JPH02222795A - Method for removing phosphorus compound from sewage with empty can - Google Patents

Abstract

PURPOSE:To effectively utilize empty cans and to efficiently remove phosphorus compds. from sewage or waste water by dissolving the metal of the empty cans and allowing the resulting metal ions to react with the phosphorus compds. in the sewage or waste water to convert the compds. into insoluble compds. CONSTITUTION:Empty cans with exposed metal surfaces are put in the activated sludge-contg. reactor and/or the sludge sedimentation tank of an apparatus for treating waste water with activated sludge. Aeration is carried out, the metal of the empty cans is dissolved and the resulting metal ions are allowed to react with phosphorus compds. in sewage or waste water to convert the compds. into insoluble metal-phosphorus compds. These compds. are settled in the sludge sedimentation tank and drawn out together with excess sludge. The empty cans are effectively utilized and the phosphorus compds. are efficiently removed from the sewage or waste water.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for treating wastewater such as sewage and industrial wastewater.

[Conventional technology] In recent years, eutrophication of lakes, marshes, and closed sea areas has progressed due to sewage discharged from households, etc., and the removal of phosphorus, nitrogen, organic pollutants, etc. that cause eutrophication has become an important issue. It has become.

The pollutants indicated by BODA (hereinafter abbreviated as BOD) of sewage and industrial wastewater are removed by aerobic activated sludge treatment.
Further, nitrogen compounds such as ammonia compounds are removed by nitrification and denitrification methods, respectively.

For phosphorus compounds, coagulation-precipitation method and biochemical dephosphorization method are used.

Crystallization method or placing a steel filter material in the aeration tank of activated sludge treatment equipment, eluting iron ions and reacting the phosphorus compounds in the wastewater with iron ions, converting them into insoluble phosphorus-iron compounds. There are known methods for removing it.

[Problems to be solved by the invention] Conventional methods for removing phosphorus from sewage and industrial wastewater have many problems. This is a method in which a flocculant such as iron is added, and the metal ions of the flocculant are reacted with a phosphorus compound to convert it into an insoluble phosphorus compound, which is then coagulated and precipitated to be removed. Although this method can efficiently remove phosphorus compounds from sewage and industrial wastewater, it is costly due to the use of flocculants, and a large amount of sludge is generated.

In the case of biochemical treatment dephosphorization method, for example, JP-A-63-1
As seen in Publication No. 26599, the biochemical reactor of activated sludge treatment equipment is divided into an anaerobic process (1) and an aerobic process (
1), anaerobic process (2), and aerobic process (2), and by alternately providing an anaerobic environment and an aerobic environment to the activated sludge, excessive phosphorus is released from the activated sludge in the anaerobic process (1). , excessive intake of phosphorus in the next aerobic step (1),
This is a method for removing phosphorus from sewage and industrial wastewater by extracting activated sludge that has taken in too much phosphorus as surplus sludge. Naori OD is produced by oxidative decomposition in the aerobic process (1), and nitrogen compounds such as ammonia compounds are produced by nitrification in the aerobic process (1) and denitrification in the anaerobic process (2). remove.

This method is economical because it does not use coagulants, etc. However, when nitrogen compounds such as ammonia from sewage and industrial wastewater are removed simultaneously with phosphorus compounds ROD by the nitrification/denitrification method, the nitrification reaction in the aerobic step (1) If the nitrogen oxides generated in the process (for example, nitrite compounds and nitrate compounds) remain in the returned sludge, the concentration of nitrogen oxides in the anaerobic process (1) will increase,
Suppressing the release of phosphorus from activated sludge in this process,
There is a drawback that excessive intake of phosphorus in the next aerobic step (1) is not sufficiently carried out, resulting in a high concentration of phosphorus compounds in the treated water.

In the case of the crystallization method, in order to efficiently remove phosphorus compounds, it is necessary to strictly adjust the processing conditions, and it is necessary to install the necessary equipment, such as pretreatment equipment 1 reaction tank sedimentation tank, etc. For this reason, there is a drawback that installation costs and running costs are considerable.

