JPH03296498A - Method for simultaneously removing BOD, nitrogen compounds, and phosphorus compounds from wastewater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) This invention is a method for removing eutrophic substances such as pollutants (BOD), ammonia compounds, and phosphorus compounds from wastewater, which are indicated by biochemical oxygen demand, in sea areas, rivers, and lakes. This article relates to a method for removing substances that cause carbonation by continuous activated sludge treatment.

(Prior art) Conventionally, Bardenpho 7t-(Bardenpho
) method (J, L, Barnard, Wate
r W astes Engg, 3'a (1974)
), or A1 described in JP-A No. 54-24774
There are 0 method and A210 method.

Furthermore, A710 described in Japanese Patent Publication No. 61-17558
A known modification of this method includes incorporating a rotating disk to immobilize organisms in the curing tank.

In these methods, BOD is mainly processed by aerobic oxidative decomposition, nitrogen compounds are released by nitrification-denitrification method, phosphorus compounds are released from activated sludge in an anaerobic environment, and activated sludge is released with excess phosphorus in an aerobic environment. It is removed by ingestion.

In addition, Jikai @ 63-126599 publication describes reactors in which activated sludge exists: 1 anaerobic tank, 1 aerobic tank, 2 anaerobic tanks.
and aerobic 2'I/g for 4 minutes to control various aerobic degrees and anaerobic degrees using the oxidation-reduction potential (ORP) as an index. A method for removing BOD, ammonia compounds, and phosphorus compounds from wastewater using fine powder and the like is described. ORP is particularly excellent as a measure of complete anaerobic degree when compared to dissolved oxygen concentration and nitrogen oxide concentration, which were used as indicators until then, and can appropriately control the removal of phosphorus compounds.

Generally, phosphorus compounds release phosphorus from activated sludge in an anaerobic state, and then in an aerobic state (when the activated sludge takes in too much phosphorus, the activated sludge that has taken in too much phosphorus is extracted as surplus sludge). , it is possible to reduce the phosphorus concentration of treated water.In this way, when phosphorus is removed biologically by burying various aerobic degrees and anaerobic degrees using ORP as an index, the phosphorus concentration of treated water or The phosphorus removal rate is strongly influenced by the amount of phosphorus released from activated sludge in anaerobic conditions (equivalent to one anaerobic tank).In other words, the greater the amount of phosphorus released from activated sludge in anaerobic conditions, the more The amount of phosphorus taken up by the activated sludge in aerobic conditions (corresponding to aerobic IWI) increases, resulting in a higher phosphorus removal rate and a reduction in the phosphorus concentration of the treated water.

(Problem to be solved by the invention) However, in this case, the anaerobic degree of one anaerobic tank, that is, the release of phosphorus from activated sludge in one anaerobic tank, is significantly affected by the concentration of sewage pollutants, the amount of inflow, etc. . For example, when a large amount of rainwater flows in during rainfall, the removal efficiency of phosphorus compounds in water treatment deteriorates, as reported in ``Water Works Association Journal J 198.''
It is pointed out in June 1999, Vol. 26, No. 306, pp. 43-53. This is the same in the case of the 4-part type, as the amount of wastewater flowing in increases and the concentration of pollutants becomes low (as a result, the degree of anaerobic treatment in the anaerobic tank becomes weaker, and the ORP is 1150m2).
When the temperature rises above V, release of phosphorus compounds from the activated sludge becomes difficult to occur, and as a result, excessive intake of phosphorus compounds in one aerobic tank does not occur sufficiently, resulting in a high concentration of phosphorus compounds in the final treated water. It was found that there was a problem that the removal rate of the compound decreased.

In addition, the phosphorus release property of activated sludge in anaerobic 1-slide is O
In addition to RP, nitrate ions (NO
ff-), nitrous acid *7 (N O2-+ 17
)to be influenced. In other words, NO, -1NO in one anaerobic tank
.

The presence of phosphorus suppresses the release of phosphorus, and as a result, the phosphorus concentration of the treated water increases as shown in FIG.

