Sludge components

Sludge treament

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.

Bacteria
Bacteria are simple, colourless, onecelled plants that use soluble food and are capable of self reproduction without sunlight. As decomposers they fill an indispensable ecological role of decaying organic matter in stabilizing organic wastes in treatment plants. They are responsible for activated sludge growing in domestic wastewater treatment. A wide variety of bacteria can be found in a sludge flake.

	Spirillum
	A genus of common motile microorganisms (Spirobacteria) having the form of spiral-shaped filaments.
	Vitreoscilla
	A genus of gram-negative, aerobic or microaerophilic, colorless filaments. It is motile by gliding. It is strictly aerobic and produces a homodimeric bacterial hemoglobin, especially under oxygen-limited growth conditions.
	Sphaerotilus
	A sheathed filamentous bacterium that exhibits a characteristic "false" branching. Once, incorrectly thought to be responsible for the majority of filamentous bulking episodes S. natans has now been recognized as only infrequently encountered. Associated with nutrient limitation, the organism is believed to not occur in plants with anoxic zones.
	Beggiatoa
	Are large, colourless sulphur bacteria that include both colonial and filamentous forms, and they can dominate microbial communities associated with marine sediments. Beggiatoa spp. appears white due to the reflection of light against their sulfur inclusions. Their size range in size from a few millimeters to several meters.
	Zoogloea
	A colony or mass of bacteria imbedded in a viscous gelatinous substance. The zoogloea is characteristic of a transitory stage through which rapidly multiplying bacteria pass in the course of their evolution.

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.

Paramecium

Rotifer

Nematode

Ciliate

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:

Stabilisation
Thickening
Dewatering
Sludge drying
Copious growth of filamentous organisms - problems and solutions
Filter presses for sludge treatment