Introduction
The treatment and final disposal of the produced primary and secondary excess sludge takes up a significant part of the material- and financial resources of the waste water treatment plant. The excess sludge from an activated sludge process has three undesirable aspects:
- Biological instability: the excess sludge is putrescible due to the high fraction of biodegradable organic matter and enters into decomposition within hours after the interruption of aeration
- The hygienic quality of the excess sludge is very poor: a very large variety of viruses, bacteria and other pathogens (protozoa, amoebae, helminth eggs) are present
- The suspended solids concentration in the excess sludge is low: in the range of 3 to 50 g.l, depending on the origin of the sludge and on the type of solid-liquid separation process used, resulting in a large volume of excess sludge to be handled
The two main objectives of sludge treatment processes are therefore to:
-
Increase the concentration of solids, in order to reduce the excess sludge volume to be treated and disposed-of
-
Reduce the fraction of biodegradable matter and the pathogen concentration, in order to obtain a stable and safe end product that does not constitute a public health risk
It will be shown that the gravitary sludge thickener is a small but indispensable unit, as it provides a low-cost method to increase the excess sludge concentration and hence reduces overall investment costs. For sludge stabilisation two biological processes can be used : aerobic- and anaerobic digestion. Both processes will have a positive influence on the hygienic quality of the sludgel. After digestion, the reduction of the water content of the sludge is effected by applying physical processes (filtration, centrifugation, flotation or evaporation), possibly preceded by preparatory processes to accelerate or enhance liquid-solid separation, such as coagulation and flocculation with metal salts or poly-electrolytes.
In this section the following subjects will be discussed:
- Excess sludge quantity and composition
- Aerobic sludge stabilisation
- Anaerobic sludge stabilisation
Contents of this section
|
|
|
| Stabilized sludge treatment and disposal
|
|
We regret that the section on "Stabilized sludge treatment and disposal" is not available as a free online resource. If you want to know more, please purchase the handbook. More info ? |
|