AU2008201191A1 - Method for Flocculation Treatment using Zeolite - Google Patents

Description

Method for Flocculation Treatment using Zeolite TECHNICAL FIELD The present invention relates to a method for flocculation treatment using a zeolite 5 which allows contaminants in water such as nitrogen, phosphorus, and heavy metals to be separated and removed simply and rapidly, and which can be applied to the treatment of lakes, rivers, various industrial wastewaters, and the like. BACKGROUND ART In the field of wastewater treatment, biological nitrification and denitrification has 10 previously been known as a nitrogen removal method. This method generally comprises two steps of "nitrification" and "denitrification". In the nitrification step, ammonium ions (NH 4 *) are oxidized to nitrite ions (N0 2 ) with a nitrite bacterium (representative species: Nitrosomonas), and the resulting nitrite ions are oxidized to nitrate ions (N0 3 ) with a nitrate bacterium (representative species: Nitrobactor). 15 N0 2 ~ and N0 3 ~ are subsequently reduced to nitrogen (N 2 ) gas with a denitrifying bacterium (facultative anaerobic bacteria such as Pseudomonas) under anaerobic conditions. Such nitrification and denitrification requires an organic carbon source, and therefore increases costs, while biological nitrification and denitrification cannot be 20 applied to wastewater containing small amounts of an organic carbon source. Also, when the raw water contains heavy metals, being toxic for organism, which makes treatment difficult. 1 Japanese Patent No. 3,983,342 discloses a technique of applying a flocculation method using a zeolite to raw water containing nitrogen components and heavy metals. This technique, however, employs calcium and magnesium compounds together, which may result in a large amount of sludge. 5 All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and 10 pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country. It is acknowledged that the term 'comprise' may, under varying jurisdictions, be 15 attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 20 'comprising' is used in relation to one or more steps in a method or process. It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice. Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only. 25 DISCLOSURE OF INVENTION The object of the present invention is to provide a method for flocculation treatment using a zeolite which allows ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, 2 and the like in raw water to be treated at low cost, and which also allows various heavy metal ions to be removed, without producing a large amount of sludge. In accordance with one aspect of the invention, a method for flocculation treatment using a zeolite, with which the aforementioned object can be achieved, comprises 5 the steps of introducing raw water containing a contaminant including at least one of nitrogen components, phosphorus components, and heavy metals into a zeolite reaction vessel, and adding a natural zeolite powder into the zeolite reaction vessel to allow the contaminant to be adsorbed by the zeolite; introducing a liquid containing the zeolite that has adsorbed the contaminant into a flocculation 10 separation vessel to which a flocculant is added to cause a flocculation reaction; and introducing a liquid containing the flocculated zeolite into a settling tank where the zeolite is sedimented and separated; wherein the natural zeolite powder comprises at least one member selected from the group consisting of clinoptilolite and mordenite; and wherein the flocculant is free of a calcium compound or a 15 magnesium compound, and consists of a polyaluminum chloride aqueous solution and a polymer flocculant. In accordance with another aspect of the invention, a method for flocculation treatment using a zeolite, with which the aforementioned object can be achieved, comprises the steps of introducing raw water containing a contaminant including at 20 least one of nitrogen components, phosphorus components, and heavy metals into a zeolite reaction vessel, and adding a natural zeolite powder into the zeolite reaction vessel to allow the contaminant to be adsorbed by the zeolite; introducing a liquid containing the zeolite that has adsorbed the contaminant into a flocculation separation vessel to which a flocculant is added to cause a flocculation reaction; 25 and introducing a liquid containing the flocculated zeolite into a settling tank where the zeolite is sedimented and separated; wherein the natural zeolite powder comprises at least one member selected from the group consisting of clinoptilolite 3 and mordenite; and wherein the flocculant is free of a calcium compound or a magnesium compound, and comprises, as a principal component, unit particles obtained by breaking down aggregates of mineral particles in a mineral raw material principally comprising fine particles of hydrous aluminum silicates 5 including soils or weathering products of rocks including volcanic ruptives. In a preferred embodiment of the invention, the unit particles of the flocculant retain a hydrous aluminum silicate structure, are present in water, and exhibit a self-flocculating property. In another preferred embodiment, the natural zeolite has a cation exchange 10 capacity of 80 meq/1 00 g or higher. Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof. BRIEF DESCRIPTION OF DRAWINGS 15 Embodiments of the present invention will be described with reference to Fig. 1. Further aspects of the present invention will become apparent from the ensuing description which is given by way of example only and with reference to the accompanying drawings in which: Figure 1 is a schematic diagram showing an embodiment of the present 20 invention. BEST MODES FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to Fig. 1. <First Embodiment> 4 Referring to Fig. 1, reference numeral 1 denotes a raw water tank, and a raw water pump 10 is disposed within the raw water tank 1. The raw water contains a contaminant including at least one of nitrogen components, phosphorus components, and heavy metals. Examples of nitrogen components include all that 5 release sources of nitrogen such as nitrogen-containing compounds (for example, ammonium chloride, ammonium nitrate, etc.), in addition to various nitrogen components such as ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen. Examples of phosphorus components include phosphoric acid ions, phosphorous acid ions, and other phosphorus-containing compounds. Examples of heavy 10 metals include zinc, lead, copper, manganese, chromium, and cadmium. In Fig. 1, reference numeral 2 denotes a zeolite reaction vessel, which comprises an agitator 20 and a zeolite feed facility 21. The zeolite feed facility 21 comprises a hopper 211 that stores a natural zeolite powder 210 and a zeolite feeder 212 disposed at a lower end of the hopper 211. 15 The raw water is fed by the raw water pump 10 to the zeolite reaction vessel 2 via a raw water feed pipe 11. The raw water feed pipe 11 is equipped with a flow rate meter 12. When the raw water is introduced into the zeolite reaction vessel 2, the zeolite feed facility 21 is operated and adds the natural zeolite powder in predetermined 20 amounts into the reaction vessel 2. The amount of the zeolite powder added can be changed suitably according to the concentration of the contaminants. Examples of powdered natural zeolites for use in the method for flocculation treatment using a zeolite of the invention are clinoptilolite, mordenite, and the like, and these materials can also be used in combination. 5 The natural zeolite used in the invention has a high cation exchange capacity, which is preferably 80 meq/100 g or higher, and more preferably about 150 meq/100 g. Both clinoptilolite and mordenite have a cation exchange capacity of 150 meq/100 5 g, and are preferable for use in the invention; however, when higher reaction rate is important, mordenite with a relatively high reaction rate is preferred. When a natural zeolite with a cation exchange capacity of 150 meq/1 00 g is used in the invention, the theoretical value with respect to ammonium (NH 4 ) removal is 150 meq x 18/100 g zeolite, and hence, 27 mg NH4/1 g zeolite. 10 In designing the actual system, however, in view of unreacted portions or various factors that may inhibit efficiency, it is preferable to add the natural zeolite in an amount two to three times the theoretical value. In the zeolite reaction vessel 2, the zeolite adsorbs the contaminants. A pH adjuster can also be added to promote the adsorption reaction. 15 The liquid containing the zeolite that has adsorbed the contaminants is then fed to the flocculation separation vessel 3 via a pipe 22. The liquid is preferably fed, not using a pump but using water head pressure, in view of operating-cost reductions. As shown in Fig. 1, the flocculation separation vessel 3 is preferably separated into two vessels according to the type of the flocculant to be added, so as to promote 20 the flocculation reaction. In Fig. 1, reference numeral 30 denotes a first flocculation separation vessel, and reference numeral 31 denotes a second flocculation separation vessel. A flocculant composed of a polyaluminum chloride aqueous solution is added to the first flocculation separation vessel 30. A polymer flocculant is added to the second flocculation separation vessel 31. 6 In this embodiment, a polyaluminum chloride aqueous solution and a polymer flocculant are used as flocculants, and calcium and magnesium compounds are not used. The exclusion of calcium and magnesium compounds results in a reduced amount of sludge produced. 5 As a polyaluminum chloride aqueous solution, a commercially available product under the tradename "PAC" is introduced into a tank 32, and fed via a pump 33 to the first flocculation separation vessel 30. As a polymer flocculant, a commercially available product in the form of a powder is dissolved in water inside a polymer tank 34 to form an aqueous solution, which is 10 fed via a pump 35 to the second flocculation separation vessel 31. When the product "PAC" is used, the amount of the polyaluminum chloride aqueous solution is preferably from 20 to 500 ppm, and more preferably from 50 to 200 ppm, by volume of the raw water. The amount of the polymer flocculant, when calculated as the powder, is preferably 1 to 5 ppm by volume of the raw water. 15 Each flocculant is added to the first flocculation separation vessel 30 or the second flocculation separation vessel 31, where a flocculation reaction takes place, and then the liquid containing the flocculated zeolite is fed via a pipe 36 to the settling tank 4. Also in this case, the liquid is preferably fed not using a pump but using head pressure. In the settling tank 4, the flocculated zeolite is sedimented and 20 separated to yield treated clear water. The sedimented zeolite is drawn out with a sludge pump 40, and then transported to a disposal place or the like. The treated water is fed to a treated water tank 5, and can be transported by a treated water pump 50 to the outside for purposes such as reuse. <Second Embodiment> 7 In the second embodiment, the following flocculant is used instead of the polyaluminum chloride aqueous solution used in the first embodiment. The flocculant used is a solution comprising, as a principal component, unit particles obtained by breaking down aggregates of mineral particles in a mineral 5 raw material principally comprising fine particles of hydrous aluminum silicates including soils or weathering products of rocks (including volcanic ruptives). The amount of the liquid flocculant added is preferably from 50 to 300 ml/L by volume of the raw water. The method for manufacturing the flocculant is first described. 