JPH0226690A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To perform the separation of flocs from supernatant water by sedimentation within a short time and to further achieve the miniaturization of equipment machinery and the reduction of treatment cost, in the purifying treatment of sewage or livestock waste water, by adding fine particulate coal ash to raw waste water under stirring before a flocculant is added to and mixed with said waste water. CONSTITUTION:Fine particulate coal ash having particle size distribution wherein ash having a particle size of 5-500mum is 70-90wt.% is preliminarily added to raw waste water or pretreated water to be mixed therewith under stirring. When existing coal ash is added at this time, the adhesion/adsorption action of the suspended substance such as colloid or org./inorg. component in waste water becomes active. However, since fine particulate coal ash having said suspended substance adhered thereto and adsorbed thereby has a slow sedimentation speed, a flocculant (e.g., ferric chloride) is further added to and mixed with the waste water. By this method, flocs are separated from supernatant water by sedimentation within an extremely short time. Since this method is low in the dilution rate of raw waste water and good in the dehydration properties of conc. sludge, post-treatment can be easily performed.

Description

[Detailed description of the invention] <Industrial application field> This invention relates to a wastewater treatment method, and more particularly to sewage.

This invention relates to a treatment method for purifying livestock wastewater such as urine or pig farm wastewater, fishery processing wastewater and other food processing wastewater, various factory wastewaters, and wastewater containing heavy metals.

<Prior art and its problems> Conventionally, various wastewaters such as raw Jim, livestock wastewater such as mill wastewater, various food processing wastewaters, etc. have been processed using aSS, 880D
The purification treatment method for wastewater containing COD includes an anaerobic digestion treatment method, an activated sludge treatment method in which raw sludge is diluted 20 to 40 times after passing through a solid separator that removes coarse residue using a screen, etc. The aerobic quenching method involves aeration of concentrated wastewater over a relatively long period of time to stabilize putrefying organic matter, and in recent years, the lagoon treatment method in which Daiyosha's aeration tank is operated at low load, and the anaerobic quenching method. Batch-type biological treatment methods, which involve repeated aerobic and aerobic treatments, were generally used.

However, such conventional treatment methods require large processing volumes such as digestion tanks and aeration tanks, and their attached equipment.

Processing costs, etc. were enormous.

However, biological treatment methods lead to the inactivation of activated sludge bacteria during the winter in cold regions, and the treatment capacity deteriorates rapidly, so the safety factor of the treatment equipment is set high, and the equipment becomes larger and larger. There were problems such as the need for heat-insulating shed equipment and heat-insulating equipment, and increased running costs.

Also, anaerobic digestion treatment method, activated sludge treatment method.

Aerobic digestion method 9 times method In the lagoon treatment method, the excess sludge generated is increased into high concentration wastewater, and the sludge is processed into a vacuum dehydrator, belt press, and filter press.

This is done using dewatering machines such as centrifugal dehydrators and screw presses, but the sludge is generally difficult to dewater, and the throughput and water content of the dehydrated cake are not good. The current situation is that dehydration processing equipment has become larger as auxiliary equipment has become larger.

<Technical problem to be solved by the invention> Therefore, as a result of many years of research, the applicant has found that fine coal ash produced from coal-fired power plants, etc. significantly increases the flocculation and sedimentation properties in this type of wastewater treatment, and It was discovered that it is extremely effective in purifying coagulated sludge, improving the dewatering properties of coagulated and settled sludge, and reducing the water content of the dehydrated cake, leading to the completion of development. The particle size range and particle size distribution range of the coal ash particles to be treated are added to the optimal range for this kind of wastewater treatment, and the properties of the coal ash are utilized to effectively treat the wastewater in a short period of time. The purpose is to provide a wastewater treatment method that enables the treatment of various types of wastewater.