Furthermore, as seen in Japanese Patent Publication No. 61-268397, an iron filter medium is installed in the aeration tank for activated sludge treatment, iron ions are eluted from the filter medium, and this is reacted with phosphorus compounds in the wastewater to make them insoluble. A method is known in which an iron-phosphorus compound is formed and removed by a precipitation method.

In this method, the insoluble iron-phosphorus compound is replaced with Fe5(
PO4)z ・8f120. Assuming FePO4-2Hzo or FePO4-x■20, the sewage contains 2 to 10■/2 (as phosphorus) phosphorus compounds, so this /mild steel dII+!・It is known that it is day.

Based on these facts, if this method is applied to a sewage treatment plant that processes 10,000 m of sewage per day, approximately 2,500 m of sewage will be processed per day.
Approximately 36,000 to 27 in an aeration tank with ~3,000 rrf
An iron filter medium with a large area of 1.000 ra is required.

For this reason, if such a large iron filter medium is installed in an aeration tank, sewage garbage and the like will get caught, making it difficult to remove the garbage. A more serious problem is that when used for a long period of time, slime adheres to the surface of the iron filter medium, which inhibits the elution of iron ions and reduces the ability to remove phosphorus. Therefore, this method using iron filter media has problems such as difficulty in removing dust and slime, and unstable removal of phosphorus.

As a countermeasure, the present inventors previously proposed
It was proposed as Publication No. 82692. In other words, this method involves electrochemically infiltrating a noble cell into an aeration tank of activated sludge treatment equipment, and electrochemically promoting the elution of metal ions from an electrochemically base metal plate (in this case, an iron plate). By doing so, the cell to be immersed can be made smaller, and phosphorus compounds can be efficiently and stably removed from sewage and industrial wastewater.

However, this method also has problems. That is, in this method, when the base metal plate is reduced by melting, it is necessary to pull up the cell and replace this metal plate.

Empty cans also pose a major social pollution problem because the technology for their effective use and treatment has not been sufficiently established.

The present invention was made to solve the problems of removing phosphorus from sewage and industrial wastewater and processing empty cans. By using empty cans with exposed metal surfaces, phosphorus compounds can be efficiently removed from sewage or industrial wastewater. The purpose of this project is to provide a method to effectively utilize empty cans.

[Means for Solving the Problems] The present invention is a method for efficiently removing phosphorus compounds from sewage and industrial wastewater, and the present invention is a method for efficiently removing phosphorus compounds from sewage and industrial wastewater. , with an empty can with exposed metal surface, aeration is performed to dissolve the metal in the empty can.

The dissolved metal ions are reacted with phosphorus compounds in sewage and industrial wastewater to convert the phosphorus compounds into insoluble compounds of metal and phosphorus, which are then settled in a sludge settling tank and extracted together with excess sludge. In addition, empty cans with exposed metal surfaces are made of one or more types of metal, and/or empty cans with exposed metal surfaces are a mixture of two or more types of empty cans made of different materials. In addition, the oxidation-reduction potential (ORP) of the reactor is maintained at a potential at which the metal in the empty can is easily dissolved, and the reactor has a reaction process that can convert organic phosphorus compounds in wastewater into inorganic phosphorus compounds, and This is a method for removing phosphorus compounds from wastewater using an empty can, in which a metal material having an electrochemically more noble ionization potential than the metal in the empty can coexists with the empty can to promote the solubility of the empty can.

(Function) Most empty cans have their surfaces and inner surfaces coated with an organic film or printed, and the metal surfaces are hardly exposed, so metal ions will not dissolve even if they are immersed in an aeration tank. Since the metal of the empty can used in the present invention is immersed and dissolved in a reactor containing activated sludge, it is necessary to expose the metal surface. The method for exposing the metal surface of an empty can is that when the empty can is incinerated at about 400 to 700°C, organic films, printing, etc. are easily removed, and the metal surface is exposed.

When such an empty can with an exposed metal surface is immersed in a reactor containing activated sludge, metal ions are eluted from the empty can. In this case, as a method for efficiently eluting metal ions from empty cans, it is possible to apply the concept of Japanese Patent Application No. 1982-28269, which has already been filed by the inventors of the present invention. That is, the iron plates are melted and connected to promote melting of the iron plates.

