Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D35/00—Filtering devices having features not specifically covered by groups B01D24/00 - B01D33/00, or for applications not specifically covered by groups B01D24/00 - B01D33/00; Auxiliary devices for filtration; Filter housing constructions
  • B01D35/06—Filters making use of electricity or magnetism
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D57/00—Separation, other than separation of solids, not fully covered by a single other group or subclass, e.g. B03C
  • B01D57/02—Separation, other than separation of solids, not fully covered by a single other group or subclass, e.g. B03C by electrophoresis
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
  • B01D61/56—Electro-osmotic dewatering
• • 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
  • C02F11/121—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering
  • C02F11/122—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering using filter presses
• • 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
  • C02F11/15—Treatment of sludge; Devices therefor by de-watering, drying or thickening by treatment with electric, magnetic or electromagnetic fields; by treatment with ultrasonic waves

Definitions

• the present invention relates to removal of liquid phase from aqueous sludges (i.e. liquid-solid phase mixtures) and is particularly applicable to sewage sludge or other sludges having similar physical characteristics.
• aqueous sludges i.e. liquid-solid phase mixtures
• the invention extends to the removal of any aqueous liquid phase from a sludge.
• the aqueous phase could be a solution.
• sludges resulting from the treatment of drinking water can usefully be treated in embodiments of the invention as well as mineral sludges such as coal tailings, other fine mineral tailings typically having particle diameters less than 0.1 mm and, in addition, sludges from the food and chemical industries.
• mineral sludges such as coal tailings, other fine mineral tailings typically having particle diameters less than 0.1 mm and, in addition, sludges from the food and chemical industries.
• a particularly significant area of application of the invention is to sludges which contain inorganic matter and comprise material which will sustain and pass an electric current.
• EDW electrodewatering
• EDW electrokinetic phenomena
• electrophoresis which involves the migration of charged particles in suspension to oppositely charged electrodes
• electro- osmosis which involves the migration of charged ions, which compensate the charges in the particles, to oppositely charged electrodes
• Lockhart discusses broadly electrodewatering and discusses experimental results from work with tailings from various mineral processing plants (coal washing, sand washing, mineral processing, fine coal products, brown coals etc) and also work on model clay suspensions. Lockhart discusses the fundamentals of electrodewatering and discusses some aspects including the significance of electrolysis in the mechanism, but concluding that it is obscure how electrolysis is involved and electrolysis considerations alone do not provide explanation for the volume of water transported per ion.
• Kondoh and Hiraoka discuss the need to decrease the water content in biological activated sludge arising from sewage treatment plants, but recognise that studies using an electro-osmotic process have demonstrated problems which have prevented any successful commercialisation.
• the authors discuss the costs of chemical treatment procedures contrasted to the cost of electrical power for aiding water removal with an electro-osmosis technique. Results in enhancing dewatering speed with the addition of an electrolyte in combination with a suitable polymer in a pressurised electro-osmotic dehydrated system are reported.
• the present invention consists in a method of reducing the liquid phase in an aqueous sludge comprising mixing fibrous material into the sludge and applying simultaneously (a) pressure or vacuum in a filtration method having a filter and (b) an electric field to the sludge supported on the filter, whereby the liquid phase is drawn through the filter.
• the invention is especially applicable to a method of processing a sludge which comprises, at least as a major component, organic material and wherein finely divided fibrous material is mixed into the sludge in an amount in the range of about 5-15% by wt (as dried solids) .
• a sludge which comprises, at least as a major component, organic material and wherein finely divided fibrous material is mixed into the sludge in an amount in the range of about 5-15% by wt (as dried solids) .
• a wider range of amount of fibrous material could be used especially where the aqueous sludge is derived from a sewage treatment plant.
• the invention is implemented in a method in which, during the filtration stage, separated liquid is pumped out and, if the process is operated as a batch process, then periodically dewatered solid material is removed.
• Methods according to the invention can use a variety of fibrous materials such as kaowool, shredded paper or other cellulosic fibres such as coconut fibre and bagasse (which is the fibrous material discharged from sugar cane crushing operations) .
• the method can include in addition some non-fibrous additives to enhance dewatering. For example, beneficial results may be achievable by the addition of salts such as calcium chloride.
• Embodiments of the invention are believed to operate on a wide range of fibrous materials and fibre sizes. It is accepted that it is very difficult to characterise fibre sizes, but as a general indication in the case of shredded paper and sewage sludge, very finely shredded news print has been used and this may be conveniently classified as having fibre sizes of length of around 0.05 to 0.5 mm.
• Figure 1 schematically illustrates known principles of assisted filtration techniques
• Figure 2 illustrates a generally accepted explanation of the mechanistic steps in filtration/dewatering of fine suspensions as discussed by Bendit et al;
• Figure 3 illustrates the results of using an embodiment of the invention with shredded newsprint as an additive
• FIG 4 illustrates the power consumption of the embodiment reported in Figure 3