10 The first step comprises collecting a mineral raw material principally comprising fine particles of hydrous aluminum silicates including soils or weathering products of rocks (including volcanic eruptives), and sorting the mineral raw material. The principal raw material for use in the flocculant of the invention may be any mineral raw material principally comprising fine particles of hydrous aluminum 15 silicates including soils or weathering products of rocks (including volcanic eruptives), such as, for example, red and yellow soils, red soils, andosols or weathering products of basalt, volcanic ash, or pumice. Note that materials containing, for the most part, pebbles that may be inconvenient for water treatment are not preferable. Also, in the case where the organic matter 20 content of treated water is legally regulated, those with high humic substance content is not preferable. The second step comprises obtaining unit particles by breaking down aggregates of mineral particles in the mineral raw material using an agitation, vibration or shaking process, with the mineral raw material being admixed with water in a 25 dispersion container; wherein the step of obtaining unit particles comprises 8 employing a process selected from the group consisting of agitation, vibration, shaking processes, and a combination thereof, to such an extent that a structure of the hydrous aluminum silicate in the unit particles is not destroyed. The soil or weathering products of rocks (including volcanic eruptives) collected 5 may contain firm aggregates of mineral particles, or loose aggregates of mineral particles. Depending on the extent of aggregation, a process may be used selected from the group consisting of agitation, vibration, shaking processes, and a combination thereof. 10 Examples of agitation processes include those using a stirrer, an impeller, an underwater pump, and an underwater mixer; examples of vibration processes include those using a high-frequency vibrator and sonic waves; and examples of shaking processes include reciprocating shaking and rotational shaking. Mineral fine particles contained in soils or weathering products of rocks are 15 principally composed of a hydrous aluminum silicate, and the structure of these mineral fine particles is easily destroyed by mechanical grinding. This results in problems such as easy dissolution of aluminum as ions. For this reason, it is not preferable to mechanically grind the the soils or weathering products of rocks used as a raw material. 20 By employing the method of the invention described above, unlike conventional grinding processes, unit particles can be obtained by breaking down aggregates of mineral particles in a raw material, without destroying the structure of the hydrous aluminum silicates. Moreover, the mineral particles of the size of silt or sand contained in the raw materials are not made finer and added into the water to be 25 treated as new suspended particles. 9 The unit particles are obtained according to the above-described dispersion process in water, and the flocculant of the invention is obtained in which the resulting unit particles are dispersed or loosely associated with one another in water. 5 Although the amount of water used is not particularly limited, it is determined in consideration of the specifications of the apparatus used for injecting water, transport cost of the manufactured flocculant, and the like. Using the above-described process, the unit particles are dispersed in water without addition of any additives. This is basically considered to be due to charge 10 repulsion. This state of dispersion may deteriorate with the passage of time, in which case a pH adjuster is preferably added to maintain the dispersion of the unit particles in water. The unit particles obtained according to the invention have a feature of exhibiting a 15 self-flocculating property. The pH or the concentration of the concomitant salt may also be adjusted so that the unit particles exhibit a self-flocculating property. As used in the specification, the term "self-flocculating property" means that the flocculant self-flocculates when added to water free of suspended particles (for example, water obtained by filtering the water to be treated using a membrane 20 filter). The flocculant thus manufactured exhibits a self-flocculating property in the raw water, and forms flocs by physically incorporating therein the zeolite (suspended particles) in the water. In the formation of flocs, it is not basically necessary to add a polymer flocculant as 25 shown in Fig. 1, but such a polymer flocculant may also be added. 10 EXAMPLES Examples of the present invention will be described. The invention is not limited by these Examples. Example 1 (Experiments of Ammonia Removal) 5 Test water was prepared by adding 0.04 ml of 25% aqueous ammonia to 1 L of tap water. The ammonium (N-NH 4 ) concentration was 9.1 mg/L. A 2.5-g quantity of a 100-mesh powder of a natural zeolite ("mordenite" manufactured by Nitto Funka K. K) was added to 1 L of the test water, and the mixture was agitated for 15 minutes with a jar tester at 150 rpm. 10 A 250-g quantity of an aluminum-based flocculant (tradename "PAC") was then added. After 3 minutes, the speed was reduced to 100 rpm, and after 45 seconds, the speed was further reduced to 50 rpm, and after 3 minutes, the agitation was stopped. The test water was allowed to stand for 10 minutes, and the ammonium