Furthermore, in Hokkaido, for example, 1,576,000 tons of coal ash is generated annually from thermal power plants, of which 447,000 tons
1,000 tons accounted for approximately 28% of the total in the civil engineering field, including cement and ready-mixed concrete admixtures, embankments, land preparation, and ground stabilizing materials (Showa 6).
The remaining 1,129,000 tons will be disposed of in ash dumps, etc. However, there has recently been a rapid increase in interest in its effective use as a national policy due to the land shortage caused by the large-scale occurrence of coal ash, as well as for environmental purposes. The social contribution will be extremely high.

Means for Achieving the Technical Problem> The technical means taken by the present invention to achieve the above object is to use granular coal with a particle size distribution containing 70 to 90 or more by weight of particles with a particle size of 5 to 500 μm. Ash is added to and mixed with raw wastewater or pretreated water, and a flocculant is added and mixed with the mixed raw wastewater or pretreated water.

According to the above-mentioned technical means of the present invention, five
Fine coal ash prepared to have a particle size distribution with a particle size of ~500 μm and a content of 70 to 90 or more by weight is used, for example, as livestock wastewater drained from a pig farm and deposited and stored in a sewage tank. Raw wastewater or a flash tank pumped up from a wastewater tank (
It is added to pre-treated water that has been pre-deburred in a raw water adjustment tank) and stirred and mixed. Then, the coal ash itself is porous and spherical with pores similar to activated carbon, and the organic matter in the wastewater,
It has the effect of adsorbing inorganic components, and in the case of pre-formed coal ash, which is made by subjecting fresh coal ash to pozzolanic action under certain conditions, fine particles stick together with many branches and become granulated (
By having a fine network structure (clumps),
The adhesion and adsorption of suspended matter such as colloids and organic and inorganic components in wastewater is further strengthened, and their removal is effectively carried out. Since the settling speed of fine coal ash, which has attached and adsorbed suspended matter such as colloids, organic matter, and amorphous components, is slow, a flocculant is added to raw wastewater or pretreated water in a fine coal ash addition mixer and stirred and mixed. By coagulating the fine coal ash with each other to form agglomerated flocs,
Coagulation sedimentation separation is obtained.

That is, due to the fine network structure generated during the granulation of fine coal ash by the pozzolanic action and the fine coal ash itself being porous with pores, suspended matter such as colloids floating in wastewater is reduced. While adsorbing the organic and inorganic components in the wastewater, the flocculant generates coagulated flocs to improve sedimentation and separation properties.As a result, floating matter under the colloid and organic and inorganic components are sedimented and concentrated as flocs. The sludge is separated into precipitated sludge and supernatant water.

<Example> To explain an example of the wastewater treatment method of the present invention, in the present invention, it is necessary to suppress the particle size of the fine coal ash within 5 to 500 μm.

The reason for this is that if the particle size is 5 μm or less, a larger amount of inorganic flocculant such as ferric chloride, which will be described later, will be required to be added when forming flocs using a flocculant, and the removal of suspended matter such as colloids In order to improve the separation, it is not only necessary to add a larger amount of the polymer flocculant described below, which promotes coarsening of the flocs, but also causes a decrease in the sedimentation separability of the flocs. If the diameter is large, it will not participate in the generation of flocs, and the flocs will settle without reliably adsorbing organic and inorganic components in wastewater, resulting in inefficient adsorption of organic and inorganic components. It is from.

The particle size distribution of coal ash is such that coal ash particles having a particle size in the range of 5 to 500 μm are contained in the shaded area of the distribution table exemplified by the particle size accumulation curve in Figure 1 in an amount of 70 to 90% by weight or more, preferably 80% by weight. The chemical composition is 5LCh, Al703 as shown in the composition table below.
accounts for 70 to 80% of the total.

-1j [Tile] This coal ash can be divided into fresh ash and pre-processed coal ash depending on whether or not it has been treated naturally, but the particle shape of fresh coal ash is similar to activated carbon, as seen in the electron micrograph in Figure 2. The spherical newly formed coal ash, etc., is formed by natural moisture and pressure for a period of time (3 months to 1 year or more), as shown in Figure 3. As seen in the electron micrograph, a pozzolanic reaction occurs, and the pozzolanic action causes the particles to adhere to each other and granulate, forming a coarse mesh structure with a fine network structure.

