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
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
• • 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
  • C02F1/5227—Processes for facilitating the dissolution of solid flocculants in water
• • 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

Definitions

• the present invention relates to a process and a composition for conditioning an aqueous system, especially a system comprising water having matter suspended therein, for example sewage.
• condition is meant bringing about a change which aids separation of water and suspended matter, as in, for example, sedimentation or filter-pressing in wastewater or sewage treatment.
• Hydrated lime hereinafter termed 'lime' (calcium hydroxide) in distinction from quicklime (calcium oxide), its industrial precursor, is traditionally used in wastewater conditioning. It is desirable to supply lime to the user in the form of an aqueous suspension, especially by means of a tanker filled and emptied by pumping. Hitherto it has hardly been possible to pump lime suspensions at solids contents above 35% by weight. This involves costs in transporting water which have in the past made such operations uneconomic.
• cationic polyelectrolytes In wastewater treatment the use of cationic polyelectrolytes is now generally preferred, because they are directly substantive to organic suspended matter in most wastewaters : in sewage, animal farm waste, paper ⁇ making effluent and many industrial effluents, suspended matter carries a negative charge and is thus best treated by cationic polyelectrolytes which carry a positive charge.
• lime is used as a part of a lime or lime-soda water-softening process; polyelectrolyte may be added to accelerate the sedimentation of suspended organic or inorganic matter and of the calcium carbonate particles precipitated by interaction of the lime with the hardness of the water.
• conditioning aids such as lime, and polyelectrolyte separately; weighting agents where used are also separately added.
• This additive could then be transported, as a suspension, by tanker or other means to the user site.
• the preparation of solutions of polyelectrolytes. is also not free from difficulty and is best carried out centrally with appropriate equipmen For this operation to be commercially successful it would be necessary for the material carried by tanker to be of high solids content so as to minimise transport charges on water. It is clearly of the greatest convenience to the user for a single additive suspension/solution to be supplied by road or rail tanker and cleanly pumped into a tank having simple facilities for avoiding sedimentation, e.g. by slow stirrer or bubble suspension.
• effluent water such as sewage
• a small quantity generally 0.05 to 0.5%) of lime to give flocculant precipitate that can be drained and then pressed to give a compact mass.
• An absorbent material for example calcium carbonate, may be added to the lime.
• the system developed by Stead and Winfield will be of particular advantage in areas where at present virtually untreated sewage is pumped into the sea or into tidal estuaries.
• the plant should enable a massive reduction in pollution to be achieved at minimal cost.
• sewage particularly in hard water areas, has a lime demand (or lime charge); typically, the lime demand of sewage in a hard water area is in the range of 180 to 240 ppm. Reduction in the lime charge used for treatment of the sewage gives poor results, in particular poor clarification and failure to remove organic matter.
• the present invention provides an aqueous composition for conditioning an aqueous system, which composition comprises (a) particles of an alkaline earth metal hydroxide, characterised in that the composition also contains (b) an anionic oligomeric polyelectrolyte.
• the composition may contain one or more components selected from (c) particulate weighting agents, (d) high molecular weight, cationic polyelectrolytes and (e ) alkali metal, ammonium or quaternary ammonium hydroxides.
• the present invention also provides a process for conditioning an aqueous system, which comprises the addition thereto of an alkaline earth metal hydroxide in the form of a composition according to this invention.
• the present invention also provides a process for conditioning an aqueous system which comprises the addition thereto of an alkaline earth metal hydroxide and a weighting agent, characterised in that a high molecular weight cationic polyelectrolyte is also added to the said aqueous system.
• the invention finds application in a number of fields. Potential uses of the suspensions of the invention clearly include any process which in the past has used lime in the form of a dry powder, since the serious disadvantages of this are avoided. Reference may be made to Robert S. Boynton, 'Chemistry and Technology of Limestone', 2nd Edition 1980, John Wiley, Chapter 11, 'Uses of Lime', particularly Table 11 - 1 'Lime and uses' on p. 384. It should be noted that in this Chapter the use of the term 'lime' includes quicklime used in metallurgy, and that 'lime' meaning hydrated lime, including the cases where this has been formed in situ from quicklime is the subject of the present invention. Other and novel uses may be envisaged.
• the invention can be utilized to advantage in the treatment of wastewater.
• the active components can be formulated as an additive" for the treatment of wastewater, which additive is fluid, pumpable, and suitable for supply by road or rail tanker.
• the invention can provide improved clarification, improved removal of dissolved, e.g. proteinaceous, matter, an increased sedimentation rate and increased density of the settled particulate matter.
• the invention also permits a treatment of water, in particular potable water, in which treatment simultaneous softening (removal of calcium compounds, whether temporary or permanent hardness) and flocculation of suspended impurities take place, and in which there is a more rapid sedimentation of the precipitated or flocculated matter.
• a process and a material for the treatment of animal farm waste e.g. pig farm slurry.
• the invention can, furthermore, be utilized in the treatment of effluents to remove heavy metals economically and effectively.
• the invention can also be utilized, together with the use of ferric chloride or the like, in the treatment of abbatoir wastes (saveall systems).
• the invention finds particular application in the treatment of sewage, whether at the primary, secondary or tertiary stages.
• the invention can be used with any customary sewage-treatme.nt plant; however, it is of particular advantage with the "once through" plant developed by Stead and Winfield, referred to above.
• compositions of the present invention can also be used to advantage in the hydrodynamic separator disclosed in United Kingdom Patent Applications 8026095 and 8124263 when used as a primary settlement facility for waste, e.q. sewage, containing colloidal organic matter.
• the invention can also be used in the conditioning (including dewatering and separation) of sewage sludge.
• conditioning including dewatering and separation
• calcium carbonate is precipitated in sewage in situ, there is an inhibition of crystal growth and of floe formation.
• an insoluble carbonate is added as a weighting agent in accordance with the present invention, protein removal is still effectively maintained, but floe formation and sedimentation are improved.
• component (a) is hydrated lime, Ca(OH) 2 .
• an aqueous suspension or slurry of particulate hydrated lime will generally contain some lime in solution in the interparticulate water.
• dolomitic lime which includes magnesium compounds
• baryta baryta
• the preferred anionic oligomeric polyelectrolytes for use as component (b) are of high charge density, e.g. polyacids and their salts.
• Particularly useful in the present invention as deflocculants are alkali metal salts of simple or complex oligomers of acrylic or methacrylic acid such as Dispex N40 (Allied Colloids Ltd., U.K.) or Orotan 850
• the preferred weighting agents to be used as optional component (c ) are substantially water-insoluble carbonates.
• Calcium carbonate is especially preferred; this can be from a naturally occurring source, ground as appropriate, such as calcite, arago ⁇ ite, limestone, coral or oyster shells, or may be from a synthetic source, for example precipitated chalk.
• barium carbonate or strontium carbonate could be used.
• barium carbonate is also effective in the removal of sulphate (as is barium hydroxide). The removal of mercaptans is particularly important in the treatment of animal farm waste where the mercaptans can produce a most unpleasant odour:
• Precipitated calcium carbonate can be prepared by the addition of calcium oxide and/or calcium hydroxide to water and treating the system with carbon dioxide. By stopping the reaction at an intermediate stage, one would obtain an aqueous slurry containing calcium hydroxide and calcium carbonate; this slurry can be used to provide components (a) and (c) for the practice of the present invention.
• the weight ratio of component (a) to component (c) can be varied widely, depending upon the application; it may be, for example, from 1:19 to 19:1, preferably from 1:9 to 9:1. However, a ratio of from 2:3 to 3:2 can give partic- ularly good results, a ratio of 1:1 being especially preferred.
• Component (a) and component (c ) are generally added at a combined dosage rate of from 20 to 1000 ppm, preferably 20 to 300 ppm, e.g. 50 to 300 ppm. Especially in the treatment of hard-water-borne sewage, a combined dosage rate of 150 to 250 ppm, in particular 200 ppm, has been found to be very effective.
• the polyelectrolyte employed as optional component (d) will generally have a molecular weight of at least 1 ⁇ 10 6 , preferably 6 ⁇ 10 and even as much as 15 ⁇ 10 .
• the high molecular weight is reflected in the fact that the polyelectrolyte gives appreciable viscosity in aqueous solution at a concentration of only 0.1% by weight.
• Cationic polyacrylamides are preferred, e.g. Zetag 92 and Percol 292. It is also practicable to supply the lime suspensions to e.g.
• a sewage treatment works without a content of such a bridge-flocculating polyelectrolyte, this being added either to the lime suspension at the treatment works or separately from the lime suspension to the sewage to be conditioned, as may be found best in practice at the particular site with the particular wastewater.
• the cationic polyelectrolyte (which acts as a flocculant in the system to be conditioned) is generally used at a dosage rate of 0.01 ppm to 20 ppm, especially 0.05 ppm to 5 ppm.
• the anionic oligomeric polyelectrolyte (b) will be present in the aqueous suspensions of this invention in an amount (as active material) of 0.1 to 5%, especially
• the preferred based for use as optional component (e) is an alkali metal hydroxide, especially sodium hydroxide.
