JPH0144397B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wastewater treatment method comprising a combination of anaerobic biological treatment and aerobic biological treatment.

In the biological treatment of wastewater, treatment methods using aerobic organisms are currently the mainstream. Broadly speaking, there are two types: the floating organism method and the fixed biofilm method.
Become a type.

Planktonic methods include the standard activated sludge method and the long-time aeration method. Although the standard activated sludge method is suitable for large-scale, high-grade treatment, it has the disadvantage that it requires advanced technology to operate and requires a large amount of expense and labor for maintenance and management. Furthermore, although the long-time aeration method is suitable for medium-scale treatment and generates a small amount of sludge, it has the drawback of long residence time and being susceptible to load fluctuations.

Fixed biofilm methods include trickling filter method, rotating disk method,
There are contact oxidation methods, etc. In both methods, biofilms form a food chain consisting of a combination of various microorganisms, so they are resistant to load fluctuations, easy to maintain, and suitable for small-scale treatment, but they require an increase in the amount of treatment. has the disadvantage of not being compatible with

As a result of various studies regarding the biological treatment of wastewater by combining aerobic biological treatment and anaerobic biological treatment suitable for high-load treatment under compatible conditions, the inventor has found the following knowledge. I ended up getting it. That is, in anaerobic biological treatment, a multi-stage anaerobic filter bed that can increase the stability of biofilm is used,
In addition, for aerobic biological treatment, we have adopted a contact oxidation tank that is resistant to load fluctuations and easy to maintain, and furthermore, by returning excess sludge from the contact oxidation tank to the contact digestion tank, we have developed a system that allows both anaerobic biological treatment and aerobic biological treatment. It has been found that not only can each of the advantages of this method be fully utilized, but also that the amount of sludge generated can be extremely reduced. According to this method, wastewater undergoes a cycle of anaerobic treatment and aerobic treatment while flowing through each tank, and is efficiently treated, resulting in stable and high quality treated water that is resistant to load fluctuations. This will result in significant reductions in maintenance costs and construction costs.

Thus, the present invention has been completed based on the above findings, and consists of treating wastewater with microorganisms by flowing it into a contact digestion tank equipped with multiple stages of anaerobic filter beds, and then flowing the treated water into a contact oxidation tank. and oxidized,
The present invention provides a novel wastewater treatment method characterized in that surplus sludge produced in the contact oxidation tank is returned to the contact digestion tank.

Embodiments of the present invention will be described below with reference to the drawings.

In the figure, A is a contact digestion tank, and B is a contact oxidation tank.
The contact digestion tank A has a structure in which a hopper part 2 is formed in a cylindrical part 1, and an inflow part 3 that communicates with a settling basin (not shown) is opened at the center of the upper end through a top plate 4. An inflow pipe 5 is vertically connected to the center of the tank, and its lower end is opened to the lower part of the hopper part 2. In the contact digestion tank A, a plurality of stages of anaerobic filter beds 6, 6, . . . are arranged vertically with a required gap 7 between them. A sludge drawing pipe 8 is connected to the lower end of the tank A, and a treated water discharge pipe 9 is connected to the upper part of the tank A.

In the contact oxidation tank B, a vertical flow pipe 10 is installed vertically in the center of the tank formed in a cylindrical shape, an aerobic filter bed 11 is provided around the flow pipe 10, and an air supply pipe 12 is installed in the lower end of the flow pipe 10. The end is open. Also,
The discharge pipe 9 is connected to the tank B, and is opened directly above the flow pipe 10. And further tank B
A purified water outflow pipe 13 is connected to the upper part of the tank B, and a sludge return pipe 14 is connected to the lower end of the tank B.
Its end is connected to the inflow section 3 of tank A.

The wastewater from the settling basin enters the lower part of the contact digestion tank A from the inflow section 3 through the inflow pipe 5, flows upward as shown by the arrow, and flows from the lower stage of the anaerobic filter beds 6, 6... Pass through to the upper level one by one. At that time, it comes into contact with the anaerobic biofilm formed on the anaerobic filter bed 6 and is purified. The purified wastewater passes through the discharge pipe 9 at the top of the tank, then enters the aerobic contact oxidation tank B, and is transported to the tank B by the supply air circulation flow from the air supply pipe 12.
The purified water circulates through the aerobic filter bed 11 and is purified by circulating in contact with the aerobic biofilm of the aerobic filter bed 11.
It is leaked from 3. The entire amount of excess sludge produced in the contact oxidation tank B is returned to the contact digestion tank from the lower end of the tank B via the sludge return pipe 14. The returned sludge is digested and decomposed together with the organic substances in the inflowing wastewater to become digested sludge and transferred to the hopper section 2.
The sludge will settle and be discharged from the sludge drawing pipe 8.

In the embodiment shown in the drawings, the wastewater flows into the contact digestion tank A from the upper part of the tank A, but if the wastewater can be uniformly supplied to the bottom stage of the filter bed, Alternatively, the water may be allowed to flow into the lower part of tank A as shown by the chain line in the figure. However, in this case, it is necessary to flow the settled digested sludge without stirring it up.

