WO2007029967A1

WO2007029967A1 - Method of purifying water comprising coagulation using excess poly aluminum hydroxy chloro sulfate

Info

Publication number: WO2007029967A1
Application number: PCT/KR2006/003545
Authority: WO
Inventors: Min Ja Park; Ho Young Lee; Soo Young Park
Original assignee: Min Ja Park; Ho Young Lee; Soo Young Park
Priority date: 2005-09-07
Filing date: 2006-09-06
Publication date: 2007-03-15
Also published as: KR20070028079A

Abstract

The present invention relates to a water treatment method comprising a chemical coagulation process that uses a coagulant, and more particularly to a water treatment method comprising a coagulation process that uses an excess amount of polyaluminum hydroxychlorosulfate (PAHCS) to coagulate even nonionic organic contaminants and to greatly increase coagulation efficiency. The inventive coagulation process can achieve a very stable coagulation efficiency, compared to a prior general coagulation process that uses alum, PAC, PACS or the like. Also, the inventive process can achieve a water treatment effect, including a reduction in disinfection by-products, which could be achieved only using advanced water treatment techniques (membrane filtration, ozone treatment, activated carbon filtration, etc.)

Description

METHOD OF PURIFYING WATER COMPRISING COAGULATION USING EXCESS POLY ALUMINUM HYDROXY

CHLORO SULFATE

Technical Field

[1] The present invention relates to a water treatment method comprising a chemical coagulation process that uses a coagulant, and more particularly to a water treatment method comprising a coagulation process that uses an excess amount of polyaluminum hydroxychlorosulfate (hereinafter, referred to as "PAHCS") to coagulate even nonionic organic contaminants and to greatly increase coagulation efficiency. Background Art

[2] Suspended solids, fine particles and the like, which cause turbidity in raw water, are negatively charged colloidal particles, and are present as a stable dispersion in water because they repel each other due to negative charges. Generally, coagulants are easily hydrolyzed in water to neutralize the surface charge of negatively charged particles with positively charged materials, and the particles, that lost their electrical repulsive force, contact each other and bind to each other due to attractive force to form floes of a removable size. Because of this mechanism, when most prior coagulants are added in an amount exceeding the upper limit of an addition level suitable for causing neutralization between the positively charged coagulants and the negatively charged colloidal particles, they will generally cause a positively charged state, leading to a great decrease in coagulation efficiency.

[3] Thus, prior coagulants such as alum (liquid aluminum sulfate), PAC (polyaluminum chloride) and PACS (polyaluminum hydroxide chloride silicate), which have been used as coagulants in prior water treatment processes, can exhibit the desired coagulation effect only at a low addition level, set depending on the turbidity of raw water. Thus, these coagulants have a problem in that they have difficulty coping with the case where the turbidity of raw water changes rapidly due to a flood. Also, because they cannot substantially remove nonionic organic substances, which carry no charge in water, they have a fundamental limitation in their ability to remove turbid matter.

[4] Particularly, during a period of time from late autumn, when the temperature of water starts to decrease, to spring, the occurrence of Synedra sp. leads to filter clogging (up to a filter run time of 5-10 hours). Such filter obstruction cannot be prevented with the prior art coagulants, even when the conditions of mixing strength and coagulation strength are maintained at optimum levels. Also, such severe filter obstruction results in a failure to secure the production of drinking water, such that water rationing must be considered. In addition, a large amount of organic matter causing turbidity is present in dam discharge water after floods, and this turbidity-causing organic matter remains without coagulating, so that it leaks into filtered water, and thus reduces the removal rate of pathogenic microorganisms.

[5] An increase in natural organic materials (NOMs), precursors of disinfection byproducts (DBPs), which have recently caused many problems, leads to an increase in disinfection by-products such as trihalomethanes (THMs) and haloacetic acids (HAAs) due to chlorination.

[6] Meanwhile, dissolved or suspended materials (mainly natural organic material

(NOM)) present in raw water will form disinfection by-products (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs) through chlorination. Such disinfection by-products have recently caused many problems with respect to the quality of tap water, and thus it is required to previously remove disinfection by-product precursors (mainly NOM) present in raw water. However, an enhanced coagulation or advanced coagulation process must be used for removal of the precursors, because it is difficult to remove the precursor organic materials using the prior coagulants. The prior enhanced coagulation or advanced coagulation process comprises carrying out coagulation at a reduced pH of about 5 and then increasing the pH, and achieves removal of the precursors; however, it has a problem in that it cannot reduce the turbidity of water, because it is conducted at a pH which is outside of a suitable pH range. Thus, the prior enhanced or advanced coagulation process is not used in practice, although it has been developed. As a substitute for this process, the introduction of advanced water treatment processes such as ozone treatment and activated carbon filtration has been considered. However, it is not easy to introduce the advanced water treatment processes in practice, because these incur high construction and operation costs and require technical expertise.