• the bases may be produced in situ from appropriate precursors such as carbonates or other salts of weak acids.
• carbonates or other salts of weak acids For example, in the presence of lime, sodium carbonate, borate, aluminate or silicate will provide sodium ions and hydroxyl ions.
• (b), (c), (d) and (e) may each be a mixture of two or more appropriate compounds.
• a weighting agent it is desirable for this to be added simultaneously with the alkaline earth metal hydroxide to the aqueous system to be conditioned. It is particularly preferred that these components be premixed before the said addition in order to allow for maximum activation of these components.
• the cationic polyelectrolyte of high molecular weight can be added before or after the other components, but is preferably added simultaneously with the hydroxide and weighting agent. The addition of the said components in admixture, and in particular as a single slurry, is thus particularly convenient.
• an anionic oligomeric polyelectrolyte will permit the preparation not only of lime suspensions of high solids content (greater than 40?i by weight and preferably 50% or higher) but also of reasonably stable suspensions of high solids content and containing the above-defined components (a) plus (c) and/ or (d).
• the invention provides a suspension of mineral particles which are normally thickened, coagulated or flocculated by a content of dissolved polyelectrolyte but which, are enabled to contain the said polyelectrolyte without the said thickening, coagulation or flocculation occurring.
• a solution of a macromolecular cationic polyelectrolyte which is normally a strong flocculant for suspended particles, can be inhibited under the above conditions, so that the polyelectrolyte solution can be added smoothly and without thickening to the particulate suspension, is most surprising. It is also surprising that the flocculating activity of the cationic polyelectrolyte is at least partially regained on dilution, particularly in hard water.
• the mineral particles In order to achieve the high solids content suspensions which are preferred for the economic operation of the present invention, it is desirable for the mineral particles to be deflocculated by an anionic agent and subjected to high shear mixing before the addition of the solution of the inhibited cationic polyelectrolyte flocculant.
• the particles will be calcareous in nature, for example hydrated lime and/or calcium carbonate.
• the divalent metal ions referred to above as being necessary for optimum effect are conveniently, supplied by an alkaline earth metal hydroxide, preferably calcium hydroxide; this compound will also supply the hydroxyl anions necessary to achieve the alkaline pH, which is also stated above to be necessary for optimum effect.
• M cationic polyelectrolyte to lose its extended molecular chain structure and to form coils which have a greatly decreased flocculating action;
• the divalent ions present repress the anionic activity of the anionic polyacid deflocculating agent which is so chosen that the formation of the calcium salts of these polyacids does not destroy the deflocculating action on the mineral particles in suspension;
• the reduction of the anionic activity of the anionic deflocculant and the reduction of the cationic activity of the cationic flocculant reduce the normal anionic/cationic interaction which normally causes great viscosity increase, gelation, and inhomogeneity.
• the anionically deflocculated lime suspensions of this invention may exhibit thickening which, of course, reduces the ease with which they can be pumped.
• a base as defined above for component (e)
• the use of sodium hydroxide is particularly effective when component (b) is a sodium salt of an oligomer of acrylic acid.
• Vigorous shear mixing is also advantageous to the production of lime-containing suspensions of high solids content.
• Particle simplification may also be useful in giving low void volume as well as suspensions of high solids content; this must be done mechanically by application of shear-energy causing inter-particle friction and attrition.
• Particle smashing e.g. by a ball-mill, is not very effective.
• Heavy duty paste mixers paste mixers (putty mixers), rotor-stator (Kady type) mills, high speed dispersers with saw-toothed impellers (Cowles dissolvers) or sand grinders are suitable. The invention is illustrated in and by the following Examples. Example I
• the calcium carbonate in Sample 2 was Snowcal 8SW; that in Samples 3 and 6 was Snowcal 3ML.
• Snowcal 8SW is a natural whiting of soft chalk origin and Snowcal 3ML derives from hard chalk. Both are products of Blue Circle Industrial Minerals Division.
• Example 7 The product (Sample 7) immediately became fluid so that it could be noisily shaken by hand in a small pot. This property was retained for 3 weeks. The sediment was easily re-incorporated by shaking. The solids content was 62%, as calcium carbonate and 'lime.
• the Hydralime was added to the mixed water and deflocculant with mechanical stirring. A flowy mix showing Theological dilatancy resulted. To this was added 0.5g of Zetag 92 as dry granular particles using mechanical stirring. The mix was then left to stand for 30 mins and was again mechanically stirred. It was a smooth product; the addition of the Zetag 92 produced little viscosity increases. Some dilution would be require for pumping.