The above-mentioned fresh ash is, for example, ash that has just been removed from a coal storage silo at a thermal power plant.On the other hand, the ready-made ash refers to ash that has been humidified and compacted at an ash processing site (ash disposal site) for about one year or more. This is lumpy ash that is granulated by a pozzolanic reaction.

Therefore, in the present invention, there is a method of directly adding and mixing fresh coal ash blended and contained in the above particle size distribution to raw wastewater or pretreated water (wastewater) to cause an adsorption reaction, and a method of causing an adsorption reaction, and fresh coal ash etc. having the above particle size distribution. Both methods are used: a ready-made method in which the desired coal ash is granulated by causing a pozzolanic reaction in advance at an ash treatment site, and a method in which it is added to and mixed with raw wastewater or pre-treated water to utilize adhesion and adsorption effects. wastewater treatment.

Next, Fig. 4 shows a wastewater treatment method using fine coal ash having a particle size distribution containing 70 to 90% by weight or more, preferably 80% by weight or more of coal ash particles having a particle size of 5 to 500 μm as described above. This will be explained using a processing equipment chart.

First, as an example of implementation, we will explain how to treat pig farming wastewater (raw wastewater) discharged from a pig farm etc. and having the following components (raw water analysis values): Raw water pH 7.5 Raw water B OD 17000 ppr Raw water S S
5900 ppm This pig farming wastewater was passed through the solids separator (1) to remove the residue, and the preliminary aeration tank (
2 in the aeration tank (2).
For 4 hours, 70 liters of air per hour was sent from the blower (3) to 1 liter of raw water to mix and aerate.

This aeration treatment maintains anaerobic wastewater (Wt wastewater) in an aerobic state, promotes oxidative decomposition of organic substances, and thoroughly stirs and mixes the wastewater to homogenize it.

Then, after preliminary aeration treatment, the reaction tank A.

B, C, D (4) (5) (6) The wastewater (pre-treated water) sent in order to (7) is reacted with each chemical added in the following order while stirring and mixing. be.

Fine coal ash with the above particle size distribution, which has been weighed in advance to have a concentration of 5% (or 70%), is put into the dissolution tank (8) and dissolved and mixed with the fresh water stored in the tank (8). . In addition, since coal ash is not water-soluble, it becomes a suspension, and is removed from reaction tank A (4).
When the supply is carried out, the dissolution tank (8) and the supply tank (9
) are constantly stirred and mixed by the stirrers (70) and (11), and at this time both stirrers (70)
The rotation speed of (11) is preferably 200 to 400 rl)l.

The wastewater is sent from the pre-aeration tank (2) by the raw water pump (12) to the metering tank (1'3), where it is metered to a certain amount and then sent to the reaction tank A (4). A coal ash dosing pump (variable capacity pump) (14) supplies and adds suspended fine coal ash, and this coal ash is stirred and mixed into wastewater by a reaction accelerating agitator (15). As a result, suspended matter such as colloids in the wastewater adheres to the fine coal ash, and an adsorption reaction of organic and inorganic components takes place.

The amount of the suspended fine coal ash added was determined by the amount of the suspended fine coal ash in the reaction tank A (4
) wastewater, 6000 pal (6000G /
m), and the capacity of the reaction tank A (4) is the time required for the adhesion of suspended matter such as colloids by fine coal ash and the adsorption reaction of organic and inorganic components to be sufficiently performed, for example, 5 to 70 m). It is ensured that the adhesion and adsorption reactions are carried out for at least 1 minute.

Then, the wastewater (mixed liquid) in which the fine coal ash is stirred and mixed flows down naturally to the next reaction tank B (5), and in this tank B (5), it is passed from the flocculant storage tank (16) to the chemical injection pump (17). An inorganic flocculant such as ferric chloride, polyaluminum chloride, or aluminum sulfate, in this example, ferric chloride is added and mixed by a stirrer (18) to the wastewater. A floc is produced by agglomerating floating substances such as colloids.

