JPS6029559B2 - wastewater treatment equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wastewater treatment device that utilizes a biofilm attached to a base material and that substantially does not produce excess sludge.

Biological wastewater treatment equipment can be broadly divided into activated sludge treatment equipment that uses microbial flocs suspended in sewage, and activated sludge treatment equipment that processes muddy water by bringing it into contact with biological film that has adhered (fixed) to the wastewater.
It can be classified as a biofilm treatment device typified by a sprinkler bed.

Here, when comparing the amount of surplus sludge generated by each device, the former activated sludge treatment device has 40% of the removed BOD.
~80%, which is very high. This is because the biota that participates in the treatment is a relatively simple biota consisting mainly of bacteria such as zooglaia, and therefore the sludge cannot be digested sufficiently. In the latter biofilm treatment device, the amount is slightly lower than in the activated sludge treatment device, which is 30 to 50% of the removed BOD. This is because there are many types of organisms involved, and in addition to small organisms such as bacteria, relatively large organisms coexist. However, in any case, the conventional biological wastewater treatment apparatus has the problem that a large amount of surplus sludge is created and its treatment is difficult. Treatment of surplus sludge usually includes the steps of concentration, dewatering, and incineration, but the incineration cost is particularly large.

Therefore, efforts are being made to reduce excess sludge as much as possible.
Some methods have already been put into practical use. For example, total oxidation methods produce virtually no excess sludge. Currently, this is the only method that does not substantially produce excess sludge as a by-product. However, this method requires extremely long blast treatment. Other means, such as anaerobic digestion means, can only achieve a digestibility of about 50% at most even after long-term treatment of 20 to 40 days; , dehydration, incineration, treatment of digested liquid, etc. - require a number of complex steps that are difficult to operate and manage. In addition, aerobic digestion method has a digestibility of 60% after long treatment of 5 to 20 days.
Furthermore, the digested sludge has problems such as poor thickening and dewatering properties compared to the original sludge, and the desorbed liquid becomes cloudy. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of conventional devices and to provide a wastewater treatment device that does not substantially generate excess sludge. To achieve the above object, the present invention provides a biofilm water treatment means that includes a wastewater inlet and a treated water outlet, and a base material for attaching biological microorganisms, and a biofilm water treatment means that can be obtained by the biofilm water treatment means. a wedge-wire screen for separating and concentrating the sludge contained in the treated water; a digestion tank for aerobically digesting the thickened sludge obtained by the wedge-wire screen; The present invention is characterized by a wastewater treatment device comprising means for returning the digestive solid liquid in the digestive tube to the biofilm water treatment means or the upstream side thereof.

To explain this invention in more detail, in this invention, the biofilm water treatment means includes a rotating type using a rotating disk, a fixed type using a structure in which a porous base material is installed vertically, Use a sprinkler floor, etc.

Most of the sludge discharged from such biofilm water treatment means is relatively large, having peeled off from fixed substrates, and has a high water content and is slippery. separation and concentration can be performed extremely easily and quickly. Another advantage of using biofilm water treatment means is the diversity of organisms that participate in the treatment. In other words, in biofilm water treatment means, since the biofilm is adhered to the base material, the base material surface lacks oxygen and becomes anaerobic, while the membrane surface that comes into contact with the wastewater has a sufficient supply of oxygen. This maintains an aerobic atmosphere. Therefore, unlike suspension system treatment such as the case using activated sludge treatment equipment, aerobic and anaerobic environments can be maintained simultaneously within the reaction tank, and the organisms generated within the pot become extremely diverse. The biota in biofilm water treatment means are the following three types.
classified into two groups. The first group is microorganisms mainly consisting of bacteria such as zooglaea, which adhere to the surface of the substrate and usually form a thickness of 2 to 1 inch.

The second group includes protozoa that adhere to or coat these attached microorganisms, such as ciliates, flagellates, and wolfopods. The third group includes large organisms called tank sludge cleaning organisms, such as nematodes, rotifers, oligochaetes, and arthropods. As a result, the 4-type organisms are preyed on by larger organisms in sequence, with the first group being preyed upon by the second group, and the second group being preyed upon by the third group. This is the so-called food chain. Various living organisms are balanced depending on the environmental conditions within the reaction tank. This phenomenon is a kind of sequential reaction of sludge digestion, and the reason why surplus sludge produced by biofilm water treatment methods is less than that produced by suspension systems is that this food chain occurs. Conceivable. In this invention, we mainly focused on the extremely high sludge digestion power of the second and third groups of biota, and separated these organisms and led them to the digestion tank to cause a digestive reaction, and then further By returning the excreted carcasses of the second and third groups of biota to the biofilm water treatment means to serve as a nutrient source for the first group, a digestion rate exceeding the conventional sludge digestion rate can be achieved. Almost 100% digestibility is achieved. In other words, the food chain cycle is caused not only locally in the device, but also along the entire flow. By the way, these large organisms are extremely susceptible to oxygen deprivation, and if kept in an oxygen deficient state for several hours, they will die and their activity will completely decline.

