JPH0155914B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a purification medium that efficiently purifies small and medium-sized rivers contaminated with domestic wastewater and the like. [Prior Art] In recent years, small and medium-sized rivers have been severely polluted by domestic wastewater, and managers are struggling to purify the rivers. As one solution to this problem, gravel contact oxidation, which requires little artificial energy to purify wastewater and skillfully utilizes biochemical oxidation, has recently attracted attention. Purification of wastewater by this gravel contact oxidation method uses cobblestones with a diameter of about 5 to 80 mm as the contact oxidation medium.
In this method, wastewater is passed through a septic tank filled with these cobblestones, and the aerobic microorganisms that live on the surface of the cobbles eat pollutants, carbohydrates, lipids, proteins, etc. in the wastewater, thereby purifying the wastewater. Also, according to this method,
Aerobic microorganisms can consume dissolved ammonia and phosphorus as nutrients and convert them into harmless nitrite-type nitrogen and other substances about 10 times faster than anaerobic microorganisms. At this time, it is known that suspended solids (SS) in wastewater are also captured by the slime produced by microorganisms and converted into harmless substances. [Problem to be solved by the invention] However, in recent years, as flood control dams have been constructed upstream of rivers, there has been a shortage of cobblestones with particle size and shape suitable for catalytic oxidation media in downstream riverbeds. Since cobblestone mining on riverbeds has been banned, the current situation is that it is difficult to install large-scale purification beds. In order to compensate for this shortage of cobblestone, it has been proposed to use crushed granite or tuff instead of cobblestone, or to use crushed blast furnace slag stone, but these natural crushed stones and crushed slag stones are Because there is moderate unevenness compared to
Although the adhesion of microorganisms is good, due to the good interlocking between the crushed stones, when the sludge adhering to the crushed stones is backwashed with water, the purified sludge is not completely removed and tends to accumulate on the surface, causing clogging in a short period of time. There is a drawback that the purpose of purification cannot be achieved. The object of the present invention is to provide a catalytic oxidation purification medium for wastewater that eliminates these drawbacks. [Means for Solving the Problems] As a result of various studies to achieve the above object, the present inventors have developed a spherical medium made by rolling and granulating specific aggregate and hydraulic cement. Because the surface is rough, the apparent specific gravity is 1.0 to 2.0, and the particle size is 5 to 80.
If a contact oxidation septic tank is constructed using this as a spherical medium of mm size instead of conventional cobblestones, microorganisms will be able to adhere well to the wastewater purification process, and the purification speed will increase, which will only improve the purification efficiency. In addition, even when backwashing a septic tank with clean water, the medium has a small specific gravity, so the medium floats in the wash water, and the interaction between the media makes it easier to remove adhered sludge from the surface of the medium, reducing cleaning time. It was discovered that the septic tank can be used repeatedly for a long period of time. Based on this knowledge, the catalytic oxidation purification medium for wastewater of the present invention is produced by rolling granulating and hardening one or more aggregates selected from fly ash, zeolite powder, and crushed ALC and hydraulic cement. It is a spherical body with a rough surface and a diameter of 5 to 80 mm.
It is characterized by an apparent specific gravity of 1.2 to 2.0. Here, "ALC" is a mixture of calcareous raw materials such as lime and cement and silicic acid raw materials such as silica stone, silica sand, slag, and fly ash, mixed with an appropriate amount of water and a foaming agent. , is a porous lightweight cellular concrete molded product obtained by curing the porous material by autoclave curing, and one of its products, a construction panel, is compliant with JIS A5416 "Lightweight cellular concrete panel (ALC panel)". ' has been enacted. The ALC crushed material used in the present invention is obtained by crushing this ALC molded body. The purification medium of the present invention is made by selecting porous inorganic materials such as fly ash, zeolite powder, and crushed ALC as aggregates, and mixing them with hydraulic cement as a binder, which is then granulated by rolling to form spherical bodies. Because the granulation surface is always sprinkled with a mixture of aggregate and hydraulic cement, the surface of the spherical bodies forms a moderately rough surface and is porous. The surface is covered with aggregate. The porous surface of the aggregate on the surface and the moderately rough surface combine to create a favorable environment for aerobic microorganisms to inhabit, promoting the purification effect. In addition, the rough surface created by rolling granulation allows sludge to be removed while leaving an appropriate amount of microorganisms during backwashing, making backwashing easy and
The purifying effect can be quickly restored upon reuse. The present invention will be explained below based on experiments. Fly ash produced from a thermal power plant (Brain specific surface area 2300cm ² /g, apparent specific gravity 2.13) 80Kg
20 kg of Portland cement was added to the mixture, and this mixture was put into a pan pelletizer and granulated while adding water to produce 118 kg of spherical media with a diameter of 5 to 40 mm. The apparent specific gravity of this medium was 1.85. This medium was used in an experimental septic tank (width:
(50cm x 50cm, height 100cm) was filled to an empty space of approximately 25%. In the figure, 1 is a septic tank, and 2 is a medium layer in which a catalytic oxidation medium is filled on the slit 3 in the septic tank 1 so that the vacancy is 25%. Further, reference numeral 4 denotes a pipe provided at the upper part of the septic tank 1. When sewage is to be purified, the sewage is introduced through this pipe, and the purified water is discharged through a pipe 6, which will be described later. 5 is an air blowing pipe provided at the bottom of the septic tank 1. Next, 6 is a pipe installed at the bottom of the septic tank 1. When cleaning the sludge adhering to the catalytic oxidation medium 2 with fresh water, clean water is sent from this pipe, and the water used for cleaning is the same as above. Discharge from pipe 4. Next, enter this experimental septic tank 1 from the sewage inlet 4.
Flow rate of 20℃ wastewater containing 30mg BOD/45mg/SS is 0.85~8.5/min (converted to residence time: 4.9~
0.5 hours), and compressed air was blown in from the air inlet 5 at a rate of 20/min.
Purified water was discharged from outlet 6. In this experiment, the wastewater was previously passed through a new oxidation purification medium for 3 hours to allow microorganisms in the wastewater to settle on the medium, and then the wastewater was injected. The results obtained from this experiment are shown in FIGS. 2 and 3. Figures 2 and 3 also show, as comparative examples, crushed granite stones with a diameter of 5 to 40 mm and an apparent specific gravity of 2.53, and cobblestones with a diameter of 5 to 40 mm and an apparent specific gravity of 2.40 in the same experimental septic tank as in Figure 1. was filled to the same vacancy rate as above, and sewage of the same composition was fed in the same manner as above, and compressed air was blown in. The results are also shown. Furthermore, after carrying out the above three types of sewage purification tests for 3 consecutive days, the feeding of sewage was stopped and clean water was fed at a rate of 20/min from the purified water inlet 6, and at the same time, from the air blowing port 5. When compressed air was aerated at a rate of 30/min for 10 minutes and the cleaning water was discharged from outlet 4 for backwashing, the media of the present invention, unlike crushed stone media and cobblestone media, was suspended by the cleaning water and caused mutual frictional movement. The results shown in Table 1 were obtained.