Here, the addition table of ferric chloride is added to wastewater (raw wastewater).
8000 ppm (8000 tusks/i) was the best.

The amount of ferric chloride added varies greatly depending on the properties of the raw wastewater, but as is clear from the table shown in Figure 5 (see Hanajima et al.: Cities and Waste Vol. 8.Nn2). Since the COD removal effect is high when the pH of the mixed water is around pH 4, the amount of ferric chloride added is controlled by a pH meter (19) so that the mixed water reaches pH 4, and the amount of ferric chloride added is adjusted. is effective.

The reason why the C()D (or BOD) removal effect is high at around pH 4 is thought to be because humic acids in wastewater co-precipitate as insoluble humic acids on the acidic side.

The wastewater in reaction tank B (5) in which coagulated flocs have been generated naturally flows down to reaction tank C (6), and in this tank C (6), it is supplied from the slaked lime supply tank (23) by a dosing pump (21). The hydrated slaked lime is added and stirred and mixed by a stirrer (22) to adjust the pH.

This slaked lime is measured in advance to make it 5% (or 70%), dissolved and mixed with clean water in the slaked lime dissolving tank (20), and then supplied to the reaction tank (6). When the reaction tank C (6) is supplied, the dissolution tank (20) and the supply tank (23
) are continuously stirred and mixed by the stirrers (24) and (25), and the amount added is determined by the pH meter (25).
6) makes the wastewater pH 5.8-8.6, preferably 6-8.6.
It is controlled so that the pH is adjusted to 8. In this example, the amount of slaked lime added was about 2000 ppm.

Note that sodium hydroxide may optionally be used as a pH adjuster for slaked lime (because the addition of ferric chloride makes the wastewater acidic, for example, pH 4).

The wastewater in the reaction tank C (6), which has been adjusted to pH 2, naturally flows down into the reaction tank D (7), and in this tank D (7), it flows from the polymer flocculant dissolving tank (27) to the chemical injection pump (28). ) is added and stirred f
i (29) for stirring and mixing. When a polymer flocculant is added and mixed, the flocs are formed into coarse flocs, and desired flocculation and sedimentation separation can be obtained.

This polymer flocculant was dissolved and mixed in clean water in a dissolution tank (27) for 4 hours to give a concentration of 0.1%, and then reacted 4i! This is what is supplied to D(7).

In addition, the stirrer (30) of this polymer flocculant dissolving tank (27)
and each reaction mA, B, C, D (4) (5) (6) (7
) stirring el (15) (18) (22)
The appropriate rotational speed of (29) is 200 to 400 rpa+.

The wastewater in the reaction tank D (7), in which the flocs have been turned into coarse flocs and flocculation sedimentation separation has been obtained, naturally flows into the thickener (31), where the colloids, etc. in the wastewater that has been turned into coarse flocs are collected. The coal ash to which suspended matter, organic matter, and inorganic components have adhered and adsorbed settles to the bottom of the thickener (31), thereby separating the suspended matter and organic matter from the supernatant water.

Sedimentation separation (separation treatment) is performed on coal ash and precipitated sludge whose inorganic components are coarsely flocculated.

The sedimentation rate of the flocs in the thickener (31) is 2 to 4 i/H, and the sedimentation rate of biological flocs in the normal activated sludge treatment method is approximately 0.4 m/H (70 m/day).
However, the increase was approximately 5 to 70 times.

Therefore, the above-mentioned treatment of raw wastewater such as pig farming wastewater is carried out in a short time, so the water area load on the thickener (31) and 8 tanks is significantly reduced, and the sedimentation separation area is also small, resulting in a more compact treatment facility. can be achieved.

As shown in Figure 6, it is clear that the sedimentation velocity of the flocs increases with the addition of fine coal ash ω (, Z), and the SV when 600 Opp of fine coal ash is added is 38.
%, 700001) Te 34% when pl is added, 20000p
It is 32% when pm is added, and it can be seen that there is a tendency to concentrate as the amount of fine coal ash added increases. In addition, the sedimentation rate of coagulated flocs increases as the amount of polymer flocculant added increases, but even if it is added above a certain value, it becomes excessive addition and the effect gradually decreases. is 20-301)l) 1st place is desirable.

