The main characteristic of the activated sludge is the occurrence of microorganisms, which take up solved food over their body surface or a cell mouth thereby contributing to wastewater cleaning. The biocoenosis of the activated sludge gives information over the condition of the activated sludge and the cleaning achievement.
| Beside bacteria, a number of species of protozoa such as flagellate-, ciliated- and amoebae protozoa have been identified in activated sludge. Protozoa are single-celled organisms that can consume food such as bacteria and particulate matter. |
These organisms are partly on the activated sludge flakes. Other protozoa move lively on or between the activated sludge flakes. The nematodes or rotifers are ranked among the multi-cellular organisms.
The sludge abstracted after the wastewater treatment process contains in the unloaded stabilized condition:
Carbon (50-70 %),
Hydrogen (6,5-7,3 %),
Oxygen (21-24 %),
Nitrogen (15-18 %),
Phosphorus (1-1,5 %) and
Sulphur (0-2,4 %).
| Water is the main component of sludge. Its amount depend on the sludge sort (primary-, secondary or tertiary sludge) and the way of stabilisation (aerobic, anaerobic). Raw sludge has a water content of 93 % to 99 %. Therefore a dewatering (up to approx. 35 % dry substance content) or drying (to over 85 % dry substance content) can be necessary for a further utilization. |
The second main component is the dry substance, which is made up of organic and inorganic substances.
Beside the main parts, sludge contains a large variety of trace components that have been separated from the wastewater. Organic and inorganic trace elements, which have its origin in wastewater, are found enriched in the sludge.
More information about sludge treatment and reduction are on the following pages: