JP4388147B2 - Wastewater treatment method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an improvement in a method for biochemically treating wastewater, and more particularly to a method for improving the speed of treatment, reducing sludge generated, and improving sedimentation.
[0002]
[Prior art]
Biological treatment using the living reaction of purified microorganisms is currently the mainstream of wastewater treatment. Among them, the activated sludge method is widely used because it can process a large amount of wastewater in a relatively short time, and the control and management of the process has been advanced and the control has become relatively easy.
[0003]
However, since the biological treatment is only for decomposing organic substances by the enzymatic action of microorganisms, there are certain limitations in two aspects. One of the limits is the so-called limit of the amount of wastewater itself or the concentration of organic matter in the wastewater exceeds the processing capacity of the apparatus. The other is the presence of a material that is difficult to decompose by microorganisms, the so-called quality limit.
[0004]
For the former, the problem can be solved by increasing the capacity of the device. However, the site for factory wastewater is limited and it is difficult to increase the size of the processing equipment. Thus, methods for efficiently treating high-concentration organic wastewater, such as contact aeration and high-speed oxidation, have been proposed, but there are problems such as high equipment costs and wastewater treatment problems during improvement work. On the other hand, in the latter case, that is, difficult-to-decompose substances or toxic substances that are difficult to be decomposed by microorganisms, such as difficult-to-decompose polymers such as sugar and starch, and artificial chemical substances (eg petroleum products, inorganic compounds, synthetic polymers). In the case of wastewater containing, in many cases, the wastewater is diluted or treated over time, or the treatment capacity is gradually increased by adapting microorganisms. This also results in a throughput problem.
[0005]
By the way, the basic pattern of wastewater treatment by the activated sludge method is to receive the influent wastewater into the adjustment tank (or first sedimentation area), adjust the water volume and the concentration of the water in time, and send this to the aeration tank where dissolved oxygen ( In the presence of aeration), the substrate (BOD component) and flocs composed of microorganisms of different solid groups are brought into sufficient contact to aerobically oxidize and decompose the BOD component, and then the precipitation tank (or final precipitate) The microbial flocs, that is, activated sludge and purified water are separated in the ground), and the separated upper layer water is taken out from the biological reaction system as treated water, while the concentrated activated sludge is returned to the aeration tank to maintain the necessary microbial concentration, Some are extracted as excess sludge and removed from the system.
[0006]
If the processing capacity of the apparatus and the BOD component concentration in the wastewater are balanced, the above processing is performed smoothly. However, once the balance is lost due to some cause such as BOD concentration or change in its components, increase in drainage, inflow of toxic substances, etc., the decomposition process is not performed sufficiently and the BOD and COD components in the treated water increase. The problem of sludge outflow (carry over) occurs. In order to deal with sludge spills, some inorganic (packs, etc.) and polymer flocculants have been introduced. However, when the flocculant is added, the flocculant is mixed in the returned sludge, which inhibits the growth of microorganisms, and therefore biological treatment becomes increasingly insufficient, resulting in a vicious circle.
[0007]
As a result of diligent research to cope with this problem, the present inventor has developed a technique for introducing a saponin-containing agent extracted from a plant into wastewater (Japanese Patent Publication No. 63-65396). In other words, when several ppm of a liquid extracted from soap tree (containing 4% kiraya saponin) is added to the wastewater, an increase in the number of microorganisms, particularly microorganisms suitable for wastewater treatment, and an increase in dissolved oxygen are observed. MLSS) was reduced and the quality of the treated water was stabilized, and the SV value (sludge sedimentation level) was improved, and in most cases sludge outflow was prevented. This is considered to be because saponin has a function of increasing dissolved oxygen as well as an activator of microorganisms. Especially in the latter case, the amount of aeration before charging is excessive. The preferred amount of liquid extracted from the soap tree is 0.5 to 5 ppm (about 10 ppm is preferable for wastewater with a high oil content).
