KR20000061897A - A method making use of ultrasonic wave for treating waste water - Google Patents

Abstract

PURPOSE: A non-biodegradable wastewater treatment method using ultrasonic waves is provided, which is characterized in that ultrasonic waves are radiated into the non-biodegradable wastewater, so that COD removal rate increases and usage of hydrogen peroxide which is very expensive is reduced. CONSTITUTION: The treatment system comprises the following parts of: a feed tank(1), an oxidation tank(3), a neutralization tank(5) injected a coagulant and sodium hydroxide (NaOH) and a settler (6). The oxidation tank(3) is equipped with a peristaltic influent pump. And the non-biodegradable wastewater reacts with ferrous chloride and hydrogen peroxide in the tank. The system is characterized in that ultrasonic waves of 300-500kHz are radiated into the oxidation tank(3).

Description

Non-degradable wastewater treatment using ultrasonic waves {A METHOD MAKING USE OF ULTRASONIC WAVE FOR TREATING WASTE WATER}

The present invention relates to a method for treating hardly decomposable wastewater using ultrasonic waves, and more particularly, to a method for treating hardly degradable wastewater using ultrasonic waves by further improving the COD removal rate of treated water by irradiating ultrasonic waves to the wastewater to be treated in an oxidation reactor.

With the development of various industries and the industrialization of large-scale equipment, the inevitably generated hazardous industrial waste is rapidly increasing in quality and quantity. These should be disposed of properly and harmlessly to prevent environmental pollution. Improper soil dumping or reclamation of these various hazardous wastes and sludges from the wastewater treatment process will cause harmful substances (heavy metals, etc.) to elute and decay. Since this large waste causes hygiene problems and secondary environmental pollution, it must be disposed of safely and safely to humans and the natural environment.

In general, organic materials can be incinerated or oxidized to be harmless.Inorganic materials (including pneumatic compounds) can be chemically precipitated and then separated from the surrounding environment through methods such as cement solidification at the time of final disposal, or contained using iron. It is possible to adopt a method of making heavy metals into ferrite composite oxides and utilizing them.

On the other hand, the Fenton oxidation reaction widely used as a hardly degradable wastewater treatment method is a method of finally oxidatively decomposing the hardly decomposable organic matter in the hardly decomposable wastewater into water and carbon dioxide using a ferric ion and hydrogen peroxide. It has the advantage of not causing pollution.

At this time, the reactor port of the fenton oxidation reaction is as follows.

^{_{Fe 2+ + H 2 O 2 ------}} → Fe 3+ + OH - + · OH ------- [1]

RH + · OH ------- → RH + H ₂ O ------------- [2]

Here, hydrogen peroxide reacts with iron ions to generate OH radicals, which exhibit a strong oxidation reaction as in Equation [1], and this radical is an oxidation reaction that desorbs organic matter and hydrogen in waste water according to Equation [2]. To decompose into water and carbon dioxide.

At this time, the iron salt used can be used both monovalent and divalent, but the monovalent iron salt is known to be more effective, and finally the trivalent iron salt is removed by precipitating with iron hydroxide by adding a base.

However, the poorly degradable wastewater treatment method by the Fenton oxidation reaction has a disadvantage in that the wastewater treatment cost is excessively consumed because a large amount of expensive hydrogen peroxide and iron salt called Fenton reagent is used.

In addition, the method of treating hardly decomposable wastewater by the Fenton oxidation reaction decreases the decomposition efficiency even when a large amount of hydrogen peroxide and iron salt are used, and the amount of Fenton inorganic sludge which is solid-liquid separated from the hardly decomposable wastewater is increased. It causes problems.

In particular, the hydrogen peroxide remaining in the treated water acts as a COD inducing factor of the treated water, which results in lowering the COD removal rate (%) of the treated water.

The present invention can suppress the use of expensive hydrogen peroxide by irradiating the ultra-degradable wastewater of the oxidation reaction tank to improve the COD removal rate of the treated water, from which it is difficult to decompose the cost of difficult-decomposable wastewater treatment. The purpose is to provide a wastewater treatment method.

