JPS5966396A - Biological denitrification of waste water - Google Patents

Abstract

PURPOSE:To denitrify night soil sludge or the like,by circulating most of a nitrified liquid in the step of nitrification to the first step of denitrification at a front stage to denitrify NOx in said circulated liquid, and introducing the remainder of said nitrified liquid together with returned sludge into the second step of denitrification. CONSTITUTION:Night soil 1 is let flow together with a circulated nitrified liquid 2 into the first denitrification tank 3 under an anaerobic condition, NOx in the nitrified liquid 2 is reductively decomposed into N2 by denitrifying bacteria using BOD components in the night soil 1 as a reducig agent, and then NH3 and residual BOD components in the night soil 1 are let flow into a nitrification tank 4 under an aerobic condition to nitrify NH3 into NOx and to oxidatively decompose residual BOD components. Most of the nitrified liqud is circulated to the first denitrification tank 3, while the remainder is let flow together with returned sludge 5 into the second denitrificatin tank 6 to reductively decompose NOx into N2 gas with mathanol 7 and a reaeration tank 8 to diffusively remove N2 gas in water under a condition opened to the atmosphere and then separated into solid matter and a liquid in a precipitation tank 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a denitrification treatment method for concentrated wastewater such as human waste water.
Hereinafter, in the present invention, human waste such as human waste, septic tank sludge, and a mixture thereof will be simply abbreviated as human waste. )
Regarding.

Human waste contains a high concentration of nitrogen compounds (hereinafter abbreviated as NYI3), but normal human waste treatment equipment can remove the nitrogen compounds.
L-N113 cannot be removed and remains in the discharged water, causing eutrophication phenomena such as red tide in the discharged water area. In order to solve these problems, biological denitrification treatment equipment for human waste has been developed, but denitrification treatment equipment is somewhat more complex than conventional simple (OI) treatment equipment, so existing 801. ) It is also difficult to convert the processing equipment into a denitrification processing equipment. Additionally, a large amount of methanol is required as a reducing agent during denitrification.
It has the disadvantage that operating costs are higher than conventional BOD treatment alone.

The present invention Il [,, the denitrification treatment method is simplified and the existing 13
The purpose of this project is to provide a method that allows 0D treatment equipment to be easily converted into a denitrification treatment equipment and to significantly reduce the amount of methanol used. BOI).

In the biological denitrification method of wastewater containing nitrogen compounds,
A first denitrification process, a nitrification process, a $2 denitrification process, a reaeration process, and a solid-liquid separation process are configured in order, and most of the nitrified liquid from the nitrification process is circulated to the first denitrification process in the preceding stage. NOx in the liquid is treated with a denitrification bed using the BOD component of wastewater, and the remainder of the nitrified liquid from the nitrification process is led to the subsequent second denitrification process along with the sludge returned from the solid-liquid separation process for denitrification. The method is characterized in that it is subjected to bed treatment, then re-aerated in a re-aeration step, and then subjected to solid-liquid separation in a solid-liquid separation step.

Next, an embodiment of the present invention will be described based on FIG.

Human waste 1 is stored in the primary tank under anaerobic conditions together with circulating nitrifying fluid 2.
Flowing into the denitrification tank 3, the N in the circulating nitrification liquid 2 is reduced and decomposed into N2 by denitrifying bacteria using the BOD components in the urine 1 as a reducing agent, and then converted to NH3 in the human waste 1 and residual BOD components. flows into the following aerobic conditions (PJ'74, N
t13 is nitrified to NO2:, and the remaining BOD components are oxidized and decomposed. Most of the nitrification liquid is circulated to the first denitrification tank 3,
The remainder flows into the second denitrification tank 6 together with the return sludge 5, and after NOx is reduced and decomposed into N2 gas by meta, )-lua or other organic matter, it flows into the re-aeration tank 8, where N in the water is decomposed.
After the two gases are diffused and removed by opening to the atmosphere, they are separated into solid and liquid in a settling tank 9, and the supernatant water 10 is released directly or after further advanced treatment into BTC, and a part of the settled sludge is sent to a second denitrification tank. 6 is returned to Z, but the remainder is pulled out of the system as surplus sludge 11 [l) 1. be disposed of.

As shown in 1st +;'l, denitrification and nitrification in the first denitrification tank 3 and nitrification tank 4 of the present invention are temporary (one
For biological treatment of tbro++gh), there is no dilution treatment in which diluted water, which is commonly used in conventional human waste treatment, is injected.The reason for this is that f, -1, L urine is When it is diluted, the amount of water increases and the first denitrification tank 3.
When the nitrification tank 4 is filled with 1-"T, it becomes impossible to secure enough residence time for the nitrifying bacteria or denitrifying bacteria floating in the mixed solution to multiply sufficiently. Since the growth rate μ is 01738 at a water temperature of 15°C, the residence time of the bacteria is the reciprocal of the growth rate μ, i.e. 17', -1
7, □7; 3-ton 5.8 Elμ is required. Since the bacterial cells are suspended in the liquid, this has the same meaning as requiring the residence time of the liquid to be 5 to 8 days or more.

