PL163761B1 - Sewage treatment method - Google Patents

Abstract

2064809 9102698 PCTABS00003 A process for the treatment of sewage or other wastewater containing organic matter which comprises the steps of: (a) mixing sewage or other wastewater containing organic matter with a coagulant/adsorbent which is finely divided particulate mineral or clay material the individual particles of which have a thin hydroxylated surface layer, under conditions whereby at least a substantial proportion of the organic material in the sewage or other wastewater containing organic matter becomes attached to the coagulant/adsorbent; (b) separating the coagulant/adsorbent with attached organic material from the mixture to leave a treated liquid effluent; (c) treating the separated coagulant/adsorbent from step (b) with alkali thereby to release the organic material therefrom, separating the coagulant/adsorbent from the resultant concentrated slurry containing the organic material; and (d) adding acid to the concentrated slurry of organic material to lower the pH to less than 4 and thereby to obtain a sludge which separates under gravity and a supernatant liquid which optionally may be recycled to acidify the incoming sewage or other wastewater containing organic matter.

Description

The present invention relates to a method of treating waste water or other waste water containing organic compounds to obtain a transparent run-off liquid that can be safely discharged, for example into an ocean or a watercourse, and a dense sediment suitable for trough leveling or other uses.

Australian Patent No. 79,700 / 87 discloses a waste water treatment method in which a particulate mineral or clay material referred to as a "coagulant" (adsorbent) is mixed with the raw waste water under slightly acidic conditions in conjunction with the addition of a coagulant. After separating the treated wastewater, a concentrated suspension containing the organic materials originally present in the raw wastewater can be produced by adding an alkali to the separated mineral particulate material or clay material and by passing the mixture through a solids separation device. The concentrated slurry is then subjected to anaerobic digestion for approximately 1 day to obtain effluent, which is discharged into a settling tank, where optional biomass is deposited. The liquid flowing overhead from the sedimentation tank is capable of being recycled for rinsing in the plant.

The concentrated slurry has a high water content and causes problems if used to smooth out depressions in the field without anaerobic digestion. Anaerobic digestion is a slow and uncertain process, subject to environmental influences and changes in water supply. The need for further treatment in sludge tanks increases the required land area and, consequently, the investment costs of the wastewater treatment plant as well as the time needed for treatment.

It has been surprisingly found that the concentrated slurry can be further concentrated by adding acid to lower the pH of the slurry to 4 or less, thereby rapidly forming a thick precipitate. The supernatant supernatant can be easily separated and used to acidify the raw sewage passing through. High solids sludge can be easily dewatered before being used to fill potholes or reused.

According to the invention, the method of treating wastewater or other used water containing organic materials comprises the following steps:

a) mixing waste water or other used water containing organic materials with a coagulant / adsorbentene, which is a fine particle or clay material, the individual particles of which have a thin hydroxylated surface layer, under conditions where at least a substantial part of the organic material in the waste water or other waste water containing organic materials is attached to a coagulant / adsorbent;

b) separating the coagulant / adsorbent with the attached organic material from the mixture to obtain purified effluent;

c) treating the separated coagulant / adsorbent from step b with an alkali to free organic material therefrom, separating the coagulant / adsorbent from the resulting organic material containing concentrated suspension; and d) adding acid to the concentrated organic material slurry to reduce the pH value to less than 4 and thus obtain a sludge that is separated by gravity and a purified supernatant liquid that may possibly be recycled to acidify incoming sewage or other spent waste water containing organic materials.

The coagulants / adsorbents that can be used in the present invention can be of two distinctly different types, namely: (I) those in which the hydroxylated layer is produced directly from the substance of the particles; and (II) those in which the layer is obtained from another substance.

The preferred coagulants / adsorbents are Type I materials and can be obtained from a wide variety of minerals and clays provided that the nature of the mineral is such that it allows easy formation of a hydroxylated surface. In this regard, oxides and silicates are especially useful.

Examples of such minerals include zinc oxide, silica, and silica materials such as sand and glass, and clay materials such as mica, porcelain clay, and pyrophyllite. The list is not exhaustive, however, and many other materials are suitable for use with the invention.

