Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/54—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents

Definitions

• the present invention relates to a method for treating impure water, and more particularly to an improved method for treating sewage to produce treated effluent of very high quality.
• Domestic or sanitary sewage and industrial wastes may be purified by the chemical precipitation process, in which suitable chemicals (e.g. aluminum sulfate, lime, iron chloride, polyelectrolytes or combinations thereof) are added to the sewage and the sewage passed to one or more flocculating tanks, normally equipped with slowly rotating agitators or paddles, in which colloidal solids are formed into particles of size and weight that will settle.
• suitable chemicals e.g. aluminum sulfate, lime, iron chloride, polyelectrolytes or combinations thereof
• the colloidal solids or floes are then separated from the liquid by being allowed to settle in subsequent settling tanks, whereafter the purified water is collected in a weir structure mounted at the surface of the water, while the sediment, consisting of floes and sludge, is removed, normally by means of sludge scrapers and/or pumps.
• the prior art teaches the addition of various types of chemicals and combinations of chemicals to sewage and other impure water to remove various pollutants therefrom.
• the invention when used to treat raw sewage or other impure water with very economical doses of three chemicals converts a very high proportion of the suspended, colloidal and dissolved pollutants in the sewage or other impure water to large, dense and stable floes which are so resistant to shear forces they can be settled out in a clarifier without the aid of inclined sedimentation means, and with an upward flow velocity of at least eighteen to twenty meters per hour. This flow rate is approximately ten times higher than than recommended by those skilled in the art for clarifiers without inclined sedimentation means.
• Aluminum Removes all of the aluminum which is dosed into the sewage or industrial effluent, in addition to approximately 70% of the small quantity of aluminum present in the influent.
• the invention is a considerable improvement over the prior art in relation to the removal of Biochemical Oxygen Demand (BOD,.), with approximately 95% of all BOD_ over 0.2 microns in size being removed, and in addition, almost one third of the BOD- less than 0.2 microns in size also being removed.
• BOD Biochemical Oxygen Demand
• the invention can be used in many locations to treat raw sewage to a standard that does not require further treatment before discharge to waterways, whereas the effluent from other chemical systems requires additional biological treatment. Furthermore, where highly polluting waste waters are treated in accordance with this invention and where the resulting treated effluent requires additional biological treatment the pollutional load on the subsequent biological system is reduced to a significant extent, thereby resulting in substantial cost savings.
• Tests have indicated that raw sewage, after being treated using the methods described by this invention, and then passed directly through an ultraviolet disinfection apparatus, was efficiently disinfected and the resultant total coliform count was only 10 per 100 ml.
• a very important advantage of this invention over the prior art is its versatility.
• the invention can be used as either a Primary and/or Secondary and/or Tertiary Treatment system, and can be combined to advantage with other chemical, physical or biological processes.
• Another important advantage of this invention is the overall speed with which the treatment process takes place. While the overall retention time required is site specific and depends on such factors as the quality of the influent and/or the quality of the effluent required, typically, for sewage treatment the overall retention time is less than thirty minutes .
• the quality of the sludge produced by the us ⁇ e of this invention while being .site specific, is generally of a very high solids content and is readily thickened in a short period of time. The resulting thickened sludge is then readily dewatered to a high solids content cake. This is a very important aspect of this invention, and distinguishes this invention over the prior art in that the total volume of sludge to be disposed of is lower than usual, resulting in important economic and environmental advantages.
• the invention provides a method for treating sewage or other impure water wherein the following three individual chemicals (but no more than two premixed together) are added to the sewage or other impure water in a mixing zone:
• Predetermined amounts of three chemicals are added to sewage or other impure water.
• Inorganic Coagulants i.e. aluminum sulphate, ferric chloride, Cationic Polymers, e.g. Polyelectrolytes, and Anionic Polymers, e.g. Polyelectrolytes are added to sewage or other impure water.
• the three chemicals are intimately mixed with the sewage or other impure water in a mixing/flocculation zone to form large dense floes from the suspended, colloidal and dissolved pollutants in the sewage or other impure water, seoaratincr these floes from the sewa ⁇ e or impure water in a separating zone, drawing of treated effluent from the separating zone, and recycling a predetermind amount of sludge from the separating zone to the mixing/flocculation zone.
• the dosages of chemicals, the sequence of addition, the specific chemicals used and the amount and location of sludge recycle are site specific and depend on design parameters such as:
• An inorganic coagulant (A) and a cationic polymer (B) are mixed in the one container and then dosed into the sewage as a single mixture, intimately mixed with the sewage, and then anionic polymer (C) is dosed into the sewage.
• An inorgaijic coagulant (A-) and an anionic polymer (C) are mixed in the one container and then dosed into the sewage as a single mixture, intimately mixed with the sewage, and then cationic polymer (B) is dosed into the sewage.
• the amount of inorganic coagulant used is preferably 10 to 1000 ppm, more preferably 10 to 300 ppm, and most preferably 30 to 200 ppm.
• the amount of each of the anionic polymer and the cationic polymer is preferably 0.1 to 50 ppm, and more preferably 0.1 to 10 ppm, and most preferably 0.1 to 5 ppm. All ppm are by weight in relation to the impure water to be treated.
• a predetermined amount of the first chemical is dosed into the sewage or other impure water through one or more injection points at a first part of the mixing/flocculation zone and is intimately mixed with the said sewage or other impure water, then:
• a predetermined amount of the second chemical is dosed into the sewage or other impure water through one or more injection points at a second part of the mixing/flocculation zone and is intimately mixed with the said sewage or other impure water, and then:
• a predetermined amount of the third chemical is dosed into the sewage or other impure water through one or more injection points at a third part of the mixing/flocculation zone and is intimately mixed with the sewage or other impure water.
• a predetermined amount of the sludge removed from the solids separating zone is recycled to the mixing/flocculation zone, and is dosed into and intimately mixed with the sewage or other impure water.
