treatment, composting rate, organic matter decomposition, seeding effect, microorganisms