Akinori Katou* and Tatsuya Noike**

* Environmental Research Laboratory, Sumitomo Heavy Industries, Ltd
** Dept. of Civil Engineering, Tohoku University

+ Correspondence should be addressed to Katou Akinori:
(1-15 Kuryogutsumi, Hiratsuka-city 254-0801 Japan)

Abstract

Large amounts of various organic wastes are discharged from agricultural and livestock industries. We investigated the waste treatment process using anaerobic digestion system in order to retrieve methane gas energy. Some wastes were found to be suitable for anaerobic treatment because of high Methane gas Production Ratio (MPR) . The MPR levels (Nml-CH4/gVS) were as follows; pig manure 236, cattle manure 158, poultry manure 320, internal pig organs 705, rice straw 264 and pressed oranges 536. It was found that rice straw and pressed oranges were particularly suitable for energy recovery during the winter season. In order to asess the economic feasibility, we conducted a case study of anaerobic digestion which treated pig manure (35,000 heads/d), cattle manure (1,500 heads/d), internal pig organs (4.2 tons/d) and pressed oranges (30 tons/d) .

The results indicated that the total methane gas production was 8,400 Nm3/d and excess methane gas was 6,400 Nm3/d which were measurements available without heating the anaerobic digestion process. Other outputs from the system were supernatant liquor (300m3/d) and digested dewatered sludge (60tons/d) . The supernatant liquor had to be purified further by nitrification and denitrification processes due to the high concentration of ammonium. The supernatant liquor when used in part was found to be an effective liquid fertilizer. The digested sludge was also found to be useful as a fertilizer.

Key words: agricultural waste, anaerobic digestion, methane gas, pig manure, cattle manure