JPS5943240B2 - Intermittent cycle activated sludge treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an intermittent cycle activated sludge treatment method in which sewage is treated while being continuously introduced into a tank without any restriction in the sedimentation and discharge steps.

Conventionally, activated sludge treatment methods include batch processing and continuous processing.

Batch treatment is a method of treating sewage by repeatedly receiving sewage into a tank, aeration for a certain period of time, performing sedimentation treatment, and discharging the supernatant liquid.

According to this treatment method, a sedimentation tank and return equipment are not required, but on the other hand, a storage tank is required to store the wastewater that flows in during the sedimentation and discharge process.

On the other hand, a continuous treatment tank requires a settling tank and return equipment.

The intermittent cycle activated sludge treatment method according to the present invention is an intermediate treatment method between the conventional batch type and continuous type.

In this treatment method, sewage flows into the tank even during the precipitation and discharge steps, so it is necessary to prevent the sewage flowing into the tank from short-circuiting during this time.

Furthermore, conventional continuous processing methods include a plug-flow system and a complete mixing system.

It is known that bulking of sludge is less likely to occur in the plug flow type than in the complete mixing type.

This invention focuses on this point and incorporates this advantage as well.

The present invention aims to provide an intermittent cycle activated sludge treatment method that does not require a sedimentation tank or return equipment like the batch method, does not require a storage tank in the previous stage like the continuous method, and can prevent sludge bulking. purpose.

A sewage treatment device to which the present invention is applied includes an activated sludge treatment aeration tank and a baffle provided in the tank to partition an inflow portion and a remaining portion, and this baffle extends across the tank and extends below the tank. It has an opening or a gap.

Although this invention is not limited to the following examples,
A preferred embodiment of this invention will be described based on the drawings.

FIG. 1 is a front sectional view of an activated sludge sewage treatment tank to which the present invention is applied.

FIG. 2 shows another embodiment of the one shown in FIG. 1, with two similar baffles.

FIG. 3 shows another embodiment of the one shown in FIG. 1, in which the fixed object is returned by a pump to an inflow section partitioned off by a baffle.

FIG. 4 shows a tank with two baffles, one for the bottom flow, one for the top flow, and a solids pump return.

FIG. 5 shows a plan schematic view of a tank with one baffle and sludge pump return.

Figure 6 shows the oxygen uptake rate mg -02/g at 20°C.
- MLSS/hr plotted against time.

FIG. 7 is a plot of the ratio of tracer concentration to initial concentration versus time.

In the above-described form of this invention, the activated sludge treatment tank 1
comprises at least one transverse baffle 2, with an opening 4 left between its lower end 3 and the tank bottom.

The baffle divides the tank into an inlet section 5 with a sewage inlet 6 and a main vent section 7 .

The main aeration section 7 includes jet aerators, coarse bubble diffusers, directional mix aeration, and other common aeration systems (not shown).

In the case of an intermittent system, the inlet 5 is sized by the BOD concentration of the incoming wastewater and the amount of wastewater expected to enter during the off-duty times of the programmed cycle.

Further, this size is determined so that the oxygen uptake rate of the activated sludge is maximized and the adsorption of the activated sludge is maximized.

Activated sludge is moved from the inflow section 5 to the main aeration section 7.

In the main ventilation section 7, the adsorbed and stored pollutants are oxidized and consumed.

The activated sludge whose adsorption power has been restored is then used again at the inlet.

This transfer to the inlet 5 takes place through an opening in the baffle.

Experiments have shown that the free-flowing area of the aperture formed below the baffle should be as large as 300-400 mm high over its entire width.

This area may be a gap formed below the baffle as shown in FIGS. 1-4.

If the load on the main ventilation section increases, this can be dealt with by increasing the residence time in the inflow section.

This can be done, for example, by making the free-flowing area as large as the one with a height of less than 300 mm.

In this way, it is possible to arrange the contact of sludge with pollutants, especially those that are soluble, in a system that closely approximates a typical plug-flow activated sludge treatment tank.

In the present invention, this is a factor that makes it difficult to cause sludge bulking, which tends to occur when the organic matter load, water amount, and water quality change in fully mixed activated sludge treatment.

It is well known that fully mixed activated sludge systems tend to produce solids that have poor settling properties.

An example occurs in a completely mixed system:
This means that sludge with different activities are produced.

This means that the sludge randomly distributed in the aeration tank adsorbs various and uneven amounts of pollutants.

Under steady state conditions, this sludge is exposed and even undergoes self-oxidation.

However, there are almost no steady states in wastewater treatment.

Organisms brought into contact with food adsorb food in an amount corresponding to the activated area they have.

The adsorption capacity of the system will then depend on the activated area of the cells and the size of the organism.