N0l-1NO2- in the returned sludge is caused by improper ORP in the two anaerobic tanks, insufficient hydrogen donor and denitrification reaction time when ammonia compounds are removed by nitrification-denitrification. However, in the case of sewage treatment, because the quality and amount of inflowing sewage fluctuates frequently, N0F is required in two anaerobic tanks to the extent that it does not adversely affect the release of phosphorus in one anaerobic tank.
It is difficult to constantly remove f-1N Ox- by denitrification reaction.

There are problems when simultaneously removing ammonia compounds and phosphorus compounds from sewage using biochemical methods. However, there is no suitable removal method for ammonia compounds that can replace biochemical methods, ie, nitrification and denitrification methods.

In addition, the bioreactors are 1 anaerobic tank, 1 aerobic tank, and 2 anaerobic tanks.
It has become clear that the following problems exist when dividing the tank into four 2m aerobic tanks and managing various aerobic degrees and anaerobic degrees using ORP as an index. In other words, the amount of sewage flowing in and the quality of water fluctuate depending on the weather, season, etc., and also depending on the time of the day. If such sewage is treated in a reactor divided into four parts, if the weather is sunny for a long time, or if the concentration of pollutants is low from 6 a.m. to 10 a.m. during the day, and a large amount of sewage flows in, the anaerobic tank will be O
RP drops steadily, in some cases -450 to -50
The voltage drops to about 0 mV, enough phosphorus is released from the activated sludge, and in the next aerobic tank, activated sludge takes in too much phosphorus, and as a result, the phosphorus concentration in the treated water drops to 1-g/g.
Reach less than l. However, the ORP of one anaerobic tank drops too much and highly anaerobic activated sludge flows into the next aerobic tank, so the ORP fJt of this aerobic tank is not reached and the nitrification reaction is not sufficient. In some cases, this may not occur, and the ability to remove ammonia compounds may decrease. And vice versa,
When sewage with low pollutant concentration flows into the anaerobic tank due to continuous rainfall, the ORP of 1 yen of anaerobic water does not decrease sufficiently, and as a result, the release of phosphorus from activated sludge does not occur sufficiently, and the removability of phosphorus compounds decreases. may decrease.

As for BOD, even if there are fluctuations in the amount of sewage inflow, water quality, etc., good treatment is performed without being affected.

(Means for Solving the Problems) The present invention is a method for simultaneously removing BOD, nitrogen compounds, and phosphorus compounds from wastewater, which is characterized by combining a biological method and a chemical method. In the biological method, a reactor containing activated sludge is separated from the inlet side where wastewater flows into one anaerobic tank,
Divided into 4 tanks: 1 aerobic tank, 2 anaerobic tanks, and 2 aerobic tanks;
Wastewater to be treated and sludge returned from the sludge settling tank are continuously injected into the tank with slight mechanical agitation, and phosphorus is released from the activated sludge, and the ORP of the next aerobic tank is controlled. The activated sludge mixture in the anaerobic tank is continuously injected into the aerobic tank, and the ORP in the aerobic tank is controlled to a level that does not adversely affect the control. If excessive phosphorus intake by activated sludge occurs, the next anaerobic 24W ORP is managed and controlled within a range that does not adversely affect the management and control, and then the activated sludge mixture from the aerobic 1 tank is transferred to the anaerobic 2 tank. Continuously supplying the wastewater, using a part of the wastewater as a hydrogen donor, and dispensing it with mechanical stirring or aeration in addition to mechanical stirring to raise the ORP to -50 to -150 mV (
The mixture was controlled and maintained for a predetermined time (gold-silver/silver chloride electrode standard) to reduce nitrogen oxides to nitrogen gas, and the mixed solution treated with anaerobic 2MM was supplied to two aerobic tanks for aeration. , the hydrogen donor BOD is oxidized and decomposed, nitrogen gas is removed in the form of bubbles, and the activated sludge mixture treated in the two aerobic tanks is supplied to the sludge settling tank to settle the sludge, and the settled sludge and upper Biological treatment that separates the treated water into clear liquid should be used, in which case OF' (P of -200 to -300 m
V (gold-silver/silver chloride electrode standard), ORP of 1 aerobic tank +
100-+1251■ (according to the standard of silver/silver chloride electrodes), chemical methods are used to aerobically remove phosphorus compounds from wastewater and water-soluble agents that form water-insoluble compounds. It is possible to add the phosphorus compound between the two tanks and the sludge settling tank to make the phosphorus compounds in the wastewater insoluble and remove them as excess sludge in the sludge settling tank.

