JPS596719B2 - Wastewater purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating and purifying sewage or wastewater containing organic substances and nitrogen compounds to the same extent as sewage.

Generally, biological treatment methods (activated sludge method) are exclusively used to treat sewage, etc., but this treatment reduces BODIO to ~20 ppm and oxygen consumption by potassium dichromate (CODcr) to 50 to 100 ppm. However, it is difficult to remove further organic matter using this method alone, and it also removes nitrogen compounds (ammonia nitrogen, nitrate nitrogen, nitrite nitrogen) and inorganic components such as phosphorus. Removal is hardly expected.

Under conventional water quality standards, there were no particular problems with normal activated sludge treatment, but due to pollution issues, stricter treated water quality has recently been required, and for the purpose of reusing treated water, organic matter and nitrogen compounds are extremely Highly clear treated water is required.

Due to these demands, nitrifying bacteria and denitrifying bacteria reduce the water Q.
Nitrogen compounds may be removed.

However, in this case, the organic matter in the water is removed by the activated sludge method, and then the treated water is subjected to denitrification treatment, so the organic matter removal effect is controlled by the activated sludge method, and the BOD
It was not possible to reduce the content to below 10 ppm, and
Since biological treatment is performed in two stages, large-scale equipment is required, and the treatment takes a long time.

The present inventor investigated a process for efficiently removing these pollutants from wastewater containing organic matter and nitrogen compounds, such as sewage, and as a result, completed the treatment method described below.

That is, the present invention deals with sewage or organic matter equivalent to sewage,
Approximately 10 to 50 iron salts are added to wastewater containing nitrogen compounds as Fe.
After flocculating and separating organic matter in water by adding ppm, the flocculated treated water has a Fe content of about 1 to 100 ppm (BQI).
An iron-microbial floc with an iron content of about 10-30% is produced by aerobically contacting microorganisms in the presence of 10 ppm of iron floc, with a pH of 6.5-8.5 and an organic matter load of about 0.0.
5-0. 2 kgBOD/day-kgMLss to decompose residual organic matter and nitrite and/or nitrate nitrogen compounds, and then maintain the treated water under anaerobic conditions in the presence of iron-microbial flocs. This is a wastewater purification method characterized by gasifying and releasing nitrite and/or nitrogen oxide in water.

The treatment method according to the present invention includes a coagulation treatment step in which wastewater is first flocculated with iron salts, and suspended and floating organic matter, soluble high-molecular organic matter, and phosphorus are precipitated and removed, and the flocculation treatment obtained thereby. It consists of a biological treatment process in which residual organic matter is decomposed and removed by bringing water into contact with microbial flocs in the presence of iron flocs, and at the same time, nitrogen compounds are decomposed and removed as nitrogen gas through nitrous acid and nitrification.

This biological treatment process is characterized by the use of microbial flocs with high iron content, and from the viewpoint of their decomposition properties, the microorganisms include microorganisms that decompose organic matter, nitrifying bacteria that oxidize ammonia nitrogen to nitrate and nitrite nitrogen, and Contains denitrifying bacteria that break down nitric acid and nitrite into nitrogen gas.

Therefore, in the biological treatment process, the flocculated water is brought into contact with microorganisms containing high iron content [Niroc] under aerobic conditions, and at the same time, the organic matter remaining in the flocculated water is decomposed, and nitrogen compounds (mainly ammonia) are decomposed by the action of nitrifying bacteria. The process of aerobic treatment using iron flocs oxidizes nitrite and nitrate nitrogen, and the treated water is kept mixed with the floc under anaerobic conditions and the action of denitrifying bacteria converts nitrate to nitrate. This includes a denitrification process in which nitrogen is released as nitrogen gas.

The present invention will be described in more detail below.

In the present invention, wastewater containing organic matter and nitrogen compounds, such as sewage and industrial wastewater, is first coagulated.

As the flocculant, iron salts such as ferric salts such as ferric chloride and ferric sulfate, and ferrous salts such as ferrous chloride and ferrous sulfate are used.

When using a ferrous salt, it is preferable to use it in a neutral pH range in combination with an oxidizing agent, since the aggregation pH is high.

The flocculation treatment may be carried out by selecting the optimum flocculation conditions in advance, as in the case of ordinary flocculation treatment of suspended water.

