Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/14—Other self-supporting filtering material ; Other filtering material
  • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
  • B01D39/1607—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous
  • B01D39/1623—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous of synthetic origin
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/08—Filter cloth, i.e. woven, knitted or interlaced material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/10—Filter screens essentially made of metal
  • B01D39/12—Filter screens essentially made of metal of wire gauze; of knitted wire; of expanded metal
• • 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
• • 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
  • C02F11/126—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering using drum filters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
  • B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
  • B01D2239/065—More than one layer present in the filtering material

Definitions

• the present invention concerns an arrangement to in- crease the concentration of solids in a solution. Even though the invention is specially developed for dewatering of sludge, it may be used generally to separate a solid soluble substance from a solvent, which do not have to be water .
• Prior Art Sludge from a digester in a sewage treatment plant has often a content of dry matter (substances) of about 2 %.
• differ- ent flocculants are normally added, whereby polymers often are used.
• the flocked sludge is then today often separated in a means using centrifugation in order to increase the content of dry matter to about 20 %.
• polymers in dried sludge give environmental problems concerning deposi- tion of the treated sludge.
• no "lumps" are formed. Such "lumps” are hard to dry and thereby to sanitize, furthermore, they may include a lot of moisture and thereby pathogenic bacteria and mould spores that may start to multiply.
• One purpose of the present invention is to be able to increase the concentration of substances in a solution, without the need of adding any flocculant. Even if the in- vention mainly is developed for treatment of sewage sludge, a person skilled in the art realizes that the principle of the invention is useful in many circumstances where an increase of the dry matter of a solution is wanted.
• a solution having solid, dissolved substances is placed on a semi-permeable membrane with a layer of air on the other side of the membrane. The membrane should only let the solvent and air through, but not the dissolved, solid substances, whereby the content of the dissolved substances will increase in the solution, in that the solvent "migrates" through the membrane.
• the mem- brane is designed to form channels letting moisture (water) and air pass.
• the invention may be used in order to increase the concentration of substances in a solution.
• One theory behind this is the well known strive of nature to level out differences in concentration.
• the possible theory of the invention will now be explained further based on digested sludge from a sewage treatment plant as an example.
• digested sludge from a sewage treatment plant it normally has a content of dry matter of about 2 %.
• the sludge hav- ing a content of dry matter of about 2 %, i.e. sludge dissolved in water is a solution.
• Another solution is water in the membrane where the content of dry matter is 0 %.
• a solution having higher concentration has a lower partial pressure than solutions having a lower concentration.
• the sludge dissolved in water has a lower concentration of water than the solution in the membrane and thereby a higher partial pressure.
• the difference in partial pressure means that the water will go into the membrane and that the content of dry matter of the sludge will increase.
• the membrane In order for this to work the membrane must be kept moist all the time and thereby moist enough in order to give the effect of an accumulation of solution.
• the concentration of water in the membrane increases the water will fall out of the membrane by gravity. Water that fall out of the membrane is preferably collected and some of it is used to moisten the membrane.
• the molecules of the solvent will penetrate into the more concentrated solution striving to level out the difference in concentration, i.e. the difference in partial pressure.
• the present in- vention may be used for in principle any solution and for any solid, dissolved substances.
• the present invention concerns an arrangement of increasing the concentration of solid, dissolved substances in a solution.
• the difference in partial pressure of a solution with or without solid, dissolved substances is used. It is done in that the solution is placed on a semi- permeable membrane, which membrane is moistened with the solvent of the solution.
• the membrane holding the solution will then pass an area with an air layer on the other side of the membrane. Due to the different partial pressures for the solutions with and without solid, dissolved substances, the solvent of the solution will migrate through the membrane from the side where the solution contains solid, dissolved substances to the other side.
