JPH04277098A - Method and device for treating waste water - Google Patents

Abstract

PURPOSE:To efficiently reduce BOD and nitrogen concn. in a finally treated water by a method wherein waste water is treated in anaerobic and aerobic treating chambers and the water residence time in the anaerobic treating chamber is set at 3-8 hours in a waste water treating process for circulating a part of aerobic treating water. CONSTITUTION:The total digestion rate beta is obtained by extrapolating the minimum nitrogen removal rate alpha of a purifying tank devoid of a partial circulation process from the removal rate in a waste water treating device having a circulating process. The total digestion rate betabecomes greater with the decreasing concn. gamma of decomposable total organic carbon(TOC) at the exit of the anaerobic treating chamber and that become almost equal to each other within certain values. Accordingly, the total digestion rate alpha of the device and the decomposable TOC concn. gamma are required to be within a desirable range not exceeding the certain values. From the relationship between the decomposable TOC concn. gamma and the residence time T of the waste water in the anaerobic treating chamber, the residence time of about 3-8 hours within the range not exceeding the certain values of the decomposable TOC concn. gamma is obtained. Although the residence time T in the anaerobic treating chamber is related to the amt. of inflow waste water, the cirulation water amount and the effective volume, the circulation water amount is obtained by substituting the residence time T and the amt. of the water discharged and the decomposable TOC concn. gamma is reduced effectively.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention adjusts the flow rate from the aerobic treatment chamber to the anaerobic treatment chamber, effectively reducing the BOD concentration and nitrogen concentration in the final treated water while ensuring economical operation. The present invention relates to a wastewater treatment method and a wastewater treatment device that can be used.

0002

[Prior Art] The present applicant previously filed Japanese Patent Application No. 1-1218
In No. 4, a septic tank for the above purpose was disclosed.

That is, as conceptually shown in FIG. 5, the septic tank has an anaerobic treatment chamber 51 and an aerobic treatment chamber 52 arranged side by side in a septic tank main body 50. It has a configuration that allows part of the treated water inside to be returned to the anaerobic treatment chamber 51 via a return pipe 53.

With this configuration, NH4 is partially passed through the reflux pipe 53 and generated by the microbial reaction in the aerobic treatment chamber 52.
The NO2 − and NO3 − generated from + are returned to the anaerobic treatment chamber and reacted with microorganisms together with the anaerobically treated water, and can be taken out as N2 gas and CO2 gas. The treated water can effectively reduce the BOD concentration and nitrogen concentration when compared with a conventional septic tank that does not recirculate aerobic treated water.

[0005]

[Problems to be Solved by the Invention] However, such septic tanks still have the following problems to be solved.

That is, in the above-mentioned septic tank, the partial return amount from the aerobic treatment chamber 52 has not been theoretically considered at all, and is determined solely by trial and error. Therefore, the BOD concentration and nitrogen concentration in the final treated water cannot be sufficiently reduced, or even if they can be reduced, the operation is extremely uneconomical.

An object of the present invention is to provide a wastewater treatment method that can effectively reduce the BOD concentration and nitrogen concentration in the final treated water while ensuring economical operation.

[0008]

[Means for Solving the Problems] The present invention provides a method for anaerobically treating wastewater in an anaerobic treatment chamber, and then supplying the anaerobically treated water to an aerobic treatment chamber to perform aerobic treatment. In a wastewater treatment method in which aerobically treated water is taken out from the treatment chamber and a portion of the aerobically treated water is returned to the anaerobic treatment chamber for nitrogen reduction treatment, etc., the residence time of the wastewater in the anaerobic treatment chamber is This relates to a wastewater treatment method characterized in that the treatment time is 3 to 8 hours.

The present invention also provides an anaerobic treatment chamber for anaerobically treating inflow wastewater, an aerobic treatment chamber installed in parallel with the anaerobic treatment chamber for aerobically treating water after the anaerobic treatment, and an aerobic treatment chamber for aerobically treating water after the anaerobic treatment. In a wastewater treatment device that serves as a partial return path for returning a portion of aerobically treated water from the treatment chamber to the anaerobic treatment chamber, the capacity of the anaerobic treatment chamber, the amount of wastewater flowing into the anaerobic treatment chamber, and the amount of partial return This invention relates to a wastewater treatment apparatus characterized in that the residence time of wastewater in an anaerobic treatment chamber is set to be 3 to 8 hours in consideration of the above.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below based on embodiments shown in the accompanying drawings.

First, using the conceptual configuration diagram shown in FIG.
The configuration of a septic tank A as a wastewater treatment device that can be used in the wastewater treatment method according to the present invention will be explained.

