1994 Volume 23 Issue 10 Pages 621-629
Anaerobic methane fermentation of “okara, ” the tohu refuse, including cellulosic biomass components was investigated in a 500ml reactor on the basis of fed-batch operation. Effects of pre-treatments of okara on the methane production efficiency were examined, using three okara suspensions as substrates, which were those untreated, irradiated with supersonic waves and boiled with NaOH in an alkaline solution.
The irradiation of okara suspension with supersonic waves or boiling of it with NaOH in an alkaline solution was significantly effective to dissolve soluble proteins in the okara. It was shown that the pre-treatment of okara suspension by irradiation with supersonic waves is fairly well to improve the methane yield and the COD removal in the methane fermentation. A maximum conversion efficiency of 93% to the ideal methane yield could be attained for the okara suspension irradiated by supersonic waves. The pre-treatment of okara by boiling with NaOH, however, did not lead to any improvement of methane production efficiency.
The methane fermentation using the suspension of untreated okara as the substrate was successfully conducted at an influent substrate loading up to 2.5 g-COD·l-1·d-1under the condition that the COD removal at a value greater than about 90% was maintained. A maximum conversion efficiency of 85% to the ideal methane yield could be attained for the untreated okara.
