JP2006167611A - Water cleaning system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent almost treatment load of a sedimentation basin and a sand filter basin from increasing even when the membrane permeate obtained by subjecting settled sludge and cleaning effluent to membrane separation is refluxed to the system. <P>SOLUTION: The water cleaning system comprises the sedimentation basin 12 in which the suspended solid in raw water 30 is separated as sedimented sludge 34, the sand filtration basin 14 which filters supernatant 36 in the sedimentation basin 12 by sand to form treated water 38, a first membrane separator 24 which subjects the sedimented sludge 34 withdrawn from the sedimentation basin 12 to membrane separation, a second membrane separator 26 which subjects the cleaning effluent 46 of the sand filtration basin 14 to membrane separation, an oxidation means 28 which subjects the membrane permeate 50 of the first membrane separator 24 to an oxidation treatment, a means which makes the oxidation-treated membrane permeate 50 confluent with the cleaning effluent 46, and a means which makes the membrane permeate 58 of the second membrane separator 26 confluent with the treated water 38. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a water purification system, and more particularly to a water purification system including a sedimentation basin that separates suspended substances in raw water as sedimentation sludge, and a sand filtration basin that uses the supernatant water of the sedimentation basin as a filtered water.

  In the sedimentation basin of this type of water purification system, sediment sludge of less than 1% is generated with respect to the amount of raw water. In addition, the sand filtration pond requires regular washing operations such as backwashing (for example, about once a day), and the amount of treated water corresponding to about 5 to 10% of the amount of raw water during this washing operation. Is used and discharged as cleaning wastewater. These settled sludge and washing wastewater are separated into concentrated sludge and separated water by concentrating, and the concentrated sludge is treated in a separate sludge treatment facility. The separated water is returned to the inlet side of the sedimentation basin, mixed with the raw water, and again flows into the sedimentation basin.

  In general, a precipitation process is employed as the concentration process. However, the separated water obtained by the precipitation treatment contains a lot of suspended solids, and when this is refluxed to the precipitation basin as described above, the treatment load of the precipitation basin and sand filtration pond is quantitatively and qualitatively increased. Increase the water purification efficiency.

  In order to improve such problems, a method using a membrane separation means as a means for concentrating precipitation sludge and washing wastewater has been proposed (see, for example, Patent Document 1 and Patent Document 2).

  In the method described in Patent Document 1, membrane permeated water finally separated by multistage treatment of precipitated sludge and washing wastewater is combined with the treated water of the sand filtration pond. According to this method, since the membrane permeated water is not refluxed to the settling basin, the treatment load of the settling basin and the sand filtration pond is not increased, and a water purification system with excellent water purification efficiency can be realized.

Moreover, the method described in Patent Document 2 similarly returns the membrane permeated water finally separated by multistage treatment of the precipitated sludge and washing wastewater to the settling basin. For this reason, the fault that the processing load of a sedimentation basin and a sand filtration pond increases quantitatively still remains. However, since the permeated water of the membrane is clear, an excellent improvement effect that the treatment load of the sedimentation basin and the sand filtration basin is hardly increased in terms of quality can be achieved.
Japanese Patent Laid-Open No. 10-165990 JP 2003-236558 A

  However, according to the experiment by the present inventor, it was found that the membrane permeated water separated by the method described in Patent Document 1 contains a relatively large amount of soluble manganese. Therefore, when this membrane permeated water is merged with the treated water of the sand filtration pond, the manganese concentration of the treated water is raised and the quality of the treated water may be deteriorated. In the method described in Patent Document 2, most of the soluble manganese in the membrane permeated water refluxed to the sedimentation basin is removed in the process of passing through the sedimentation basin and sand filtration basin. Therefore, there are almost no cases where the manganese concentration of the treated water in the sand filtration pond exceeds the drinking standard. However, as described above, the method described in Patent Document 2 has a drawback that the processing load of the settling basin and the sand filtration basin is quantitatively increased.

  The object of the present invention is to improve the above-mentioned problems of the prior art, and in a water purification system having a sedimentation basin and a sand filtration pond, the membrane permeate obtained by membrane separation of sedimentation sludge and washing wastewater is returned to the water purification system. It is an object of the present invention to provide a water purification system that can increase the treatment load of a settling basin and a sand filtration basin almost without increasing the soluble manganese concentration in the treated water.

  In order to achieve the above object, a first water purification system according to the present invention includes a sedimentation basin that separates suspended substances in raw water as sedimentary sludge, and sand filtration that uses the supernatant water of the sedimentation basin as a sand filter to obtain treated water. A pond, a first membrane separation device for separating the sludge extracted from the sedimentation basin, a second membrane separation device for membrane separation of the waste water from the sand filtration pond, and a membrane permeate for the first membrane separation device Oxidizing means for oxidizing the membrane, means for joining the membrane permeated water oxidized by the oxidizing means to the washing waste water, and means for joining the membrane permeated water of the second membrane separation device to the treated water It is characterized by having.