[7] Thus, solving the problems with the coagulation process with the aim of increasing the efficiency of the coagulation process is preferable to introducing the advanced water treatment process. For this purpose, there is an urgent need to develop a coagulation process, which increases the effect of coagulants on the coagulation of suspended materials in water treatment processes, can reduce the contents of inorganic materials such as aluminum, iron and manganese, and organic materials such as hazardous metals and potassium permanganate, can maintain a stable water treatment process to cope with high turbidity and a rapid change in turbidity in the rainy season, and can remove even organic materials as precursors (NOM) of disinfection byproducts. In connection with this, prior studies focused mainly on changes in physical conditions, including mixing, coagulation and agitation strengths and settling efficiency, but the results thereof were insignificant. The present invention aims to sig- nificantly increase the efficiency of the coagulation process through hydrochemical approaches.

Disclosure of Invention

Technical Problem

[8] The present inventors have conducted studies to overcome the limitation of the prior coagulation process and significantly increase the efficiency of the coagulation process and, as a result, developed a unique coagulation process that uses poly aluminum hydroxy chlorosulfate (PAHCS), which is completely different from the prior coagulants. Specifically, unlike the prior coagulants, which cause good coagulation only at the proper addition level for causing neutralization between the positively charged coagulants and negatively charged colloidal particles, when PAHCS is added in an excess amount corresponding to 2-7 times the amount of use of the prior coagulants, it can rather greatly increase the coagulation rate, and can coagulate and remove even dissolved organic materials which were difficult to remove using the prior methods, so that it can significantly reduce the turbidity of treated water and can greatly reduce disinfection by-products. Also, the inventive coagulation process comprising adding an excess amount of PAHCS can achieve stable coagulation treatment even under conditions of high turbidity and rapidly changing turbidity in the rainy season, because the proper addition range of PAHCS, which causes good coagulation, is very wide.

[9] Accordingly, it is an object of the present invention to provide a coagulation process that uses an excess amount of PAHCS to be able to maximize the removal efficiency of turbidity, effectively remove turbidity-causing organic matter, which has been difficult to remove, maintain a stable coagulation effect even at rapidly changing turbidity, overcome filter obstruction caused by algae, reduce disinfection by-products, improve the taste of water, and effectively remove even trace amounts of various organic components which could not have been removed through chemical coagulation in other water treatment processes.

[10] Also, the present invention provides several embodiments in which an auxiliary process is optionally added before or after the inventive PAHCS coagulation process in order to further increase the efficiency of the coagulation process.

[11] The above and other objects, features and advantages of the present invention will be described below and will be more clearly understood through the embodiments of the present invention.

Advantageous Effects

[12] A combination of the inventive coagulation process, which uses an excess amount of PAHCS, with an auxiliary process, has been developed to treat high-turbidity raw water, low- alkalinity raw water, raw water containing a large amount of organic materials, or the like, or to overcome the limitation of prior coagulation processes upon a rapid change in water quality. The inventive coagulation process can effectively coagulate and remove even turbidity-causing material (low-molecular- weight organic material or unknown material) which has not been removed in the prior chemical coagulation process, such that the turbidity of treated water can be significantly reduced compared to that in the prior coagulation process. The turbidity removal efficiency of the inventive coagulation process will exceed that of an ultra-filtration process when the inventive coagulation process is combined with a general sand filtration process.

[13] Also, because the range of addition amount of PAHCS is very wide, the inventive coagulation process can stably coagulate the materials causing turbidity of all low- turbidity, medium-turbidity and high-turbidity water in a specific range of addition amount, and thus can effectively treat raw water, which rapidly changes in quality during the rainy season, without precise adjustment of the addition amount of the coagulant.

[14] Also, because the inventive coagulation process easily coagulates organic materials causing turbidity, it can effectively treat even materials causing turbidity in dam discharge water after flood, which are not easily removed using general coagulants, and it can also maintain the removal rate of pathogenic microorganisms.

[15] Also, the inventive coagulation process has high efficiency of removal of disinfection by-product precursors, and thus the content of disinfection by-products in treated tap water can be reduced. This removal efficiency is thought to be higher than that of the prior coagulation process, although it is lower than those of ozone treatment and activated carbon filtration. Also, the inventive coagulation process can be immediately implemented in existing water treatment facilities, and does not require new facility operation technology, and thus is very inexpensive compared to advanced coagulation processes. Specifically, the inventive coagulation process incurs no additional cost because it uses existing facilities, incurs about 2-3 times the chemical cost of the prior process, and does not change the labor cost compared to the prior process. Thus, it is preferable to consider the introduction of the inventive coagulation process, before introducing advanced water treatment facilities such as ozone and activated carbon filtration facilities.

[16] Also, because the inventive coagulation process, which uses an excess amount of

PAHCS, enables a coagulation basin, a sedimentation basin and a pH adjustment unit to be greatly reduced in scale, it can greatly reduce the size of a construction site for a new water treatment plant, leading to a great reduction in installation expenses, and can be operated at low cost, leading to an increase in economic efficiency.

[17] The combination of the inventive PAHCS coagulation process with the auxiliary process provides an improvement over the prior water treatment process through a hy- drochemical approach and, as a result, is a process that ensures sufficient stability, and does not cause difficulties other than an increase in the amount of sludge. [18] Thus, the combination of the inventive PAHCS coagulation process with the auxiliary process can substitute for the prior coagulation processes that have been developed and used to date. Thus, it is can be used as a fundamental water treatment process that can cope with a reduction in the quality of raw water and produce better quality tap water in all water treatment plants.