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In the most preferred embodiment of the invention, the particulate material is magnetic or magnetizable. Iron oxides, such as, for example, gamma or magnetite iron oxide, or ferrites, such as barium ferrite or spinel ferrite, are excellent for this purpose.

The coagulant / adsorbent particles should be 50 µm or less, preferably 1-10 µιη, more preferably 1-5 µm.

The preparation of Type I coagulant / adsorbent fine particles each having a hydroxylated surface layer is readily accomplished, usually by suspending the particles in an alkaline, preferably alkaline, solution for a short period of time, preferably in the presence of air. Sodium hydroxide is suitable, but potassium hydroxide, calcium hydroxide, or ammonium hydroxide can also be used. Typically the alkali concentrations should be at least 0.01 M, preferably about 0.05 M to 0.1 M, at which level the treatment is already effective after about 10 minutes. Shorter processing times can be obtained by using elevated temperatures and / or higher concentrations of alkali. The proposed temperature range is 40-60 ° C. For example, a satisfactory material is obtained using either 0.1 M sodium hydroxide at room temperature (i.e., about 20 ° C) for 10 minutes or 0.05 M sodium hydroxide solution at about 60 ° C for 5 minutes.

Since the type II hydroxylated coagulant / adsorbent layer is formed by a different substance than the material of the mineral or clay particles, the range of starting materials is wider. A wide variety of minerals and clay can be used provided that the nature of the mineral or clay is such that it allows the hydroxide gel to be readily deposited on its surface. In this regard, oxides, sulfates, silicates, and carbonates are especially useful. Examples of such materials include calcium sulfate, calcium carbonate, zinc oxide, and boron sulfate. This list is not exhaustive and many other minerals are suitable for use with the invention. In some cases, pretreatment of the mineral surface may be required to form a satisfactory hydroxide layer. Yet another alternative is to use hollow microspheres, for example glass, to form gel particles that can be separated from the purified effluent after adsorption of organic material in step (a) by flotation rather than sedimentation.

The hydroxylated layer of Type II coagulant / adsorbent particles may be formed by one of a variety of metal hydroxides, the condition being substantially water-insoluble and the metal valency of preferably 3 or more.

Suitable metals with such properties are iron, aluminum, zirconium and thorium. Ferric hydroxide is preferred as it is cheap and extremely insoluble over a wide range of pH values. For example, nothing dissolves easily at a high pH value, as is the case with aluminum hydroxide.

Preparation of the coated type II particle is also easy to carry out, usually by suspending the particles in water, adding a salt of a suitable metal, followed by an alkali material, preferably in an aqueous solution, which precipitates the metal hydroxide, which then forms a coating on the particle. Chlorides, sulfates, nitrates or other salts of inorganic acids are typically suitable. Examples are ferric chloride or aluminum sulphate. The alkaline material may be sodium hydroxide, calcium hydroxide, ammonium hydroxide, or other suitable soluble material. The concentration and temperature at which this preparation takes place are generally not critical.

In the case where magnetite or other iron oxide materials are used as the basis for type II particles, the metal salt used to form the hydroxide layer can be obtained by first adding acid to the particle suspension (to obtain ferric and / or ferrous salts in the oxide solution). iron) and then adding the alkaline material.

After preparation, it is best not to allow the coated particles to dry. This can be avoided by keeping them under water. The thickness of the hydroxylated layer on the particles is not important as fluoculation or coagulation is a surface phenomenon.

An important advantage of the process according to the invention is that the coagulant / adsorbent particles can be recycled many times. To achieve this, the adsorbed material is removed by increasing the pH of the adsorbent suspension in water. In the case of type I coagulants / adsorbents, the coagulation properties can be recovered by treatment with an alkaline solution. Both of these processes can be linked together.