1 is a schematic diagram showing a hardly decomposable wastewater treatment apparatus equipped with an ultrasonic irradiation apparatus according to the present invention,

Figure 2 is a graph showing the relationship between the dose of iron salt, the frequency of ultrasound and the COD removal rate,

3 is a graph showing the relationship between the dose of iron salt, the frequency of ultrasound, and the transmittance.

<Explanation of symbols for main parts of drawing>

1: Storage tank 2: Metering pump 3: Oxidation reaction tank 5: Neutralization coagulation tank 6: Precipitation tank

In order to achieve the above object, the present invention oxidizes the hardly degradable wastewater with iron salt and hydrogen peroxide in an oxidation reaction tank, and then, in the hardly decomposable wastewater treatment method for solid-liquid separation of sludge and supernatant while passing through a neutralization coagulation tank and a precipitation tank. The present invention provides a method for treating hardly decomposable wastewater using ultrasonic waves, which comprises irradiating 300-500 kHz ultrasonic waves to hardly decomposable wastewater oxidized by iron salts and hydrogen peroxide in a reactor.

Hereinafter, the present invention will be described in detail.

Figure 1 is a schematic diagram showing a difficult-degradable wastewater treatment apparatus equipped with an ultrasonic irradiation apparatus according to the present invention, Figure 2 is a graph showing the relationship between the dose of iron salt, the frequency of ultrasound and the COD removal rate, Figure 3 is the administration of iron salt It is a graph showing the relationship between the amount and frequency of ultrasonic waves and transmittance.

In general, the ultrasonic wave (Power Ultrasound) having a frequency higher than the human audible frequency range of 16 Hz (> 16 kHz) is a high temperature and high pressure condition in the bubble caused by cavitation (Cavitation) is formed when bubbles collapse It involves a pyrolysis reaction at high temperature and a chemical reaction involving OH radicals generated during the pyrolysis process.

That is, when ultrasonic waves come into contact with the liquid, the fine bubbles therein expand in the half cycle on the decompression side to receive gas or vapor from the surrounding liquid, and in the half cycle on the boost side, the gas in the bubbles dissolves or condenses the liquid vapor. .

At this time, the bubbles in the liquid are vibrated and the average diameter is increased, and when the diameter is maximized as the vibration width increases, the pressure and the pressure of several hundred atmospheres calculated from the following equations [3], [4] and [5] It generates the heat of the island, creating an energy source for chemical reactions.

This cavitation occurs in a very short time of the nano second order, and it can be seen as an adiabatic process in that part because the generated heat is not enough time to transfer around.

In addition, the local temperature of the portion adjacent to the bubble instantly rises to form a hot-spot, and the temperature at this portion reaches thousands of degrees. At this time, the high local temperature increases the kinetic energy of the reactant particles in the surroundings. Therefore, not only the movement of the molecules is active, but also the sufficient activation energy necessary for the reaction is obtained, and the high pressure increases the mixing effect, which speeds up the reaction.

M (pollutant) ------- → Product (Pyrolysis Reaction). … … … … [3]

T _max = T _o P _m (K-1) / P -------------------------- [4]

P_max= P [P_m(P-1) / P]^{(K / (K-1))}-------------------------- [5]

Where T _O : ambient temperature

K: Polytropic Index of gas mixture or gas vapor

P: The pressure in the bubble at the largest size, usually the same as the vapor pressure of the liquid.

P _m : Pressure in the liquid at the moment the bubble breaks

On the other hand, when cavitation takes place in a homogeneous liquid, the process proceeds to the nucleus generation stage, the bubble growth stage, and the internal rupture stage. When it is placed in a large negative pressure environment, the volume grows and ultimately breaks up into small free bubbles due to internal bursting.

Therefore, when a sound wave with a frequency of 1.5 kHz or more is passed through the water, a chemical reaction occurs due to the action of pressure and temperature which rises momentarily during the breakage of the vapor-filled cavity due to the expansion wave and the compression wave or immediately after the breakage. In the same sonochemical reaction, pyrolysis and radical reaction take place simultaneously. In the case of volatile reactants, pyrolysis is carried out directly in the gas of the broken bubble or in the hot interface surrounding the bubble. Pyrolysis at the interface prevails and at low concentrations free radical reactions prevail.

