JP2009108590A - Method of treating inflow water in rainy weather - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treating method using filtration in a combined sewerage that can reduce the capacity of a reservoir to a half or less to reduce the number of times of untreated discharge by half. <P>SOLUTION: This method for treating inflow water in rainy weather is carried out by performing filtration treatment of inflow water not subjected to high grade treatment, out of inflow water in rainy weather and then discharging the inflow water as primary treated water in the combined sewerage, wherein the reservoir is used as a buffer tank to carry out continuous filtration treatment of the inflow water increased in rainy weather. The capacity of the reservoir required to store the inflow water is thereby reduced to a half or less, and the treated water is discharged as primary treated water to the outside of a system. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a treatment method using filtration for treating inflow sewage in rainy weather in a combined sewer where sewage and rainwater are collected by the same pipe.

  In the sewage treatment facility, the facility is designed based on the maximum daily sewage amount that flows in on a clear day. Usually, in the sewage treatment plant, the inflow sewage is treated in order through the first sedimentation basin → biological reaction tank → final sedimentation basin.

  In the combined sewerage system, a large amount of sewage is treated by intercepting rainwater and sewage during rainy weather. In rainy weather, when the maximum sewage amount is 1Qsh, the sewage is normally intercepted up to 3Qsh and received in the treatment plant, and the amount exceeding the interception amount is untreated and discharged into the water area. In addition, the sewage accepted into the treatment plant during rainy weather is normally treated for 1Qsh as in fine weather, and discharged after being disinfected. On the other hand, sewage exceeding 1 Qsh and up to 3 Qsh is first treated in a settling basin, and then a simple treatment is performed to disinfect and discharge.

A simple simulation of the current situation during rain in the combined sewer system based on the annual precipitation from each weather station data shows that the national average value is about 700 mm overflow, 71 untreated discharges, and 212 hours overflow time. is there. (For example, see Non-Patent Document 1)
In recent years, measures to improve these combined sewers have been mandated. From 2014, water quality standards of 40 mg / l or less in rainy weather are required, and depending on the region, it is required to meet the level of diversion. There is also guidance to reduce the number of untreated discharges by half. (For example, see Non-Patent Document 2)
Therefore, as measures to improve these combined sewers, increase the interception ratio by increasing the water supply volume by installing a reservoir, installing rainwater storage pipes, raising the weir at the pumping station, etc. For example, high-speed stormwater treatment at a pumping station.

  By installing a stagnation pond and rainwater storage pipe, it is possible to store rainwater with a high load at the beginning of rainfall and perform normal treatment after the end of the rain, thereby reducing the untreated discharge flow rate and discharge load amount. Increasing the interception factor has been implemented in many cities as a measure to prevent the outflow of early-stage pollution. Moreover, in the high-speed rainwater filtration process in a treatment plant or a pumping station, the amount of untreated effluent water and the effluent load at the time of rain can be reduced by always filtering a certain amount of inflow water during rainfall and discharging the treated water.

  Furthermore, a more efficient reduction of the amount of untreated effluent water and effluent load can be expected by a combination of the above technologies.

  However, the effect of such technology is greatly affected by the rainfall conditions at that time. Reservoir ponds and storage pipes are less effective in the case of long rains with a low load and a large amount of rainfall. In order to reduce the amount of untreated effluent, a large reservoir is required, and securing land and construction costs are problems. In addition, it often takes about 2 days to drain the water in the reservoir, and even for independent rainfall with an interval of 4 hours or more, the stored water in the reservoir cannot be treated for rainfall with a narrow interval. Can not cope with the rain.

  The increase in the amount of interception is effective to a certain extent, but even if the amount of interception is increased above a certain amount, the amount of simple treated water increases, and the load reduction rate decreases. Moreover, the filtration is less effective when a large amount of rain falls in a short time and the inflow water amount and load are large, and a certain amount or more cannot be treated and is discharged as untreated effluent water.