The concentration analysis values of the supernatant water obtained by the sedimentation separation treatment using the thickener (31) of this example are as follows.

Treated water DH7.7 Treated water BOD 98Gppm (removal rate 91.1%)
Treated water 83 17Dl)l (removal rate 99.1%)
Became.

However, the amounts of chemicals added are as follows: fine coal ash 6000 ppm ferric chloride aooo ppm (inorganic flocculant) slaked lime 200G DI) 1 polymer flocculant 20 Elf) 1 (anionic type).

Further, Fig. 7 shows the dewaterability of sludge under the thickener, so-called concentrated sludge, which is obtained by sedimentation and separation of flocs in the thickener (31).

The dehydration properties shown in Figure 7 were obtained by adding ferric chloride aooo pp+t (inorganic flocculant) slaked lime 2000 ppH and polymer flocculant 20 ppm to the pig farming wastewater having the following components as described above. The amount of fine coal ash added with a particle size distribution containing 80% by weight or more of coal ash particles with a particle size of 5ooμ door is 70%.
When changing the pressure from 00 to 20,000 ppm, the dehydration properties obtained under the same conditions are the same as those obtained with the -belt press.

Therefore, as is clear from Fig. 7, as the amount of fine coal ash added increases, the filtration rate increases from 60 to 450, 9 DSS/h,
The water content of the dehydrated cake also decreased to 83 to 55%, indicating that the dehydration property was significantly improved.

The supernatant water separated and treated in the thickener becomes A-bar water, which is stored downstream in the treated water tank (32), subjected to biological treatment (activated sludge treatment method, etc.), and then released or reused. At the same time, the concentrated sludge under the thickener is collected in the center of the thickener (31) by the rake raking l1l (33) of the thickener (31), and is drawn into the intake tank (35) by the sludge pump (34). The concentrated sludge stored in the intake tank (35) is dehydrated by a desired dehydrator such as a belt press, vacuum dehydrator, filter press, or centrifugal dehydrator, and is dehydrated as a dehydrated cake. It is deposited and discharged to the cake tray Jl (36).

In this embodiment, the dehydrator uses belt shake, su (31
), and the concentrated sludge in the intake tank (35) is sent by a sludge supply pump (38) to a belt press (31) in a fixed amount for dewatering treatment. At this time, depending on the floc formation state of the concentrated sludge, the above-mentioned polymer flocculant is added again in the 70-thickelator tank (39), and the desirable addition amount is 20 to 40 ppml.
Belt press (37) by re-adding ij degree
This improves dehydration properties.

Next, as a second practical example, we will look at the concentration analysis values of supernatant water in the thickener (31) obtained from the treatment method of the present invention of seafood processing wastewater (meal factory wastewater) having the following components discharged from a seafood processing plant. and raw water pH 6.5 raw water 800 27800 ppm raw water COD
14700 ppm raw water S S
17600 pp ugly hexane extract 3191)
E1m After pre-aeration for 24 hours in the same manner as in the example of implementation described above, fine coal ash 70000 ppm ferric chloride
12000 DI) 1 (Inorganic flocculant) Slaked lime 3500 ppm Polymer flocculant 30 ppm 200-40
After stirring and mixing at a rotational speed of 0 rp-, the flocculation reaction is performed, and the treated water is separated by sedimentation using a thickener (31). The supernatant water flowing down and stored in (32) is treated water pl-17.5 Treated water BOD 454 ppl removal rate 98.4%) Treated water COD 70705 ppl removal rate 99.3%) Treated water 83 38 ppl removal rate 99.8 %) Hexane extracted substance: Less than 1 ppm (removal rate: 99.1%) Dehydrated cake filtration rate: 230 gDss/h, (2) Dehydrated cake moisture content: 61%.

