JPH10328536A - Water treatment method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To obtain safe tap water from which protozoa have been removed. SOLUTION: The purified water subjected to the sedimentation separation treatment step and the rapid filtration treatment step is introduced into the membrane filtration step, and the filtration having a pore size smaller than the minor axis of the parasite cyst and oocyst contained in the purified water in the membrane filtration step. A method for treating purified water, comprising filtering under pressure through a membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating purified water obtained by purifying river water and lake water, particularly to remove protozoa contained in the purified water.

[0002]

2. Description of the Related Art FIG. 3 is a flowchart showing a flow of a conventional water purification process by a rapid filtration method. As shown in this, in a conventional water treatment plant, after introducing raw water introduced from a river or the like into a landing well, an agent such as a coagulant is added,
Agitation mixing is performed in the mixing pond.

[0003] Then, in a sedimentation separation process using a slant plate sedimentation basin or the like, sedimentation and separation of the aggregated turbid matter is performed, and the supernatant liquid is introduced into a rapid filtration process for filtering by sand filtration or the like. Suspension removal is performed. As a result, the obtained purified water is stored in a water purification reservoir after chlorination and is distributed to each household.

[0004] In addition, sediment sludge in which sediment generated in the sedimentation separation process is concentrated, and washing wastewater generated when the washing treatment is performed in the rapid filtration treatment process are discharged directly to a river, or Introduced to the dehydration step, solid-liquid separation is performed using a centrifugal dehydrator or the like. The desorbed liquid from which the turbid matter has been removed in the dehydrator is discharged into a river or the like, and the dehydrated cake is subjected to a drying treatment and then incinerated.

[0005]

In tap water supplied to each household, microorganisms such as Escherichia coli are basically killed because of sterilization by chlorination, but recently, It has been pointed out that there are cases in which protozoa, which have a bad effect on the human body, are mixed in tap water. Examples of protozoa contaminating tap water include Cryptosporidium and Giardia, which usually exist as protozoan oocysts (zygote cysts) and cysts (cysts).

[0006] Of these protozoa, for example, cryptosporidium is a protozoan belonging to the spore family, and when taken into the human body, proliferates violently in the microvilli of intestinal epithelial cells while repeating sexual reproduction and asexual reproduction. In addition to causing diarrhea and the like, an enormous number of oocysts formed by sexual reproduction are excreted together with feces, which further causes secondary contamination. Cryptosporidium oocysts have an approximately circular shape with a diameter of 4.5 to 5 μm.

[0007] These protozoa enter the water purification treatment process from river water, lake water, etc., but cannot be filtered out by the sedimentation separation treatment process or the rapid filtration treatment process, and have a disinfection resistance. Since it is extremely high and does not die even after the subsequent chlorination, it is mixed in tap water used in each household and invades the human body to cause onset.

In the conventional water purification treatment process, the above-mentioned settled sludge and washing wastewater are discharged into a river as they are, or solid-liquid separation is performed in a dehydration process using a dehydrator or the like. However, even when dehydration is performed in this dehydration step, it is possible to filter turbid substances having a large particle size, but it is not possible to separate the protozoa present in the settling sludge and the washing wastewater. Will be discharged again into the river.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of such inconvenience, and in order to obtain safe tap water from which protozoa have been removed, furthermore, protozoan cysts from wastewater discharged to rivers, The purpose was to develop a method for treating purified water to remove oocysts.

[0010] That is, the gist of the present invention is to introduce purified water subjected to the sedimentation separation step and the rapid filtration step into the membrane filtration step, and to shorten the parasite cysts and oocysts contained in the purified water in the membrane filtration step. The present invention provides a method for treating purified water, which comprises filtering under pressure through a filtration membrane having a pore size not larger than the diameter.

Preferably, when a step of returning the backwash wastewater generated in the membrane filtration step to the landing well is further provided, the load of the precipitation separation step and the rapid filtration step does not greatly increase, and the recovery rate is improved. The load on the wastewater treatment process can be reduced.

In addition, at least one of sedimentation sludge generated in the sedimentation separation process, washing wastewater generated in the rapid filtration process, and chemical washing wastewater generated in the membrane filtration process is introduced into the membrane concentration process. If the step further includes a step of performing suction filtration using a filtration membrane having a pore diameter smaller than the minor axis of the protozoan cyst and oocyst, wastewater from which the protozoa have been removed can be obtained.