(N-NH

4 ) concentration in the supernatant was measured. 15 Also, the procedure of the above-described experiment was repeated, except that the amount of the natural zeolite powder used was varied to 2 g, 1.5 g, 1 g, 0.5 g, or none, and the concentration of ammonium (N-NH 4 ) in each supernatant was measured. The results are shown in Table 1. Table 1 amount of the natural zeolite powder ammmoniumu concentrarion (mg/L) 0. 4 0.5. 2.3 1.0. 1.7 1.5. 1.2 2.0. 0.9 2.5. 0.8 11 Example 2 In accordance with the procedure of Example 1, experiments were similarly conducted using the following flocculant instead of the aluminum-based flocculant (tradename "PAC"). 5 <Preparation of Flocculant> A weathering product of volcanic ash with an organic carbon content of 0.1% was air-dried and used as a raw material. A 200-g quantity of the raw material was placed in a 1 -L vessel, and water was slowly added, while mixing it well with the raw material, to a total volume of 1 L. 10 The pH was then adjusted to 4.5 by adding 2 mol/L of hydrochloric acid. The resulting mixture was was processed using "T-A 4280" Ultrasonic Generator, manufactured by Kaijo Corporation, at a power of 200 W and at an ultrasonic frequency of 19.5 kHz, for 30 minutes. <Experimental Results> 15 The results are shown in Table 2. Table 2 amount of the natural zeolite powder ammmoniumu concentrarion (mg/L) 0. 3.7 0.5. 2.3 1.0. 1.6 1.5. 1.1 2.0. 0.9 2.5. 0.8 Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims. 12

Claims (5)

1. A method for flocculation treatment using a zeolite, comprising the steps of: introducing raw water containing a contaminant including at least one of nitrogen components, phosphorus components, and heavy metals into a zeolite reaction vessel, and adding a natural zeolite powder into the zeolite reaction vessel to allow the contaminant to be adsorbed by the zeolite; introducing a liquid containing the zeolite that has adsorbed the contaminant into a flocculation separation vessel to which a flocculant is added to cause a flocculation reaction; and introducing a liquid containing the flocculated zeolite into a settling tank where the zeolite is sedimented and separated; the natural zeolite powder comprising at least one member selected from the group consisting of clinoptilolite and mordenite; and the flocculant being free of a calcium compound or a magnesium compound, and consisting of a polyaluminum chloride aqueous solution and a polymer flocculant.

2. A method for flocculation treatment using a zeolite, comprising the steps of: introducing raw water containing a contaminant including at least one of nitrogen components, phosphorus components, and heavy metals into a zeolite reaction vessel, and adding a natural zeolite powder into the zeolite reaction vessel to allow the contaminant to be adsorbed by the zeolite; 13 introducing a liquid containing the zeolite that has adsorbed the contaminant into a flocculation separation vessel to which a flocculant is added to cause a flocculation reaction; and introducing a liquid containing the flocculated zeolite into a settling tank where the zeolite is sedimented and separated; the natural zeolite powder comprising at least one member selected from the group consisting of clinoptilolite and mordenite; and the flocculant being free of a calcium compound or a magnesium compound, and comprising, as a principal component, unit particles obtained by breaking down aggregates of mineral particles in a mineral raw material principally comprising fine particles of hydrous aluminum silicates including soils or weathering products of rocks including volcanic ruptives

3. The method according to claim 2, wherein the unit particles of the flocculant retain a hydrous aluminum silicate structure, are present in water, and exhibit a self-flocculating property.

4. The method according to claim 1, 2, or 3, wherein the natural zeolite has a cation exchange capacity of 80 meq/1 00 g or higher.

5. A method as substantially described herein with reference to the description and attached representations. 14