In addition, the pyrolysis and radical reaction occur simultaneously in the negative chemical reaction by ultrasonic irradiation. The OH radicals generated during the pyrolysis process are involved in the chemical reaction, and the radicals are H radical and OH under the high temperature condition at which the water molecules are collapsed. It splits into radicals, where the OH radicals react with the organics and at the same time recombine with each other.

H ₂ O ------- → OH. … … … … … … … … [4]

OH · M −-------- → products… … … … … … … [5]

OH · + OH ------------- → H ₂ O ₂ . … … … … [6]

For example, when ultrasonic waves of 200 kHz are irradiated, the temperature reaches up to about 800 K at the outside of the bubble-liquid contact outside of the bubble, and the chemical reaction rate constant occurring therein becomes much higher as the temperature increases.

In addition, the oxidation reaction by ultrasonic waves is oxidized when ultrasonic waves (about 30-500 kHz, pressure amplitude = 3 atm (30 kW / m ² )) are oxidized to produce hydrogen peroxide (H ₂ O ₂ ), Nitrogen (N ₂ ) jumped into is NO by ultrasonic action, which is oxidized to nitrous acid (HNO ₂ ).

Hereinafter, the present invention will be described in more detail with reference to Examples.

In the present invention, as an embodiment for the non-degradable wastewater treatment, after storing the treated water discharged from the aeration treatment process in the storage tank (1), and supplies a fixed amount to the reaction tank (3) while adjusting the reaction supply amount with the metering pump (2) In the reaction tank (3), iron salt and hydrogen peroxide were injected at a constant rate while adjusting the reaction pH with sulfuric acid and sodium hydroxide.

In addition, a pH meter probe was used to confirm the influence of pH on the reaction in the reaction tank 3, and an ORP meter probe was used to determine the degree of oxidation and reduction of the reaction. Heat was measured with thermocouples.

In addition, in the present invention, the frequency of the ultrasonic wave irradiated from the lower part of the reaction tank 3 is measured by an oscilloscope, and the treated water processed in the ultrasonic reaction tank 3 is passed to the upper part and sent to the neutralizing coagulation tank 5.

At this time, in the neutralization coagulation tank 5, NaOH was injected into the metering pump to maintain the pH at about 8, and the polymer coagulant was slowly stirred with a stirrer while injecting the coagulant in the range of about 3 to 4 ppm.

Then, the treated water processed in the neutralization flocculation tank 5 overflows and is sent to the settling tank 6, in which the sludge is gravity settled and discharged to the bottom, and the supernatant flows out to the top.

On the other hand, the present invention is to apply the ultrasonic application technology in order to increase the treatment efficiency when treating the difficult-degradable wastewater, the ultrasonic wave 300, 350, 400, 450, Irradiation was carried out while changing at a frequency of 500 kHz, and the reaction time was reacted with varying the injection amounts of iron salt and hydrogen peroxide at reaction pH 3.5.

Example 1

First, in irradiating the ultrasonic wave from the lower part of the reactor 3 containing the hardly degradable waste water, the reaction time is 30 minutes, the reaction pH is 3.5, and only the injection amount of iron salt at the angular frequency of the ultrasonic wave is not added with hydrogen peroxide. The results of the experiments were changed to the results shown in Table 1 below.

Table 1. COD removal efficiency (%)

FeCl ₂ (mg / L) kHz 300 350 400 450 500 0300 5001,000 1,5002,000 54.959.361.568.171.273.5 58.061.164.671.274.877.9 61.565.969.974.377.980.1 62.467.371.275.278.880.5 63.768.172.176.179.680.5

That is, when the response frequency 300kHz FeCl ₂ COD removal efficiency in the injection amount is 0 mg / L of (%) was 54.9%, COD removal efficiency at the 1,000 mg / L injection amount of FeCl ₂ (%) is increased to 68.1% and FeCl ₂ The injection amount of was about 73.5% at 2,000 mg / L.

Then, the greater the response frequency removal efficiency when the response frequency 400 kHz to be elevated COD removal efficiency in the 0 mg / L injection amount of FeCl ₂ (%) is 61.5%, the COD removal rate at 1,000mg / L injection amount of FeCl ₂ ( %) Rose to 74.3% and the amount of FeCl ₂ injected was about 80.1% at 2,000 mg / L.