The amount of coagulant added to sewage is approximately 10 to 50 ppm (Fe
), it is possible to obtain a BQD concentration suitable for the next treatment.

By adding such a flocculant and stirring, the organic matter in the water is turned into flocs.

By removing the generated flocs through solid-liquid separation such as precipitation, we can produce coagulated treated water (COD) with low organic matter content.
100 ppm or less, BOD of about 10-50 ppm).

Furthermore, even if phosphorus is contained in the wastewater, it is removed in this coagulation treatment step.

An example of coagulation treatment of raw sewage is shown in Table 1 below.

As is clear from this result, in the case of raw sewage, the coagulation effect is very large, and most of the BOD, COD and phosphate ions are almost completely precipitated and removed.

For this reason, if a normal activated sludge method is used as a secondary treatment for flocculation, the organic matter load will be very low, making the treatment unstable.

In addition, lime is often used as a flocculant in sewage flocculation treatment, but when lime is used, the treated water becomes alkaline and requires neutralization, and in the aeration tank of the second stage biological treatment, carbonate Biological treatment is often impossible due to lime precipitation.

In this regard, when iron salt is used, the amount of addition thereof is smaller than that of lime, and the effect of removing strain BOD and COD is high.

In addition, in the flocculation treatment process, organic matter and phosphorus are removed as much as possible, but even if some iron is carried over into the flocculation treatment water, it will not have a negative effect on the second stage biological treatment; It has the great effect of being able to supply iron O to microbial flocs with high iron content, which is the most important feature.

Next, the flocculated treated water thus obtained is transferred to a biological treatment process, but the general raw sewage is treated with ferric salt (30 ppma
sFe), the treated water has a pH of 5 to 6,
When this treated water is treated with the normal activated sludge method, the BOD is 40 to 50 ppm.
Only 10 to 20 ppm of D treated water can be changed.

In the present invention, when treatment is carried out using microbial flocs with high iron content made with iron hydroxide as an adsorption phase for microorganisms in the biological treatment process, BOD can hardly be detected or only about 2 to 3 ppm can be treated. water is available.

In the biological treatment process of the present invention, iron hydroxide flocs are first made to exist in an aeration tank, flocculated treated water is passed through, and aerobic treatment is performed by supplying oxygen such as aeration.

Iron hydroxide flocs may be prepared by adding iron salt and an alkaline agent to the aeration tank in advance to form iron flocs in the tank, or by adding iron flocs created in a separate tank to the aeration tank. It's okay.

Further, since iron flocs are generated in the initial aggregation treatment step, the iron flocs can be used.

When the iron floc is present in an amount of approximately 1 to 10 ppm of Fe based on 100 ppm of BOD, a dense and sedimentary floc can be produced.

In the flocculation process, flocs are separated by sedimentation, but a small amount of iron flocs still remains in the flocculation treated water, and normally there is no need to separately supply iron flocs to the aeration tank.

Of course, if there is little residual floc, it can be replenished at will.

In the aeration tank, microorganisms are adsorbed on the surface of the iron floc to form a microorganism floc with a high iron content.

This iron-microbial floc has an iron content of about 10 to 30
%, it can be held in the aeration tank as a floc with poor dispersibility.

The microorganisms adsorbed on this iron floc are the same as activated sludge in ordinary aeration tanks: microorganisms that decompose organic sludge, nitrifying bacteria that oxidize ammonia nitrogen to nitrite nitrogen and/or nitrate nitrogen, It contains denitrifying bacteria that break down nitrite and nitric acid into nitrogen gas.

When the above-mentioned flocculated water is introduced into such an aeration tank and mixed with iron microbial flocs under aerobic conditions, the organic matter in the water is decomposed by the action of the microorganisms.
At the same time, ammonia nitrogen in water becomes nitrite nitrogen and (
or) oxidized to nitrate nitrogen.

The pH decreases due to the formation of nitric acid and/or nitric acid;
In this aerobic treatment in the aeration tank, the pH of the aerated water is about 6.5 to 8.5, preferably about 6.5 to 8.5.
It is necessary to adjust the pH to 7.5. If the pH is below about 6.5, the activity of nitrifying bacteria will be significantly reduced, and if the pH is above about 7.5, especially about 8.5, the flocs will be very low. Easily disperses (and the ability to decompose organic matter decreases).