Brief Description of the Drawings [19] FIG. 1 is a block diagram showing an embodiment of the present invention, in which a coagulation process that uses PAHCS is combined with auxiliary processes. [20] FIG. 2 is a block diagram showing another embodiment comprising an intermediate chlorination process added to the embodiment of FIG. 1. [21] FIG. 3 shows test results for changes in the turbidity of low-turbidity water according to the kind of coagulant chemical. [22] FIG. 4 shows test results for changes in the turbidity of medium-turbidity water according to the kind of coagulant chemical. [23] FIG. 5 shows test results for changes in the turbidity of high-turbidity water according to the kind of coagulant chemical. [24] FIG. 6 shows measurement results for turbidity removal rate and KMnO consumption rate in prepared water containing 5 ppm humic acid. [25] FIG. 7 shows measurement results for changes in the pH of treated water.

[26] FIG. 8 shows jar test results for changes in the turbidity of PAHCS-treated water according to changes in the pH of raw water. [27] FIG. 9 shows jar test results for changes in KMnO of PAHCS-treated water according to changes in the pH of raw water. [28] FIG. 10 shows jar test results for changes in the turbidity of PAHCS-treated water according to the addition of polymer. [29] FIG. 11 shows jar test results for changes in KMnO of PAHCS-treated water according to the addition of polymer. [30] FIG. 12 to 15 are graphic diagrams showing changes in UV , potassium per-

254 manganate consumption, TTMHFP and HAAFP, respectively, according to the addition amount of each of coagulants. [31] FIGS. 16 to 18 show the production rates of coagulated floes in low-turbidity, medium-turbidity and high-turbidity water, respectively, according to the kind of coagulant chemicals. [32] FIGS. 19 and 20 show changes in settled water after treatment in the Banwol water treatment plant (Korea) and the Shiheung water treatment plant (Korea), respectively.

[33] FIGS. 21 and 22 show changes in filter run time in the Banwol water treatment plant (Korea) and the Shiheung water treatment plant (Korea), respectively.

[34] FIGS. 23 and 24 show filter run times in water treatment plants located in the suburbs of Seoul, Korea, which were measured on November 19, 2004 and December 2, 2004, respectively.

[35] FIG. 25 shows the distribution of floes according to the size thereof in various positions in a settling basin. Best Mode for Carrying Out the Invention

[36] The inventive coagulation process, which uses an excess amount of a coagulant, comprises adding a large amount of coagulant PAHCS to raw water. In the inventive coagulation process including the use of an excess amount of PAHCS, PAHCS is added in an amount about 2-7 times as much as the usage amount of the prior general coagulant, such as PAC or PACS. The concrete addition amount of PAHCS is determined depending on the quality of water, and is generally determined in the range of 2.5-3 times (or more depending on water quality) as large as the use amount of a general coagulant. In the inventive coagulation process, the range of addition amount of the coagulant, which causes good coagulation, is a few times to a few tens of times as wide as that of the prior general coagulation process, and the turbidity of treated water is greatly reduced to a level of 1/2-1/6 times that of the general coagulation process.

[37] Specifically, the present invention provides a water treatment method comprising a coagulation process, which comprises adding poly aluminum hydroxy chlorosulfate (PAHCS) to raw water at a high concentration of 30-120 mg/L to coagulate turbid material and dissolved organic material.

[38] Also, the present invention provides a water treatment method comprising a coagulation process, which comprises adding polyaluminum hydroxychlorosulfate (PAHCS) to raw water having a low turbidity of less than 10 NTU in a concentration of 15-30 mg/L to coagulate turbid material.

[39] To further increase coagulation efficiency, the inventive method may additionally comprise, before or after the coagulation process, an auxiliary process such as pH adjustment or polymer addition. FIG. 1 is a schematic block diagram showing an embodiment of the present invention, which comprises pH adjustment and polymer addition processes conducted before and after the coagulation process including the use of an excess amount of PAHCS.

[40] Before the addition of PAHCS, a pH adjusting agent is added to adjust the pH of raw water, and then a high concentration of PAHCS is added to raw water, so that the pH of the treatment process is about 7.0-7.5. In test results, when the pH of the treatment process was 7.0-7.5, PAHCS showed the best coagulation efficiency. As the pH-adjusting agent, any material can be used without particular limitation, as long as it can be used in water treatment. For example, to reduce pH, sulfuric acid, carbon dioxide and the like can be used, and to increase pH, caustic soda, slaked lime and the like can be used. Generally, in order to adjust the pH of the treatment process to about 7.0-7.5, the pH of raw water is adjusted to about 7.5-8.0. Thus, when the pH of raw water is in the above-specified range, pH adjustment does not need to be separately performed. However, the pH range of raw water can be changed depending on the amount of coagulant that is added.

