Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F11/00—Treatment of sludge; Devices therefor
  • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
  • C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
  • C02F11/143—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents using inorganic substances
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F11/00—Treatment of sludge; Devices therefor
  • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
  • C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
  • C02F11/143—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents using inorganic substances
  • C02F11/145—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents using inorganic substances using calcium compounds

Definitions

• the invention relates to a method for lowering the specific resistance to filtration of biological sludge in order to facilitate their dewatering, and their compaction by mechanical filtration.
• the invention applies to biological sludge, that is to say sludge from sewage treatment plants working by biological means, this sludge generally being in the form of bacterial flocs (aggregates of micro- organisms possibly associated with a binder or with support particles); the process of the invention makes it possible to obtain a dehydration of the biomass under remarkable conditions of efficiency.
• Diatoms are more efficient but their cost is high and they have an abrasive character which is detrimental to transfer and filtration equipment (pumps, filter cloths, etc.). It is also found that most of the known additives tend to make the sludge sticky, leading to rapid clogging of the filtration members; this drawback is serious in practice because it imposes manual operations of "deburring", unclogging and cleaning of the filtration members, which considerably increase the costs of implementation (cost of personnel and immobilization of equipment). Furthermore, DE-A-4,025,063 describes, in its example n ° 6, a process consisting in adding to biological sludges coming from treatment plant a hydrophilic silicate and a sulphate in order to favor the dehydration of these.
• the present invention aims to dehydrate biological sludge from treatment plants with greatly improved efficiency, by implementing conventional mechanical filtration processes in order to benefit from the low cost of this type of process compared to the quantity of materials treated (compared to the cost of other processes such as thermal or vacuum dehydration for example).
• dehydration is meant the specific step having as its object the evacuation of part of the water from the biological sludge (after, if necessary, clarification and thickening).
• the efficiency of an additive is classically qualified by the reduction of the "specific resistance to filtration” to which it leads (specific resistance expressed in m / kg; cf filterability test under vacuum defined in the "Technical Note of the Eau ", 1989, 9 th Edition, Tome 1, DEGREMONT pages 372-373).
• the main objective of the invention is to provide a process making it possible to significantly lower the specific resistance to filtration of biological sludge.
• An objective of the invention is thus to allow efficient mechanical filtration by adding relatively small amounts of additives to the sludge in order to avoid an excessive increase in the amounts of solid waste produced. Another important objective is to reduce the "sticky" character of the dehydrated sludge in order to facilitate their detachment from the filtration members and avoid clogging of the latter.
• Another objective is to lead, after filtration, to good dryness with much lower amounts of added material than in the case of most of the known processes working by mechanical filtration.
• Another objective is to provide a process whose cost of implementation is lower than that of processes by mechanical filtration using known mineral additives.
• the process targeted by the invention for lowering the specific resistance to filtration of biological sludge in order to facilitate their dewatering and compacting by mechanical filtration is characterized in that:
• mineral particles composed of hydrophobic species of magnesium silicate and hydrophilic species of magnesium aluminum silicate and / or magnesium carbonate and / or calcium are added to the biological sludges. amount between 0.05 and 0.4 kg per kg of dry sludge solid matter,
• the relative weight ratio (R) between hydrophobic species and hydrophilic species being between 20/80 and 80/20,
• Said mineral particles having a particle size distribution such that the average diameter D 50 is between 3 and 30 microns,
• mechanical filtration is meant any operation aimed at separating the water from the solid materials by a mechanical effect such as passage of the materials through a filter press (plate filter press, belt filter press).
• diameter D 50 is meant a diameter such that 50% of particles by weight have a size smaller than said diameter, the particle size distribution having a spectrum of small or medium width such that 90% of the particles (D 90 ) have a smaller size 5 times the D 50 .
• the particles which are added to the biological sludge are in particular formed from the following two species: hydrated magnesium silicate, and hydrated magnesium and aluminum silicate (these compounds may contain substitutions in their structure , mainly by Fe). These particles can in particular be obtained by selective sorting in quarries or talc mines where they occur naturally in certain areas, the two silicates being generally bonded to form mixed particles.
• the particles used in the invention have a stable and inert mineral structure, provided with hydrophobic sites (provided by magnesium silicate) and hydrophilic sites (provided by magnesium and aluminum silicate and / or magnesium carbonate and / or calcium): the presence of these particles does not entail any risk of parasitic reactions.
• mineral particles are used, the hydrophobic and hydrophilic species of which have a relative weight ratio between 40/60 and 60/40 and an average diameter D 50 included between 5 and 15 microns; the zone concerned has been delimited in broken lines on the graph in FIG. 1.
• the quantity of mineral particles used in the invention is less than 0.4 kg per kg of dry solid matter (only the initial solid matter to be dehydrated being taken into account). In general, this amount will be of the order of 0.2 to 0.3 kg per kg, which is three to six times less than the amounts added of conventional additives.
• mechanical filtration can be carried out by means of any equipment suitable for operating dehydration by mechanical action, in particular known filter press (plate filter press or band filter press).
• filter press plate filter press or band filter press
• Biological sludge is generally brought to stay, at the outlet of the treatment plant, in a flocculation chamber which is followed by the filter press.
• the mineral particles with hydrophobic sites and with hydrophilic sites can in particular be added to the sludge between said flocculation chamber and said filter press. It is also possible to add these particles to the flocculation chamber.
• FIG. 1 is a graph defining the mineral particles used in the invention by their parameters R (weight ratio of hydrophobic species and hydrophilic species) and D 50 (mean diameter of the particles).
• samples were treated in accordance with the invention by adding thereto, per kg of dry matter, 0.3 or 0.4 or 0.5 or 0.6 kg of particles made up by weight of 50% hydrated magnesium silicate and 50% magnesium silicate and hydrated aluminum, these silicates being bound in the same particles and selectively extracted from the quarry of TALC DE LUZENAC in LUZENAC in ARIEGE (FRANCE).
• the average diameter D 50 of these particles is 9.8 microns and the D 90 of 31 microns.
• the biological sludge from the station is first subjected to a thickening step in a static thickener 1, then they are admitted into a flocculation chamber 2 where the conventional additives are added.
• the particles in accordance with the invention (and the diatoms of the comparative test) are added to a conditioner mixer 3 located between chamber 2 and the filter press 4.
• the products are added to the flocculation chamber 2.
• the filter press used is a conventional type band filter press and the same quantities of particles in accordance with the invention and of diatoms are added in the two tests to allow comparison (quantity equal to 0.35 kg per kg of dry matter).
• biological sludge is treated on a filter press with vertical plates.
• This sludge from heavy chemical effluents is conditioned, in a first series of tests, only to ferric chloride and lime (control tests), and in a second series, to ferric chloride and lime and by means of particles according to the invention (identical to case 1).

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Hydrology & Water Resources (AREA)
• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Water Supply & Treatment (AREA)
• Organic Chemistry (AREA)
• Treatment Of Sludge (AREA)

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• 2000
  • 2000-02-22 FR FR0002188A patent/FR2805180B1/fr not_active Expired - Fee Related
• 2001
  • 2001-02-20 WO PCT/FR2001/000487 patent/WO2001062679A1/fr not_active Application Discontinuation
  • 2001-02-20 EP EP01907844A patent/EP1257506A1/de not_active Withdrawn

Non-Patent Citations (1)

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