[0013] Further, a step of introducing the concentrated liquid generated in the membrane concentration step to the dehydration step and returning the desorbed liquid generated in the dehydration step to the membrane concentration step is further provided, whereby the turbidity containing protozoa in the system is provided. Quality can be removed from the wastewater treatment process.

[0014] The backwash wastewater generated in the membrane filtration step is returned to the landing well, the settling sludge generated in the sedimentation separation step, the washing wastewater generated in the rapid filtration processing step, and the chemical washing generated in the membrane filtration step. The wastewater is introduced into the membrane concentrating step, and suction filtration is performed using a filtration membrane having a pore diameter smaller than the short diameter of the protozoan cyst and oocyst. If a step of returning the syneresis to the membrane concentration step is further provided, the water purification treatment can be performed with high treatment efficiency.

Further, the sludge generated in the sedimentation separation step is introduced into a dehydration step, and the desorbed liquid generated in the dehydration step is introduced into a membrane concentration step. When a step of performing suction filtration with a filtration membrane having a pore size equal to or smaller than the diameter is further provided, the load on the amount of water in the dehydration step can be reduced, and the efficiency of treating wastewater can be improved.

Further, if a step of returning the concentrated liquid generated in the membrane concentration step to the dehydration step is further provided, the turbid substance containing protozoa can be removed from the wastewater treatment step.

The washing wastewater generated in the rapid filtration process and the backwash wastewater generated in the membrane filtration process are returned to the landing well, and the settled sludge generated in the sedimentation separation process is introduced into the dewatering process. The desorbed liquid generated in the step and the chemical washing wastewater generated in the membrane filtration step are introduced into the membrane concentration step, and in the membrane concentration step, suction is performed by a filtration membrane having a pore diameter smaller than the minor axis of the parasite cyst and oocyst. If a step of feeding the concentrated liquid generated to the dehydration step while filtering is further provided, the purified water can be treated with high treatment efficiency.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a flowchart showing one embodiment of the water purification method of the present invention. In the treatment method of water purification of the present invention, the sedimentation separation treatment step, the purified water subjected to the rapid filtration treatment step is introduced into the membrane filtration step, in this membrane filtration step, the parasite cysts, the average pore diameter of less than the minor diameter of the oocyst By performing pressure filtration with a filtration membrane having
Purified water from which protozoan cysts and oocysts have been removed can be obtained.

For example, in the case of Cryptosporidium, its minor diameter is 4.5 to 5 μm, so its pore diameter is 4.5 μm.
If a filtration membrane exceeding m is used, the removal of protozoa from the purified water is insufficient, which is not preferable. The filtration membrane used in the membrane filtration step can be any of a flat membrane and a hollow fiber membrane as long as it has a pore size smaller than the minor axis of the protozoan cyst or oocyst to be removed. To perform a filtration treatment of the introduced purified water.

In the membrane filtration step, by performing pressure filtration using a filtration membrane, compared with the case of performing filtration by a suction type, the capacity can be reduced even if it is attached to existing equipment.
And filtration of purified water can be performed with a high throughput.

In the membrane filtration step, as the filtration treatment of the introduced purified water is continued, the pores of the filtration membrane are gradually closed by turbidity and the differential pressure rises. It is preferable to perform a washing treatment. By performing the backwashing treatment of the filtration membrane, it is possible to remove the turbid matter that has closed the micropores of the filtration membrane, and thus it is possible to reduce the rise in differential pressure. It is preferable to provide a step of returning backwash wastewater generated by this backwash treatment to a landing well.

The raw water introduced into the membrane filtration step has been filtered in the previous step, and the concentration of the suspended solids in the backwash wastewater is low. The load does not increase significantly, and the recovery rate can be improved and the load on the wastewater treatment process can be reduced.

In the membrane filtration step, even if the above-mentioned backwashing treatment is performed, the pressure difference gradually increases. Therefore, it is preferable to wash the filtration membrane with a chemical (chemical washing).
The timing of performing the chemical washing varies depending on the filtration membrane used and the filtration conditions, but is performed when the recovery of the transmembrane pressure difference due to the backwashing operation becomes small. As a chemical solution used for chemical washing, a dilute aqueous solution of caustic soda, hydrochloric acid, or the like can be used. By performing chemical washing of the filtration membrane in the membrane filtration step, the increased differential pressure can be recovered.