[41] At the stage following the coagulation, a polymer coagulant for water treatment is added to water in an amount of 0.1-0.3 mg/L. The addition of the polymer is carried out after rapid mixing, and results in a significant increase in coagulation efficiency. Test results showed that, in the case where the inventive coagulation process including the use of an excess amount of PAHCS was combined with the pH adjustment and polymer addition processes, the turbidity of treated water was significantly lower than in the case where only the inventive coagulation process was carried out. As the polymer coagulant, any polymer coagulant such as polyamine or sodium alginate, which could be used in water treatment in the prior art, can be used in the present invention. Particularly, polyamine can be used in the present invention.

[42] FIG. 2 is a block diagram showing another embodiment of the present invention, in which settled water is subjected to intermediate chlorination after the coagulation process including the use of an excess amount of PAHCS. In this case, dissolved organic materials as disinfection by-product precursors are removed through the coagulation process including the use of an excess amount of PAHCS, so that disinfection byproducts such as THMs and HAAs are significantly reduced. Even when the coagulation process including the use of an excess amount of PAHCS is carried out after pre-chlorination, it is possible to expect an effect in which disinfection byproducts themselves such as THMs and HAAs are removed due to coagulation caused by the use of an excess amount of PAHCS. However, in this case, the disinfection byproducts enter a more stable state compared to general precursors, and thus are more difficult to remove through the coagulation process. Thus, it is preferable to subject settled water to intermediate chlorination without carrying out pre-chlorination.

[43] Also, the present invention provides a coagulation method comprising adding polyaluminum hydroxychlorosulfate (PAHCS) to raw water, having rapidly changing turbidity, in an addition amount range selected from among four addition amount ranges of 30-40 mg/L for a turbidity range of 10-50 NTU, 40-50 mg/L for a turbidity range of 50-200 NTU, 50-60 mg/L for a turbidity range of 200-400 NTU, and 60-80 mg/L for a turbidity of more than 400 NTU. In the case of prior general coagulants such as PAC and PACS, the range of coagulant addition amount, which provides good coagulation, is very narrow, and thus the addition amount of the coagulant must be precisely adjusted in response to changes in the turbidity of raw water. Thus, the prior coagulant is difficult use when responding to cases in which the turbidity of raw water is rapidly changed due to flooding, etc. However, the inventive coagulation process including the use of an excess amount of PAHCS has a wide range of suitable addition amount of PAHCS, and thus can effectively remove the materials causing turbidity from raw water even upon a turbidity change from 10 NTU to 400 NTU or more by adding the coagulant PAHCS in an addition amount range selected from about four addition amount ranges.

[44] Also, the inventive coagulation process that uses an excess amount of PAHCS is shown to have excellent coagulation efficiency and settling efficiency, such as settling rate, compared to a prior inclination plate settler. Thus, if this rapid coagulation characteristic is reflected in the design of a water treatment plant, the length of a coagulation basin can be reduced to 1/2-2/3 of that of a general coagulation process. Also, if the rapid settling rate and high settling efficiency are reflected in the design of a water treatment plant, the length of a settling basin can be reduced to 1/3-2/3 of that of a prior settling basin (provided that the flow rate in the settling basin is maintained at the same level as that of the prior settling basin). Also, a combination of the inventive coagulation process including the use of an excess amount of PAHCS, with auxiliary processes, shows a very low pH decrease rate, and possible coagulation in a wide pH range, such that a pH adjustment system can be provided to have a greatly reduced size compared to that of a general coagulation process. As used herein, the term "general coagulation process" is meant to include all coagulation processes that use prior general coagulants, such as alum, PAC and PACS, and a coagulation process that uses PAHCS in an amount less than 15 mg/L.

[45] The design of the inventive coagulation process including the use of an excess amount of PAHCS, in combination with auxiliary processes such as pH adjustment and polymer addition processes, has been developed to overcome the limitation of prior coagulation processes, and will very effectively remove low-molecular- weight organic materials causing turbidity or unknown materials causing turbidity which have not been removed through prior chemical coagulation processes. Thus, the turbidity of treated water subjected to the inventive coagulation process is much lower than that of water treated in prior coagulation processes, and the inventive coagulation process effectively removes the organic materials causing turbidity and disinfection by-product precursors of dam discharge water after floods. The turbidity removal efficiency of the inventive coagulation process including the use of an excess amount of PAHCS is comparable to that ultra- filtration, and the extent of reduction in disinfection byproducts in the inventive coagulation process is slightly lower than those of ozone treatment and activated carbon filtration, but is significantly higher than that of the prior processes.

[46] A combination of the inventive coagulation process including the use of an excess amount of PAHCS, with auxiliary processes, has been developed through hy- drochemical approaches, ensures sufficient stability, and does not entail difficulties other than an increase in the amount of sludge, when used in practice. Mode for the Invention

[47] Hereinafter, the present invention will be described in detail with reference to

Examples and Test Examples. It is to be understood, however, that these examples are not to be construed to limit the scope of the present invention, and those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

[48] Test method

[49] 1) Test period : June to November, 2004

[50] 2) Coagulants used: polyaluminum chloride (PAC, 17% Al O ), polyaluminum hydroxide chloride silicate (PACS, 17% Al O ), and polyaluminum hydroxide chloride silicate (PAHCS, 12.5% Al O ).