• the location of the sludge recycle point in the mixing/flocculation zone and the quantity recycled is site specific and depends on the design parameters as previously described herein.
• the sludge recycle rate can vary from 1-20% of the impure water flowrate, but is preferably at a flowrate of about 10%.
• the sludge can be recycled to the incoming impure water at various locations, the best location being found by site trials.
• the time interval between successive chemical doses can vary, e.g. from just a few seconds up to about 8 minutes, but generally a 5 minute interval or less has been found satisfactory.
• the upward velocity in the sedimentation tank can vary, e.g. from 10-20 metres per hour.
• an inorganic coagulant is mixed in one container with one of the polymers and then dosed into the sewage or impure water as one homogeneous mixture and then the other polymer is dosed into the sewage, the following general procedure is adpoted:
• a predetermined amount of the inorganic coagulant and one of the polymers is mixed in one container and dosed as one homogeneous mixture into the sewage or other impure water through one or more injection points at a first part of the mixing/flocculation zone and is intimately mixed with the sewage or other impure water, and then
• a predetermined amount of the other polymer i.e. of opposite charge to the polymer in.Step (i) above is dosed into the sewage or other impure water through one or more injection points of a second part of the mixing/flocculation zone and it is intimately mixed with the said sewage or other impure water.
• a predetermined amount of the sludge removed from the separating zone is recycled to the mixing/flocculation zone and is dosed into and intimately mixed with the sewage or other impure water.
• the location of the sludge recycle point in the mixing/flocculation zone and the quantity recycled is site specific and depends on the design parameters as previously described herein.
• the time interval between the addition of the homogeneous mixture of the first two chemicals (i.e. an inorganic coagulant and a polymer) and the third chemical i.e. the polymer of opposite charge to that mixed with the inorganic coagulant in the mixing/flocculation zone is site specific and depends on the design parameters as previously described herein.
• the process is suitable for treating sewage or other impure water without any further form of treatment, but in some instances, depending on the quality of the influent or the quality of the effluent required, it may be necessary to adjust the pH or the alkalinity of the influent or the effluent by the use of methods well known in the art.
• inorganic coagulations can be used in the application of this invention, for example, aluminum sulphate, alum, and ferric chloride and lime.
• the specific type of inorganic coagulant to be used is site specific and depends on the design parameters.
• anionic polyelectrolytes may be used, and the following have been used with success:
• One method for the treatment of sewage or other impure water is disclosed wherein three chemicals are added to the sewage in the following specific sequence to produce treated effluent.
• An inorganic coagulant such as alum or ferric chloride is added to the sewage and is intimately mixed therewith to provide pretreated sewage; then an anionic polymer is added to the pretreated sewage and is intimately mixed therewith to provide and interim pretreated sewage: then a cationic polymer is added to the interim pretreated sewage and is intimately mixed therewith to provide chemically-treated sewage.
• the chemically-treated sewage is supplied to [e.g] a separating zone wherein the chemically-treated effluent and sludge are separately removed. A predetermined amount of sludge is recycled back to the mixing/flocculation zone.
• the anionic polymer is added to and intimately mixed in the sewage to provide pretreated sewage; then an inorganic coagulant, such as alum is added to and intimately mixed with the pretreated sewage to provide an interim pretreated sewage; cationic polymer is added to and intimately mixed with the interim pretreated sewage to provide chemically treated effluent.
• the chemically treated efluent may be supplied to a separating zone wherein the chemically treated effluent and sludge are separately removed. A predetermined amount of sludge is recycled back to the mixing/flocculation zone.
• high molecular weight cationic polymer is added to and intimately mixed with the sewage to provide pretreated sewage, then an inorganic coagulant such as alum is added to and intimately mixed with the pretreated sewage to provide an interim pretreated sewage; then anionic polymer is added to an intimately mixed with the interim pretreated sewage to provide chemically treated sewage. Then the chemically-treated sewage is supplied to a separating zone wherein chemically-treated effluent and sludge are separately removed. A predetermined amount of sludge is recycled back to the mixing/flocculation zone.
• the inorganic coagulant e.g. alum or ferric chloride
• the cationic polymer is mixed in the one container with the cationic polymer to form a homogeneous mixture which is then added and intimately mixed with the sewage to provide an interim pretreated sewage; then at a later time an anionic polymer is added and intimately mixed with the interium pretreated sewage to provide chemically-treated sewage.
• the chemically-treated sewage is supplied to a separating zone wherein the chemically treated effluent and sludge are separately removed. A predetermined amount of sludge is recycled back to the mixing/flocculation zone.
• the inorganic coagulant e.g. alum or ferric chloride
• the anionic polymer is mixed in the one container with the anionic polymer to form a homogeneous mixture which is then added and intimately mixed with the sewage to provide an interim pretreated sewage; then at a later time a cationic polymer is added and intimately mixed with the interim pretreated sewage to provide chemically treated sewage.
• the chemically treated sewage is supplied to, a separating zone wherein the chemically treated effluent and sludge are separately removed. A predetermined amount of sludge is recycled back to the mixing/flocculation zone.
• the amount of predetermined sludge recycled back in the process is typically of the order of 1 to 10%, although rates of 20% or more can be used. This percentage may vary depending on the quality of the influent and the desired effluent quality. It may be recycled to the influent or various locations, the best location being found by site trials.
• Table 1 sets out the results of numerous tests carried out on a mixture of sewage and industrial effluent, using an inorganic coagulant (alum) , followed by an anionic polyelectrolyte, followed by a cationic polyelectrolyte.
• alum inorganic coagulant
• anionic polyelectrolyte followed by a cationic polyelectrolyte.
• the method also results in a very high level of microorganism removal.
• a sample of raw sewage was found to have a total eoliform bacteria count of over 1,800,000 per lOOmls, and the treated effluent produced by the method of this invention had a eoliform count of only 5500 per lOOmls, representing a removal efficiency of over 99.7%.