(Operation) In the present invention, BOD and nitrogen compounds in sewage are removed by a biochemical method, and phosphorus compounds are removed by a combination of a biochemical method and a chemical method.

First, nitrogen compounds, mainly reducing nitrogen compounds such as Kerburg nitrogen compounds and ammonia compounds, are oxidized to nitrate and/or nitrite nitrogen compounds by a nitrification reaction in an aerobic tank, and then oxidized into nitrate and/or nitrite nitrogen compounds in an anaerobic tank. It is removed by denitrification reaction in a tank. Therefore, it is necessary to preferentially set the aerobic tank 1 to conditions where the nitrification reaction of reducing nitrogen compounds in sewage occurs sufficiently, and the ORP must be +100 mV or more, and the residence time in this tank must be at least 2 hours. It is. but,
If the ORP is too high, a fairly strong aeration will be required to maintain the 40RP condition, which will cause the activated sludge to fragment and flow into the treated water without settling sufficiently in the sludge settling tank, resulting in poor treated water quality. Also, if the ORP of aerobic 1 tank is too high, the next anaerobic 2 tank will deteriorate. ! The ORP of I is the appropriate ORP for the denitrification reaction to occur, i.e. -50~-
It becomes difficult to maintain within the range of 150 Ugly ■. For this reason, the ORP range for one aerobic tank is appropriate.

If the ORP of one aerobic tank is maintained in the range of +100 to +125 mV, in addition to the nitrification reaction, oxidative decomposition of BOD and phosphorus uptake by activated sludge will occur sufficiently, so there will be no particular problem in removing BOD and phosphorus. , organic phosphorus compounds, which account for 20 to 60% of the phosphorus compounds in sewage, are
If the ORP of the tank is maintained within this range, most of the lean will be oxidized and decomposed into non-chronic phosphate compounds, which is convenient for removing lean by chemical methods.

In order to maintain the ORP of the aerobic 1 tank at +100 to +125 so, the anaerobic degree of the activated sludge continuously supplied from the anaerobic IWI to the aerobic 1 tank is affected. In other words, if the anaerobic degree of activated sludge supplied to aerobic tank 1 is too strong, specifically, if activated sludge with an ORP of -300 mV or less is supplied to aerobic tank 1, the ORP of aerobic tank 1 will be within the appropriate range. becomes difficult to maintain.

On the other hand, if the ORP of the anaerobic tank 1 is set to high (then the release of phosphorus from the activated sludge will not occur sufficiently, the ORP at which phosphorus will be released will be increased).
That is, it is necessary to maintain it below -150@V. From these facts, the ORP of one anaerobic tank is -200 to 300+
A range of sV is suitable.

1 anaerobic tank, 1 aerobic tank and 21 anaerobic tanks! F like this O
When RPy>17@ is maintained, the activated sludge mixture at the outlet of the two aerobic tanks is collected, filtered with filter paper, and the water quality of the filtrate is analyzed.The BOD is 10 mg/l or less and the total nitrogen compound is 5s+g. /I (as nitrogen), these are sufficiently removed. However, the removal rate of phosphorus compounds is approximately constant at about 80 to 90%. therefore,
This removal rate may not be sufficient if the phosphorus emission regulation value of the final treated water is less than IB/I or less than 0.5 B/l. For example, if sewage with an abnormally high phosphorus concentration flows in due to continuous sunny weather and is treated using a biochemical method under the above conditions, the phosphorus concentration in the treated water will drop to 1 g/l, or 0.5 mg/l. It may be exceeded. Alternatively, NO, -1NO, - generated in one aerobic tank
If the phosphorus is not sufficiently denitrified in the anaerobic 24w and remains in the returned sludge, suppressing the release of phosphorus from the activated sludge in the anaerobic 1 tank, the phosphorus concentration of the treated water will become low. It may not be lower than the value.

Thus, placing emphasis on the biochemical removal of nitrogen compounds in sewage may result in the inflow of sewage with abnormally high pollutant concentrations,
N0j-1NO remaining in the denitrification reaction.

removability may be unsatisfactory.

