JPS59150597A - Dephosphorizer - Google Patents

Abstract

PURPOSE:To maintain the concentration of phosphorus in treated water constant, by providing an anaerobic tank, an aeration tank for aerobic treatment, a biological dephosphorizer having a means for the solid-liquid separation of an aerated liquid and then a tank for a phosphorus adsorbent. CONSTITUTION:Raw water 5 and returned sludge 6 in state mixed with each other are introduced into an anaerobic tank 1 and gently agitated therein under a condition isolated from air to perform anaerobic treatment. An aeration tank 2 is constituted in a manner such that aerobic treatment can be performed by supplying air through a sparger pipe 7, and a solid-liquid separation tank 3 is constituted in a manner such that an aerated liquid can be separated into a liquid and solid matter by precipitation. The interior of a tank 4 for a phosphorus adsorbent is packed with a phosphorus adsorbent, e.g. activated alumina, a magnesia compound, a phosphate mineral or ion-exchange resin, to form the bed of the phosphorus adsorbent. A liquid having flowed out of the solid-liquid separation tank 3 is brought into contact with the fluidized or stationary bed to adsorb or discharge phosphorus in said liquid. Thus, the concentration of phosphorus is adjusted to a constant level.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for biologically removing phosphorus.

Biological dephosphorization devices have been proposed to remove phosphorus from organic matter and phosphorus-containing waters such as sewage and wastewater. This equipment mixes raw water containing phosphorus, such as phosphates, with returned sludge, retains it in an anaerobic tank for 30 to 360 minutes, and then retains it in an aeration tank for 90 to 360 minutes.
After removing the OD, the aeration liquid is separated into treated water and precipitated sludge in a settling tank. A portion of the precipitated sludge is returned and the remainder is discharged as surplus sludge.

The mechanism for removing phosphorus and BOD in this device is estimated to be as follows. That is, sewage is mixed with return sludge,
When stirred in an anaerobic tank, microorganisms in the sludge consume phosphorus compounds (magnesium salt of polyphosphoric acid) stored in their bodies as an energy source, release phosphorus (orthophosphoric acid), and produce B.
OD is adsorbed or absorbed, and in the next aeration tank, the absorbed BOD is oxidized through respiration, and the released phosphorus and inflow phosphorus are absorbed and stored in the body in the form of phosphorus compounds as an energy source. The sludge that has accumulated phosphorus is returned to the anaerobic tank and the same process is repeated. The phosphorus content of excess sludge in the normal activated sludge treatment method is 1.5 per dry weight of sludge.
~2.5%, but by alternately repeating anaerobic and aerobic environments, the phosphorus content of excess sludge can reach approximately 8% per dry weight of sludge. Therefore, phosphorus in wastewater can be removed at a high removal rate.

By the way, in such a biological dephosphorization device,
The dephosphorization effect is affected by the residence time of the anaerobic tank and aeration tank, the MLSS concentration, the ratio of BOD concentration to phosphorus concentration in the target water, etc. In particular, the phosphorus concentration at the anaerobic tank outlet, that is, the aeration tank inlet, is a major factor in the quality of treated water, and this phosphorus concentration is also affected by the amount of inflow water, etc.

When dealing with sewage, the amount of inflow water shows hourly fluctuations in a daily cycle, and as a result, the residence time in the anaerobic tank and aeration tank changes in a certain cycle, and the phosphorus concentration in the anaerobic tank and in the treated water also changes. do.

For example, when the amount of inflow water decreases, the residence time in the anaerobic tank increases, the amount of phosphorus released from the sludge as orthophosphoric acid increases, and the phosphorus concentration in the liquid increases. If the amount of inflow water increases following this situation, a large amount of liquid with high phosphorus concentration in the anaerobic tank will be transferred to the aeration tank, but because the amount of inflow water is large, the residence time in the aeration tank will be shortened, and the liquid with high phosphorus concentration in the anaerobic tank will be transferred to the aeration tank. As a result, the time required for phosphorus intake is not available, and the phosphorus concentration in the treated water increases. As described above, in the conventional biological dephosphorization apparatus, there was a problem that the quality of treated water fluctuated due to changes in the amount of inflow water, the quality of inflow water, etc., and stable treatment was not possible.

This invention is intended to improve the problems of the conventional equipment as described above. After the biological dephosphorization equipment, a phosphorus adsorbent is used to adjust the phosphorus concentration in the flowing water discharged from the biological dephosphorization equipment. The purpose of the present invention is to provide a dephosphorization device that is equipped with a layer that can maintain a substantially constant phosphorus concentration in treated water (3) despite fluctuations in the amount of inflow water, quality of inflow water, etc.