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Similar to the Sirofloc water purification process described in Australian Patent No. 512,553 by the same applicant, the process of the present invention can be assisted by adding to the treated liquid a suitable coagulant, such as a polyelectrolyte (cationic, anionic or non-ionic) and / or an inorganic coagulant which is provides polyvalent cations such as Fe ²⁺ (e.g. ferrous sulfate). Often polyvalent cations will have a valency of three or more, such as Fe 3+ or Al ³⁺ (e.g. from alum or ferric chloride). These coagulants are not essential, but when both types are present (i.e. polyelectrolytes and inorganic coagulants) they complement each other. The polyelectrolyte may be in the range 0-10 mg / l, preferably 2-5 mg / l. The inorganic coagulant may be in the range 0-500 mg / l, preferably 20-50 mg / l.

The separated coagulant (the adsorbent from step (c) may be recycled to step (a). Any strong acid may be used to lower the pH value in step (d). Acids of this type include inorganic acids such as sulfuric acid or acid hydrochloric, and organic acids such as fluoroacetic acid.

The sludge produced by the process of the invention comprises metal hydroxides and organic materials, and may optionally be dried by any convenient method such as centrifugation, extrusion or the use of microwave irradiation. Alternatively, organic material may be removed from the sludge by a method called "wet air oxidation", leaving only a small volume of metal oxides to be removed.

The preferred coagulant / adsorbent is magnetite and a similar detailed description below will apply to this material. It should be noted, however, that the reference to magnetite includes "mutatis mutandis other coagulants / adsorbents."

The invention is further described with reference to the drawing, in which Fig. 1 is a flow diagram showing the method of the invention in its principal form. Wastewater or other waste water containing organic compounds is mixed with fine-grained, purified recycled magnetite, which can be regenerated by suspending it in a caustic soda solution to form a thin hydroxylated surface layer, and the mixture is mixed to ensure good contact of the waste water or other waste water containing organic materials with regenerated magnetite particles, which preferably have a size of 1-10 µm. The pH can be adjusted by adding an acid to be in the range 5-9, preferably 5.5-6.5, and additionally adding an inorganic coagulant and / or a secondary coagulant (e.g. polyelectrolyte) may also be necessary to obtain a satisfactory quality. of the effluent treated liquid, depending on the concentration and composition of the incoming feed. After 2-20 min. preferably 10-15 min. contact, the magnetite slurry is separated from the treated liquid, which can be drained into sedimentation tanks for final purification prior to discharge. The magnetite particles to which most of the organic material originally present in the wastewater or other waste water has now adhered are then purified by separating the organic material with a dilute solution of sodium hydroxide, ammonium hydroxide or potassium hydroxide, or for example a lime slurry that also regenerates magnetite. The magnetite may then be recycled, with the liquid slurry produced in the organic separation or regeneration step acidified to a pH value of less than four by adding sulfuric acid. Acidification causes the sediment of organic materials to separate by gravity. This precipitate forms within a few minutes of adding the acid, but it takes about 30 minutes for complete precipitation under the purified liquid above it. The sludge can also be quickly separated by dissolved air flotation. The sludge thus obtained can then be easily dewatered by a number of conventional methods, such as centrifugation, belt filtering, and then sand dried to produce a granular material suitable for backfilling in the field. The acidic supernatant liquid can be recycled to acidify incoming wastewater or other spent water containing organic material.

The invention is further described and illustrated in the following examples. These examples do not limit the invention in any way.

The following abbreviation is used: - COD = Chemical Oxygen Demand.

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Example 1 Preliminary experiments were carried out in which 50 ml of concentrated sewage (old stock, stored for a week in a cold store) was acidified from a pH value of 10 to about 7. However, at pH 7, there was little coagulation. The polyelectrolyte was then added to the concentrated waste water after the pH had been reduced to 7, and again no further coagulation was observed. The pH of the concentrated wastewater was further reduced by the slow addition of acid. The onset of coagulation was observed at a pH of about 3.5, the amount of acid added was 30 mmol H ⁺ / l of concentrated waste water.