On the other hand, combining a water reservoir and filtration can be expected to reduce the capacity of the water reservoir and to process the amount that could not be stored in the water reservoir by filtration (for example, see Non-Patent Document 3). For example, the initial pollutant load (first flush) with a high load can be stored in a catchment basin, and rainwater that continues to fall afterwards can be processed by filtration.
Ministry of Land, Infrastructure, Transport and Tourism, Urban and Regional Development Bureau, Sewerage New Technology Promotion Organization, “Survey Report on Improvement Measures for Combined Sewerage”, Part 5, Chapter 4, Review of Combined Sewerage Improvement Measures, March 2014, Merger Type Report of the Sewerage Improvement Measures Review Committee, p. II121-II180 Sewerage Law (provision promulgated in September 2015), Article 6 "Introduction of high-speed filtration facility in rainy weather by utilizing existing facilities" The 42nd Sewerage Research Presentation Lecture Meeting, Japan Sewerage Association, June 20, 2005, p.393-395

  However, even when the pond and filtration are combined, the combination method that has been considered so far is to put inflow water into the basin from the start of rainfall until the basin is full, and to filter when the basin is full. It was to switch. Therefore, when there is an inflow exceeding the filtration rate after the pond is full, all the inflow water exceeding the filtration rate will be discharged as untreated effluent.

  Furthermore, since many existing pumps installed in treatment plants and pump stations have large capacities and operate by ON-OFF operation, they often send a large amount of water at a time and pause for a while. Therefore, when using these existing pumps to send water to the filter, the filtration function of always filtering a constant amount does not work efficiently, and filtration is performed while being greatly affected by the operation time of the pump and the amount of water supplied. End up. As a result, there was a problem that the filtration device moved only when the water was fed by the pump, and the amount of water sent exceeding the filtration rate out of the amount of water delivered by the pump was discharged as untreated discharged water.

  On the other hand, when making a filtration device that matches the amount of water sent by the pump, it must be matched to the large amount of water that is sent in a short time during which the pump operates, and a large-scale filtration device is required.

  Therefore, there are cases in which the performance of each other cannot be effectively exhibited even in the combination of a reservoir and filtration, and in particular, it has been difficult to halve the current number of untreated discharges.

  The present invention uses the stagnation pond as a buffer tank even in the case where the number of untreated discharges in rainy weather is halved in the combined sewer, and does not increase the capacity required for the stagnation pond, and the processing of the filtration device An object of the present invention is to provide a processing method that can be completed with a small capacity.

  The inventors of the present invention have used the reservoir basin as a buffer tank, and efficiently combined the buffer tank and the filtration device to continuously store the stored water while storing a large amount of inflow sewage in the rain in the buffer tank. The present inventors have found the fact that the above problem can be solved by filtration, and have reached the present invention.

  That is, the present invention relates to a treatment method in which inflow water that is not subjected to high-level treatment among inflow water in the rain in a combined sewer system is filtered and discharged as simple treated water. Inflowing water in rainy weather, characterized in that the inflowing water is introduced into the buffer tank and stored, and in parallel, the inflowing water in the buffer tank is introduced into the filtration device and subjected to filtration The summary of the method is as follows.

  According to the present invention, the influent water in the rainwater in the combined sewer system is efficiently filtered, and the capacity of the basin required for halving the number of untreated discharges is reduced to less than half, and the basin with the original capacity is further reduced. The above-mentioned untreated discharged water reduction effect can be produced.

  In addition, by providing a buffer tank in the filtration device, it is possible to reduce the influence of the supply rate and amount of incoming sewage on the processing capacity of the filtration device. For example, the filtration device is a large-capacity pump in which the incoming water moves by ON-OFF operation. Even when the filter is supplied to the filter, the processing capacity of the filtration device can be made smaller than that conventionally required.