Therefore, in the present invention, a biochemical phosphorus removal method and a chemical phosphorus removal method are used in combination to improve the removability of phosphorus compounds. In other words, inorganic phosphorus compounds in wastewater, such as orthophosphate, react with metals such as iron and aluminum to form insoluble phosphorus compounds. A method is known in which the phosphorus compound is added to insoluble phosphorus and metal compounds to be precipitated and removed, but in the present invention, the phosphorus compound that has not been sufficiently removed biochemically is chemically removed. And so.

As mentioned above, since 80 to 90% of phosphorus compounds in sewage can be removed by biochemical treatment, the remaining phosphorus compounds can be removed by chemical methods.

For example, if the sky continues to be sunny and the pollutant concentration is low, the phosphorus concentration is 5.
~7 g/l (as total phosphorus) of sewage flows in,
Since 80-90% can be removed by biochemical methods,
The phosphorus concentration in the two aerobic tanks is estimated to be 0.5-1.4-g/l. In other words, the phosphorus emission regulation value is 0.5 m
g,/l, the removal of phosphorus by chemical method is only about 1 g/l. Therefore, phosphorus compounds and insoluble phosphorus compounds are formed between the two aerobic tanks and the sludge settling tank. If iron chloride, PAC1 sulfate clay, etc. are added, residual phosphorus compounds react with these water-soluble metal salts to form insoluble phosphorus-metal compounds, which settle in a sludge settling tank and can be removed together with excess sludge. can.

When removing phosphorus by such a chemical reaction, the phosphorus compound in the form of an inorganic phosphorus compound, such as orthophosphate, has better phosphorus removal performance. However, since 20 to 50% of phosphorus compounds in sewage are organic phosphorus compounds, simply adding a water-soluble metal compound can remove inorganic phosphorus compounds, but it is difficult to remove organic phosphorus compounds. In contrast, the present invention provides aerobic 1
In the tank, most of this organic phosphorus compound is oxidized and decomposed into inorganic phosphorus compounds, and this inorganic phosphorus compound is ingested by the activated sludge in one aerobic tank, so the small amount of phosphorus that remains uningested is absorbed by the activated sludge. Not only can the compounds be removed by chemical methods, but since most of the remaining phosphorus compounds are inorganic phosphorus compounds, they can be easily removed by chemical methods. Therefore, compared to the case where sewage phosphorus compounds are removed using water-soluble metal salts from the beginning, the amount of metal salts used can be significantly reduced, and the reaction with the metal salts is carried out efficiently, resulting in a higher phosphorus removal rate. Excellent and stable.

The water-soluble metal salt used in the present invention is ferric chloride, PAC
A coagulant used for wastewater treatment such as pan 1 sulfate may be used.

The optimum location for adding these water-soluble metal salts is between the two aerobic tanks and the sludge settling tank.

Furthermore, instead of using a water-soluble metal salt, an iron-copper cell in which an iron plate and a copper plate are connected by a conductive wire, or only the iron plate may be installed in two aerobic tanks to elute iron ions.

From the above, the present invention has the following advantages.

■Nitrogen compounds are removed under conditions suitable for nitrification and denitrification, so removal performance is excellent.

(2) As with nitrogen compounds, BOD is oxidatively decomposed under conditions suitable for oxidative decomposition, so it has excellent removal performance.

■Since most of the phosphorus compounds in the water are converted into inorganic phosphorus compounds in one aerobic tank, they react efficiently with water-soluble metal salts.

■Most of the phosphorus compounds are removed by biochemical methods, so only a small amount of water-soluble metal salts are used for chemical removal.

In this way, if BOD and nitrogen compounds are removed by biochemical methods, and phosphorous compounds are removed by a combination of biochemical and chemical methods, these pollutants can be removed efficiently, and moreover, these pollutants can be removed from treated water. The pollutant concentration is BO
D is 10 mg/l or less, nitrogen compounds are 5 mg/l (as nitrogen) or less, and phosphorus compounds are 0.5 ng/l (as phosphorus) or less.

