Clarification sludge

The clarification sludge are principal the Déchet S produced by a Purification plant, these Sédiment S waste especially consists of Bactérie S dead and mineral-bearing organic matter. An average installation produces approximately an excess of 40 G dry matter per day and.

Types

One distinguishes various types of muds according to the treatments applied to purify water.

  • the primary Muds: They are the deposits recovered by simple a Décantation of the Waste water (in the decanter-digesters for example. They present concentrations raised out of mineral matters (Sable, ground…) but also out of organic matter being able to evolve/move.

  • the physicochemical Muds: they resemble primary muds except that during the treatment of waste water, it was added a reagent (aluminum, iron salts, and other agents Flocculating S) to agglomerate the fine particles and to improve the decantation.

  • the biological Muds: they are also called secondary muds, they come from a biological purification of water (activated sludge, biological discs, bacterial beds…). These muds, of poor concentrations (10 g/l), are very organic because they are mainly made up of bacterial bodies and their secretions.

One also distinguishes:

  • the mixed Muds consisted of a mixture of primary and biological muds, they come from the majority of the complete stations of treatment.

  • the Muds of ventilation prolonged, obtained without primary decantation with intensively ventilated polluting matters. Muds are concentrated little, less organic and thus less likely to produce harmful effects.

Characteristics

A mud is also represented by several numerical data which make it possible to characterize it. muds consist of water and dry matters. Dryness is the mass percentage of dry matter. Thus a mud with a dryness of 10% has a moisture of 90%.

  • the dry volatile matter rate (MVS).

the dry matter consists of mineral matters and organic matters which are called dry volatile matters. The concentration in MVS is a rate compared to the total dry matter. The follow-up of this rate makes it possible to know the stability of a mud.

  • consistency.

It is an obligatory data to know for any handling of muds. Consistency is a physical status depend on dryness.
* Slurries/dryness from 0 to 10%
* pasty Muds/dryness from 10 to 25%
* solid Muds/dryness from 25 to 85%
* Boues dries/dryness higher than 85%

According to the treatments of purification applied muds have different characteristics:

bacterial Bed: dryness 2 to 5%; MVS 60 to 70%
natural Lagunage: dryness 5 to 10%; MVS 30 to 60%
Decanter-digester: dryness 4 to 7%; MVS 40 to 60%
Muds of the basin of ventilation in station with Activated sludge: dryness 0,4 to 0,6%; MVS XXX%
Muds of the clarifier in station with Activated sludge: dryness 1%; MVS XXX%

Treatment

Muds undergo several treatments such as the conditioning which will make it possible to make them stable (of stable muds are nonfermentable muds) using physical methods (thermics) and/or chemical (addition of mineral reagents, of Polymère S of synthesis or polyelectrolytes), then thickening will reduce the volume of muds by natural or mechanical compressing (drying, drainage…). Lastly, dehydration (by centrifugation, filter press, filter pressing bands…) who will release most of water constituting the majority of the volume of muds.

Outlets

Muds can be developed in Agriculture for the spreading or then be incinerated, only or with household refuse. Their setting in discharge is prohibited since 2002 except for the muds considered as ultimate waste, ashes resulting from the incineration are accepted there.

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