In addition, when the reaction frequency is 500 kHz, the amount of FeCl ₂ injected is 0 mg / L, the COD removal rate (%) is 63.7%, and the amount of FeCl ₂ injected is about 80.5% at 2,000 mg / L. The COD removal rate (%) was found to rise almost linearly as shown in FIG.

On the other hand, the treatment frequency of the ultrasonic wave was about 8.98% at 400 kHz and 9.52% at 500 kHz than 300 kHz.

According to the above experimental results, as shown in FIG. 3, the frequency of the ultrasonic treatment increased more significantly at 400 kHz than at 300 kHz, but it was slightly increased at 400 kHz compared to 400 kHz.

As shown in Fig. 3, the chromaticity (transmittance,%) of the treated water is 63% when the injection frequency of FeCl ₂ is 300 mg / L and the injection rate of FeCl ₂ is 1,000 mg / L, as shown in FIG. (%) Jumped to 65% and the injected amount of FeCl ₂ to 98.0% at 2.000 mg / L, becoming almost transparent.

In addition, even when the reaction frequency was 500 kHz, the FeCl ₂ injection amount was 0 mg / L, the transmittance (%) was 65%, and the FeCl ₂ injection amount was rapidly increased to 98.0% at 1,000 mg / L, and became almost transparent.

From the above results, the chromaticity (transmittance,%) was not affected by the reaction frequency, but the higher the frequency was, the better the results were.In the case of iron salt, the injection amount of iron salt was almost unaffected by the reaction frequency at 1,000 mg / L. Similar transmittance (%) 96-98% was shown to be very effective in removing the color.

Example 2

In irradiating ultrasonic waves from the lower part of the reactor containing hardly degradable waste water, the reaction time was 30 minutes, the reaction pH was 3.5, and the iron salt injection amount was 1,000 mg / L and 1,500 mg / L at each frequency of ultrasonic waves. Experiments were performed with varying doses from 0 to 500 mg / L.

Table 2. COD removal rate (%)

H ₂ O ₂ (mg / L) kHz 300 400 500 0100300500 68.169.073.074.8 74.375.782.384.5 76.177.984.185.4

According to the experimental results, as shown in Table 2 above, when the injection amount of iron salt was increased to 1,000 mg / L and the reaction frequency was increased to 300 mg / L from 0 mg / L to 500 mg / L at 300 kHz, the COD removal rate of the hardly degradable wastewater ( %) of the injected amount of H ₂ O ₂ yieoteuna 68.1% in the 0 mg / L, the injected amount of H ₂ O ₂ is injected amount of 73.0%, H ₂ O ₂ at 300mg / L was increased from 500mg / L to 74.8%.

In addition, the treatment efficiency increases as the reaction frequency increases, but the COD removal rate (%) of the dye wastewater at 1000 mg / L of iron salt and the reaction frequency of 400 kHz was 74.3% at 0 mg / L of H ₂ O ₂ . The dose of H ₂ O ₂ increased from 300 mg / L to 82.3%.

In addition, the injection amount of the iron salt 1,000mg / L, COD removal rate (%) of the response at 500kHz frequency recalcitrant wastewater is yieoteuna the injected amount of H ₂ O ₂ 76.1% in the 0 mg / L, the injected amount of H ₂ O ₂ 300mg The COD removal rate (%) increased to 85.4% at 84.1% / L and 500 mg / L injection of H ₂ O ₂ .

On the other hand, when the iron salt injection amount increased to 1,500 mg / L, the results were similar to the above. As shown in Table 3 below, the injection rate of hydrogen peroxide increased from 0 mg / L to 500 mg / L at 300 kHz. If to, I increased COD removal rate of the degradable waste water (%) is the injection amount of 81.4%, H ₂ O ₂ in the injection amount of H ₂ O ₂ 300mg / L from 500mg / L to 83.6%.

And, yieoteuna the injection amount of the iron salt 1,500 mg / L, COD removal rate (%) of the reaction frequency dyeing waste water from 400kHz is the injection amount of H ₂ O ₂ 77.9% In 0mg / L, in the injected amount of H ₂ O ₂ 300mg / L Increased to 87.2%.

