高効率エネルギー回収を目的とした高濃度下水汚泥と稲わらの混合嫌気性消化に関する研究

摘要

エネルギー回収の効率化を図れることから，下水汚泥の高濃度消化が注目されている．本研究では， 実験室規模で高濃度の下水汚泥（TS：4.8％）と稲わらの混合嫌気性消化の連続実験を中温条件（36℃）および高温条件（55℃）で実施した．下水汚泥と稲わらの投入比はTS基準で1：0.5とした．稲わらの前処理法として，約5mmのサイズに粉砕したのち，蒸留水に浸漬させる水処理系と．酵素溶液中に浸漬させる酵素処理系の2条件を設定し，その影響を比較した．その結果，水処理系よりも酵素処理系において高い固形分分解率およびメタン転換率が得られた．また，高温消化の方が中温消化よりも高い固形分分解率およびメタン転換率を示した．しかし，消化汚泥の溶解性CODやアンモニア濃度は中温消化よりも高温消化において高かった．消化汚泥の脱水性も高温消化汚泥の方が低かった．本研究では，回収エネルギー（メタン）を投入エネルギーと比較するシステムのエネルギー評価も行った．%Anaerobic digestion of high concentrations of sewage sludge has been paid attention for improving the energy balance in sewage sludge treatment system. Laboratory-scale mesophilic (36℃) and thermophilic (55℃) digesters were operated to investigate the performance of anaerobic co-digestion of high concentration (TS: 4.8%) sewage sludge and rice straw in this study. The feeding ratio of sewage sludge and rice straw was 1:0.5 based on TS. Two different rice straw pretreatment methods were compared; grinding (ca. 5mm) plus soaking in distilled water (water pretreatment), and grinding plus soaking in an enzyme solution (enzyme pretreatment). As the results, both TS degradation efficiency and methane conversion efficiency were improved by using enzyme pretreatment. Higher TS degradation and methane conversion were observed in thermophilic digestion than in mesophilic digestion. However, soluble COD and ammonia concentrations in thermophilic digested sludge were higher than those in mesophilic digested sludge. Lower sludge dewaterability was also observed in thermophilic digestion. To assess the energy balance of the digestion system, the energy output (produced methane) was compared with the total input in this study.