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
  • C02F1/28—Treatment of water, waste water, or sewage by sorption
  • C02F1/281—Treatment of water, waste water, or sewage by sorption using inorganic sorbents
• • 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 process of removing phosphate from water, in particular waste water.
• the process according to the invention is characterized by what is stated in the characterizing portion of claim 1.
• the invention further relates to an apparatus for use when carrying out the process.
• a reduction of the phosphate content may be effected by biological and/or chemical methods.
• a biological removal of phosphate may be effected by means of autotrophic microorganisms which under certain conditions accumulate more phosphate than necessary for the metabolic processes. The method, however, demands completely specific operating conditions and microorganism, and it is impossible to observe the demands which today are made on the effluent from purification plants.
• the chemical processes for removal of phosphate can be divided into three groups dependent on the stage in the aggregate purification procedure at which the reagents are dosed: Pre-precipitation, where the reagents are dosed and the precipitated sludge removed before the biological purification is initiated. Simultaneous-precipitation, where the reagents are introduced during the biological purification and where the precipitate is removed together with the biological sludge. Post-precipitation, where the reagents are dosed and the chemical precipitation occurs after the biological purification. In all three precipitation types chemical sludge is produced, resulting in increased sludge production from the purification plants with entailing increased costs. In all three cases the precipitated phosphate is deposited without possibility of reuse, even through it constitutes a potential phosphorus resource.
• 2 021 087 discloses a process for removing phosphorous compounds from waste water, by which it has been sought to solve the above problems by treating the waste water with at least one reagent which forms a crystalline sparingly soluble salt and contacting the water with an inoculum which furthers the crystallization. This contact takes place in a fluidized bed of particles of the inoculum.
• the water to be purified must thus have a chemical composition within certain limits. This goes for the calcium concentration which is adjusted by addition of Ca(OH) 2 or CaCl 2 , and in particular for the pH-value which is critical during the entire course of the process.
• the transient hardness of the water i.e. bicarbonate content
• pH must again be raised to precipitate phosphate, e.g.
• GB publication No. 2 053 884 discloses a method of removing phosphate from waste water in a fluidized bed of metal phosphate particles.
• the phosphate is crystallized as metal phosphate on the metal particles after treatment of the waste water with one or more metal compounds selected from Fe(III)- and Al-compounds.
• it is however necessary to perform several adjustments of pH to make the process proceed satisfactorily and to obtain a purified waste water which without risk can be discharged to the recipient.
• the necessity of adjusting pH is a consequence of the precipitation reaction
• the effluent flow from the mechanical and biological plant must be oxidized prior to the phosphate removal proper. This may be effected either by passing the water over oxidation steps or by blowing air through the water.
• a pH-lowering is superfluous because the velocity decisive stage is not the precipitation of Fe(III) phosphate, but the oxidation of Fe(II) to Fe(III), which proceeds slowly and controllably at normal degrees of acidity.
• the drawing shows a column 1 which in one embodiment is a cylinder having a height of 4 m and a diameter of 60 cm.
• the column is partly filled with a particle material 2 which e.g. may be particles of the same material which it is desired to precipitate, i.e. iron(III)-phosphate.
• a particle material 2 which e.g. may be particles of the same material which it is desired to precipitate, i.e. iron(III)-phosphate.
• Another material which has been found suitable is ordinary quartz sand which is attractive not least for reasons of economy.
• phosphate containing waste water by means of a pump 4 is introduced into the column through a feed tube 5.
• phosphate containing waste water by means of a pump 4 is introduced into the column through a feed tube 5.
• a feed tube 5 From a container 6 an almost saturated solution of a Fe(II) salt is passed into the column 1 by means of a pump 7, and by suitable flow-regulation a solid, stirred or fluidized bed of
• the purified waste water leaves the apparatus via an overflow 8.
• the dosing of the Fe(II) solution may take place immediately above the bottom of the column or it may take place at several levels or at several points at a level dependent upon the selected apparatus size which is not critical .
• the particle material may advantageously be quartz sand, but it is also obvious to use particles of the same compound as it is desired to precipitate, i.e. Fe(III)-phosphate containing particles.
• the particle size is typically a diameter of 0.1-1.0 mm, preferably a diameter of 0.3-0.6 mm. It is desirable to use small particles to achieve a large crystallization area, but large particles to achieve a high hydraulic surface load.
• the metal compound which in aqueous solution is introduced into the column may advantageously be an almost saturated solution of FeSO 4 ⁇ 7H 2 O.
• Fe(II)-salt solutions may well be used, but iron(II) sulphate is particularly advantageous as it is a cheap and easily accessible material which e.g. occurs as by-product in titanium dioxide production.
• Another suitable Fe(II) salt is Fe(II) chloride.
• the reaction is very fast, the typical residence time being some minutes. This is a very short residence time. in waste water context where residence, times of several hours are often used, and it is obvious that in this way a significantly improved utilization of the apparatus is achieved.
• the particles may be used as filler material in the building sector.
• Another possibility is to use the particles for producing phosphoric acid.

Landscapes

• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (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)
• Removal Of Specific Substances (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8148615

Family Applications (1)

Country Status (3)

Cited By (4)

Citations (4)

• 1988
  • 1988-11-14 DK DK634588A patent/DK634588D0/da not_active Application Discontinuation
• 1989
  • 1989-11-13 AU AU46316/89A patent/AU4631689A/en not_active Abandoned
  • 1989-11-13 WO PCT/DK1989/000266 patent/WO1990005705A1/en unknown

Patent Citations (4)

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