The settled sludge generated in the sedimentation separation process, the washing wastewater generated in the rapid filtration process, and the chemical washing wastewater generated in the membrane filtration process are mixed with protozoa at a relatively high concentration. It is preferable to provide a step of introducing at least one of these into the membrane concentration step and performing suction filtration using a filtration membrane having a pore diameter smaller than the short diameter of the protozoan cyst and oocyst. By adopting such a configuration,
Wastewater from which raw water has been removed can be obtained, and the wastewater produced by the water purification treatment is preferable because it does not cause secondary contamination of rivers and the like with protozoa.

[0025] More preferably, the concentrated liquid, in which the turbid matter is concentrated, generated in the membrane concentration step is introduced into a dehydration step using a dehydrator or the like, and the desorbed liquid generated in the dehydration step is returned to the membrane concentration step. When the step of performing the step is provided, the turbid substance including the protozoa can be removed from the water purification step.

The concentrated liquid obtained by concentrating the turbid matter obtained in the membrane concentration step is introduced into a dehydration step using a centrifugal dehydrator or the like to further perform solid-liquid separation. Since the separated effluent is returned to the membrane concentration step, solid-liquid separation of the concentrate can be performed without draining wastewater containing protozoa to the outside at all. The dehydrated cake obtained in the dehydration step is disposed by incineration or the like after drying.

More preferably, the sediment sludge generated in the sedimentation step, the washing wastewater generated in the rapid filtration step, and the chemical washing wastewater generated in the membrane filtration step are led to the membrane concentration step, where the parasite cysts and oocysts have a minor axis or less. By performing suction filtration using a filtration membrane having a pore size, introducing a concentrated solution generated in the dehydration step, and returning a desorbed solution generated in the dehydration step to the membrane concentration step, water purification can be performed with high treatment efficiency. Processing can be performed.

As the filtration membrane used in the membrane concentration step, any flat membrane, hollow fiber membrane, or tubular membrane can be used as long as it has a pore size smaller than the minor axis of the parasite cyst or oocyst. The filtration process is performed using the module. In addition, the membrane filtration in the membrane concentration step is performed by suction filtration with a small increase in differential pressure in order to filter sludge having a high turbid concentration. More preferably, if an air diffuser is provided below the module and suction filtration is performed while air scrubbing is performed, the filtration process can be performed stably for a long period of time.

FIG. 2 is a flowchart showing another embodiment of the water purification method of the present invention. In this embodiment,
The sludge generated in the sedimentation separation process is introduced into the dehydration process directly or, if necessary, through a thickening process such as a thickener, and the desorbed liquid generated in the dehydration process is introduced into the membrane concentration process. In the step, a step of performing suction filtration using a filtration membrane having a pore size smaller than the minor axis of the protozoan cyst and oocyst is provided.

With this configuration, only the permeate from which the protozoan cysts and oocysts have been removed can be discharged to the outside, and only the settled sludge from the settling separation process is introduced into the dehydration process. In addition, it is possible to reduce the load of water in the dewatering step without lowering the concentration of the settled sludge to be introduced into the dewatering step, and it is possible to improve the efficiency of treating wastewater. Further, if a step of returning the concentrated liquid generated in the membrane concentration step to the dehydration step is further provided, the turbid matter concentrated by performing solid-liquid separation can be discharged out of the system.

Further, the washing wastewater generated in the rapid filtration process and the backwash wastewater generated in the membrane filtration process are returned to the landing well, and the settled sludge generated in the sedimentation separation process is introduced into the dewatering process. The desorbed liquid generated in the dehydration step and the chemical washing wastewater generated in the membrane filtration step are introduced into the membrane concentration step, and in the membrane concentration step, a filtration membrane having a pore diameter smaller than the minor axis of the parasite cyst or oocyst If a step of supplying the generated concentrated liquid to the dehydration step is further provided while performing suction filtration by using the method described above, the purified water can be treated with higher treatment efficiency.

[0032]

According to the water purification method of the present invention, the purified water subjected to the sedimentation separation treatment step and the rapid filtration treatment step is subjected to:
Since it is introduced into the membrane filtration step and subjected to pressure filtration through a filtration membrane having a pore diameter smaller than the short diameter of the parasite cysts and oocysts, it is possible to obtain safe purified water obtained by removing the parasites from purified water with a compact device.