Example II. A series of experiments were carried out to investigate the effect of the pH value on fresh concentrated sewage. The amounts of acid added were: 30, 40 and 50 mmol H ⁺ / l of concentrated sewage. The results are given in Table 1. The pH value of the concentrated wastewater decreased to 3.5.3 and 2.5, respectively, while the percentage of COD removed from the concentrated wastewater increased from 80 to 85%. The volume of the sediment after 45 minutes of settling was 35% of the total volume. The sludge volume can be further reduced in the thickener.

Example III. Experiments were carried out to investigate the influence of temperature and acid dosage on coagulation in the acidification process. The temperatures selected were 30, 40, 50 and 60 ° C. The results of these experiments are shown in Table 2. The same concentrated (two-day) wastewater batch was used as in Example II. The results show that the percent COD removal was relatively independent of temperature and acid dosage (greater than 40mmol H + / 1 of concentrated waste water) and that fresh concentrated waste water could be coagulated better than the old one. The results are also shown in Fig. 2.

Example IV. The effect of higher acid doses on both iron release into solution and organic compound capture from fresh or stored concentrated wastewater is shown in Table 3 as the results obtained using the method of Example 2. Since COD removal is not substantially influenced by temperature (see example II) the experiments were performed at room temperature (20 ° C). 50-70% of the iron contained in the concentrated sewage can be brought into solution by adding 80-100 mmol H + / l of concentrate. At this acid dose, about 90% of the COD was precipitated in the concentrated sewage. The flakes formed at higher doses of acid were visibly larger and settled faster. Greater iron removal has advantages where the purified supernatant is recycled to acidify the incoming waste water.

EXAMPLE 5 A study was carried out to determine the effect of the pH value on the release of aluminum and COD into solution during acidification of concentrated wastewater obtained from wastewater treatment by the "Sirofloc" method. Aluminum sulphate was used as a coagulant in the Sirofloc process, and the concentrated wastewater from this process was used to carry out the above-mentioned tests. The test results with the use of increased amounts of sulfuric acid to lower the pH value of concentrated wastewater are shown in Table 4.

The deposition properties of the formed flakes and the purity of the final treated concentrated wastewater changed with the pH value. At pH 7.1, flake formation was not good and the resulting solution was very cloudy resulting in a high COD in the concentrated effluent treated. The concentration of aluminum in the solution was also high, which was to be expected at this pH value. At a pH of 3.0-5.2, flake formation was good as the solubility of aluminum was low, however, the flakes formed slowly deposited. The resulting purified solution was pure and had a low COD value. At a pH below 3.0, the solubility of the aluminum increased and the resulting flakes settled faster at the bottom than at the higher pH. The COD released into the solution increased as the pH decreased. Obviously, there was a trade-off between the release of the COD into solution and the recovery of the aluminum in solution. _. ,

Table 1

Number samples Temp. ° C Acid / l mmol / H * / Final pH % COD removed Percent volumetric sediment initial 1 26 thirty 3.5 80 38 2 26 40 3.0 84 35 3 26 50 1.5 85 35

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Table 2

Number samples Temp. ° C Acid / l mmol (H +) Final pH Liquid above the sediment, concentration marry Fe (ppm) % COD removed Percent by vol. the sediment initially 1 60 thirty 3.6 60 65 37 2 60 40 2.4 18 81 36 3 60 50 2.0 25 80 40 4 50 thirty 3.2 60 61 43 5 50 40 2.3 25 77 35 6 50 50 2.0 33 77 35 7 40 thirty 3.1 80 61 70 8 40 40 2.3 25 78 38 9 40 50 2.0 33 79 35 10 thirty thirty 3.3 200 55 80 11 thirty 40 2.5 25 73 62 12 thirty 50 2.2 28 77 38

Table 3

Acid dose applied (mmol H + / l) Final pH Liquid above the sediment, concentration of Fp (MgFe / l) Liquid over the sediment, COD (mg / l) stocked fresh stocked fresh stocked fresh 0 6.0 9.5 1465 1083 10,000 13800 10 2.6 4.4 225 275 660 2700 15 2.4 - 273 - 730 - twenty 2.0 2.2 308 78 770 1030 thirty 2.0 1.9 383 150 890 1290 40 1.9 1.7 535 330 910 1240 60 - 1.5 - 450 - 1340 80 1.8 1.4 1) 18 550 1000 1370 100 - 1.3 - 608 1380 150 - 1.1 - 565 1470

Note: The gassed concentrated wastewater was taken from the Lower Plenty Wiktoria experimental treatment plant and stored at a temperature of 5 ° C. The experimental plant used 47 mg Fe / 1 for the sewage water basin, and the flushing water flow was 3.3% of the raw sewage flow.