• the arrangement according to the present invention is well suited for use in an automated process, in which the arrangement often is only a part of a larger process. Further objects and advantages of the present invention will be obvious for a person skilled in the art when reading the detailed description below.
• Fig. 1 is a principle sketch in the form of a sectional view of an arrangement using the principles of the present invention
• Fig. 2 is a sectional view of a conveyor of the ar- rangement of Fig. 1
• Fig. 3 is an enlarged sectional view of a membrane according to the present invention
• Fig. 4 is a principle sketch in end view and in section of another arrangement using the principles of the present invention
• Fig. 5 is a side view of the arrangement of Fig. 4
• Fig. 6 is a sectional view of a part of the arrangement of Figs. 4 and 5
• Fig. 7 is a principle sketch of a part of the ar- rangement of Figs. 4 to 6.
• FIG. 1 one example of an arrangement according to the present invention is shown, which arrangement is used for dewatering of digested sludge.
• the arrangement is enclosed in a case or house 1.
• the house 1 has an inlet 2 to receive non-dewatered sludge, e.g. digested sludge from the digester of a sewage treatment plant. Furthermore, there are two outlets, one outlet 3 for water and one outlet 4 for dewatered sludge.
• the outlet 4 for dewatered sludge leads to a drying apparatus 5 for further dewatering of the sludge.
• a conveyor ⁇ is arranged, on which the sludge 8 feed through the inlet 2 is received.
• the conveyor 6 has a number of rollers 9 carrying a wire cloth 10 in a trough-like shape.
• a person skilled in the art realizes that the exact design of the conveyor may vary, as long as it fulfils the most elementary demands for the invention to work. These demands are that the water should be let through, that the sludge 8 should be received in a secure way etc. It is e.g.
• a semi-permeable membrane 11 is placed on top of the wire cloth 10 of the conveyor 6, i.e. closest to the sludge 8. A layer of air is formed beneath the wire cloth 10 and, thus, the membrane 11.
• the wire cloth 10 is a support for the semi-permeable membrane 11, but if the membrane 11 has enough bearing strength on its own the wire cloth 10 may be taken away.
• the membrane 11 is formed of a number of layers having alternating convex threads 12 and concave threads 13.
• the convex and concave threads 12, 13 are arranged alternating, giving cells of varying shape between the convex and concave threads 12, 13.
• the cells are indicated in Fig. 3.
• the surfaces of the cells are closely arranged to give a relatively large total surface.
• the membrane 11 may be made of any suitable material, such as e.g. nylon fibres. Nylon fibres are suitable e.g. for dewatering of sludge from digesters of sewage treatment plants.
• the cells of the membrane 11 may be formed of many different materials.
• Suitable materials for the membrane are commercially available.
• the solvent in this case water
• the membrane 11 is hereby moistened continuously, at the same time as there is an air gap or air layer between the upper part of the conveyor 6 and the water level 7.
• the membrane 11 is normally rinsed during half of its turn, which is enough to keep up the moisture content.
• the membrane 11 may also be moistened in other ways, e.g. in that a water jet moistens the membrane 11 just before the sludge 8 is received.
• the lower part of the house 2 has two sections separated by a partition 15. In the bottom of one of the sections the water outlet 3 is arranged, while the outlet 4 for dewatered sludge is arranged in the bottom of the other section.
• the partition 15 keeps separated water in the space above the water outlet 3, without any risk of it to spill over into the other section.
• a scraper 14 is arranged to scrape off possible remaining material on the conveyor.
• the scraper 14 is arranged on the partition 15 between the two lower sections of the house 1.
• the size of the water outlet 3 may be controlled in order to keep the water level 7 at a suitable height. In one example this is done by means of a switch closing and opening the outlet 3 in such a way that the water level 7 is placed between maximal and minimal allowed levels. Due to the air gap between the water level 7 and the upper part of the conveyor 6 excess water will rapidly fall out of the membrane 11 and down into the collection of water in the lower part of the house 1.
• the membrane 11 has a cell size of about 1 ⁇ m while the wire cloth has a cell size of about 50 ⁇ m, which has proven to function well.
• the wire cloth may be made of stainless steel.
• FIG. 4 to 7 The embodiment of Figs. 4 to 7 will now be described as an example with digested sludge from a sewage treatment plant.
• This embodiment comprises a drum 16, having two opposite end walls and a wall forming the cylinder of the drum.
• the drum 16 is submerged into a receptacle 17 receiv- ing sludge 32 from an inlet 18.