If it can be made to work properly, it is important that the method of feeding the influent sewage to the sludge resembles plug flow.

Sludge depends on inflow water volume and, in intermittent systems, supernatant discharge rate;
Normal continuous systems expand and contract due to changes such as overflow loads.

However, we noticed that the main influences on activated sludge treatment are sludge activity, settleability, SVI, instantaneous F/M change, denitrification and settling time.

However, SVI (S) in an intermittent cycle activated sludge system
Ludge Volume Index) is a parameter used to calculate the required tank capacity for holding sludge.

Conventionally, the design of an aeration tank is based on the F/M ratio (kg-BOD/
kg-MLSS/day).

However, this F/M ratio is likely an imprecise parameter.

This is because this is determined by the following equation in steady state.

Steady state sludge age However, this doesn't actually happen.

If a fully mixed system is designed with an F/M ratio of 0.3, we determine that the F/M ratio varies from 0.02 to 1.2.

This is because there are temporary fluctuations in organic matter load and flow rate load.

In the intermittent cycle activated sludge treatment method without baffles, the settling properties of activated sludge are poor, and the SVI is 350 to 900 m1/
It is not at all rare for it to become g.

This is because in the completely mixed type, the dispersion of the incoming substrate into the activated sludge becomes non-uniform due to temporary changes in substrate loading.

The baffle also serves as a physical barrier to prevent short-circuiting of wastewater flowing into the intermittent cycle activated sludge process during the sedimentation process and supernatant discharge process.

In order to deal with this, we changed the sea fence of the cycle without installing a baffle to prevent sewage from flowing in during the sedimentation and discharge process, but as a result, there was a lack of capacity to sufficiently remove the sludge. Sludge sedimentation becomes poor and SV
I was 350 m1/g or more.

Furthermore, the imbalance between the vent and non-vagators in the vent tank produces sludge that has poor settling properties.

Returning the sludge to the inlet 5 takes place without pumping.

There are basically three types of exposure systems:

1 In a system with baffles, the inflow section is aerated with a jet aerator in the main aeration section.

2. A system with baffles, which uses the same jet aeration as above, but with the inlet side of the pump as the main aeration part so that the activated sludge in the main aeration part can be sent to the inlet part.

3. Uses a biojet or coarse bubble diffuser that sprays air horizontally in a system with baffles, but generates water flow through surface aeration.

The exchange of the contents of the inlet is limited by the area of the baffle opening.

The baffles may be arranged in a variety of ways as shown in the drawings.

FIG. 1 shows a very simple construction with only one baffle allowing flow underneath.

FIG. 2 shows a similar system with a second baffle 10.

This system is used when regulations are strict, for organic matter, and when the shock load of flow rate is severe.

Fig. 3 is equipped with a baffle that allows the flow to flow downward, and the inlet side of the pump is the main air part, and the adsorbed substrate is consumed.
An example is shown in which a jet aeration system is used in which activated sludge is returned to the inlet.

Figure 4 shows a similar system, with mechanical return means 13.
is used in combination with a lower flow baffle 14 and an upper flow baffle 15.

In the example shown in FIGS. 1 and 2 in which the sludge that has consumed the adsorption substrate is not actively returned by the pump, the sludge is returned from the main aeration section 7 to the inflow section 5 by backflow.

These main vent sludges are 15mg-0□/g-MLSS/hr per unit of activated sludge per unit time.
It has an activity that consumes less oxygen.

This is the average value of the activity of sludge returned to the inlet.

The general effects of having baffles in the tank are as follows.

The first buffer serves to prevent inflowing untreated wastewater from short-circuiting to the supernatant liquid drainage mechanism when air agitation is not performed in intermittent cycle activated sludge treatment.

Second, baffles, if used correctly in the design along with other parameters of an activated sludge treatment system, form an initial adsorption zone called the inlet, so that the final activated sludge
R (oxygen utilization rate) is 20mg-0, 7g-ML S
It functions to keep S/hr or less.

In addition, the activated sludge that remains in the inlet during the time when vigorous stirring is not performed is subjected to gentle and random agitation by the mechanical energy of the inflowing sewage.

While random agitation occurs, soluble and fine colloids in the influent sewage are adsorbed onto the sludge in the contact zone or inlet.

To explain this system in simple terms, it resembles a sponge.

That is, in the contact zone the sponge is fully hydrated, in the main ablation zone it is wrung out and water is expelled, and in the contact zone it absorbs water.

The mechanism of substrate adsorption and oxidation by activated sludge is also the same.

The adsorption capacity of sludge can be measured by the oxygen utilization rate of sludge.

In other words, the oxygen utilization rate is 15mg-0□/g-MLSS
A value of /hr indicates high adsorption capacity.

A high value such as 60 rng 02/g MLS s/hr indicates a low adsorption capacity.