In FIG. 1, 10 is an anaerobic treatment chamber equipped with a waste water inlet 11, and is equipped with an anaerobic filter bed 10a for carrying out anaerobic treatment. The wastewater inlet 11 is connected to a wastewater supply pipe 20, and a flow rate regulating valve 21 is attached to the wastewater supply pipe 20 as required.

On the side of the anaerobic treatment chamber 10, an aerobic treatment chamber 13 equipped with a treated water outlet 12 is arranged. A floor 13a is provided.

The anaerobic treatment chamber 10 and the aerobic treatment chamber 13 are connected by an anaerobic treated water transfer pipe 14 and a partial reflux tube 15, and through the anaerobic treated water transfer pipe 14,
Anaerobically treated water can be transferred to the aerobic treatment chamber 13, and a portion of the aerobically treated water can be returned from the aerobic treatment chamber 13 to the anaerobic treatment chamber 10.

In addition, a partial reflux pump 16 is installed in the middle of the partial reflux pipe 15, and the aerobic treatment chamber 13
An aeration device 17 equipped with an aeration pipe 17a is disposed inside.

Furthermore, the above-mentioned flow rate regulating valve 21 and partial reflux pump 16 are connected to a control device C. These flow rate adjustment valve 21 and partial reflux pump 16 are connected to the operation panel 22.
and water level sensors S1 and S2 installed in the anaerobic treatment chamber 10 and aerobic treatment chamber 13, respectively.
It is possible to adjust the amount of wastewater flowing into the anaerobic processing chamber 10 and the amount of partial recirculation flowing back from the aerobic processing chamber 13 to the anaerobic processing chamber 10, respectively.

[0017] Hereinafter, by using the septic tank A having the above configuration,
How to purify wastewater from home toilets and kitchens.
This will be explained with reference to FIG.

The treated water flowing into the anaerobic treatment chamber 10 from the wastewater inlet 11 and the water and organic matter (components such as carbohydrates, proteins, lipids, urea, etc.) contained in the treated water are filtered through an anaerobic filter. While passing through the bed 10a, the filter bed 1
0a undergoes anaerobic decomposition by anaerobic bacteria attached to the surface of the filter medium.

That is, first, organic substances in the treated water are reduced in molecular weight by acid-producing bacteria and converted into organic acids such as acetic acid (CH3COOH) and propionic acid (CH3CH2COOH).
After that, anaerobic bacteria such as methane bacteria decompose the organic acid to generate methane (CH4) and carbon dioxide (CO2), and release these gases outside of septic tank A. This produces treated water containing ammonia nitrogen (NH4 + -N), which is a decomposition product of water.

[0020] By performing such anaerobic treatment, organic matter can be effectively removed from the treated water, and as a result, the treated water after the anaerobic treatment contains ammonia nitrogen.
(NH4 + -N) and a small amount of untreated organic matter is transferred from the anaerobic treatment chamber 10 to the aerobic treatment chamber 13 through the anaerobic treated water transfer pipe 14.

Next, the purification process in the aerobic treatment chamber 13 will be explained. In the aerobic treatment chamber 13, air is blown into the treated water from the aeration pipe 17a of the aeration device 17, and oxygen in the air is blown into the treated water. Ammonia nitrogen (NH4 + -N) in the treated water is converted into nitrate nitrogen (NO3
--N) and nitrite nitrogen (N02--N).

Furthermore, in this embodiment, all of the treated water that has been subjected to the anaerobic treatment and aerobic treatment is not directly discharged to the outside of the septic tank A, but is instead subjected to aerobic decomposition treatment in the aerobic treatment chamber 13. A part of the treated water is partially returned to the anaerobic treatment chamber 10 through a reflux pipe 15 by driving a reflux pump 16 .

[0023] Therefore, nitrate nitrogen (NO3 − −
When treated water containing N) and nitrite nitrogen (N02- -N) flows into the anaerobic treatment chamber 10, the denitrifying bacteria present in the anaerobic treatment chamber 10 utilize the oxygen of these inorganic compounds, Organic matter flowing into the anaerobic treatment chamber 10 is decomposed to obtain energy for survival. As a result, inorganic compounds are reduced to molecular nitrogen (N2
) and nitrous oxide (N2O), and the organic carbon is decomposed to become carbon dioxide (CO2), which is released outside of the septic tank A.

In this manner, the decomposition treatment of organic matter in the anaerobic treatment chamber 10 can be carried out not only by anaerobic treatment but also by partially refluxed water from the aerobic treatment chamber 13 and denitrifying bacteria acting on it.

Therefore, ammonia nitrogen (NH4 + -N
) (which works in the direction of suppressing the activity of anaerobic bacteria) can be suppressed, and this suppressing effect makes it possible to maintain the activity of anaerobic bacteria in a suitable state at all times. The decomposition treatment of organic matter in the anaerobic treatment chamber 10 can be improved.