[51] Table 1

[52] Raw water applied: raw water from water intake station Nos. 1 and 2 in Paldangho

Lake, Korea

[53] (i) low-turbidity (less than 10 NTU): normal times

[54] (ii) medium- turbidity (about 50 NTU): in rain

[55] (iii) high-turbidity (about 100 NTU): in pouring rain

[56] 4) Test items

[57] (i) Jar-test: turbidity, pH, etc.

[58] (ii) other water quality analysis: UV , TTHMFP, HAA5FP, KMnO consumption, etc.

[59] 5) Test methods

[60] (i) jar- test: rapid mixing at 150 rpm for 1 min, and slow mixing at 70 rpm and 40 rpm for 10 min and 20 min, respectively, were conducted. A coagulant diluted to

1%(V/V) and a 2-L gator jar were used. [61] (ii) turbidity: measured using HACH Model-2100A Tubidimeter together with

Nippon Denshoku Water analyzer 2200K. [62] (iii) UV : A sample filtered through a GF/C filter was measured with the Varian

Cary 300C spectrophotometer.

[63] (iv) TTHMFP: GC analysis according to the Standard Method.

[64] (v) HAA5FP: GC analysis according to the Standard Method.

[65] (vi) KMnO consumption: tested in accordance with the Official test methods for water quality

[66] Test Example 1 : Coagulation process including use of excess amount of PAHCS

[67] 1. Change in turbidity according to addition amount of coagulant [68] 1) Low-turbidity raw water

[69] FIG. 3 shows test results for low-turbidity raw water (raw water conditions (June

14, 2004): Temp = 22.4 ⁰C, pH = 7.75, and turbidity = 7.5 NTU). As shown in FIG. 3, when PAC was added in an amount of 8 ppm, the turbidity of supernatant water in the jar test was 0.65 NTU, which was the lowest. An increase in the addition amount of PAC led to a rapid increase in turbidity, so that, at a PAC addition amount of 16 ppm, the turbidity was 1.5 NTU, indicating a great reduction in the turbidity removal efficiency of PAC. However, PAHCS showed a continued increase in the turbidity removal efficiency thereof with an increase in the addition amount thereof, so that a PAHCS addition amount of 16 ppm led to a turbidity of 0.24 NTU, which was significantly lower than the lowest value for PAC. FIG. 16 shows a change in flocculation rate according to the addition of the coagulants. The production of coagulated floes caused by PAHCS started at the slow mixing stage, but the flocculation time of PAHCS was about 2 minutes and 20 seconds, which was shorter than that of PAC.

[70] In conclusion, PAC showed good coagulation in an addition amount range of 8-10 ppm, and when the addition amount thereof was outside of the above- specified range, it showed poor coagulation, suggesting that the range of suitable addition amount thereof was very narrow. The coagulant PACS also showed substantially the same pattern as PAC. However, PAHCS could greatly increase coagulation efficiency, even when it was added in slightly excess amounts. Also, the range of suitable addition amount of PAHCS was much wider than that of PAC, suggesting that the coagulation process could be stably operated. Thus, it is believed that, in the case of stable normal water having low turbidity, the addition of a slightly excess amount of PAHCS to water can stably provide good-quality water throughout the year.

[71] 2) Medium- turbidity raw water

[72] FIG. 4 shows test results for medium-turbidity raw water (raw water conditions

(July 6, 2004): Temp = 21.7 ⁰C, pH = 7.19, and turbidity = 38.5 NTU). As shown in FIG. 4, when each of PAC and PACS was added to water in an amount of 20 ppm, the turbidity of supernatant water in the jar test was 1.22 NTU, which was the lowest. Then, a continued increase in the addition amount thereof led to a rapid increase in turbidity, so that, at an addition amount of 60 ppm, PAC and PACS showed turbidities of 9.5 NTU and 11.7 NTU, respectively. However, PAHCS showed a turbidity of 0.93 NTU at an addition amount of 20 ppm, and an increase in the addition amount thereof led to a continued increase in the coagulation efficiency thereof, so that, at an addition amount of 90 ppm, it showed a turbidity of 0.30 NTU. The lowest turbidity value of water treated with PAHCS was about 1/4 of the lowest turbidity value of water treated with each of PAC and PACS. Also, a turbidity of 1.22 NTB for water treated with each of PAC and PACS was lower than a turbidity of 38.5 NTU for raw water, but was an unsatisfactory value for drinking water. Thus, it could be seen that, in the case of raw water having medium turbidity, a satisfactory turbidity removal effect could not be obtained through a general coagulation process using the prior coagulant.

[73] FIG. 17 shows the change in flocculation rate according to the addition of coagulants. As shown in FIG. 17, the production of floes appeared at the end of rapid mixing up to an addition amount of 40 ppm, and started to slow slightly with an addition amount of 80 ppm or more.

[74] In conclusion, PAC and PACS showed coagulation in a narrow range of addition amount of about 20 ppm, and when the addition amount thereof was out of said range, they showed poor coagulation. However, PAHCS showed a turbidity of treated water of 0.30-0.42 NTU in a range of a high addition amount of 50-120 ppm, suggesting that it had a very excellent and stable coagulation effect.