[0008]
[Problems to be solved by the invention]
However, there is a case where sludge sedimentation is poor and sludge spillage cannot be prevented even if a kirayasaponin-containing agent is added. Chemical wastewater in explosives factories, paint factories, surfactant factories, etc., and wastewater containing sugar and starch. Therefore, the inventor tried to install a magnet in the aeration tank or introduce a substance that is said to be good for water treatment such as chitosan or cristobalite powder as an auxiliary agent. These were partially effective, but were ineffective against chemical wastewater. However, if the Kirayasaponin-containing agent is added 5 to 10 times the usual amount, the sedimentation of the sludge is somewhat improved, but it is not preferable because of cost.
[0009]
[Means for Solving the Problems]
Therefore, as a result of further research on how various plant extracts that also contain saponin have an effect on the sedimentation state of activated sludge, the extract of horsetail has an extremely good sedimentation property. It has been found that the present invention has been completed.
[0010]
Saponin is a kind of glycoside contained in a plant body, and is a general term for a colloidal solution that produces a remarkably abalone like soap, and has been found in many plants. The above-mentioned Kiraya saponin is contained in a soap tree (scientific name: Quilaia saponaria Mol. Rosaceae) that grows naturally in Chilly, Bolivia, Peru, etc. in South America, but some saponins are also found in Sugina. . The inventor paid attention to horsetail, because it is a common plant that can be easily collected in large quantities, and is rich in proteins (enzymes), silicic acid and other minerals.
[0011]
Horsetail is a kind of vegetative stem (the spore stem is the spore stem) of summer green ferns of the family Crestaceae, and is a common plant commonly found in wilderness and roadsides in various regions, and exhibits an excellent fertility. The horsetail is 3-16% (vs. dry matter, weight%) of silicate (silicic anhydride, SiO ₂₎ other, Ekisetonin (a kind of saponins), Ekisechin (a kind of alkaloid), Furanoboido, vitamin C, fat, phytosterins It is widely used as a folk medicine.
[0012]
In this invention, the extract which heat-extracted horsetail with the mixed solvent of alcohol and water was used. This cedar extract (9.8% alcohol, about 62% water in the total amount) is about 0.5% cereal saponin (exetonin) (about 1% as natural saponin), 1.3% crude protein, sugar content Is 4.1% and ash is 4.3%. In addition, the cedar extract boiled cedar contains about 2% ash and about half of the extract of other components. However, SiO ₂ is not included little in horsetail extract and horsetail in the extract. In the case of horsetail, the content of saponin and sugar is lower than that of the soap tree, but the crude protein is contained in the same amount or more. The extract of horsetail showed the same or better digestion promoting effect and sludge sedimentation effect than the soap tree extract. Further, when cedar pulverized powder was used instead of the extract, a further effect was observed. Of course, the combined use of the horsetail extract and the quillaja saponin-containing material also showed an effect superior to that of the quillaja saponin-containing material alone.
[0013]
The wastewater treatment method to which the present invention can be applied includes, in addition to the standard activated sludge method, a contact oxidation method, a vagina activated sludge method, and other modified or improved activated sludge methods. Not only the activated sludge method but also other biological water treatment methods, such as the flooded filter bed method, can be applied because the sludge and treated water are separated in the sedimentation tank. The drainage refers to all treated water including domestic wastewater and industrial wastewater.
[0014]
【Example】
(Example 1)
Next, the present invention will be described based on experimental results. Chemical wastewater (powder production plant wastewater) that caused sludge outflow trouble due to sludge sedimentation was collected, and 1 liter of each was placed in three 2-liter graduated cylinders. This chemical wastewater is mixed with a 2 ppm saponin-containing agent (a liquid agent containing 4% kiraya saponin), but sludge sedimentation was extremely poor.
[0015]
Add 1 to each of the graduated cylinders, and add 2 to the other 2 with 8 ppm saponin-containing agent and 3) 8 ppm sugina extract, respectively. The following batch experiment was conducted. The aeration condition was 180 measured with an ORP meter. This is an over-aerated condition (usually 130-150). And the SV value was calculated | required by observing the sedimentation state of each liquid after progress for 30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, and 180 minutes. As a result, in (1), there was almost no change at this place, and the decrease was only about 10% even after 180 minutes. However, it decreased by about 50% in the case of (2) and about 70% in the case of (3). Similarly, when the same experiment was carried out for those obtained by adding 100 mg / L of horsetail powder and those obtained by adding 1000 mg / L, the SV value decreased by 50% and 75%.
