Bacterial Populations and Degradation of Sludge Components in a Modified Two-Series Digestion Process Including Sludge Liquefaction

抄録

Distributions of bacterial populations and degradation of sewage sludge components in a two-series digestion process with liquefaction of thickened surplus sludge (hereinafter called the modified two-series digestion) and in a conventional mono-phase digestion (hereinafter called the conventional digestion) process were investigated. A high level of 2.7 × 10¹⁰ MPN/ml acidogenic bacteria in the thermophilic liquefaction reactor of the modified two-series digestion was observed at a volatile suspended solid (VSS) volumetric loading rate of 14 g/l⋅d. This count was three orders of magnitude higher than that of all other anaerobic bacteria enumerated in the reactor. At a VSS loading rate of 6 g/l⋅d, the levels of hydrogenotrophic and aceticlastic methanogens in the mesophilic digestor of the modified two-series digestion were 1.2 × 10⁸ and 1.9 × 10⁷ MPN/ml, respectively, which were 3 and 1.5 times higher than those in the reactor of the conventional digestion. In the modified two-series digestion, the degradation efficiencies of lipid, protein, carbohydrate and lignin in the sludge were 69.8%, 57.7%, 46.8% and 24.5%, respectively, at a VSS loading rate of 3 g/l⋅d. These values were over 10% higher than those of the conventional digestion at the same loading rate, except for lignin which was only 5% higher. The specific resistances of sludges after treatment by the modified two-series and conventional digestions were 4.58 × 10¹¹ m/kg and 6.15 × 10¹¹ m/kg, respectively. The modified two-series digestion process demonstrated performance superior to the conventional digestion process.