The pH is adjusted by adding an alkaline agent such as sodium hydroxide or sodium carbonate, but this may not be necessary depending on the pH of the coagulated water.

In addition, the organic matter load in the aeration tank is approximately 0.0
5~o. By setting the amount of 2 kg BOD/day to kg MLS, it is possible to perform nitrification as well as BOD removal.

If the load is lower than this, the formation of microbial flocs will be poor, and if the load is higher than this, the decomposition of organic matter and the oxidation of ammonia will be reduced.

After the decomposition of organic matter and the oxidation of ammonia are completed, the treated water is introduced into a denitrification tank while being mixed with iron-microbial flocs, where it is maintained in an anaerobic state in the presence of iron-microbial flocs.

Appropriate organic substances such as methanol, acetic acid, and sugars are added to the denitrification tank as a nutrient source for denitrifying bacteria, and if necessary, gentle stirring is performed.

In this way, the denitrifying bacteria contained in the floc become active, and due to their action, nitrate and nitrite nitrogen are released as nitrogen gas.

The amount of nutrients added such as methanol is 2.0 of nitrate nitrogen.
~3.0 times is appropriate.

The treated water that has undergone denitrification treatment enters the re-aeration tank while still containing iron microbial flocs, where it is aerated to separate air bubbles attached to the surface of the flocs, and at the same time is used as a nutrient source in the denitrification tank. Excess organic matter added is also completely decomposed.

This re-aeration tank can also be omitted by adjusting the agitation and the amount of nutrients added in the denitrification tank.

Next, the treated water is led to a sedimentation separation tank, where solid-liquid separation is performed to separate it into clear water and microbial flocs.

The treated water thus obtained is extremely clear compared to conventional methods, and BOD and total nitrogen can be removed to a few ppm or less, and phosphorus can be almost completely removed.

The equipment required for such processing is smaller and the processing time is shorter than in conventional methods.

On the other hand, the separated microbial flocs with high iron content are returned to the aeration tank to maintain the floc concentration in the aeration tank.

Surplus flocs, which are relatively small, will be disposed of using conventional sludge treatment methods.

In the present invention, water with a low organic matter content that has undergone a flocculation process is subjected to biological treatment, but in conventional biological treatment, when there is little organic matter, microbial growth is also low, and the sludge is dispersed and flows out, making it impossible to continue the treatment.

In the present invention, since the biological treatment is carried out in the presence of iron flocs, the microorganisms are adsorbed and multiplied by the flocs, and the slimy substance produced by the microorganisms allows the microorganisms to grow into very dense iron-microbial flocs with good sedimentation properties.

In particular, in the flocculation process, phosphorus in the water reacts with iron salts to produce iron phosphate, and from this flocculation process, a small amount of iron phosphate flows into the aeration tank and is mixed with the above-mentioned phlegm. Mix to form a more easily settled floc.

These iron microbial flocs have poor dispersibility and are retained in the aeration tank, and the flocs can be sufficiently separated in the sedimentation separation tank, so the amount of flocs returned to the aeration tank is small even if the number of flocs does not increase significantly due to low proliferation. It is stable and can always maintain a constant concentration of microorganisms in the aeration tank.

As a result, even if there is only a trace amount of organic matter in water, it is possible to stably decompose the organic matter.

In addition, since the flocs have good sedimentation properties, there is no flow of flocs into the final treated water, which is one reason why clear water can be obtained.

Furthermore, in the present invention, it is possible to stably oxidize ammonia nitrogen at the same time as decomposing organic matter in the aeration tank.

Generally, in activated sludge treatment of sewage, it is difficult to completely oxidize ammonia at the same time as the decomposition of organic matter because the growth rate of nitrifying bacteria is extremely slow (the growth rate of nitrifying bacteria is usually 1% of the rate of bacteria that decompose organic matter). /20001/5 0
It is known that the growth rate of activated sludge is only about 0.0 0), and the apparent growth rate of activated sludge cannot be maintained, making it difficult to maintain nitrifying bacteria, especially in the winter.