[75] 3) High-turbidity raw water

[76] FIG. 5 shows test results for high-turbidity raw water (raw water conditions (July

14, 2004): Temp = 22.4 ⁰C, pH = 6.93, and turbidity = 121 NTU). As shown in FIG. 5, when each of PAC and PACS was added to raw water in an amount of 20 ppm, they showed the lowest turbidity of supernatant water of 3.1 NTU in the jar test, and then, an increase in the addition amount thereof led to a rapid increase in the turbidity of treated water, so that, at addition amount of 40 ppm, they showed turbidities of 62.6 and 67.5 NTU, respectively. However, PAHCS showed a turbidity of 0.9 NTU in an addition amount of 30 ppm, and the lowest turbidity of 0.5 NTU in an addition amount of 40 ppm. Also, the lowest turbidity value of water treated with PAHCS was about 1/6 of the lowest turbidity value of water treated with each of PAC and PACS. Also, a turbidity of 3.1 NTU for water treated with PAC and PACS was a very turbid state, unsatisfactory for drinking water, suggesting that PAC and PACS had a very poor coagulation effect. Thus, it can be seen that, in the case of raw water having high turbidity, a satisfactory turbidity removal effect could not be obtained through a general coagulation process using the prior coagulant.

[77] FIG. 18 shows the production rate of coagulated floes in high-turbidity raw water.

As shown in FIG. 18, PAHCS showed a rapid production rate of coagulated floes at the end of rapid mixing, and showed significantly excellent flocculation ability compared to that of PAC and PACS.

[78] In conclusion, PAC and PACS caused coagulation in a narrow range of addition amount near 20 ppm, and when the range of addition amount thereof was outside of said range, they showed very insufficient coagulation. However, PAHCS showed a continued increase in the turbidity of treated water with an increase in the addition amount thereof, even to addition amounts higher than 30 ppm, so that it showed a turbidity of 0.5-0.9 NTU and thus an excellent effect. [79] 2. Effect of removal of high-concentration organic materials

[80] To confirm the effect of removal of organic materials, coagulation test was conducted for sample water prepared by adding 5 ppm of humic acid thereto. The prepared water having a humic acid concentration of 5 ppm and pH 6.4 was subjected to a jar test and measured for turbidity and KMnO consumption. The test results are shown in FIG. 6. As shown in FIG. 6, the general coagulants showed a very low turbidity removal rate or KMnO consumption rate, whereas PAHCS showed a very high turbidity removal rate and KMnO consumption rate of 80% in an addition

4 amount of more than 50 ppm.

[81] 3. Change in pH of treated water

[82] A change in the pH of water obtained by treating raw water having a high turbidity of 121 NTU was measured, and the measurement results are shown in FIG. 7. As shown in FIG. 7, a change in pH with a change in the addition amount of PAHCS was very low. Thus, it could be observed that, even when PAHCS was added in large amounts during an enhanced coagulation process, the pH range of treated water was in a range suitable for drinking water, and thus a separate process for pH adjustment did not need to be applied.

[83] 4. Summary of effects

[84] 1) As shown in FIGS. 3 to 5, in the inventive coagulation process that used an excess amount of PAHCS, the suitable range of addition amount of PAHCS ("B" in FIG. 4) was significantly wider than the suitable range of addition amount of a coagulant ("A" in FIG. 4) in a general coagulation process. Thus, the inventive coagulation process can achieve effective removal of materials causing turbidity, even when PAHCS is added in large amounts. However, when other coagulants are added in large amounts, the turbidity removal rate thereof will be reduced instead.

[85] 2) The lowest turbidity of water treated in the inventive coagulation process using an excess amount of PAHCS was about 1/2-1/6 of the lowest turbidity of water treated in the general coagulation process. This suggests that the inventive coagulation process provides a significant improvement in coagulation efficiency over the prior coagulation process.

[86] 3) The inventive coagulation process including the use of an excess amount of

PAHCS showed an excellent turbidity removal effect in a PAHCS addition amount about 2.5-3 times as large as the coagulant addition amount in the general coagulation process. However, the addition amount of PAHCS may vary slightly depending on the quality and intended use of water, and the addition of PAHCS in an amount slightly lower than said amount is sufficient to simply increase turbidity removal efficiency.

[87] 4) The inventive coagulation process including the use of an excess amount of

PAHCS effectively removed organic materials compared to the general coagulation process and, at the same time, effectively removed materials causing turbidity which could not be removed in the general enhanced coagulation process.

[88] 5) In the inventive coagulation process that used an excess amount of PAHCS, the decrease rate of pH was very low. Thus, separate facilities or processes for increasing pH do not need to be provided in the stage following the coagulation process, and if any, can be provided on a small scale.