  Moreover, the 2nd water purification system which concerns on this invention is a sedimentation basin which isolate | separates the suspended substance in raw | natural water as a sedimentation sludge, the sand filtration pond which sand-filters the supernatant water of the said sedimentation basin, and the said sedimentation basin A first membrane separation device for separating the precipitated sludge extracted from the membrane, a second membrane separation device for membrane-separating the washing waste water of the sand filtration pond, and an inlet of the sedimentation basin for the membrane permeated water of the first membrane separation device And a means for joining the permeated water of the second membrane separation device to the treated water.

  According to the 1st water purification system which concerns on this invention, the membrane permeate finally obtained by carrying out the membrane separation of the sedimentation sludge and washing | cleaning waste_water | drain is clear, hardly contains soluble manganese, Maintains water quality equivalent to treated water. Therefore, the membrane permeated water can be directly merged with the treated water of the sand filtration pond without returning to the inlet side of the settling basin. For this reason, the processing load of a sedimentation basin and a sand filtration pond is not increased, and the soluble manganese concentration in treated water can be kept low.

  According to the 2nd water purification system which concerns on this invention, the membrane permeated water of the 1st membrane separator was returned to the entrance side of a sedimentation basin. This membrane permeate is clear but contains a relatively large amount of soluble manganese. However, the amount of membrane permeated water is less than 1% at most with respect to the amount of raw water, and even if such a clear and small amount of membrane permeated water is mixed with raw water, the treatment load on the sedimentation basin and sand filtration pond is almost the same. Does not increase. In addition, most of the soluble manganese contained in the permeated water is removed during the process of coagulating sedimentation in the sedimentation basin and sand filtration in the sand filtration basin, so the concentration of soluble manganese in the treated water is lowered. Can be suppressed. Moreover, in this 2nd water purification system, an oxidation means can be abbreviate | omitted and the system can be simplified compared with a 1st water purification system.

  FIG. 1 is a system diagram showing an embodiment of a first water purification system according to the present invention. The water purification system is divided into a water purification production system A and a sludge / washing waste water treatment system B. The water purification production system A is mainly composed of a landing well 10, a sedimentation basin 12, a sand filtration basin 14, and a treated water storage tank 18. The sludge / washing waste water treatment system B is mainly composed of a precipitated sludge storage tank 20, a washing waste water storage tank 22, a first membrane separation device 24, a second membrane separation device 26, and an oxidizing means 28.

  By adding the flocculant 32 to the raw water 30 supplied to the sedimentation basin 12 through the landing well 10, the suspended substances in the raw water 30 are aggregated to form a flock. These flocs settle at the bottom of the sedimentation basin 12 and are extracted as sedimentation sludge 34. The supernatant water 36 of the sedimentation basin 12 is sent to the subsequent sand filtration basin 14. In the sand filtration pond 14, fine suspended substances contained in the supernatant water 36 are sand-filtered to obtain treated water 38. The sand filtration pond 14 also has an action of removing soluble iron and manganese contained in the supernatant water 36. The treated water 38 is temporarily stored in the treated water storage tank 18, then added with a chlorine-based disinfectant and distributed as tap water 42.

  In the sand filter pond 14, fine suspended substances adhere to and accumulate on the surface of the sand filter medium and the gaps between them for a long time, causing clogging. For this reason, the sand filter medium layer is periodically cleaned (for example, once a day). The cleaning water 44 used for cleaning is filled with the processing water stored in the processing water storage tank 18. A large amount of washing waste water 46 is generated by the washing operation of the sand filtration pond 14.

  In the sludge / washing wastewater treatment system B, the treated sludge 34 extracted from the bottom of the sedimentation basin 12 and the washing operation of the sand filtration basin 14 are treated. That is, the sedimentation sludge 34 from the sedimentation basin 12 is temporarily stored in the sedimentation sludge storage tank 20. A concentrated liquid 48 from the second membrane separation device 26 described later joins the sedimented sludge storage tank 20. The precipitated sludge 34 stored in the precipitated sludge storage tank 20 is sent to the first membrane separation device 24 and subjected to membrane separation. As the first membrane separation device 24, a rotating flat membrane separation device disclosed in Patent Document 2 is preferably used. Although the rotary flat membrane separator is expensive, it has an advantage that stable operation can be continued for a long time even under severe conditions. Therefore, it is suitable for the concentration of sludge having a high concentration like the precipitated sludge 34. In addition, as described in the background section, the amount of precipitated sludge 34 generated is as small as less than 1% of the amount of raw water, so the cost burden when adopting a rotary flat membrane separator is not so heavy. Don't be.