When this method is applied to melting empty cans, the rate of metal dissolution is faster in empty cans made of two or more metals, such as aluminum and iron, than in empty cans made of one type of metal. In this case, aluminum has a passivation film formed on its surface and is electrochemically Empty cans dissolve iron ions and are effective in removing phosphorus compounds from sewage and industrial wastewater, but aluminum and tin cans do not dissolve easily and are hardly effective in removing phosphorus compounds.

It is possible to promote the dissolution of metal in an empty can more than in an empty can made of one type of metal. Specifically, these empty cans with exposed metal surfaces are placed in a cassette ([) made of a metal that is more electrochemically sensitive than the metal of the empty can and immersed in a reactor, thereby removing the metal of the empty can. Dissolution is promoted.

Also, empty cans made of different metal materials, such as iron cans,
An empty aluminum can or an empty tin can.

In addition, in order to efficiently dissolve empty cans with exposed metal, the environment of the reactor where activated sludge exists is important. That is, the dissolution (1!i) rate of metal in water is influenced by pH, dissolved oxygen concentration, oxidation-reduction potential (ORP), chloride ion concentration, stirring speed, etc. For example, the lower ρ■, the higher the dissolved oxygen concentration, the higher the ORP, and the higher the stirring speed, the faster the metal dissolution rate.

However, in the case of activated sludge treatment, conditions that promote the dissolution of metals in empty cans cannot be applied if conditions that inhibit the function of activated sludge are used, so it is important to find conditions that allow both to proceed smoothly. .

Therefore, in activated sludge treatment where empty cans with exposed metal surfaces coexist, it is important to control the pFI, ORP, dissolved oxygen concentration, and stirring speed of the aeration tank, and in reality, p++ is 6°5 to 6°5.
7.5, ORP is -280 to +200mV (A
g/AgC1 electrode standard), dissolved oxygen concentration is 0.5 to 3■
/l, and the stirring speed is such that the water flow in the reactor is 5 to 5.
It is appropriate to stir at a speed of about 40c+a/sec.

Next, the reactivity of metal ions eluted from empty cans with phosphorus compounds in sewage or wastewater is significantly influenced by the form of the phosphorus compounds. That is, when a dissolved metal reacts with a phosphorus compound, an inorganic phosphorus compound, such as an orthophosphate, reacts more easily than an organic phosphorus compound to form an insoluble metal-phosphorus oxide.

Since phosphorus compounds in sewage and industrial wastewater often contain a mixture of organic and inorganic phosphorus compounds, it is preferable to convert the organic phosphorus compounds into inorganic phosphorus compounds.

The simplest conversion method is to decompose organic phosphorus compounds into inorganic phosphorus compounds through aerobic activated sludge treatment.

In addition, in order to prevent eutrophication of lakes and closed sea areas, it is necessary to remove nitrogen compounds and BOD in addition to phosphorus compounds. Therefore, as a result of intensive research, the inventors discovered that phosphorus compounds, nitrogen compounds, and B.
We have found a way to remove OD at the same time.

The process is shown in Figure 1.

3 in Figure 1 is a reactor in which activated sludge exists,
It is divided into four parts via a partition plate 11, and various functions will be explained below.

The anaerobic tank 14 is maintained in an anaerobic state to release excessive phosphorus from the activated sludge. In order to maintain the appropriate amount of phosphorus released at this time, the ORP in the tank is -280 mV (Ag/
AgC1 electrode reference, hereinafter li) below &Zf, controlled so as not to exceed.

The aerobic tank--5 maintains the activated sludge in an aerobic state to allow the activated sludge to take in excessive amounts of phosphorus, decomposes 80 sludge, and oxidizes nitrogen compounds such as ammonia to nitric acid and/or nitrite compounds. In order to make these three reactions occur smoothly,
Control the ORP in the tank to +50 to 200a+V.

The aerobic tank -16 reduces the nitrogen oxides produced in the aerobic tank -5 to nitrogen gas in an anaerobic state. At this time, in order to suppress re-release of phosphorus and to ensure smooth reduction of nitrogen oxides, the ORP in the tank is controlled at -150 mV.