[89] Test Example 2: Combination of coagulation process using excess amount of

PAHCS. with auxiliary processes

[90] 1. Change in turbidity with change in pH of raw water

[91] Jar test results for changes in the turbidity of PAHCS-treated water with changes in the pH of raw water are shown in FIGS. 8 and 9. FIG. 8 shows jar test results for changes in the turbidity of PAHCS-treated water with changes in the pH of raw water, and FIG. 9 shows jar test results for changes in KMnO of PAHCS-treated water with changes in the pH of raw water. As shown in FIGS. 8 and 9, the coagulant PAHCS showed turbidity, which was lower at pH 7.0-7.5 than at other pHs. Also, at said pH range, KMnO consumption, an indirect index of organic material concentration, was low. Thus, it could be concluded that, when the pH of raw water in the coagulation process was maintained within said pH range, the coagulation efficiency of the coagulant could be increased.

[92] 2. Change in turbidity according to the addition of polymer

[93] Jar test results for changes in turbidity according to the addition of polyamine are shown in FIGS. 10 and 11. FIG. 10 shows jar test results for changes in the turbidity of PAHCS-treated water according to the addition of polyamine (raw water conditions (December 22, 2004): Temperature = 12.4 ⁰C, pH = 7.46, and turbidity = 1.39 NTU). FIG. 11 shows jar test results for changes in the KMnO consumption of PAHCS- treated water according to the addition of polyamine (raw water conditions (December 22, 2004): Temp = 12.4 ⁰C, pH = 7.46, and turbidity = 1.39 NTU). As shown in FIGS. 10 and 11, at a polyamine addition amount of 0.1-0.3 ppm, turbidity was reduced along with KMnO consumption, an indirect index of organic material concentration. Thus, it could be concluded that, when the inventive coagulation process, which uses an excess amount of PAHCS, was combined with the polymer addition process, the coagulation efficiency of PAHCS could be further increased.

[94] 3. Summary of effects

[95] When the coagulation process that uses an excess amount of PAHCS was combined with the pH adjustment and/or polymer addition process, the coagulation efficiency of PAHCS was significantly increased. Particularly, not only the turbidity of treated water, but also KMnO consumption, an indirect index of organic material concentration, were significantly reduced. The coagulant PAHCS showed excellent treatment effects at a raw water pH of 7.0-7.5 and in a polymer addition amount of 0.1-0.3 ppm.

[96] Example 3: Chlorination of settled water

[97] After the combination process of the PAHCS coagulation process with the auxiliary processes was carried out as in Test Example 1 without pre-chlorination, the settled water was subjected to intermediate chlorination, and the treatment effect thereof was evaluated. Changes in UV , potassium permanganate consumption, TTMHFP and HAAFP according to the addition amount of each of PAC, PACS and PAHCS were measured, and the measurement results are shown in FIGS. 12 to 15.

[98] As shown in FIGS. 12 to 13, the addition of PAHCS led to significant reductions in

UV and potassium permanganate consumption, suggesting that disinfection byproduct precursors were effectively removed. Also, as shown in FIGS. 14 and 15, the addition of PAHCS led to reductions in the amount of TTHMFP and HAAFP.

[99] Thus, it could be concluded that, in an actual water treatment process, when the coagulation process including the use of an excess amount of PAHCS was combined with the pH adjustment and polymer addition processes in order to increase treatment efficiency, to which the process of chlorinating settled water was further added, high coagulation efficiency could be obtained and disinfection by-products could also be significantly reduced.

[100] Example: Application of inventive coagulation process in water treatment plants

[101] The inventive coagulation process was applied in actual water treatment plants to evaluate the water treatment effect thereof. In this Example, raw water from water intake Nos. 1 and 2 in Paldangho Lake, Korea, was used. Also, PAC, PACS and PAHCS were used as coagulants.

[102] 1. Change in turbidity of settled water

[103] Test results for changes in the turbidity of settled water after coagulation are shown in FIG. 19 (Banwol water treatment plant, Korea) and FIG. 20 (Shiheung water treatment plant, Korea).

[104] In FIG. 19, the symbol "•" represents the turbidity of integrated settled water, "D" represents the turbidity of settled water in a fourth settling basin, and "Δ" represents the turbidity of settled water in a first settling basin.

[105] FIG. 20 shows the turbidity of drinking water treated in the Shiheung water treatment plant during the year 2004. As shown in FIG. 20, the water treatment was carried out in five divided stages consisting of a stage of 20 ppm PACS addition, a stage of 10-12 ppm PAHCS addition, a stage of 10-15 ppm PAC addition, a stage of 10-27 ppm PAHCS addition and a stage of addition of PAHCS in an amount which was about 5 ppm more than the optimal addition amount of the other coagulants. As a result, as shown in FIG. 20, it could be observed that, during a period after the end of August, 2004, during which PAHCS was added in an amount 5 ppm more than the optimal addition amount of the other coagulants, treated water showed a stable turbidity of 0.03 NTU. Because this effect could be obtained even by the addition of a slightly excess amount of PAHCS, it is preferable to added PAHCS to raw water, having normal quality, in slightly excess amounts in view of economic efficiency.

[106] 2. Filter run time

[107] Filter run time upon an outbreak of Synedra was evaluated. The period of the

Synedra outbreak was from October 5, 2004 to December 14, 2004. The number of Synedra was an average of 1,166 cells/mL, and a maximum of 2,550 cells/mL (November 18, 2004). The sand filter used in each of the water treatment plants was as follows.