This oxygen utilization rate also represents the properties of the polluted substrate.

For example, wastewater containing large amounts of soluble substrates that are highly biodegradable has a high oxygen utilization rate.

In the intermittent cycle activated sludge treatment method of this invention, the state of activation by aerobic decomposition of sludge after the start of the aeration step is shown in FIG.

The same thing happens on a smaller scale during the aeration process.

In other words, the sludge that has been aerated and activated (its adsorption power has been restored) in the main aeration section once again flows into the inflow section and adsorbs the substrate again.

This invention enables effective sludge precipitation and supernatant discharge in a continuous flow intermittent cycle activated sludge treatment method.

The oxygen utilization rate, or biological activity, of activated sludge treatment depends first on the organic matter load.

This activity is then reduced by sufficient oxidation for a sufficient period of time.

Also, this varies depending on temperature, sludge concentration and other parameters.The precipitation of highly active sludge is due to the rapid consumption of dissolved oxygen during the settling process and the subsequent appearance of anaerobic conditions, which causes the sludge to rise to the surface. becomes.

Such conditions lead to deterioration in the quality of effluent water, outflow of activated sludge flocs, and exceeding effluent regulation values.

Sludge flotation in a normal activated sludge secondary sedimentation tank can be avoided by controlling the activity of activated sludge to 20 mg-02/g-MLSS/hr or less.

In the case of highly concentrated organic wastewater with a BOD exceeding 500 mg/l, it is impossible to avoid this without using a baffle.

However, according to the present invention, the degree of activity of activated sludge in the main aeration section can be lowered, so floating of sludge can be prevented.

In this invention, the precipitation step is programmed to last at least 1 hour including the supernatant water discharge step.

Note that since both processes are carried out consecutively, the activated sludge experiences a total non-destructive period.

The activity of activated sludge at the end of the aeration process is 20mg-〇□
/g-MLSS/hr or less enables effective precipitation and supernatant discharge.

The overflow load during discharge shall be up to 251/sec/m per weir length in a tank with a depth of 4.5 m.

Although the quality of the treated water obtained by the intermittent cycle activated sludge treatment method of this invention is comparable to that in the conventional activated sludge method, denitrification effects can also be expected during periodic non-extraction periods.

As described above, the intermittent cycle activated sludge treatment method of the present invention is a treatment method in which sewage flows into a tank during which the aeration process, sedimentation process, and discharge process are repeated during the sedimentation process and the discharge process, and the interior of the tank is in the downward direction. It is divided into a small-capacity inflow section and a large-capacity main air vent section by a baffle having an opening at the bottom, which has the following effects.

■ Since a baffle is provided, wastewater that has flowed in during the sedimentation and discharge processes will not be short-circuited and discharged.

The wastewater is brought into contact with the settled sludge, and pollutants are adsorbed and removed.

■ Since sewage can flow into the tank even during the sedimentation and discharge processes, there is no need to provide a storage tank of a size commensurate with the amount of inflow during the process, unlike in normal batch treatment.

In addition, like the normal batch method, precipitation and return equipment are not required.

■ Adsorption treatment is carried out in the inlet section even under high load, and then sufficient aeration is carried out in the main aeration section, so at the end of the aeration process, the sludge in the main aeration section has a low oxygen utilization rate, and bulking can be prevented and has good sedimentation properties.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view of an activated sludge sewage treatment tank of the present invention. FIG. 2 shows another embodiment of the one shown in FIG. 1, with two similar baffles. FIG. 3 shows another embodiment of the system shown in FIG. 1, in which solids are returned by a pump to an inlet partitioned by baffles. Figure 4 shows a tank with downflow, upflow baffles and solids pump return. FIG. 5 shows a top schematic view of a tank with one baffle and solids pump return. Figure 6 shows the oxygen uptake rate mg-02/g at 20°C.
- MLSS/hr plotted against time. FIG. 7 is a plot of the ratio of tracer concentration to initial concentration versus time. 1...Sewage treatment tank, 2...Baffle, 3...(baffle) lower end, 4...
Opening, 5... Inflow part, 6... Sewage inlet, 7... Main aeration part.

Claims (1)

[Claims] 1. An intermittent cycle activated sludge treatment method in which sewage is treated by flowing it into a tank that repeats an aeration process, a precipitation process, and a discharge process, and the inside of the tank crosses the tank,
and is divided by at least one baffle with a downward opening into a small volume inlet and a large volume main aeration zone to limit the flow of waste water into the tank even during the settling or draining process. The intermittent cycle activated sludge is characterized in that the sewage is introduced into the inflow part without any problem, the sewage in the inflow part is introduced into the savior aeration zone through the opening, and the precipitated supernatant liquid in the savior aeration zone is discharged and discharged. Processing method.