[0026] Furthermore, due to the improved ability to decompose organic matter, the anaerobic treatment chamber 10 can be
The untreated organic matter contained in the treated water transferred to can also be significantly reduced, and the generation of sludge in the aerobic treatment chamber 13 caused by the untreated organic matter can also be reduced as much as possible.

On the other hand, nitrate nitrogen (NO3 − -N) and nitrite nitrogen (
The concentration of N02- -N) can also be determined by returning a portion of the treated water to the anaerobic treatment chamber 10 and decomposing these ions into molecular nitrogen (N2) and nitrous oxide (N2O) by denitrifying bacteria. Therefore, it can be reduced as much as possible.

[0028] The treated water after the aerobic decomposition treatment is
The treated water is discharged through the treated water outlet 12 to the downstream side of a treated water discharge pipe (not shown).

In this way, the final treated water purified from the toilets, kitchens, etc. of the home and discharged to the downstream side of the treated water drainage pipe is transferred to the aerobic treatment room a3, as described above.
Since the structure is such that a part of the treated water inside is refluxed, the BO
D concentration and nitrogen concentration can be reduced.

By the way, the amount of wastewater flowing into the anaerobic treatment chamber 10 is Q1, and the amount of water flowing from the aerobic treatment chamber 10 to the anaerobic treatment chamber 13 is
Partial return amount of aerobically treated water to Q4, aerobic treatment room 13
If the final amount of water to be treated is Q3, then the anaerobic treatment room 10
Quantity of anaerobically treated water Q2 transferred from to the aerobic treatment chamber 13
is expressed as Q2=Q1+Q4. Of course, Q1=
It is Q3.

[0031] Conventionally, the above quantities Q1, Q2,
Little research has been done on the correlation between Q4. That is, no consideration was given to the optimal treatment of wastewater necessary to increase the maximum treatment capacity in the minimum treatment time.

As a result of the considerations described below, the present invention has been developed so that the anaerobic treatment chamber 1 has an amount of wastewater Q1 flowing into the anaerobic treatment chamber 10.
Residence time at 0 is 3 to 8 hours, preferably 4 to 5.5 hours.
We have learned that it is possible to perform optimal treatment of wastewater from the viewpoint of treatment capacity and economic efficiency when considering the amount of time.

(Consideration 1) The minimum nitrogen removal rate α in the current septic tank (a septic tank that performs an aerobic treatment room after anaerobic treatment but does not partially perform reflux treatment) is 25%, and this value is set as 25%. When extrapolated to the wastewater treatment equipment, as shown in FIG. 2, the total nitrification rate β of the entire wastewater treatment equipment when the minimum allowable nitrogen removal rate α is 25% is approximately 32.5%.

(Consideration 2) Next, when examining the relationship between the total nitrification rate β of the entire wastewater treatment equipment and the decomposable TOC (total organic carbon) concentration γ at the outlet of the anaerobic treatment chamber 10, it is found that FIG. As shown in Figure 2, in order to make the total nitrification rate β 32.5% or more, the degradable TOC concentration γ needs to be 6.3 or less.

Furthermore, from FIG. 3, the total nitrification rate β increases as the degradable TOC concentration γ decreases, but the
When the C concentration γ becomes approximately 3.2 or less, the total nitrification rate β
are almost the same.

Therefore, the degradable TOC concentration γ is approximately 6.3
Hereinafter, the range is preferably about 3.2 or less,
This is desirable when considering not only processing capacity but also economic efficiency.

(Consideration 3) Next, when examining the relationship between the degradable TOC concentration γ at the outlet of the anaerobic treatment chamber 10 and the residence time T of the wastewater in the anaerobic treatment chamber, as shown in FIG. T.O.
In order to keep the C concentration γ in the range of about 6.3 or less, the residence time T in the anaerobic treatment chamber needs to be 2.85 hours or more. However, as is clear from FIG. 4, it is still possible to effectively reduce the degradable TOC concentration γ even when the residence time T in the anaerobic treatment chamber is 3.8 hours or more; on the other hand, the inflection region a in FIG. After exceeding this point, the degradable TOC concentration γ decreases only at a gentle slope even if time passes.

Therefore, the residence time T in the anaerobic treatment chamber is approximately
If it is set in the range of 3 to about 8 hours, preferably a certain width before and after the inflection point a, that is, 4 to 5.5 hours, it is possible to effectively reduce the degradable TOC concentration γ while being economical. Recognize.

(Consideration 4) In the above considerations 1 to 3, based on the correlation between each quantity Q1, Q1, and Q4, the anaerobic properties necessary to effectively reduce the degradable TOC concentration γ while being economical. The treatment chamber residence time T was determined, and below, with reference to FIG. 1, a specific example will be given and the aerobic treated water partial recirculation amount Q4 required when the anaerobic treatment chamber residence time T is 3 hours. seek.

