Methane Production and Nitrogen Mineralization in Paddy Soil Treated with Low-temperature Anaerobically Digested Sludge

Abstract

Methane fermentation under lower temperature conditions than normal (35 °C) and the use of digested sludge as a fertilizer are promising as an energy efficiency improvement technology. However, there is little information available on the influence of digestion under low temperature condition on the compositions and characteristics of sludge as a fertilizer. In this study, we conducted incubation testing to examine the characteristics of methane production and nitrogen mineralization in paddy soil treated with the low-temperature anaerobically digested sludge.

Relatively more methane was produced in soil treated with sludge digested at 15 °C, because organic matter that is not decomposed under anaerobic digestion is used as a substrate for methane production in soil. On the other hand, little methane production was observed in soil treated with sludge digested at more than 25 °C. Moreover, only a small amount of ammonium nitrogen (3 to 13%) was released from anaerobically digested sludge after application under all low temperature conditions. Therefore, an appropriate rate of application of anaerobically digested sludge can be determined based on the ammonium nitrogen in the sludge.