ABSTRACT
The contributing population and the level of sludge production is often not accurately known because census data and drainage areas do not coincide and a large proportion of the population often commute to work or school outside the area. Thermophilic aerobic digestion (TAD) is considered to be much more flexible than anaerobic digestion. TAD produces sludge with good consolidation properties, better than those of anaerobically digested sludge. Digestion does not seem to have any adverse effect on the fertiliser properties of sludge. Aerobic sludge digestion in small waste water treatment works has been studied to optimise the operational conditions at lower temperatures. Sludge treatment wetlands have been used in Europe for sludge dewatering and stabilisation since the late 1980s. Sludge is spread directly into the basins from the aeration tanks or is homogenised beforehand in a buffer tank prior to its discharge into the wetlands.