• Example IV Suspension of chalk whiting and lime
• a suspension was prepared according to the following formula:
• Example V Demonstration of the value of lime, calcium carbonate and cationic polyelectrolyte flocculant in sewage treatment
• a series of tests were effected in order to compare the effect on primary sewage of a treatment with hydrated lime and Zetag 92 with a treatment employing a hydrated lime and calcium carbonate mixture and Zetag 92. It is extremely difficult to use fully built slurries as a basis for laboratory jar tests since it. is essential to dilute the slurries from 70% down to 1% in order accurately to dispense them into the test solutions.
• the hyd.rated lime and calcium carbonate were prepared as separate suspensions at a concentration of approximately 1% w/w.
• the required volumes of hydrated lime and calcium carbonate suspensions were pipetted into small beakers and mixed before addition to the sewage samples.
• the Zetag 92 was added with more rapid stirring for 30-60 seconds. The stirrer speed was then reduced to gentle agitation so that the floe formation could be observed. After 10 minutes the stirrers were stopped and the sample was allowed to settle for 5 minutes.. Turbidity and pH readings were then taken.
• the experimental results demonstrate that the lime/ carbonate/Zetag 92 treatment, which is in accordance with the present invention, compares favourably with the treatment with lime and Zetag 92 alone. Furthermore, the mixture according to the present invention permits a considerable variation in dosage level to be tolerated without marked deterioration in the efficiency.
• the compositions of the present invention clearly offer increased economy and allow costs of storage and dispensing equipment to be considerably reduced and will, in addition, simplify the overall treatment of the system to be conditioned.
• Table 1 summarizes a comparison of the known lime/Zetag treatment with a calcium carbonate/Zetag 92 treatment and with the lime/calcium carbonate/Zetag 92 treatment of this invention
• Table 2 shows the effect of varying the dose of a 50/50 mixture of lime/carbonate and a 40/60 mixture of lime/carbonate;
• Table 3 shows the effect of omitting the Dispex N40 using a 50/50 mixture of lime/carbonate; and
• Table 4 shows the effect of using Empycryl (Albright & Wilson) as a dispersant with a 50/50 mixture of lime/carbonate.
• the calcium carbonate suspension in Tests 1-18 contained 0.2So Dispex N40 w/w in the weight of calcium carbonate.
• the "Floe Rating” was on a scale from 1 (poor) to 6 (good). A rating of 2 was considered “poor” whereas a rating of 3-5 was considered “fair”.
• the turbidity of the supernatant liquor is given in nephelometric units and was measured, as was the pH, 5 minutes after the treatment.
• a series of laboratory jar flocculation tests was carried out in order to compare the effects on a primary sewage of suspensions according to the invention and of the components added as suspensions prepared directly from the dry powders.
• Fresh raw comminuted sewage was obtained from the Water Research Association, Stevenage, U.K., and tests were carried out using a 6-jar standard laboratory flocculator with stirrers operating at the same speed in each jar containing 500 ml of sewage.
• the tests were carried out by adding the conditioners or flocculants to different jars, running the stirrers at high speed for 1 minute and then at slow speed for 10 minutes. After stopping, the formation of flocs, the rate of sedimentation and the clarity of the supernatant liquid were observed.
• the dose of Hydralime and of polyelectrolyte (Zetag 92 to give the best clarification of the sewage were first determined in order to provide a standard. This was determined as 200mg/l of lime or 125mg/l of lime, and 125mg/l of Snowcal 3ML and 0.4mg/l of Zetag 92. The equivalent proportions of lime and Snowcal were then added as a 62% suspension (Sample 7 of Example II) and equivalent lime was added as a 52.5% solids content lime suspension (Sample 5 of Example I). Floe formation, floe settlement and supernatant liquor clarity were similar to the standard in both cases.
• Example VII Indicating the value of an addition of sodium hydroxide in improving strability.
• Example IV showed slow thickening on storags, and after 3 months had gelled.
• To this gelled sample was added 0.1g of solid sodium hydroxidej the sample was then mechanically stirred at high speed by a laboratory propeller stirrer when it thinned down completely. This sample did not gel again after 7 months storage.
• Example VIII Indicating the value of an addition of sodium hydroxide in improving strability.
• Example IV showed slow thickening on storags, and after 3 months had gelled.
• To this gelled sample was added 0.1g of solid sodium hydroxidej the sample was then mechanically stirred at high speed by a laboratory propeller stirrer when it thinned down completely. This sample did not gel again after 7 months storage.
• Example VIII Example VIII

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• Life Sciences & Earth Sciences (AREA)
• Inorganic Chemistry (AREA)
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• 1982
  • 1982-03-22 CA CA000399002A patent/CA1181653A/en not_active Expired
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• 1984
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• 1986
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