<Effects of the Invention> Since the wastewater treatment method of the present invention is the treatment method described in detail above, desirable coagulation sedimentation separation can be obtained, and supernatant water and suspended matter such as colloids, organic and inorganic components can be separated in an extremely short time. It can be separated by sedimentation as flocs. That is, fine coal ash with a particle size distribution of 70 to 90% by weight or more of particles with a particle size of 5 to 500 um is used as a nucleus for adhesion and adsorption during coagulation sedimentation separation in wastewater treatment, and its solid specific gravity is Since the specific gravity of around 2.1 is higher than the specific gravity of suspended matter such as colloids and organic and inorganic components in other wastewater, desirable flocculation-sedimentation separation can be obtained by using a flocculant to generate flocs with good sedimentation properties.

Therefore, high SS and high BOD of livestock wastewater such as bed method or pig farming wastewater, fishery processing wastewater and other food wastewater, various factory wastewater, etc.
Conventional biological treatment methods require dilution of several tens of times for wastewater containing COD and COD, and require a large aeration tank volume and a processor.
On the other hand, the anaerobic digestion method requires several weeks of processing time, resulting in larger equipment and higher running costs. Although the water content of WA water cake was not good, it is easy and short (several minutes to 30 minutes) to use raw wastewater as it is or dilute it as low as 2 to 3 times. Since the sludge can be separated by sedimentation and coagulated into supernatant water and concentrated sludge, it is possible to downsize equipment and reduce processing costs.

Furthermore, the concentrated sludge that is coagulated and separated has good dewatering properties because the coal ash acts as a dewatering aid together with slaked lime, and the water content of the dehydrated cake is significantly lower than in conventional treatment methods, so it is not necessary to dry or incinerate it during post-processing. , it is possible to reduce the burden on landfill disposal, etc., which is beneficial.

In addition, dehydrated cakes such as livestock wastewater, seafood processing wastewater, and other food wastewaters contain a large amount of organic components and are extremely effective as fertilizers and soil conditioners. This is extremely advantageous in reducing the drying cost when commercializing these fertilizers, soil conditioners, etc. as dung posts.

Furthermore, fine coal ash, which has such excellent purification and dehydration promoting effects, is generated in large quantities as waste from thermal power plants, etc., and the wastewater treatment method of the present invention is an inexpensive wastewater treatment method that can effectively utilize it. It is extremely effective in terms of effective use of waste.

Therefore, the intended purpose was achieved.

[Brief explanation of the drawing]

The drawings show an example of the wastewater treatment method of the present invention, Fig. 1 is a distribution table showing the particle size distribution of fine coal ash, Fig. 2 is an electron micrograph of coal ash particles, and Fig. 3 shows the pozzolanic effect of coal ash. Dimensional electron micrograph, Figure 4 is a chart of wastewater treatment equipment,
Figure 5 is Table 1 showing the relationship between the amount of flocculant (inorganic flocculant) added and COD removal, and Figure 6 is a table showing the relationship between the amount of fine coal ash added and the settling speed of coagulated flocs. FIG. 7 is a table showing the relationship between the amount of fine coal ash added and the dewaterability of concentrated sludge (dehydrated cake moisture content). Frozen Qin addition meter x 703 area (eu, JIFJJ'ffZ'fF heaven 8.000P
PM, :Mh/#2000PPM-Anmeko hard shaving 2o
2 34 5 6 7 8 9 70 II
+2 13H *4a'4-24'k1. :Yo! MPHL: Q[I
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t<Jsuj) Dami 2000ρPt→enemy'lJ:r'? 1
-J1e*li 20PPM k21taM'J-Procedure m official book (method) July 17, 1985 1, Display of the case 1988 Patent Application No. 2, Name of the invention Wastewater Treatment Law 3, Person making the amendment Name related to the incident

Claims (1)

[Claims] Fine coal ash with a particle size distribution containing 70 to 90 or more by weight of particles with a particle size of 5 to 500 μm is added and mixed to raw wastewater or pretreated water, and then added to the mixed raw wastewater or pretreated water. A wastewater treatment method characterized by adding and mixing a coagulant.