This method is applicable to biochemical treatment methods other than those described above, such as A! It can also be applied to a method that simultaneously removes BOD, nitrogen compounds, and phosphorus compounds from sewage by a method that combines anaerobic treatment and aerobic treatment, such as the 0 method and AO method.6 In addition, batch activated sludge treatment In the method, when an anaerobic treatment step and an aerobic treatment step are combined in one cycle to remove BOD, nitrogen compounds, and phosphorus compounds, phosphorus can be removed by combining the method of adding a water-soluble metal salt compound. performance is significantly improved.

Next, the present invention will be explained in detail.

(Example) In order to simultaneously remove BOD, nitrogen compounds, and phosphorus compounds from sewage using a sewage treatment device consisting of a bioreactor containing activated sludge and a sludge settling tank, the inlet side of the bioreactor to which sewage and return sludge are supplied is 1 anaerobic tank,
It is divided into 4 tanks: 1 aerobic tank, 2 anaerobic tanks, and 2 aerobic tanks.
Experiments were conducted using a pilot Buchund experimental device that can supply a quantitative amount of iron aqueous solution. In addition, the main feature of the pilot plant experimental equipment is that the bioreactor has an effective volume of 3.
The effective volume of the sludge settling tank is 2 (diameter 1.5 x depth 1.5 m).

Various anaerobic degrees and aerobic degrees are determined using ORP as an index: anaerobic 1 tank is 1250 ug, aerobic IWI is +120 ug, anaerobic 2 tanks is 1100@IV, and aerobic 2 tanks is +150 ug. It was managed and controlled as follows. In other words, the anaerobic tank is stirred to prevent the activated sludge from settling, and when the ORP drops below the set value, aeration is performed from the bottom of the tank, and when the set value is recovered, the aeration is stopped. The air tank is constantly aerated to prevent activated sludge from settling, and ORP
Control was performed by increasing the rotation speed of the Roots Proer using the ORP control device to increase the amount of aeration when the value decreased below the set value, and by lowering the rotation speed and reducing the amount of aeration when the value was restored to the set value.

For sewage, sewage overflow from a sand settling basin, whose average properties are shown in Table 1, is poured into an anaerobic 1 tank at 41/min, and anaerobic 2 sewage is used as a hydrogen donor for the denitrification reaction.
Each was fed to the tank at a rate of 31/min. Furthermore, the sludge return rate was set at 25%.

Iron chloride #112 aqueous solution (38% aqueous solution, specific gravity = 1.4
44) is aerobic 2′! On the premise that the water-soluble phosphorus concentration of the fI activated sludge mixture is 1 to 2 g/l (average 1.5 g/l) and the phosphorus concentration of the final treated water is 0.5-g/l or less. , and the reaction between ferric chloride and phosphorus compounds in two aerobic tanks was assumed as follows.

FeCl, +A, Pot→FePO5+3AC However, A
is a monovalent cation.

If the amount of the aqueous solution of ferric chloride to be added is calculated based on these assumptions, it will be approximately 5 so 1 per 1 aerobic 2'WI activated sludge mixed solution. Since the sewage treatment amount of this pilot plant is approximately 10 m'/day, 50 m'/day of ferric chloride aqueous solution
The treatment was carried out by continuously supplying 1/day.

The results are shown in Table 1. The experimental period was approximately 11
It was November, and there was almost no rainfall during or before that period, so sewage was flowing in with considerably higher pollutant concentrations than normal. In addition, the activated sludge mixture at the outlet of the two aerobic tanks was
The analytical values of the filtered water filtered through the filter paper are also shown in Table 1 for comparison.

Table 1 Sewage, aerobic 2! From the results in Table 1, the average concentration of pollutants in the fI-filtered water and the final treated water shows that the final treated water has a BOD of 5B71 or less, a COD of 10.1 mg/I, and an SS of 7.8 +++
g/M, total nitrogen 4, 3 +B/I, total phosphorus 0.1
2. The g/l ratio is good.

This experimental result shows that if the treatment conditions are set to efficiently remove BOD and nitrogen compounds, BOD and nitrogen compounds can be successfully removed from the filtrate water at the outlet of the two aerobic tanks, which is only biochemical treatment. However, biochemical treatment has removed approximately 78% of the phosphorus compounds in sewage, and most of the remaining phosphorus compounds have been removed by reaction with ferric chloride. It is clear that the removal of phosphorus by chemical treatment after biochemical treatment can efficiently remove phosphorus compounds, since it is easily converted into inorganic phosphates.