Since the number of days that human waste remains in a tank is expressed by the following equation, in order to maintain a constant retention time, the capacity of the -C tank must be increased in accordance with the amount of dilution water, resulting in an increase in construction costs.

V (yy/) = RT (day)... song/surface (1) Q (e'/day) + nQ (i/day)■: Tank capacity f
*(,/) Q: Amount of allantoic film (n27 days) n: Dilution water ratio RT: Residence time (B') For example, I (T = 5.8 B, no dilution treatment and 2
In the treatment using twice as much dilution water, the tank volumes are calculated as 5.8Q and 17.4Q, respectively, from equation (1), resulting in a large difference in tank volume. Therefore, if dilution water is unavoidably injected, the volume of the tank must be increased.

The circulating amount of nitrifying solution is 2 of the allantoic membrane input amount Q in the case of no dilution.
It is desirable that the dilution water be around 0 times, but the circulating fluid also changes depending on the dilution water. The target of nitrification liquid circulation is NOYC in nitrification liquid.
Denitrification is caused by the BOI component of human waste, but if the circulation amount is constant, as the amount of dilution water increases, as shown in the following equation, the amount of NOx-id circulated in the The amount of NOx flowing into the nitrogen tank increases. This can be expressed as the following formula.

N: ? g 1 NOx, -N circulated to the denitrification tank
(Kz/day) N2: NO□-N flowing into the funeral 2 denitrification tank
(〃 )Z: NH3-N of human waste (K
y/n? ) n': l, circulation multiple for urine input htQ However, methanol is valuable for denitrification in the second denitrification tank =
Since all of the NOx must be used, it is undesirable that operating costs will increase due to an increase in the amount of NOx flowing into the second denitrification tank.
In order to do this, it is desirable to reduce Nagisa) Shakusui's sensitivity to +J as much as possible. The activity of nitrifying bacteria and denitrifying bacteria increases as the temperature rises, but injection of dilution water decreases the BOD of urine from 1 to N.
It is desirable to inject as little dilution water as possible, as this will prevent the rise in liquid temperature due to the heat of reaction generated by the oxidation reaction of H3, which is also undesirable from the standpoint of bacterial activity.
Delicious.

For solid-liquid separation of the effluent from the reaeration tank 8, in addition to the commonly used sedimentation method, mechanical solid-liquid separation methods such as pressurized flotation and centrifugal concentrators can be used to increase the concentration of returned sludge. Second denitrification tank 6
The MLSS error of the mixed liquid can be increased, and the volume of the second denitrification tank 6 can be reduced accordingly.

Next, No. i flowing into the second denitrification tank will be compared between the present invention and the conventional method of returning sludge separated into solid and liquid in the sedimentation tank to the first denitrification tank. The condition is 1-th cyclic multiple n'
= 20,'' - dilution factor n = 0, sludge return rate to the first denitrification tank r = = 1 (r - return sludge concentration (/raw water amount Q). Under these conditions, in the conventional method, the first denitrification The ratio of No-N (N1') flowing into the nitrogen tank is reduced to 0.91Z by the following formula, and from this, NOx N (N flea) fd Z O,91Z = distributed to the second denitrification tank
Calculate it as 0.09Z.

On the other hand, in the present invention where sludge is not returned to the denitrification tank +(S1;0, N2 is n' -=20, n =
0 From equation (3), N2' = 0.05Z is calculated, and compared to the conventional method, N0x-Nj is approximately 4", or
2 Does not flow into the denitrification tank. From this, it can be seen that in the present invention, the number of methanol additions is reduced to about 77 compared to the conventional method.

Next, an example of converting the most existing human waste anaerobic digestion method to the denitrification treatment apparatus of the present invention will be explained based on FIGS. 2 and 3.

Figure 2 shows the flow of the equipment for anaerobic digestion of human waste. 1 digestion tank 1
2. B OI) component via L2 through the second digestion tank 13.

After the SS is decomposed and removed, it is mixed with the returned sludge 5 and dilution water 16 to flow into the aeration tank 18. After the residual BOD in the digestion and desorption liquids 1 and 4 is removed, it is solidified in the settling tank 9. It separates liquid (15 indicates digested sludge).

As shown in FIG. 3, the digestion treatment system shown in FIG. 2 can be easily modified to adopt the method of the present invention. When remodeling, the nitrification tank and the second digester used in construction 3 are opened to the atmosphere, and a diffuser such as an aeration pipe or an aerator is installed inside the tank to ensure that the liquid in the tank is kept under aerobic conditions. On the other hand, since the stage before the aeration tank 18 is used as the second denitrification tank 6, care must be taken to maintain anaerobic conditions.