  In addition, by using the reservoir as a buffer tank, the stored water inside the reservoir can be continuously filtered to clean up the stored water. It becomes possible.

  Hereinafter, the present invention will be described in detail. 1 and 2 are schematic views of a processing flow showing an embodiment of the present invention. In FIG. 1, the inflow sewage enters the settling basin 1 and is sent from the settling basin 1 to the buffer tank 2 by the pump 4 and stored in the buffer tank 2, and at the same time sent to the filtration device 3 by the pump 5 and filtered. It is released.

  In FIG. 2, the inflowing sewage enters the sand basin 1 and is sent to the buffer tank 2 by the pump 4. A buffer tank 2 is provided on the filtration pond, and water flows into the filtration device 3 under natural flow, and is discharged after being filtered.

  The buffer tank 2 used in the present invention is not particularly limited as long as it can temporarily store the inflowing sewage during rainy weather, and can be used as a buffer tank of a filtration device such as a reservoir or a rainwater storage pipe. Anything is possible. As the capacity, 50 m3 to 10,000 m3 is effective, but it is not particularly limited as long as it has a buffer capacity between the rainfall condition and the inflow condition of sewage and the filtration speed. As the shape, rectangular, circular, cylindrical, etc. are generally considered, but it is only necessary to temporarily store inflow sewage and to have a buffering capacity between the rainfall situation and the inflow situation of sewage and the filtration speed. It is not limited.

  In addition, the water feeding method in the introduction from the sand basin to the buffer tank and the introduction from the buffer tank to the filtration device may be by natural flow or by a pump. is not. The supply of sewage to the buffer tank can use an existing pump such as a sedimentation basin or a pump station, such as a sewage pump in rainy weather or a rainwater pump, and the inflow speed to the buffer tank can depend on the capacity of the existing pump. In addition, the sewage supply speed from the buffer tank to the filtration device is the minimum cost that can clear the target discharge BOD concentration and the overflow frequency by half in the combination of the buffer tank and the filtration device according to the situation of the installation location. Can be determined from Further, it is determined from the combination that minimizes the life cycle cost.

  Various types of conventional sand basins and filtration devices can be used and are not particularly limited.

Hereinafter, the present invention will be specifically described by way of examples.
Example 1
In the sewage treatment plant and pumping station, the number of untreated discharges during rainy weather was 72 times / year, of which the worst "rainy water quality during rainy weather" was the worst rainwater quality (rainfall is 1). An example is shown in a treatment area in which the amount of untreated effluent water was 116,760 m3 and the concentration of treated water BOD was 45.8 mg / l. Here, “treatment quality during rainy weather” is the total load of the treated water, filtered treated water, untreated effluent water of high-quality treated water at the treatment plant, retained water after the end of rainfall, and untreated effluent. It was. The concentration of the BOD treated water BOD in the treatment area of this example is 38.5 mg / l.

  It implemented according to the processing flow shown in FIG. The inflowing sewage that flowed into the sand basin 1 during rainy weather was sent to the reservoir 2 used as a buffer tank by the pump 4 and stored. At the same time, the sewage was supplied to the filtration device 3 by the pump 5, filtered and discharged. The capacity of the buffer tank 2 was 8,500 m3 and the filtration speed of the filtration device 3 was 80 m3 / min. As a result of applying this facility, untreated effluent was not generated, the entire amount of the stored water in the reservoir was treated by filtration, and the treated water BOD concentration was 29.5 mg / l. The target treated water BOD concentration of 40 mg / l or less was cleared, and the value was lower than that of the separated-stream treated water BOD concentration of 38.5 mg / l.

  In addition, as a result of applying this facility, the number of untreated discharges was reduced to 33 times / year, and the BOD concentration in rainy treated water was 38.5 mg / l or less in all annual rainfall.