The aerobic tank -■7 is aerated to remove nitrogen gas and further activate the nitrogen gas produced in the anaerobic tank -■6, which adheres to the sludge and causes the sludge to float in the sludge settling tank 8. Re-uptake of phosphorus into the sludge.

In this way, reactor 3 is divided into an anaerobic tank and an aerobic tank,
In the method of simultaneously removing phosphorus, nitrogen, and BOD, if the concentration of pollutants in the inflowing sewage is low, or if the returned sludge 2 contains unreacted nitrogen oxides in the anaerobic tank 6, the anaerobic tank 14 Since the ORP of the aerobic tank 15 is not sufficiently lowered, phosphorus is not released sufficiently, and therefore the phosphorus intake in the aerobic tank 15 is not sufficient, resulting in a problem that the phosphorus concentration of the treated water 9 becomes high. Another problem is that when the sludge settling tank 8 becomes anaerobic with an ORP of -150 mV or less, phosphorus is re-released from the activated sludge, causing an increase in the phosphorus concentration of the treated water 9.

However, in such a method of biochemically removing phosphorus from sewage or industrial wastewater, as shown in FIG. 1, empty cans are preferably placed in reactor 3 shown in FIG. 1, especially in an aerobic reactor. In other words, when an empty can is placed in the aerobic tank 15 or the aerobic tank 7, the metal dissolves well and reacts with the phosphorus compound.

In addition, if an empty can with exposed metal surfaces is placed in the anaerobic tank 4.6 or sludge settling tank 8, the dissolution rate of the metal is slower than in the aerobic tank, but the metal dissolves and reacts with the phosphorus compound. death,
Phosphorus compounds can be removed from sewage or industrial wastewater.

For empty cans with exposed metal surfaces, when a cell such as stainless steel is installed, iron ions will elute and react with phosphorus compounds to form insoluble iron-phosphorus compounds, stably removing phosphorus compounds from sewage or industrial wastewater. be able to.

Next, we will explain how to put empty cans with exposed metal surfaces in activated sludge treatment of sewage or industrial wastewater.

An empty can with an exposed metal surface is used to remove the phosphorus compound, and then placed in a cassette, which is then set in a reactor of an activated sludge treatment facility for wastewater such as sewage or industrial wastewater. Also, when using empty cans with exposed metal surfaces, the metal will melt while in use and will need to be refilled. It's simple.

[Example] Examples of the present invention are shown below.

Example 1 Empty cans of beer, soft drinks, etc., whose tops are aluminum lids and bodies are made of iron, are baked at 500 to 700'C, and then placed in stainless steel cassettes (1) and disposed of in urban sewage. The sample was immersed in an aeration tank for uniformly mixed aerobic activated sludge treatment, and activated sludge treatment was performed in the usual manner.

As a result, the average concentration of phosphorus compounds in activated sludge treated water was 1. At about In+g/n, the removal rate of phosphorus compounds was about 80%. The concentration of phosphorus compounds in the treated water without empty cans was approximately 2.3II1g/1, and the removal rate was approximately 58%. From this, it has become clear that placing empty cans with exposed metal surfaces in the aeration tank for activated sludge treatment is effective in removing phosphorus compounds from sewage.

Example 2 Empty cans collected from the car were baked at 500 to 700'C, then placed in a stainless steel cassette (It).
Activated sludge treatment of urban sewage was carried out by putting it into the aerobic tank-I5 of the activated sludge treatment facility shown in FIG.

For each (7) ORP, set the anaerobic tank-I4 to -280 mV.
D, aerobic tank -15 to +100mV, anaerobic tank -■6 to 1
The voltage was controlled at 50 mV, and the aerobic tank -7 was controlled at +50 mV.

Processing performance is shown in Table 1.

Table 1 Treatment performance (mg/f) (Note) K-N, Kjeldahl nitrogen compound (as N) T-P
Total phosphorus compounds (aa P) From the results in Table 1, even if the water quality of the sewage flowing into the reactor changes, the method of the present invention has excellent performance in removing pollutant components from sewage, and in particular, B
Excellent ability to remove OD and total phosphorus compounds.