For this purpose, the front stage of the aeration tank 18 can be sealed to isolate it from the atmosphere, but even if the structure is not airtight, it is possible to use slow agitation with rotating blades or a small amount of air so that the oxygen in the atmosphere does not dissolve sufficiently. Even if mild aeration is performed, it is possible to maintain the liquid mixture under anaerobic conditions while stirring the liquid mixture. It is preferable to provide a partition wall 19 in the aeration tank 18 to separate it into the second denitrification tank 6 and the re-aeration tank 8, but if the flow of the mixed liquid in the aeration tank 18 is a sufficient piston flow, it is not necessary. Even without providing the partition wall 19, it is possible to maintain the front part of the aeration tank under anaerobic conditions and the rear part under aerobic conditions depending on the intensity of aeration.

In addition, 1 new pipe (as you can see by comparing Figures 2 and 3) has a circulation line and a methanol supply line (11). If 1,511 points of urine are retained, there is a total of 130 days worth of urine, and the water temperature is 15 degrees Celsius.
There is a sufficient number of retention days (as mentioned in 7 above, the retention time F in the nitrification tank is sufficient at 15° C. for 5 to 8 days).

According to the present invention, the following ignition effect can be obtained.

■ The method of returning the solid-liquid separated sludge to the conventional Air stage denitrification tank is different from the method of the present invention: The present invention has the ability to significantly reduce the amount denitrified in the former stage, while the proportion denitrified in the latter stage is large. Therefore, the amount of methanol added can be reduced.

Most of the mulberries consumed in biological denitrification are 4!
Since it is methanol, economical denitrification treatment can be performed according to the present invention.

■ By operating the first denitrification tank and nitrification tank, the processing process is simplified (1), and the existing human waste anaerobic digestion tank can be easily converted to a denitrification process. , treated water that does not contain nitrogen can be discharged.

Next, Example CY of the present invention: , I-, - Test results obtained with urine and artificially concentrated wastewater will be described.

1. Test device The device shown in Figure 1. The guest rooms are as follows.

1st denitrification tank...50 Nitrification tank... -50.7 2nd denitrification tank...
...5 Re-aeration tank...2,5t ■Test conditions and results (1) Urine treatment Table 1 Treatment column ('l and treated water quality 1 Circulation liquid -:]OO // ”Kje-N(t
/ 135001 40 1mm return sludge amount 5 //
ji N)-13-N('/ )131001 2'
.

In order to compare with the conventional method, 5 tons of returned sludge was transferred to the first denitrification tank.
Approximately 50 I + 1 liter was added to the treated water after 10 days.
il/, /, NO1 to N remained. Therefore, the addition tA of methanol was increased to 2. When ByAK was increased, it was NO as shown in Table 1.

I was able to obtain a score of -N-='l'r.

(2) Treatment of artificially concentrated wastewater Table 2 Treatment conditions, treated water quality, circulating fluid volume 200 R'1NH3-N(n)
l 5oool, O1 (11,'-/4 seeds.5./11.1'1.11 people) Regarding the treatment of artificially concentrated wastewater, compared to the conventional method, the return sludge was sent to the first denitrification tank in 21 days. When I let it flow in, it was about 4
0 m1iIA No3-N remained in the treated water, but
The amount of methanol added was doubled from 0.57/day to 1.0 y/[ko, as shown in Table 2! 11] quality of treated water could be obtained.

[Brief explanation of drawings]

Fig. 1 is a flow sheet showing an embodiment of the present invention, Fig. 2 is a flow sheet of a conventional anaerobic digestion equipment, and Fig. 3 is a modified version of the equipment shown in Fig. 2 to be able to carry out the method of the present invention. 7
This is a flow sheet of the device. 1 ・[7 Urine, 2... Circulating nitrification liquid, 3... First denitrification tank, 4... Nitrification tank, 5... Return sludge, 6... Second
Denitrification tank, 7...methanol, 8...reaeration tank, 9.
...Sedimentation tank, 10...1-clarification, 11...excess sludge, 12...1st digestion tank, 13...A32 digestion tank, I
4... Digestion and desorption liquid, 15... Digested sludge, I6...
Dilution water, 18... Aeration tank, 19... Partition wall. Patent applicant: Patent attorney representing Ebara Infilco Co., Ltd.
Asthma 5 -

Claims (1)

[Claims] 1. In the biological denitrification method of wastewater containing high concentrations of BOD and nitrogen compounds, such as urine-based wastewater, the first denitrification process, nitrification process, second denitrification process, reaeration process, and solidification process are sequentially performed. A liquid separation process is configured, and most of the nitrified liquid from the nitrification process is circulated to the first two denitrification stages in the previous stage to remove N in the circulating liquid B.
Ox is denitrified using the BOD component of the wastewater, and the remainder of the nitrified liquid from the nitrification process is led to the subsequent second denitrification process along with the sludge returned from the solid-liquid separation process, where it is not denitrified. A biological denitrification method for wastewater, which is then subjected to re-aeration treatment in a re-aeration step, followed by solid-liquid separation in a solid-liquid separation step.