Furthermore, it has been found that the amount of water-soluble metal salts, such as ferric chloride, can be used in a smaller amount than in a method in which phosphorus compounds are removed by chemical methods from the beginning.

(Effect of the invention) The present invention has the following effects.

(2) BOD and nitrogen compounds can be removed efficiently.

■Since organic phosphorus compounds in sewage are converted into inorganic phosphorus compounds through biochemical treatment, phosphorus compounds can be easily removed by chemical methods.

■ Since most of the phosphorus compounds in sewage are removed by biochemical methods, the amount of water-soluble metal salts used in chemical phosphorus removal can be significantly reduced.

■By combining biochemical and chemical methods, treated water with sufficient removal of BOD, nitrogen compounds, and phosphorus compounds can be obtained, and the amount of water-soluble metal salts used is lower than with conventional methods. Therefore, processing costs are significantly reduced, and the amount of surplus sludge generated is also small.

[Brief explanation of the drawing] Figure 1 shows 1 anaerobic tank, 1 aerobic tank, and 2' anaerobic tank! and filtration of the activated sludge mixture in two aerobic tanks, and is a diagram showing the total phosphorus concentration of the filtrate in relation to the nitrate and nitrite nitrogen concentrations.

Claims (4)

[Claims] (1) A method for simultaneously removing BOD, nitrogen compounds, and phosphorus compounds from wastewater, which is characterized by combining a biological method and a chemical method. (2) In the biological method, the reactor containing activated sludge is divided into four from the inlet side where wastewater flows into one anaerobic tank, one aerobic tank, two anaerobic tanks, and two aerobic tanks; The wastewater to be treated and the sludge returned from the sludge settling tank are continuously injected while mechanically stirring, and phosphorus is released from the activated sludge, which also has a negative impact on the management and control of ORP in the next aerobic tank. Next, the activated sludge mixture from one anaerobic tank is continuously injected into one aerobic tank, and the ORP of one aerobic tank is maintained.
The oxidative decomposition of wastewater BOD, the nitrification reaction, and the excessive uptake of phosphorus by activated sludge are managed and controlled within a range that does not adversely affect the ORP management and control of the next two anaerobic tanks, and then the aerobic one. The activated sludge mixture in the tank is continuously supplied to two anaerobic tanks, and a part of the wastewater is used as a hydrogen donor, and while it is dispensed, the ORP is reduced to -50 by mechanical stirring or aeration in addition to mechanical stirring. The mixture was controlled in the range of ~-150 mV (gold-silver/silver chloride electrode standard) and maintained for a predetermined time to reduce nitrogen oxides to nitrogen gas, and the mixed solution treated in two anaerobic tanks was supplied to two aerobic tanks. Aeration is performed to oxidize and decompose the hydrogen donor BOD, and nitrogen gas is removed in the form of bubbles.
Claim 1 characterized in that it is a biological treatment in which the activated sludge mixture treated in two aerobic tanks is supplied to a sludge settling tank, the sludge is allowed to settle, and the treated water is separated into settled sludge and supernatant liquid. A method for simultaneously removing BOD, nitrogen compounds, and phosphorus compounds from wastewater as described. (3) ORP of one anaerobic tank -200 to -300-mV (
gold-silver/silver chloride electrode standard), +10 ORP for one aerobic tank
3. The method for simultaneously removing BOD, nitrogen compounds, and phosphorus compounds from wastewater according to claim 2, characterized in that they are controlled and controlled at 0 to +125 mV (gold-silver/silver chloride electrode reference). (4) A chemical method involves adding water-soluble agents that form water-insoluble compounds with wastewater phosphorus compounds between the two aerobic tanks and the sludge settling tank, making the wastewater phosphorus compounds insoluble. 4. The method for simultaneously removing BOD, nitrogen compounds, and phosphorus compounds from wastewater according to any one of claims 1 to 3, wherein the wastewater is removed as surplus sludge in a sludge settling tank.