Comparative Example 1
In the same treatment area as in Example 1, a 17,000 m3 reservoir was installed. The inflow sewage that flowed into the sand basin was pumped to the spill pond, stored up to 17,000m3 in the spill pond, and the part exceeding 17,000m3 was discharged as untreated effluent. The stored water stored in the reservoir was sent to the sewage treatment plant for normal processing after the rain.

  As a result of applying this facility to the rain 1 as in Example 1, the amount of untreated discharged water was 99,760.5 m3 and the BOD concentration of treated water was 42.04 mg / l.

  As a result of applying this equipment, the number of untreated discharges was 38 times / year.

  In Example 1, an 8,500m3 reservoir is used as a buffer tank, and inflow sewage is stored in the buffer tank and simultaneously sent to the filtration device, and filtered at 80m3 / min. Compared with Comparative Example 1 where a 17,000m3 reservoir is installed, the annual number of untreated discharges can be reduced, and the number of untreated discharges can be reduced to 36 or less, half of 72 times a year. We were able to.

Example 2
In the same processing section as Example 1, it implemented according to the processing flow shown in FIG. The inflowing sewage that flowed into the sand basin 1 during rainy weather was sent to the buffer tank 2 by the pump 4 and supplied to the filtration device 3 under natural flow, filtered and discharged. Inflow sewage that flowed in beyond the capacity of the buffer tank was directly discharged as untreated effluent. The existing pump in the sand basin was used for the pump 4 with a water supply rate of 115 m3 / min, a capacity of the buffer tank 2 of 150 m3, and a filtration speed of the filtration device 3 of 35 m3 / min. As a result of applying this equipment, it was possible to reduce the scale of the filtration device to 35 m3 / min by providing a buffer tank even if an existing pump of 115 m3 / min was used. Furthermore, the treated water BOD concentration was 38.3 mg / l, which cleared the target treated water BOD concentration of 40 mg / l or less, and was a value lower than the shunted treated water BOD concentration of 38.5 mg / l.

Comparative Example 2
In the same treatment section as in Example 1, the process was carried out with the 8,500 m3 reservoir 2 and the 55 m3 / min filtration device according to the process flow shown in FIG. The inflow sewage that has flowed into the sand basin is sent to the lagoon 2 by the pump 4 and is stored in the lagoon 2 up to 8,500m3. Was discharged directly as untreated discharge water. In addition, the stored water stored in the reservoir 2 was sent to a sewage treatment plant for normal processing after the end of rainfall. As a result of applying this equipment, the quality of treated water was 38.5mg / l.

  In Example 2, by providing a buffer tank, the existing large pump of 115 m3 / min in the sand basin can be used as it is, and the scale of the filtration device is 35 m3 / min compared with 55 m3 / min in Comparative Example 2. We were able to reduce it to min. Moreover, by using the stagnation pond as a buffer tank, the scale of the stagnation pond could be reduced to 150 m3 compared to 8500 m3 in Comparative Example 2. Furthermore, the quality of the treated water was 38.5 mg / l or less, which was the same as that of the diversion, and good results were obtained.

It is the schematic of the processing flow which shows one Example of the processing method using the filtration of the inflow sewage in the combined sewer of this invention. It is the schematic of the processing flow which shows the other Example of the processing method using the filtration of the inflow sewage in the combined sewer of this invention. It is a processing flow figure showing an example of the conventional processing method given in comparative example 2 about the processing method using filtration of inflow sewage in the combined sewer of the present invention.

Explanation of symbols

1 Sedimentation basin 2 Reservoir pond or buffer tank 3 Filtration device 4 Pump 5 Pump

Claims (1)

In the combined sewer system, the inflowing water that is not treated in high-quality in the rainy weather is filtered and discharged as simple treated water, and the buffer pond provided in the previous stage of the filtration device is used as the buffer tank. A method for treating rainwater inflowing water, wherein the inflowing water is introduced into and stored in the buffer tank, and the inflowing water in the buffer tank is introduced into a filtration device in parallel.