• the receptacle 17 is part of a housing in which the arrangement is received.
• a semi-permeable membrane 28 is placed on the outside of the cylinder wall of the drum 16, letting water through but not solid, dissolved substances of the sludge 32.
• the membrane 28 of this embodiment corresponds to the membrane 11 of the previously described embodiment.
• the membrane is formed of a number of layers having alternating convex and concave threads 12, 13.
• the semi-permeable membrane 28 is carried on a sheet metal 26, forming the cylinder of the drum 16.
• the sheet metal 26 of the drum 16 is furnished with a number of openings 27.
• Sludge is lifted from the receptacle 17 on the outer side of the drum 16, which is rotated by a motor 30.
• Dewatered sludge is feed out through an outlet 19.
• the end walls of the drum 16 are placed adjacent walls of the housing.
• Inside the drum 16 one or more vanes 20 are received on a hollow shaft 21.
• the vanes 20 extend over the total width of the drum 16, with a small gap to the end walls of the drum 16.
• the number of vanes 20 inside the drum 16 may vary.
• vanes 20 are received with a spacing of 30° on the hollow shaft 21 inside the drum 16. One end of each vane 20 abuts the inside of the drum 16. In the shown embodiment the vanes 20 have a bent outer part at the end abutting the inside of the drum 16. In the hollow shaft 21 a slit 24 is arranged in connection with each vane 20.
• Each slit 24 opens into a cavity 25 inside the hollow shaft 21.
• water is lead into the cavity 25 of the hollow shaft 21.
• the cavity 25 ends in a water outlet 22.
• a vacuum pump 31 is at- tached to the water outlet 22 to increase the dewatering effect of the arrangement.
• the vanes 20 may be replaced with rows of suction tubes for transport of the water to the cavity 25 of the hollow shaft 21.
• the drum 16 is rotated by a motor 30, which is connected to the hollow shaft 21.
• the hollow shaft 21 going through the drum 16 is received in bearings placed in opposite walls of the house receiving the drum 16.
• the end walls of the drum 16 and the vanes 20 are fixed to the hollow shaft 21.
• the drum 16 and the vanes 20 will rotate with the hollow shaft 21, but there will be no mutual movement between the drum 16 and the vanes 20.
• the motor 30 is arranged on the opposite side of the hollow shaft 21 to the water outlet 22 and the vacuum pump 31.
• the drum 16 was rotated at a speed of 6 rpm and the vacuum pump 31 reduced the pressure at the water outlet 22 to about 50 kPa.
• the pressure given by the vacuum pump 31 should not exceed about 80 kPa.
• a scraper 23 is arranged, to scrap dewatered sludge from the drum 16.
• the scraper 23 is to abut the outer surface of the drum 16, or more precisely the membrane 28 received on the outside of the drum 16.
• the position of the scraper 23 may be adjusted to control the contact pressure against the drum 16.
• the scraper 23 extends the total length of the drum 16. As stated above sludge will be lifted from the receptacle 17 by the rotation of the drum 16.
• the membrane 28 on the drum 16 receiving the sludge is moistened by a collec- tion of water 29 at the bottom of the drum 16, which collection of water 29 is formed in the drum 16 during operation.
• the drum 16 may have to make some revolutions before the membrane 28 is moistened enough.
• water of the sludge will go into the membrane 28 in the same way as referred to above for the embodiment of Figs. 1 to 3. Excess water of the membrane 28 will fall into the inside of the drum 16.
• the water is then collected by the vanes 20 and will follow the vanes down to the hollow shaft 21 and through the slit 24 of the hollow shaft 21 at each vane 20.
• the water is finally feed out through the cavity 25 of the hollow shaft 21 to the water outlet 22.
• a vacuum pump 31 By connecting a vacuum pump 31 to the cavity 25 the dewatering effect of the arrangement increases.
• the dewatered sludge is scraped off from the drum by means of the scraper 23 and will fall into the sludge outlet 19.
• the dewatered sludge may then be treated further in any suitable way.
• this embodiment has a sludge collection zone and a dewatering zone.
• the sludge collection zone being the part of the drum 16 submerged into the sludge and the dewatering zone being the part of the drum above the level of the sludge in the receptacle 17.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Hydrology & Water Resources (AREA)
• Environmental & Geological Engineering (AREA)
• Water Supply & Treatment (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Textile Engineering (AREA)
• Treatment Of Sludge (AREA)
• Separation Using Semi-Permeable Membranes (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=32589871

Family Applications (1)

Country Status (3)

Cited By (1)

Citations (12)

• 2004
  • 2004-06-02 SE SE0401417A patent/SE528037C3/sv not_active IP Right Cessation
• 2005
  • 2005-05-31 EP EP05746885A patent/EP1765736A1/en not_active Withdrawn
  • 2005-05-31 WO PCT/SE2005/000816 patent/WO2005118491A1/en active Application Filing

Patent Citations (12)

Also Published As

Similar Documents

Legal Events