Generally, the residence time T in the anaerobic treatment chamber is expressed by the following formula.

[0041]

[Math 1]

Now, if the septic tank A is used for a standard household (5 people), the capacity V1 of the anaerobic treatment chamber 10 is 1.5 m3, and the capacity V1 of the anaerobic treatment chamber 10 is 1.5 m3, according to the calculation of the human waste septic tank structure standard.
The amount of wastewater Q1 flowing into the area is 1.25 m3/day.

Substituting these values into the above equation yields the following.

[0044]

[Math 2]

From this, Q4 = 10.75 (m
3/day). That is, 10.75 (m3/d
If a part of the aerobically treated water is refluxed with ay) or a smaller amount, the residence time in the anaerobic treatment chamber can be maintained at 3 hours or more, effectively reducing the degradable TOC concentration γ,
Optimal treatment of wastewater can be carried out.

Next, the partial recirculation amount Q4 of the aerobic treated water is determined when the residence time T in the anaerobic treatment chamber is set to the optimum time width (4 to 5.5 hours).

[0047]

[Math 3]

From this, 5.30≦Q4≦7.75
(m3/day). That is, by setting the aerobically treated water partial recirculation amount Q4 within the above range, the residence time in the anaerobic treatment chamber can be maintained within the optimum time range (4 to 5.5 hours).
The degradable TOC concentration γ can be further effectively reduced, and wastewater can be optimally treated.

Adjustment of the aerobically treated water partial recirculation amount Q4 is performed by the control device C outputting a drive signal based on the detection outputs of the flow rate sensors S1 and S2 attached to the wastewater inlet 11 and the partial recirculation pipe 15, respectively. This can be easily done by sending the part to the reflux pump 16.

[0050] If necessary, flow rate sensors S1, S
This can also be done by the control device C sending a drive signal to the flow rate adjustment valve 21 based on the detection output of No. 2 to adjust the amount of water discharged.

[0051]

[Effects] As explained above, the present invention has the following effects.

That is, in the present invention, after the wastewater is anaerobically treated in the anaerobic treatment chamber, the water after the anaerobic treatment is supplied into the aerobic treatment chamber to perform aerobic treatment, and the water is then purified from the aerobic treatment chamber. In a wastewater treatment method in which aerobic treated water is taken outside and a part of the aerobic treated water is returned to the anaerobic treatment chamber for nitrogen reduction treatment, etc., the residence time of the wastewater in the anaerobic treatment chamber is set to 3 to 8 hours. It is characterized by the following. By doing this, it is possible to effectively reduce the decomposable TOC concentration γ of the anaerobically treated water while being economical, and as a result,
The purification capacity of the septic tank can be maintained at an optimal state at all times. Therefore, the BOD concentration and nitrogen concentration in the final treated water can be effectively reduced.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram illustrating the configuration of a wastewater treatment device according to the present invention.

FIG. 2 is a graph showing the correlation between the total nitrification rate and the nitrogen removal rate of the wastewater treatment device according to the present invention.

FIG. 3 is a graph showing the correlation between the total nitrification rate and the decomposable TOC concentration at the outlet of the anaerobic treatment chamber.

FIG. 4 is a graph showing the correlation between the degradable TOC concentration at the outlet of the anaerobic treatment chamber and the residence time in the anaerobic treatment chamber.

FIG. 5 is an explanatory diagram of a conceptual configuration of a conventional wastewater treatment device.

[Explanation of symbols]

A Septic tank 10 Anaerobic treatment room 13 Aerobic treatment room 15 Partial return pipe for aerobic treated water 16 Partial reflux pump

Claims (2)

[Claims] Claim 1: After anaerobically treating wastewater in an anaerobic treatment chamber, the anaerobically treated water is supplied into an aerobic treatment chamber to perform aerobic treatment, and the aerobically treated water is discharged from the aerobic treatment chamber. In a wastewater treatment method in which a part of the aerobically treated water is taken out to the outside and returned to the anaerobic treatment chamber for nitrogen reduction treatment, etc., the residence time of the wastewater in the anaerobic treatment chamber is set to 3 to 8 hours. Characteristic wastewater treatment method. Claim 2: An anaerobic treatment chamber for anaerobically treating inflow wastewater; an aerobic treatment chamber installed in parallel with the anaerobic treatment chamber for aerobically treating water after anaerobic treatment; In a wastewater treatment equipment that serves as a partial return path for returning part of the aerobic treated water to the anaerobic treatment chamber, the capacity of the anaerobic treatment chamber, the amount of wastewater flowing into the anaerobic treatment chamber, and the amount of partial return to the anaerobic treatment chamber are A wastewater treatment device characterized in that the residence time of wastewater in the treatment chamber is set to be 3 to 8 hours.