Therefore, if sludge discharged from biofilm water treatment means is separated by sedimentation, large organisms will die and the activity will be lost. need to be supplied. Therefore, in this invention, in order to separate and concentrate the sludge combined with the treated water obtained by the biofilm water treatment means,
A slanted wedge wire screen in which a large number of wedge wires each having a V-shaped cross section are arranged is used. The separation speed depends on the concentration of sludge supplied from the biofilm water treatment means, but the unit area of the separation element and the amount of water treated per unit time are 10 to 10,000 〆/〆・day, preferably 100 to 5
000〆/de・day. The concentration of separated and concentrated sludge is 5000 9/liter or more, preferably 20000
It is more than 9 no liters. Transfer the thickened sludge to the digestion tank using a belt conveyor or other device that does not apply shearing force to the sludge, or drop the sludge directly through a wedge, wire, or screen. Preferably, this is done by This is because large organisms die immediately when a strong cutting force is applied to them, making it impossible to expect them to digest the sludge in the digestion tank. As the digestion tank, an aerobic digestion tank is usually used, but it is also possible to incorporate other sludge treatment means into the sludge circulation cycle, such as adding an anaerobic digestion tank.

The higher the sludge concentration in the digester, the better, usually 5000
at least 10,000 o/liter, preferably at least 10,000 o/liter. The digestion time in the digester is usually
It is 5 to 60 days, preferably 10 to 30 days. The digested solid liquid may be returned anywhere as long as it is on the inflow side of the biofilm water treatment means.

For example, the raw water inlet of biofilm water treatment means and its vicinity;
The source water is returned to the storage tank, the inlet of the storage tank, between the storage tank and the biofilm water treatment means, etc. The particular differences between the apparatus of the present invention and the conventional apparatus are as follows.

First, the sludge that has been solubilized or finely divided in the digestion tank is returned to the biofilm water treatment means, and most of the sludge is adsorbed or absorbed on the biofilm surface along with organic substances in the raw water, and is absorbed into living organisms. It is taken up, decomposed, and becomes a new biofilm.

This phenomenon can be called the assimilation coarsening phenomenon of solubilized sludge or finely divided sludge. Second, among the returned sludge, some of the undigested sludge that is returned to the biofilm water treatment means is in a form where it can be easily mechanically separated again using a screen due to the above-mentioned assimilation coarsening phenomenon. Here, it is separated, concentrated, and returned to the digester for re-digestion.

In other words, even somewhat degradable sludge can be completely digested (multiple digestion). Thirdly, the sludge in the biofilm water treatment means is different from that in the digestion tank, where complete mixing takes place, and the sludge in the adherent type predominates, resulting in a different biota from that in the digestion tank. be. Therefore, in the biofilm water treatment means, as mentioned above, a unique sludge digestion occurs due to the predation action of various organisms. However, since the digestion is carried out by different organisms from those in the digestion tank, even sludge that is non-degradable in the digestion tank can be sufficiently digested. This is a kind of multi-stage digestion. In conventional equipment, the solubilized substances in the digested sludge are separated from the insolubilized substances by washing, and mainly only the solubilized substances are returned to the raw water side or treated in another treatment process. As mentioned above, the latter waste is sent to the next dehydration and incineration process even though there are enough components left that can be biodegraded. Fourth, it can be expected to have the effect of washing away poisonous substances.

That is, in this invention, the generated sludge is separated and concentrated using a mirror-oblique wedge, wire, and screen, digested in a sludge tube, and then returned to the biofilm water treatment means or its upstream side. While the food is fed back into the digester, substances that interfere with the digestive reaction are washed away or broken down by bacteria. Therefore,
There is almost no reduction in reaction speed due to the accumulation of toxic substances, which occurs in normal aerobic digestion. Therefore, the digestibility of sludge can be maintained at a high level. As stated above, this invention enables the complete biological food chain and maintains the optimal environment for the growth of organisms necessary for this purpose, thereby making it possible to use decomposition energy that living organisms have insufficiently. By making thorough use of things that could only be used in the past, they have achieved a substantial shift to North Rudge.

Hereinafter, this invention will be explained in more detail with reference to Examples.

Example 1 Using the apparatus shown in FIG. 1, o/liter wastewater with a BOD of 250 was treated.