In addition, the backwash wastewater generated in the membrane filtration process is returned to the landing well, the settling sludge generated in the sedimentation separation process, the washing wastewater generated in the rapid filtration process, and the wastewater generated in the membrane filtration process. The chemical washing wastewater is introduced into the membrane concentration step, and the filtrate is suction-filtered using a filtration membrane having a pore diameter smaller than the short diameter of the protozoan cyst and oocyst. If a step of returning the desorbed liquid to the membrane concentration step is further provided, water purification treatment can be performed with a high treatment amount, and wastewater from which parasite cysts and oocysts have been removed is discharged out of the system. Secondary contamination can be prevented.

The washing wastewater generated in the rapid filtration process and the backwash wastewater generated in the membrane filtration process are returned to the landing well, and the settled sludge generated in the sedimentation separation process is introduced into the dewatering process. The desorbed liquid generated in the dehydration step and the chemical washing wastewater generated in the membrane filtration step are introduced into the membrane concentration step, and in the membrane concentration step, a filtration membrane having a pore diameter smaller than the minor axis of the parasite cyst or oocyst By performing suction filtration and further providing a step of feeding the generated concentrated liquid to the dehydration step, not only can the secondary contamination of rivers and the like be prevented, but the water load in the drainage step can be reduced, Wastewater treatment efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of a method for treating purified water according to the present invention.

FIG. 2 is a flowchart showing another example of the water purification method of the present invention.

FIG. 3 is a flowchart showing a conventional water purification method.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Ikuo Ikami 4-160 Sunadabashi, Higashi-ku, Nagoya City, Aichi Prefecture Mitsubishi Rayon Co., Ltd. Product Development Laboratory

Claims (8)

[Claims] 1. The purified water subjected to the sedimentation / separation treatment step and the rapid filtration treatment step is introduced into the membrane filtration step, and has a pore diameter smaller than the minor axis of the parasite cysts and oocysts contained in the purified water in the membrane filtration step. A method for treating purified water, comprising filtering under pressure through a filtration membrane. 2. The method according to claim 1, further comprising a step of returning backwash wastewater generated in the membrane filtration step to a landing well.
A method for treating purified water as described. 3. At least one of sedimentation sludge generated in the sedimentation separation process, washing wastewater generated in the rapid filtration process, and chemical washing wastewater generated in the membrane filtration process is introduced into the membrane concentration process. 3. The method for treating purified water according to claim 1, further comprising a step of performing suction filtration using a filtration membrane having a pore diameter smaller than the minor axis of the protozoan cyst and oocyst in the step. 4. The method according to claim 3, further comprising a step of introducing a concentrated liquid generated in the membrane concentration step to the dehydration step, and returning the desorbed liquid generated in the dehydration step to the membrane concentration step. Water treatment method. 5. The backwash wastewater generated in the membrane filtration step is returned to the landing well, the settled sludge generated in the sedimentation separation step, the washing wastewater generated in the rapid filtration step, and the wastewater generated in the membrane filtration step. The chemical washing wastewater is introduced into the membrane concentration step, and the filtrate is suction-filtered using a filtration membrane having a pore diameter smaller than the short diameter of the protozoan cyst and oocyst. 2. The method for treating purified water according to claim 1, further comprising a step of returning the desorbed liquid to the membrane concentration step. 6. The sediment sludge generated in the sedimentation / separation treatment step is introduced into a dehydration step, and the desorbed liquid generated in the dehydration step is introduced into a membrane concentration step. 2. The method for treating purified water according to claim 1, further comprising a step of performing suction filtration with a filtration membrane having a pore diameter equal to or smaller than the diameter. 7. The method according to claim 6, further comprising the step of returning the concentrated liquid generated in the membrane concentration step to the dehydration step.
A method for treating purified water as described. 8. The washing wastewater generated in the rapid filtration step and the backwash wastewater generated in the membrane filtration step are returned to the landing well, and the settled sludge generated in the sedimentation separation step is introduced into the dewatering step. The desorbed liquid generated in the dehydration step and the chemical washing wastewater generated in the membrane filtration step are introduced into the membrane concentration step, and in the membrane concentration step, a filtration membrane having a pore diameter smaller than the minor axis of the parasite cyst or oocyst 2. The method for treating purified water according to claim 1, further comprising a step of performing filtration by suction and feeding a generated concentrated liquid to the dehydration step.