Fresh concentrated effluent was taken from the Lower Plenty Wiktoria test site and used immediately. The experimental oysbcsalaiz used 38 mg Fe / l for the wastewater treatment, and the flushing flow doWb was 3.3% of the raw wastewater flow.

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Table 4

Added acid (mmol H + / l) Final PH Concentration of liquid above sediment (mg / l) COD Al 0 10.3 4820 234 twenty 7.1 3617 190 thirty 5.2 713 11 32.5 4.7 651 15 35 4.2 618 28 37.5 3.9 685 51 40 3.5 745 69 45 3.0 800 140 50 2.6 863 177 100 2.0 996 210

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Sediment to be removed or sold

FIG. 1

30 ° C

4O ^e C - 50 ° C - 6O * C * - 26 ° C

FIG. 2

Publishing Department of the UP RP. Circulation of 90 copies

Price: PLN 10,000

Claims (12)

Patent claims A method of treating waste water or other used water containing organic materials, characterized in that it comprises the steps of: a) mixing wastewater or other used water containing organic materials with a coagulant / adsorbent, which is a fine-grained mineral or clay material, the individual particles of which have a thin hydroxylated surface layer, under conditions where at least a substantial part of the organic material in the wastewater or other used water containing the organic material attaches to the coagulant / adsorbent; b) separating the coagulant / adsorbent with the organic material from the mixture to obtain a purified effluent; c) treating the separated coagulant / adsorbent from step b) with an alkali to separate organic material therefrom, separating the coagulant / adsorbent from the resultant organic material containing concentrated suspension; and d) adding acid to the concentrated organic material slurry to lower the pH value below 4 and thus obtain a sludge that is separated by gravity and a supernatant liquid that can possibly be recycled to acidify the waste water or other waste water containing the material organic. 2. The method according to p. The process of claim 1, wherein the coagulant / adsorbent is of a magnetic or magnetizable material. 3. The method according to p. The process of claim 2, wherein gamma iron oxide, magnetite or ferrite is used as the magnetic or magnetizable material. 4. The method according to p. The process of claim 1 or 3, wherein the coagulant / adsorbent has a particle size of 50 µm or less. 5. The method according to p. The process of claim 1 or 4, characterized in that the coagulant is added to the waste water or other waste water containing organic material. 6. The method according to p. The process of claim 5, characterized in that an inorganic coagulant providing polyvalent cations is used as the coagulant and is mixed with the waste water or other waste water containing organic materials and the coagulant / adsorbent particles in an amount of 0-500 mg / l of the waste water or other used water containing organic material. 7. The method according to p. The process of claim 6, characterized in that the multivalent cations are selected from Fe ²⁺ , Fe 3+ and / or Al ³⁺ . 8. The method according to p. A method according to claim 5 or 7, characterized in that a polyelectrolyte is used as the coagulant and is mixed with sewage or other waste water containing organic material and with coagulant / adsorbent particles in an amount of 0-10 mg / l of waste water or other used water containing organic material. 9. The method according to p. The process of claim 1 or 8, characterized in that the pH of the mixture of waste water or other used water containing organic material and coagulant / adsorbent particles is set in the range 5-9. 10. The method according to p. A process as claimed in claim 1 or 9, characterized in that the alkaline compound used in step c) is a solution of sodium hydroxide, ammonium hydroxide or potassium hydroxide, or a lime suspension. 11. The method according to p. The process as claimed in claim 1 or 10, characterized in that the coagulant / adsorbent particles from step c / are returned to step a /. 12. The method according to p. The method of claim 1 or 11, characterized in that the sludge is separated by dissolved air flotation. 163 761