[Table]
From the above experiments, we found that the BOD removal rate when using the medium of the present invention is 95% when the residence time is about 2 hours as shown in Figure 2, and this removal rate is higher than that of cobblestones and crushed stones used as comparative examples. An improvement of about 1.5 times was observed. Furthermore, as shown in Figure 3, the removal rate of SS reached almost 100% when the residence time of wastewater was about 2 hours, and this removal rate confirmed that the removal performance was significantly higher than that of the comparative example. Furthermore, from Table 1, it was found that the removal rate of sludge adhering to the medium according to the present invention was 1.5 to 2.3 times higher than that of other comparative examples. Hydraulic cements used in the present invention include Portland cement, blast furnace cement, fly ash cement, silica cement, jet cement, and alumina cement, and all hydraulic cements can be used. The medium of the present invention is obtained by rolling granulation and hardening of hydraulic cement and one or more types of aggregate selected from a specific aggregate, ie, Aria Ash, zeolite powder, and crushed ALC. A spherical body with a rough surface and a diameter of 5 to 80 mm,
All materials with an apparent specific gravity of 1.2 to 2.0 are used. If the diameter of the catalytic oxidation purification medium of the present invention is smaller than 5 mm, it is undesirable because clogging with sludge tends to occur during wastewater purification, and if it is larger than 80 mm, proper granulation is difficult during rolling granulation. be. The mixing ratio of these aggregates and hydraulic cement is preferably 10 parts of aggregate to 1 part of hydraulic cement by volume or less. Note that, in the present invention, a spherical body refers to a spherical shape or something close to a spherical shape. In order to purify wastewater using the medium of the present invention, a cylinder without slits on the sides as shown in Fig. 1 can be used; By using a box with slits of approximately 100 to 100 mm, it is possible to purify wastewater even more effectively.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a septic tank filled with the medium of the present invention, and FIGS. 2 and 3 show experimental results of the medium of the present invention.
The figure shows the relationship between sewage retention time and BOD removal rate.
The figure is a diagram showing the relationship between wastewater residence time and SS removal rate in wastewater. In the figure, 1... septic tank, 2... contact oxidation medium tank, 3... slit, 4... sewage inlet for sewage purification or wash water outlet for media cleaning,

Claims (1)

[Claims] 1 Fly ash, zeolite powder and granules
A spherical body with a rough surface and a diameter of 5 to 80 mm, made by rolling granulating and hardening one or more aggregates selected from crushed ALC and hydraulic cement,
A catalytic oxidation purification medium for wastewater with an apparent specific gravity of 1.2 to 2.0.