• Figure 5 illustrates comparative data for embodiments using a range of fibrous additives
• Figure 6 shows contrasting data of simply using non- fibrous additives as opposed to fibrous additives
• Figure 7 is another comparative graph showing electrodewatering results using pressure in an electric field, but without any additives.
• Figure 8 is a diagram of a laboratory scale filter used to derive the results of Figures 3-7.
• Figure IA illustrates the principles of filtering using only an electric field, but without pressure and it will be seen that the particulate matter migrates preferentially under the electric field to the upper anode.
• Figure IB illustrates known pressure filtering without electric field in which the solid particles migrate to the filter F shown here at the bottom of the cell.
• Figure IC illustrates the mechanism for electrically assisted pressure techniques in which a combination of features occur and it is believed that the better separation characteristics are obtained because, in crude terms, there is a reduction in the rate of compaction of a filter cake due to some solids moving towards the upper anode.
• FIG 2A is a view on a greatly enlarged scale of a fragment of the structure showing schematically a filter 10 having filter material 11 and pores 12 supporting initially an aqueous mass of solid particles 14 and liquid 15.
• Figure 2B illustrates the initial suspension and as liquid phase is removed and pumped from the cell the volume of retained material progressively decreases and Figures IC to ID respectively show initial bridging across the filter pores, cake build up, full cake formation and completion of the filtration stage followed, in Figure IE, with cake compaction with water expression, at which point desaturation of the compacted cake can be caused by forced air or steam penetration. Finally in Figure 2F there is illustrated air breakthrough due to cake cracking.
• an initial mixture was formed of 10% by weight of finely shredded newsprint along with a sewage sludge and 0.8 kg/tonne of flocculent (Zetag 92) which was subjected to pressure of 10 bar and simultaneously an electric field of 100 amps/sq.m.
• the apparatus used is illustrated in Figure 8 in which the filter apparatus comprises a cylindrical body 20 having a cylindrical main bore 21 and a conical counter-bore 22 leading to an axial drain tube 23.
• a vacuum is applied to the drain tube 23 to draw off water from a sludge, which is placed in central zone 24 of the apparatus.
• a cylindrical plunger 25 is installed in the bore 21 and is adapted to be pressed downwardly by an applied pressure P.
• a disc-shaped centred metal cathode 26 is mounted at the bottom of the bore 21 and this cathode is perforated and supports a filter cloth 27A.
• the cathode 26 is connected by conductor 28 to a negative DC potential.
• a sintered metal perforated anode 29 is mounted in a disc-shaped cavity in the end of the plunger 25 and also is covered by a filter cloth 27B, a disc-shaped fluid extraction cavity 30 being located above and behind the anode 29 and connected to a discharge duct 31 which leads to a pipe 32 connected to a vacuum and adapted to draw up water which is removed from the sludge through the filter cloth 27B and anode 29.
• the volume of liquid expelled as a function of time was monitored and filtration was performed for 30 minutes.
• FIGS. 3 and 4 show progress of dewatering net of the effect of the added solids.
• an additive such as fibrous newsprint in contrast to a corresponding set of data where there is no additive.
• a range of fibrous additives have been tested as shown in the data of Figure 5. In these examples 25%-30% by weight additive of fibrous material was incorporated in the sludge before commencement of the treatment process. Bagasse and coconut fibre proved faster.
• the contrasting data of Figure 6 relates to powder additives with the same sludge feedstock and the same effective dose as the data reported and shown in Figure 5. Thus the fibrous additives had a marked beneficial effect compared with powder additives.
• Figure 7 shows the results of an experiment performed under similar conditions, but in the absence of any additive. As before pressure was applied by vacuum at 10 bar with an electric field of 100 amps/sq.m was applied. It should be noted that in Figures 5 and 6 the total solids in the filter cake are referred to and therefore the final value of sludge solids in filter cake must be reduced in value by 10% weight. Thus on average in the sludges referred to, the final sludge solids should be reduced from about 40% weight to 30% weight (due to the inclusion in the initial material of 25%-30% by weight of the additive) .
• the inventor suggests that the inclusion of solids of a relatively coarse size compared to the size of sludge particles does increase the permeability of the filter cake.
• a fibrous additive the inventor suggests that it is possible the fibres form a continuous network throughout the filter cake and can thus provide an extra pathway (either outside or inside the fibre, if the fibre is porous) along which water can travel. It is thought the increase in permeability achieved and the extra pathway are major factors in improving dewatering.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Water Supply & Treatment (AREA)
• Life Sciences & Earth Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Hydrology & Water Resources (AREA)
• Health & Medical Sciences (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Electrochemistry (AREA)
• Electromagnetism (AREA)
• Physics & Mathematics (AREA)
• Urology & Nephrology (AREA)
• Molecular Biology (AREA)
• Treatment Of Sludge (AREA)
• Filtration Of Liquid (AREA)

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• 1995
  • 1995-08-16 AU AUPN4834A patent/AUPN483495A0/en not_active Abandoned
• 1996
  • 1996-08-14 CA CA002229642A patent/CA2229642A1/en not_active Abandoned
  • 1996-08-14 JP JP9508749A patent/JPH11511068A/ja active Pending
  • 1996-08-14 WO PCT/AU1996/000509 patent/WO1997007065A1/en not_active Ceased
  • 1996-08-14 EP EP96926270A patent/EP0854845A4/de not_active Withdrawn

Non-Patent Citations (2)

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