In the present invention, it is particularly important that the anaerobic filter beds 6 are provided in multiple stages vertically within the contact digestion tank A. The filter media constituting the filter bed 6 may be granular materials made of other plastics such as bamboo shinobu or crushed stone, or
A plate-like body, a cylindrical body, a net-like body, etc. to which biofilms can easily adhere can be used. Then, the filter media are stacked to a required thickness to form several stages of filter beds 6, and each filter bed 6 is
A gap 7 of a required height is formed between them. In anaerobic filter beds, biofilms generally have weak adhesion, and if the flow rate through the bed is too fast or turbulence occurs, the biofilms will peel off and the treatment effect will be significantly reduced. Therefore, it is necessary to use a filter medium with as good adhesion as possible, and it is also necessary to bring wastewater into contact with the filter medium as uniformly as possible, and to correct turbulent flow. By providing the filter beds 6 in multiple stages at intervals, uniform contact and rectification of the wastewater with the filter medium is maintained, and the treatment effect is significantly enhanced. That is, the wastewater whose flow has been disturbed by passing through the filter bed 6 is rectified by passing through the gap 7 between the filter beds before entering the next filter bed 6, and then flows into the next filter bed 6. This results in uniform contact conditions with the filter medium.

In the treatment methods conventionally used for sewage treatment,
Even with the most advanced standard activated sludge method, the BOD removal rate is limited to 90%. For example, if the BOD of influent wastewater is 200mg/by standard activated sludge method, the treated water
BOD will be 20mg/.

However, if the inflow wastewater has a high BOD concentration of 200mg/or more, if the water temperature drops below 10℃, or if the retention time is too long, it will be difficult to manage the activated sludge and the BOD removal rate will drop significantly. do.

In contrast, with the present invention, the BOD removal rate is always
95% or more can be maintained, for example, BOD of flowing sewage is 200
mg/, the BOD of the treated water will be 10 mg/or less. In addition, even if the BOD of inflow wastewater is high concentration of 200 mg/or more, it is possible to increase the By installing oxidation tank B in multiple stages,
BOD removal rate of 97% or more is possible.

To give an example of how to combine design values for retention time, if the BOD of influent wastewater is 300mg/, the retention time in contact digestion tank A is 30 hours, and the retention time in contact oxidation tank B is 10 hours. If this is set, the water purified in contact digestion tank A will have a BOD of 90mg/
The final treated water further purified in the catalytic oxidation layer B has a BOD of 9 mg/BOD, and the BOD removal rate is 97%. Furthermore, if the retention time in contact digestion tank A is set to 48 hours and the retention time in contact oxidation tank B is set to 15 hours, the water purified in contact digestion tank A will have a BOD of 75 mg/, and the water purified in contact digestion tank A will have a BOD of 75 mg/. The final treated water purified at BOD7.5
mg/, the BOD removal rate is 97.5%. by conventional method
In order to achieve a BOD removal rate of 95% or more, so-called tertiary treatment is required after the normal treatment, which not only increases construction costs but also requires time and effort to maintain.
Maintenance costs will also increase. However, with the method of the present invention, the scale of the facility is comparable to or smaller than that of the conventional method.
A BOD removal rate of 95% is achieved, and there is no need for tertiary treatment.

In addition, since contact digestion tank A can achieve a BOD removal rate of 70% or more without power, contact oxidation tank B can achieve a BOD removal rate of over 70%.
The amount of BOD removed is reduced, and the amount of air required is also small.Therefore, the electric capacity of the blower, which accounts for most of the water treatment power, is about half that of conventional methods, resulting in a significant reduction in power consumption.

Even with the contact oxidation method, which is said to generate the least amount of sludge among conventional methods, the amount of surplus sludge is 20% to 30% of the amount of BOD removed, but with the present invention, the amount of surplus sludge is extremely low. Reduces and removes BOD
Approximately 2% of the amount.

In addition, 100% of the excess sludge is returned to the contact digestion tank A and anaerobically digested, so the amount of sludge produced is much smaller than in the conventional method, so direct mechanical dewatering is also possible in addition to the drying bed. It becomes possible.

[Brief explanation of drawings]

The drawing is a side sectional view showing an embodiment of the invention. A... Contact digestion tank, B... Contact oxidation tank, 3...
Inflow section, 5... Inflow pipe, 6... Anaerobic filter bed, 7...
...Gap, 8...Sludge drawing pipe, 9...Discharge pipe, 10
... Distribution pipe, 11 ... Aerobic filter bed, 12 ... Air supply pipe, 13 ... Purified water outflow pipe, 14 ... Sludge return pipe.

Claims (1)

[Claims] 1 Wastewater is purified by flowing into a contact digestion tank equipped with multiple stages of anaerobic filter beds, and the treated water is further flowed into a contact oxidation tank to be oxidized, and the sludge generated in the contact oxidation tank is A method for treating wastewater, which comprises returning the wastewater to the contact digestion tank, digesting and decomposing it together with organic substances in the inflowing wastewater, and discharging the digested sludge out of the tank.