Biodegradability and change of physical characteristics of particles during anaerobic digestion of domestic sewage

At the high-rate anaerobic treatment of domestic sewage, both biological an d physical processes play an important role. Therefore, the anaerobic biode gradability of raw, paper-filtered and membrane-filtered sewage and black w ater has been investigated in batch experiments. Additionally, the effect o f anaerobic digestion on physical characteristics, like particle size, surf ace tension and zetapotential, of the present particles is studied. The bio degradability of domestic sewage and black water at 30 degreesC is almost s imilar (71-74%). Moreover, a high methanogenesis of the colloidal fraction in domestic sewage (86 +/- 3%) is achieved, showing that the low removal of colloidal particles in continuous high-rate anaerobic reactors is due to l ow physical removal rather than biodegradability. The lowest biodegradabili ty is demonstrated for the disserved fraction (62%). The results show that after anaerobic digestion the average radius of particles with diameter <4. 4 and <0.45 mum increased for domestic sewage, while it decreased for black water. Part of the surface-active components in domestic sewage is not bio degraded during anaerobic batch digestion, as indicated by the development of the surface tension. The negative seta-potential of all particles hardly changes during digestion, showing that colloidal interactions were not aff ected by anaerobic digestion. (C) 2001 Elsevier Science Ltd. All rights res erved.