This invention provides an anaerobic tank for anaerobically treating raw water mixed with returned sludge, an aeration tank for aerobically treating the mixed liquid that has been anaerobically treated in this anaerobic tank, and a solid liquid for converting the aerated liquid discharged from this aeration tank into a solid liquid. This dephosphorization device is characterized by comprising a biological dephosphorization device including a separation means for separating, and a phosphorus adsorbent layer for adjusting phosphorus concentration after the biological dephosphorization device.

Hereinafter, this invention will be explained with reference to the drawings. The drawing is a system diagram showing one embodiment of the present invention. In the drawing, 1 is an anaerobic tank, 2 is an aeration tank, 3 is a solid-liquid separation tank, and 4 is a phosphorus adsorbent layer, which are connected in series.

The anaerobic tank 1 is configured to perform anaerobic treatment by introducing a mixture of raw water 5 and return sludge 6, and gently stirring the mixture while blocking air. The aeration tank 2 is configured to perform aerobic treatment by aeration through an aeration pipe 7, and the solid-liquid separation tank 3 is configured to perform solid-liquid separation of the aerated liquid by precipitation (4).

The phosphorus adsorbent tank 4 is filled with phosphorus adsorbents such as activated alumina, magnesia-based compounds, phosphate rock, and ion exchange resin to form a phosphorus adsorbent layer, and the solid-liquid separation tank 3
The phosphorus concentration is adjusted to a constant level by adsorbing or releasing phosphorus in the liquid through a fluidized bed or a fixed bed.

The above-mentioned phosphorus adsorbent has the property of adsorbing phosphorus (orthophosphoric acid) in the liquid, and the amount of phosphorus adsorbed differs depending on the phosphorus concentration in the liquid. In other words, under conditions where the phosphorus concentration in the liquid is high, the amount of phosphorus adsorbed increases, under conditions where the phosphorus concentration in the liquid is low, the amount of phosphorus adsorbed decreases, and when the phosphorus concentration further decreases, the amount of phosphorus adsorbed increases. Phosphorus is eluted from the adsorbent into the liquid. Therefore, when a liquid with varying phosphorus concentration is brought into contact with such an adsorbent, the range of fluctuation in phosphorus concentration becomes small and the phosphorus concentration in the liquid is adjusted to be approximately constant.

The particle size of the phosphorus adsorbent varies depending on the type, but in general, a particle size of about 4 to 70 mesh is used. Among these, the larger one is suitable for a fixed bed, and the smaller one is suitable for a fluidized bed. In the case of a fixed bed, it is filled with a phosphorus adsorbent having a particle size of 4 to 60 mesh, and brought into contact by flowing upward or downward at a flow rate of SV2 to 10 hr-'.

In the case of a fluidized bed, a phosphorus adsorbent of lO~70 mesh is used, and contact is made by passing the liquid through with an upward flow of LV1~50 m/hr.

In the biological dephosphorization device configured as described above, basic processing is performed in the same manner as in the conventional device, and organic matter and phosphorus are removed. First, the raw water 5 is mixed with the returned sludge 6 and retained in the anaerobic tank 1, and the dissolved oxygen is also removed by N 0
Anaerobic treatment is performed under conditions in which 2 and NO are hardly present.

At this point, phosphorus in the sludge is released, and some or all of the organic matter in the raw water is incorporated into the sludge. Next, the flowing water from the anaerobic tank is sent to the aeration tank 2, where it is passed through the aeration pipe 7.
Ventilate and aerate to perform aerobic treatment. Here, the activated sludge takes in phosphorus in the liquid and decomposes BOD. Furthermore, if ammonia nitrogen is contained in the raw water, it is oxidized to NO2 and N03 in the aeration tank. When removing this nitrogen, a denitrification tank can be added as usual.

The mixed liquid in the aeration tank 2 is drawn out in portions and subjected to solid-liquid separation in the solid-liquid separation tank 3, and the separated liquid is sent to the phosphorus adsorbent tank 4 via a stream 8. Further, part of the separated sludge is discharged as surplus sludge 9, and the remainder is returned to the anaerobic tank 1 as return sludge 6. Note that the solid-liquid separation tank 3 may employ other separation means such as centrifugation or flotation. As mentioned above, the phosphorus concentration in the effluent from the biological dephosphorization equipment depends on the amount of raw water, the phosphorus concentration, and the B
It changes as the OD# degree changes. Therefore, if the biological dephosphorization method is used alone, the phosphorus concentration may be too high to be discharged as is.

