上昇流嫌気性スラッジブランケット (UASB) 反応器におけるグラニュール汚泥の細胞外バイオポリマーとメタン生成活性の挙動

抄録

The influence of loading rate on the content of extracellular biopolymer (ECP) and the methanogenic activity of granular sludge developed in a UASB reactor were investigated by varying the influent strength stepwise from 1.0 g COD·l^-1 to 5.0 g COD·I^-1 at a HRTof 12 h for a period of 150 days. The ECP yield along sludge bed varied with loading rate, ranging from 37 to 57mg ECP·gVSS^-1. The size of the granules increased with the increasing sludge loading. Granules having larger size tend to accumulate at lower portion of sludge bed and possessed higher amount of carbohydrate in ECP. The ratio of protein to carbohydrate in ECP increased with the sludge bed height in the range from 0.7 to 2.1. The carbohydrate content in ECP seemed to be more significantly responsible for granulation, rather than the ECP yield and the protein content in ECP.
The dependence of methanogenic activity on granule size was assessed using sludge taken from both lower and upper portions of sludge bed at each loading. Hydrogen-utilizing methanogenic activity decreased consistently with granule size. In contrast, granules with medium size (1mm-2.5mm) exhibited higher activity both from acetate and from propionate, rather than those of small size (0.5mm-1mm) and of larger size (>2.5mm). These results indicate that an excessive maturation of granule size (above 2.5mm) is not favorable owing to the prevalence of substrate diffusional limitation. A sludge loading larger than 0.45kgCOD·kgVSS^-1 caused a shift in morphology of the predominant acetoclastic methanogen, Methanothrix spp. from a long filament to a short one composed of only a few cells.