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• 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)
• Inorganic Chemistry (AREA)
• Separation Of Suspended Particles By Flocculating Agents (AREA)
• Water Treatment By Sorption (AREA)

Applications Claiming Priority (6)

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• 1987
  • 1987-08-03 WO PCT/GB1987/000549 patent/WO1988000927A1/en not_active Application Discontinuation
  • 1987-08-03 AU AU77557/87A patent/AU621032B2/en not_active Ceased
  • 1987-08-03 BR BR8707785A patent/BR8707785A/pt unknown
  • 1987-08-03 JP JP62504713A patent/JPH02500724A/ja active Pending
  • 1987-08-03 EP EP87905229A patent/EP0316348A1/en not_active Withdrawn
  • 1987-08-04 ES ES8702285A patent/ES2004466A6/es not_active Expired
  • 1987-08-04 CA CA000543724A patent/CA1334543C/en not_active Expired - Fee Related
  • 1987-08-04 PT PT85484A patent/PT85484B/pt not_active IP Right Cessation
  • 1987-08-04 GR GR871232A patent/GR871232B/el unknown
• 1988
  • 1988-03-24 KR KR1019880700324A patent/KR880701687A/ko not_active IP Right Cessation
  • 1988-03-25 DK DK166788A patent/DK170557B1/da not_active IP Right Cessation
  • 1988-03-29 NO NO881414A patent/NO174416C/no unknown
• 1989
  • 1989-02-03 FI FI890533A patent/FI890533A/fi not_active Application Discontinuation

Non-Patent Citations (1)

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