In the present invention, the phosphorus concentration in the treated water can be kept at a substantially constant low level (7) by passing the liquid through the phosphorus adsorbent layer subsequent to the biological dephosphorization device. As a result, even if the amount of raw water or the component content fluctuates, the quality of the treated water is hardly affected and normal operation can be continued.

Since the phosphorus adsorbent used in the present invention utilizes phosphorus adsorption and desorption phenomena, it does not need to be regenerated unlike general adsorbents. However, if the surface of the phosphorus adsorbent is contaminated by other factors such as slime, backwashing is performed as usual to keep the surface clean.

Furthermore, when the phosphorus adsorbent layer of the present invention is used as a fixed bed, SS phosphorus contained in the outflow water from the biological dephosphorization equipment is also removed by the offshore overaction, resulting in more stable water quality treated water. Obtainable. In this case, it is preferable to perform backwashing as appropriate in order to remove captured solids. As described above, in the present invention, a phosphorus stratification agent layer is provided to adjust the phosphorus concentration, following the biological dephosphorization device that is affected by fluctuations in the amount and quality of raw water. This has the effect of making it possible to reduce the range of fluctuation in the phosphorus concentration in the water, thereby keeping the phosphorus concentration in the treated water almost constant.

Next, test examples of the present invention will be explained.

Test Example: pH 7.0, alkalinity 100m9/13, phosphorus concentration 4m9/E.

BOD l Oomt2/! The synthetic sewage from step 3 was mixed with the returned sludge and retained in the anaerobic tank for 85 hours, and then in the aerobic tank for 2 hours, resulting in an MLS of 82,000 to 4,000.
Aerobic treatment was carried out at 0 m9/1, and solid-liquid separation was performed in a final settling tank. A portion of the separated sludge was returned to the anaerobic tank to achieve a return rate of 30%, and the remainder was treated as surplus sludge.

On the other hand, the supernatant liquid was transferred to an acrylic resin column with an inner diameter of 30+m% and a length of 500mm with a particle size of 0.5-1. 300 ml/hr in a layer filled with Omm activated alumina xsotnl
The liquid was passed in an upward flow at a flow rate of . In addition, in order to remove the SS trapped in the activated alumina filled layer, the activated alumina filled layer was washed once every 2 to 3 days using the final treated water.

As a result of continuous water flow treatment under the above conditions for one month, the phosphorus concentration of the treated water was continuously below 0.1 m9/13. Subsequently, the raw water was continuously treated for one month under conditions in which the phosphorus concentration of the raw water was varied every few hours in the range of 4 to 7 m9/13. The phosphorus concentration in the treated water continued to be below O,lta/β.

Comparative Example As a comparative example, the phosphorus concentration of the biologically dephosphorized water was continuously measured in the case where the liquid was not passed through the activated alumina packed layer in the above test example.

When the raw water phosphorus concentration is 4m97B and water is continuously passed for one month, the phosphorus concentration in the treated water is o,t -0,7In9/
It was 13.

In addition, continuous treatment was carried out for one month under conditions in which the raw water phosphorus concentration was varied every few hours in the range of 4 to 7 Da/form. The phosphorus concentration of the treated water varied in the range of 0.1 to 1.61 n9/l.

[Brief explanation of the drawing]

The drawing is a system diagram showing an embodiment of the present invention. In the figure, l represents an anaerobic tank, 2 represents an aeration tank, 3 represents a solid-liquid separation tank, and 4 represents a phosphorus adsorbent tank. Patent applicant Kurita Industries Co., Ltd.

Claims (1)

[Claims] (11) An anaerobic tank for anaerobically treating raw water mixed with returned sludge, an aeration tank for aerobically treating the mixed liquid anaerobically treated in this anaerobic tank, and aeration discharged from this aeration tank. A dephosphorization device comprising a biological dephosphorization device including a separation means for separating a liquid into solid and liquid, and a phosphorus adsorbent layer for adjusting phosphorus concentration after the biological dephosphorization device. (2 ) The dephosphorization device according to claim 1, wherein the phosphorus adsorbent is one or more selected from activated alumina, magnesia-based compounds, phosphate rock, and ion exchange resins. (3) The phosphorus adsorbent layer is fixed. The dephosphorization device according to claim 1 or 2, which is a bed or a fluidized bed.