However, in the present invention, most of the organic matter is precipitated and removed in the flocculation treatment, and the load of organic matter in the biological treatment is lowered, so the amount of surplus sludge generated is small and the apparent growth rate of organic matter decomposing bacteria is also reduced. Since the concentration of nitrifying bacteria can be maintained at a low level, the concentration of nitrifying bacteria in the aeration tank can be maintained, and complete oxidation of ammonia by nitrifying bacteria can proceed simultaneously with the oxidation of organic matter.

This effect can be said to be due to the combination of the coagulation treatment process and the biological treatment process due to the presence of iron flocs.

In the present invention, iron microbial flocs are also present in the denitrification tank, so the denitrifying bacteria are adsorbed to the flocs and increased in number.
It can be held in the tank as a floc with poor dispersibility and can be involved in denitrification.

Therefore, denitrification, which has conventionally been difficult for low BOD water, can be efficiently performed with the same simple operation as for high BOD water.

In addition, if the liquid contains sulfur compounds, hydrogen sulfide will be produced by keeping it anaerobic in the denitrification tank, which will have a negative impact on nitrifying bacteria, but due to the presence of iron flocs, it will not be possible to precipitate it as iron sulfide. Yes, this problem will not occur.

As described above, the present invention efficiently removes organic matter and nitrogen from wastewater in a relatively short time using a small device and a simple process.
It is industrially useful because it can almost completely decompose and remove polluting components such as phosphorus, prevent water pollution, and enable water reuse.

Example A coagulation sedimentation tank with a capacity of 150 liters, an aeration tank with a capacity of 400 liters, a denitrification tank with a capacity of 400 liters isolated from the atmosphere,
A treatment device was constructed by directly connecting a 50 J capacity re-aeration tank and a 150 J sedimentation separation tank.

Sewage water is passed through this equipment at a water flow rate of 100.g per 7 days, and ferric chloride (30ppm, Fe
) was added, and the coagulated and settled sludge was continuously drained.

In the aeration tank, 800
Add ferric chloride so that the concentration is ppm, neutralize it with a caseinider to create a floc of iron hydroxide, and install a pH control device so that the pH in the tank becomes 7.0 while water is flowing. Caseinider was added and aeration was performed.

In the denitrification tank, a stirrer is installed at 30 to 40 rpm.
The mixture was rotated at a speed of 2.5 m to prevent precipitation of microbial flocs, and methanol was added in an amount 2.5 times the amount of nitrogen.

In addition, aeration was carried out in the re-aeration tank, and clear water and flocs were separated by sedimentation in the sedimentation separation tank.

In this way, after approximately two weeks of continuous operation, almost stable decomposition of organic matter was observed, and after another two weeks, sufficient nitrification and denitrification activities were observed.

During this period, iron hydroxide floc made from iron chloride was replenished once or twice.

After one month, the MLSS in the aeration tank was 2200 ppm, and its iron content was 23%.

After the microorganisms had acclimatized for about one month, the quality of the treated water became stable and clear treated water was obtained.

Table 2 shows the results of water quality analysis of the treated water under normal conditions.

In addition, Table 3 shows the results of treating the same flocculated water with activated sludge without adding iron to the aeration tank in advance.

Although denitrification treatment was possible with this activated sludge, the effect was poor, and there was a large difference in the BOD removal rate between the two, and the treatment effect on microbial flocs with a high iron content was clear.

Furthermore, Table 4 shows the results of directly treating this sewage with normal activated sludge treatment.

The removal rates of BOD, TN, and PO4 were extremely low.

Claims (1)

[Claims] 1. Approximately 10 to 50 ppm of iron salt as Fe is added to sewage or sewage containing the same amount of organic matter and nitrogen compounds to coagulate and separate the organic matter in the water, and then the coagulated treated water is treated as BOD.
Approximately 1 to 10 ppm as Fe to 100 ppm
aerobically contacting microorganisms in the presence of iron flocs of m to produce iron microbial flocs having an iron content of about 10 to 30%;
pH 6.5-8.5, organic load approximately 0.05-0.2k
gBOD/day - kqML'ss decomposes residual organic matter and nitrites and/or nitrates nitrogen compounds, then the treated water is maintained under anaerobic conditions in the presence of iron-microbial flocs and released into the water. A wastewater purification method characterized by gasifying and releasing nitrite and/or nitrogen oxide.