  By the first membrane separation device 24, the precipitated sludge 34 is separated into the membrane permeated water 50 and the concentrated sludge 52. The concentrated sludge 52 is sent to a processing facility outside the system, for example, after being subjected to dehydration treatment, it is treated and disposed of by appropriate means. On the other hand, the membrane permeated water 50 is sent to the oxidizing means 28. In the oxidation means 28, the membrane permeated water 50 is oxidized. For example, ozone gas or sodium hypochlorite aqueous solution is preferably used in the case of adding the oxidizing agent 54 as the oxidizing treatment, but air can be aerated instead of these oxidizing agents.

  The purpose of oxidizing the membrane permeated water 50 is to oxidize manganese dissolved in the membrane permeated water 50 into insoluble manganese oxide. That is, according to the experiment by the present inventor, it was found that the membrane permeate 50 contained a relatively large amount of soluble manganese, for example, around 1 mg / L. This soluble manganese originally relies on raw water 30 taken from rivers and underground. Although part of the soluble manganese is insolubilized and removed by the addition of the flocculant 32 in the settling basin 12, most of it remains as soluble manganese. The insolubilized manganese is also unstable and may be re-eluted in the process of staying in anaerobic conditions for a long time in the precipitated sludge storage tank 20 or the first membrane separation device 24. Therefore, the oxidation means 28 oxidizes the membrane permeated water 50 for the purpose of removing dissolved manganese, and oxidizes the dissolved manganese to form insoluble manganese oxide. As the oxidizing means 28, in addition to the means for adding the oxidizing agent 54, a catalytic oxidation type means such as a manganese sand tower can be used.

  Further, the cleaning wastewater 46 generated by the cleaning operation of the sand filtration pond 14 is stored in the cleaning wastewater storage tank 22. As described above, the washing wastewater is regularly generated at a frequency of about once a day, but the amount of water is a large amount corresponding to about 5 to 10% of the amount of raw water. For this reason, the cleaning waste water storage tank 22 has a capacity capable of temporarily storing a large amount of the cleaning waste water 46 generated by one cleaning operation. Then, the stored cleaning waste water 46 is supplied to the second membrane separation device 26 in the subsequent stage so that the cleaning waste water 46 in the cleaning waste water storage tank 22 is almost eliminated by the next cleaning operation. Membrane permeated water 50 </ b> A passing through the oxidizing means 28 is introduced into the washing drainage tank 22, and the membrane permeated water 50 </ b> A merges with the washing drainage 46.

  The combined water 56 in which the washing waste water 46 and the membrane permeated water 50A merge is supplied to the second membrane separation device 26 and subjected to membrane separation. This combined water 56 is relatively clear and has a large amount of water. As the membrane module of the second membrane separation device 26 for treating such combined water 56, a hollow fiber membrane module made of a microfiltration membrane or a stationary immersion flat membrane module is suitable. The membrane permeated water 58 from which the fine suspended solids in the washing waste water 46 and the insoluble manganese oxide in the membrane permeated water 50A are separated by the membrane separation in the second membrane separation device 26 is clear, and soluble manganese is also dissolved. The water quality is almost the same as that of the treated water 38 of the sand filter pond 14. Therefore, the membrane permeated water 58 is directly joined to the treated water 38 of the sand filtration basin 14 without being refluxed to the inlet side of the sedimentation basin 12. As described above, the concentrate 48 in the second membrane separation device 26 containing fine suspended solids and insoluble manganese oxide is guided to the sedimentation sludge storage tank 20 and merged with the sedimentation sludge 34 to form a membrane in the first membrane separation device 24. Get separated. Therefore, the concentrated sludge 52 discharged from the first membrane separation device 24 includes the precipitate coagulated and settled in the sedimentation basin 12, the fine suspension separated by the washing operation of the sand filtration basin 14, and the oxidation in the oxidation means 28. All solids generated by this purification system, such as insoluble manganese oxide produced by the treatment, are collected and included.

  As described above, according to the embodiment of the first water purification system of the present invention, the membrane permeated water 58 finally obtained by membrane separation of the precipitated sludge 34 and the washing waste water 46 is clear and soluble. Manganese is hardly contained, and the water quality is maintained at the same level as the treated water 38 of the sand filtration pond 14. Therefore, the membrane permeated water 58 can be directly merged with the treated water 38 of the sand filtration basin 14 without returning to the inlet side of the sedimentation basin 12. For this reason, the processing load of a sedimentation basin and a sand filtration pond is not increased, and the soluble manganese concentration in treated water can be kept low.