As a biofilm water treatment means, a rotating disk device 1 (capacity: 10
0 liter), and as the oblique wedge wire 1 and screen 2, "Static Sheave Screen" manufactured by Ando Screen Manufacturing Co., Ltd. (separated material area: 0.0
As the digestion tank 4, a complete mixing type aerobic quenching tank (capacity: 80 liters) was used. Further, an air diffuser 6 using air supplied from a compressor 5 was provided at the lower part of the digestion tank 4.
First, raw water is supplied from the wastewater inlet 8 to the rotating disk device 1 for treatment (residence time: 2 hours), and the obtained treated water is supplied to the screen 2 through the treated water outlet 8' and the separated water 9 and concentrated sludge 10 (sludge concentration: 9/liter of 40,000)
It was separated into

Further, the thickened sludge 10 was supplied to the digester 4 by the belt conveyor 3, and aerobic digestion was performed while aeration was performed by the air diffuser 6 (sludge concentration in the digester: 9 of 18,000).
/liter, residence time: 30 days). The digested solid liquid was returned to the waste water inlet 8 of the rotating disk device 1 by the pump 7 via the digested solid liquid return line 11. In this example, the concentration rate of sludge by the screen 2 was very high, and the amount of concentrated sludge supplied and the amount of returned digested solid liquid were 0.8% of the amount of raw water supplied to the rotating disk device 1. As a result of treatment, BOD of treated water
was 10 imitation norittle, and its SS was 10 females/liter or less.

For comparison, when treatment was carried out using only the rotating disk device 1 with a residence time of 2 hours, the BOD of the treated water was 20 female/liter, and its SS was 110 female/liter, both of which were very high. Ta. Example 2 In this example, as shown in FIG. 2, a tower 1 was used instead of the rotating disk device in Example 1 as a biofilm water treatment means.
Porous base material 1 such as plastic net inside 2 and 13
4 was immersed in the base material, and a structure was used in which aeration was performed by an aeration device 6 provided at the bottom of the base material.

Additionally, belt conveyors are not used to transport the thickened sludge.
The sludge is made to fall directly from the screen 2 into the aerobic digestion tank 4 by its own weight. The reason why the biofilm water treatment means is divided into two tanks is to change the biota in each tank and clearly separate the functions of each tank. In other words, the first waste 1
In No. 2, BOD components are mainly decomposed in the wastewater and Oka liquid returned from the digestion tank, and in No. 2 No. 13, the gradual circulation of blast air is used to assimilate fine sludge into coarse particles and to remove large organisms such as oligochaetes. We decided to maintain the growing environment and further demonstrate the sludge digestion function. Note that the digested solid liquid can also be returned to the second tank 13 as shown by the broken line in FIG. Now, when 2/liter wastewater with a BOD of 315 was treated using the above-mentioned apparatus, the treated water from the first waste 12 was BOD315.
The OD142 was o/liter and the SS was 98/liter, and in the second batch 13, this became below BOD21 c/liter and SS8 p/liter. For comparison, when the treatment was carried out using only the biofilm water treatment means, the 80D of the treated water from the first tank 12 was 173 mp/liter, and the SS was 182 p/liter, which were very high. Depending on the treatment, BOD 38 is 9 liters,
As expected, it was quite expensive compared to SS76's Tano Little.

Next, FIG. 3 shows an apparatus of the present invention in a different embodiment from that used in each of the above embodiments.

In FIG. 3, the biofilm water treatment means 12, wedge wire screen 2, and aerobic digestion tank 4 are the same as those used in Example 2. In the apparatus of this embodiment, the solid liquid that has undergone aerobic digestion in the digestion tank 4 is sent to the anaerobic digestion tank 18 by the pump 7 for anaerobic digestion, and then the digested solid liquid is sent to the raw water storage tank 19 via the pump 7. sending,
From here, the water is supplied to the biofilm water treatment means 12. The apparatus of this embodiment is suitable for treating sludge that is difficult to decompose using aerobic digestion alone.

[Brief explanation of the drawing]

1 to 3 are schematic side views showing different embodiments of the device of the invention. 1: Rotating disk device (biofilm water treatment means), 2: Inclined wedge wire screen, 3: Belt conveyor, 4: Aerobic digestion tank, 5: Air supply compressor,
6: Degas equipment, 7: Digestion solid liquid transfer pump, 8: Wastewater inlet, 8': Treated water outlet, 9: Separated water, 10: Thickened sludge, 1
1: Digested solid liquid return line, 12, 13: Tank (biofilm water treatment means), 14: Porous substrate, 18: Anaerobic digestion tank, 1
9: Raw water storage tank. Plan 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A biofilm water treatment means equipped with a wastewater inlet and a treated water outlet, and a base material for attaching biological microorganisms;
A tilted wedge wire screen for separating and concentrating sludge contained in treated water obtained by the biofilm water treatment means and a thickened sludge obtained by the wedge wire screen are preferred. A wastewater treatment device comprising: a digestion tank for pneumatic digestion; and means for returning the digested solid liquid in the digestion tank to the biofilm water treatment means or the upstream side thereof.