[108] -Dukso: deep bed sand filter

[109] -Wabu, Songnam, Suji and Ilsan: Anthracite/sand double filter

[110] -Banwol and Shiheung: general sand filter

[111] FIG. 21 shows changes in filter run time in the Shiheung water treatment plant. As shown in FIG. 21, a usual filter run time of 50-90 hours was reduced to an average of 25-45 hours or less, and a maximum of 10 hours or less, after November 18, 2004. FIG. 22 shows changes in filter run time in the Banwol water treatment plant.

[112] FIGS. 23 and 24 show measurement results for filter run time in water treatment plants located in the suburbs of Seoul, Korea. The results in FIG. 23 were measured on November 19, 2004, and the results in FIG. 24 were measured on December 2, 2004. In FIG. 23, the following coagulants were used in water treatment plants: 20 ppm PAHCS in Dukso, 15 ppm PAHCS in Wabu (III), 15 ppm PACS in Wabu (IV), 13 ppm PACS and 0.2 ppm polyamine in each of Songnam (III) and Songnam (IV), PAHCS ppm in each of Banwol and Shiheung, 12 ppm PACS and 0.2 ppm polyamine in Suji, and 12 ppm PACS and 0.15 ppm polyamine in Ilsan. In FIG. 24, the following coagulants were used in water treatment plants: 13 ppm PACS in each of Dukso (IV) and Dukso (V), 11 ppm PACS and 0.2 ppm polyamine in each of Songnam (III) and Songnam (IV), 25 ppm PAHCS in Banwol and Shiheung, 30 ppm PAHCS and 0.1 ppm in Suji, and 13 ppm PACS and 0.15 ppm polyamine in Ilsan. In the case of the Suji water treatment plant, it was evaluated that the coagulation process including the use of an excess amount of PAHCS showed a 300% improvement in filter run time.

[113] 3. Floe distribution and settling efficiency in settling basin

[114] ( 1 ) Examination method

[115] In the Shiheung water treatment plant, PAHCS was used in an amount of 10-27 ppm, and the distribution of floes according to the size thereof was examined in a channel before a coagulation basin, various stages in the coagulation basin, and various positions in a settling basin to examine settling efficiency. [116] -positions examined: 16 positions (channel before coagulation basin, coagulation basin stage 1 and stage 2, and 0, 10, 20, 30, 40, 48, 58, 68 and 78 m from settling basin inlet)

[117] -depth examined: 0.5 m from water surface

[118] -floe size: 0-30 D, 31-40 D, 41-50 D, 51-70 D, 71-100 D, 101-120 D, 121-150 D, 151-200 D,

201-250 D, 251-300 D, 301-400 D, 401-500 D, 501-600 D, 601-700 D, 701-1000 D, and 1001-1200 D. A floe size of more than 1200 D did not exist, or could not be detected due to possible breakdown upon collection.

[119] -Tester: Floe Size Analyzer (Model FSA-1000, Sam Bo Scientific Co. Ltd).

[120] The test results are shown in FIG. 25, which shows the distribution of floes in the

PAHCS coagulation process. As shown in FIG. 25, the floes formed in the coagulation basin were completely settled within a distance of 10 m from the settlement basin inlet.

Claims

[1] A water treatment method comprising a coagulation process, which comprises adding polyaluminum hydroxychlorosulfate (PAHCS) to raw water in an excess amount of 30-120 mg/L to coagulate turbidity-causing material and dissolved organic material.

[2] A water treatment method comprising a coagulation process, which comprises adding polyaluminum hydroxychlorosulfate (PAHCS) to raw water, having a low turbidity of less than 10 NTU, in an excess amount of 30-120 mg/L, to coagulate turbid material.

[3] The method of Claim 1 or 2, which further comprises, after adding the PAHCS, adding a polymer coagulant for water treatment in an amount of 0.1-0.3 mg/L.

[4] The method of Claim 1 or 2, which further comprises, before adding the PAHCS, adjusting the pH of the raw water to adjust the pH of the coagulation process to 7.0-7.5.

[5] The method of Claim 1 or 2, which further comprises, after carrying out the coagulation process without pre-chlorination, subjecting settled water to intermediate chlorination.

[6] A water treatment method comprising a coagulation process, which comprises adding polyaluminum hydroxychlorosulfate (PAHCS) to raw water, having rapidly changing turbidity, in an addition amount range selected from among four addition amount ranges of 30-40 mg/L for a turbidity range of 10-50 NTU, 40-50 mg/L for a turbidity range of 50-200 NTU, 50-60 mg/L for a turbidity range of 200-400 NTU, and 60-80 mg/L for a turbidity of more than 400 NTU.

[7] The method of any one of Claims 1, 2 and 6, wherein a coagulation basin having a size reduced to 1/2-2/3 of a general coagulation process is used.

[8] The method of any one of Claims 1, 2 and 6, wherein a settlement basin having a size reduced to 1/2-2/3 of a general coagulation process is used.