  FIG. 2 is a system diagram showing an embodiment of a second water purification system according to the present invention. In FIG. 2, since the element which attached | subjected the code | symbol same as FIG. 1 is substantially the same as the element demonstrated by the said 1st water purification system, the description is abbreviate | omitted. In this embodiment, the oxidation means 28 according to the first water purification system is omitted, and the membrane permeated water 50 of the first membrane separation device 24 is returned to the landing well 10 which is the inlet side of the settling basin 12. ing. The membrane permeated water 50 is clear but contains a relatively large amount of soluble manganese as described above, and is contained, for example, at around 1 mg / L. However, the amount of the membrane permeate 50 is less than 1% at most with respect to the amount of raw water as described above. Therefore, even if such a clear and small amount of membrane permeated water 50 is returned to the landing well 10 and mixed with the raw water 30, the processing load of the sedimentation basin 12 and the sand filtration basin 14 is hardly increased. Further, most of the soluble manganese contained in the membrane permeated water 50 is removed in the process of undergoing coagulation sedimentation in the sedimentation basin 12 and sand filtration in the sand filtration basin 14. That is, the adverse effect caused by mixing the membrane permeated water 50 with the raw water 30 is at a negligible level. According to the second water purification system, as in the first water purification system, the treatment load of the settling basin 12 and the sand filtration basin 14 is hardly increased in quantity, and the dissolution in the treated water 38 is performed. The manganese concentration can be kept low. According to the embodiment of the second water purification system, the system can be simplified as compared with the first water purification system. Note that the second water purification system does not intend to completely eliminate the oxidation treatment of the membrane permeated water 50, and includes a mode in which the membrane permeated water 50 is returned to the inlet side of the settling basin 12 after being oxidized. .

  In each of the above-described embodiments, the concentrated solution 48 separated by the second membrane separation device 26 is joined to the precipitated sludge 34 and subjected to membrane separation again by the first membrane separation device 24. However, the present invention is not limited to such a configuration, and the concentrated liquid 48 is independently extracted without being combined with the precipitated sludge 34, and is combined with the concentrated sludge 52 of the first membrane separation device 24. You may make it send to the processing facility.

It is a distribution diagram showing an embodiment of the 1st water purification system concerning the present invention. It is a distribution diagram showing an embodiment of the 2nd water purification system concerning the present invention.

Explanation of symbols

  10 ... …… Acquisition well, 12 ......... Sedimentation basin, 14 ......... Sand filtration pond, 16 ......... Activated carbon adsorption pond, 18 ......... Treatment water storage tank, 20 ......... Sedimentation sludge storage tank, 22 ......... Washing drainage tank, 24 ......... first membrane separator, 26 ......... second membrane separator, 28 ......... oxidation means, 30 ......... raw water, 32 ......... flocculant, 34 ......... settling sludge 36 ......... Supernatant water, 38 ......... Treatment water, 40 ......... Treatment water, 42 ......... Tap water, 44 ......... Wash water, 46 ......... Wash water, 48 ......... Concentrate, 50 ......... Membrane permeated water (of the first membrane separator), 52 ......... Concentrated sludge, 54 ......... Oxidant, 56 ......... Mixed water, 58 ......... Membrane (of the second membrane separator) Permeated water.

Claims (3)

  A sedimentation basin that separates suspended matter in raw water as sedimentation sludge, a sand filtration pond that uses sand filtration of the supernatant water of the sedimentation basin, and a first membrane separation that membrane-separates the sedimentation sludge extracted from the sedimentation basin An apparatus, a second membrane separation device for membrane-separating washing wastewater from the sand filtration pond, an oxidation means for oxidizing the membrane permeated water of the first membrane separation device, and the membrane permeation oxidized by the oxidation means A water purification system comprising means for joining water to the washing waste water and means for joining membrane permeated water of the second membrane separation device to the treated water.   A sedimentation basin that separates suspended matter in raw water as sedimentation sludge, a sand filtration pond that uses sand filtration of the supernatant water of the sedimentation basin as treated water, and a first membrane separation that membrane-separates the sedimentation sludge extracted from the sedimentation basin An apparatus, a second membrane separation device for membrane separation of the waste water from the sand filtration pond, a means for returning the membrane permeated water of the first membrane separation device to the inlet side of the settling basin, and the second membrane separation device And a means for merging the membrane permeated water with the treated water.   3. The water purification system according to claim 1, further comprising means for merging the concentrated solution separated by the second membrane separation device with the precipitated sludge. 4.

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