Example 3 Empty cans collected from cars were baked at 500 to 700°C, placed in a stainless steel cassette, and placed in the first
Activated sludge treatment of urban sewage was performed by placing the activated sludge in the anaerobic tank 6 and sludge settling tank 8 of the activated sludge treatment equipment shown in the figure. The various ORPs are -280mVkm for anaerobic tank I4, 15komV for aerobic tank, and -150m for anaerobic tank 6.
V, and aerobic tank -7 was controlled to +50 mV.

The concentration of BOD, nitrogen compounds and phosphorus compounds in the treated water is
Almost the same performance as in Table 3 of Example 2 was obtained.

In addition, the phosphorus and iron content of excess sludge is 6 to 25 phosphorus.
%, iron was 5-35%. From this result, phosphorus compounds in sewage react with iron eluted from empty cans to form insoluble phosphorus-iron compounds, which settle in the sludge settling tank 8.
It was estimated that the sludge would be extracted and removed as surplus sludge 10.

Example 4 Empty cans collected from inside a car were baked at 500 to 700'C, then placed in a stainless steel cassette (basket) and placed in various types of activated sludge treatment experimental equipment and sludge settling tank 8 shown in Fig. 1. and activated sludge treatment of dairy factory wastewater. In addition, the ORP of each 1a is -280 mV for the anaerobic tank -14.
, aerobic tank -15 +100mV D, anaerobic tank ■6 -
150 mV, and aerobic Jfl-07 to +50 mV,
Each was controlled. The treatment time was approximately 12 hours, and the sludge return rate was approximately 100%.

Table 2 summarizes the properties of the dairy factory wastewater and activated sludge treated water used in the experiment.

2 Properties of dairy factory wastewater (Units: p [■/1 excluding 1) As shown in Table 2, the method of the present invention allows high concentrations of eutrophic substances such as phosphorus compounds and nitrogen compounds as in dairy industry wastewater. It has become clear that pollutants such as phosphorus, nitrogen, and ROD can be efficiently removed by applying this method to industrial wastewater containing pollutants such as phosphorus, nitrogen, and ROD.

(Effects of the Invention) As explained above, the method of Zero's invention can easily remove phosphorus compounds from wastewater such as sewage and industrial wastewater by using empty cans with exposed metal surfaces. Many problems caused by this can be solved at the same time.

[Brief explanation of the drawing]

Figure 1 shows phosphorus compounds, nitrogen compounds and B used in the present invention.
It is a schematic diagram showing an example of an activated sludge processing device which can remove OD efficiently. 1...Inflow sewage, 2...Return sludge, 3...Reactor 4...Anaerobic tank-I, 5...Aerobic tank-I, 6...
・Anaerobic tank ■, 7...Aerobic tank-■, 8-sided mud sedimentation tank, 9・
... Treated water, lO ... Excess sludge, 11 ... Partition plate, Sai1 representative, patent attorney Masamitsu Akizawa, and 1 other person

Claims (5)

[Claims] (1) Empty cans with exposed metal surfaces are placed in the reactor and/or sludge settling tank where activated sludge of the wastewater activated sludge treatment equipment exists, and the metal in the empty cans is dissolved, and the dissolved metal ions and wastewater phosphorus are dissolved. A method for removing phosphorus compounds from wastewater using empty cans, which comprises converting phosphorus compounds from wastewater into insoluble compounds of metal and phosphorus by reacting with a compound to remove phosphorus compounds from wastewater. (2) Use empty cans with exposed metal surfaces that are made of one or more types of metal, and/or empty cans with exposed metal surfaces that are a mixture of two or more types of empty cans made of different materials. Claim (1) characterized in that
) Method for removing phosphorus compounds from wastewater using empty cans. (3) A method for removing phosphorus compounds from wastewater using an empty can according to claim (1) or (2), characterized in that the oxidation-reduction potential (ORP) of the reactor is maintained at a potential at which metal in the empty can is easily dissolved. . (4) The empty can according to any one of claims (1) to (3), characterized in that the reactor has a reaction step capable of converting organic phosphorus compounds in wastewater into inorganic phosphorus compounds. A method for removing phosphorus compounds from used wastewater. (5) Waste water using empty cans according to claim (1), characterized in that a metal material having an electrochemically nobler ionization potential than the metal of the empty can coexists with the empty can to promote solubility of the empty can. How to remove phosphorus compounds.