[0016]
(Example 2)
Next, the case where a horsetail extract is used will be described. FIG. 1 is a flow diagram of the experimental apparatus, and two systems were prepared: a tank A using a horsetail extract and a tank B not used. For each system, artificial sewage with a BOD of about 200 mg / l is used, and the inflow rate is adjusted so that the BOD volumetric load becomes 0.6, 0.8, 1.0, and 0.4 kg / m ³ day every 10 days. It was changed and operated by adjusting. The horsetail extract was adjusted to 20 ppm with respect to artificial sewage. In this example, operation was performed at a sludge return rate of 40% and an aeration rate of 3.0 liters / minute (simple aeration at 5-minute intervals).
[0017]
As a result, as shown in FIG. 2 and FIG. 3, the addition of the horsetail extract resulted in a small amount of generated sludge. That is, the increase in the amount of sludge per day in both tanks was 1.14 g in tank B, compared with 1.14 g in tank A. That is, the sludge conversion rate was about 1.5 times less and the sedimentation property was excellent. Horsetail extract contains about half the active ingredients of Horsetail extract. When attention is paid to saponin, the extract of cedar is about ¼ of the extract of soap tree, so the added amount of sugina extract is 2 to 20 ppm (40 ppm). However, the sedimentation may be caused by components other than saponins.
[0018]
(Example 3)
Two reaction tanks with an effective capacity of 4 liters were installed in a thermostatic bath, and 1 liter of artificial sewage and 1 liter of tap water were put in each reaction tank, and 10 g of dried horsetail was immersed in one of them (BOD). (Volume load: 0.5 kg / m ³ day). Aeration was performed at 1 liter per minute. As a result, as shown in FIG. 4, the MLSS in which the horsetail was immersed was less than that in the case where it was not used. In addition, SV and SVI at the time when 30 minutes had passed after aeration stop were lower when using horsetail as shown in FIGS.
[0019]
The reason why the horsetail is soaked is to prevent the amount of sludge from being affected. Actually, a method of adding horsetail powder to the waste water is taken. The addition amount in this case is about 100 mg / L to 2500 mg / L.
[0020]
【The invention's effect】
As described above, the wastewater treatment method of the present invention is to add horsetail, horsetail extract or an extract thereof during the process of biochemically treating wastewater. As a result, it became possible to reduce the sludge disposal cost by reducing the amount of generated sludge and to perform stable treatment by reducing the SV value. In addition, various excellent effects can be achieved such that biological wastewater can be quickly treated even with difficultly treated wastewater such as chemical wastewater.
[Brief description of the drawings]
FIG. 1 is a flow diagram of an experimental apparatus.
FIG. 2 is a graph showing changes over time in the amount of accumulated extracted sludge when using a horsetail extract.
FIG. 3 is a graph showing the cumulative removed BOD amount when a horsetail extract is used.
FIG. 4 is a graph showing changes in MLSS over time when horsetail is used.
FIG. 5 is a graph showing the daily change of SV when horsetail is used.
FIG. 6 is a graph showing daily changes in SVI when horsetail is used.

Claims (3)

When wastewater containing chemical or wastewater containing sugar or starch in an explosives factory, paint factory, or surfactant factory is treated by the activated sludge method or the submerged filter bed method , cedar powder in the wastewater, Or the wastewater treatment method characterized by adding the horsetail extract containing a horsetail saponin and promoting the reduction | decrease and sedimentation of sludge. The wastewater treatment method according to claim 1, wherein 2 to 20 ppm of cedar extract containing 0.5% of cedar saponin is added to the effluent at a concentration of 100 mg / L to 2500 mg / L. The wastewater treatment method according to claim 1, wherein the extract of a soap tree containing Quillaja saponin is added together with a cedar powder or a cedar extract containing cedar saponin .

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