Further, yieoteuna the injection amount of the iron salt 1,500 mg / L, COD removal rate of the reaction frequency dyeing waste water from 500kHz (%) was 79.6% in the injected amount of _{H 2 O 2 0 mg / L} , the injected amount of H ₂ O ₂ 300 mg The injection rate of 88.1% at / L and H ₂ O ₂ increased to 89.4% at 500 mg / L.

Table 3. COD removal rate (%)

H ₂ O ₂ (mg / L) kHz 300 400 500 0 71.2 77.9 79.6 100 73.0 79.2 81.0 300 81.4 87.2 88.1 500 83.6 89.4 89.4

On the other hand, according to the experimental results, when the injection time of iron salt increased the injection amount of 1,000 mg / L hydrogen peroxide from 0 mg / L to 500 mg / L at a reaction time of 30 minutes and a reaction pH of 3.5, %) is to the reaction frequency, as shown in Table 4 were reduced at 96%, 100mg / L in the injected amount of H ₂ O ₂ 0 mg / L on the 300kHz to 89% of this injection amount of H ₂ O ₂ 300mg / It increased to 95% at L and 98% at 500 mg / L.

At 400 kHz, the H ₂ O ₂ dose was about 98% at 0 mg / L and 98% at 100 mg / L, and the H ₂ O ₂ dose was 99% at 300 mg / L and 99 at 500 mg / L. % Rose.

In addition, even when the reaction frequency is 500 kHz, the H ₂ O ₂ dose is about 98% at 0 mg / L and 98% at 100 mg / L, and the H ₂ O ₂ dose is 99% at 300 mg / L and 99 at 500 mg / L. The response frequency was not different from that of 400kHz.

When the reaction time is 30 minutes and the injection amount of iron salt is 1,500 mg / L, as shown in Table 5 below, when the injection amount of hydrogen peroxide is increased from 0 mg / L to 500 mg / L at a reaction pH of 3.5, it is difficult to decompose wastewater. transmittance (%) of treated water is the reaction frequency is 97% in the injected amount of H ₂ O ₂ 0 mg / L on the 300kHz, 98%, 99% in the injected amount of H ₂ O ₂ 300mg / L at 100mg / L, 500mg At / L it rose to 99%

In addition, when the reaction frequency was 400kHz, the H ₂ O ₂ injection amount was 98% at 0 mg / L and 99% at 100 mg / L, and the chromaticity of the treated water showed a similar phenomenon even when the H ₂ O injection amount was increased. Even at the frequency of 500 kHz, the injection amount of H ₂ O ₂ was 98% at 0 mg / L and 99% at 100 mg / L.

As such, when a small amount of hydrogen peroxide is added at an injection amount of 1,000 mg / L, the chromaticity (permeability,%) of the treated water is slightly reduced. Ultrasonic irradiation is performed when the hydrogen peroxide and iron salt are oxidized to suspend and disperse the reaction solution. It is thought that the permeability decreases because the coagulation effect by iron salt increases when the iron salt is injected at 1,500 mg / L. Can be.

In addition, the effect of the hydrogen peroxide injection amount on the permeability of the treated water shows a good color removal efficiency since the remaining hydrogen peroxide does not affect the permeability of the treated water.

However, when the residual hydrogen peroxide acts as a cause of COD in the treated water and the excess hydrogen peroxide is present, the COD removal rate (%) is lowered.

Table 4. Chromaticity change (permeability%)

H ₂ O ₂ (mg / L) kHz 300 400 500 0100300500 96899598 98989999 98989999

Table 5. Chromaticity change (permeability,%).

H ₂ O ₂ (mg / L) kHz 300 400 500 0100300500 97989999 98999999 98999999

Example 3

In irradiating ultrasonic waves from the lower part of the reactor containing hardly degradable waste water, the reaction time was 30 minutes, the reaction pH was 3.5, the iron salt injection amount was 1,000 mg / L and 1,500 mg / L, and the hydrogen peroxide injection amount was 0 to 700 mg. The experiment was carried out with changes up to / L.

At this time, when the injection amounts of hydrogen peroxide and iron salt were 500 mg / L and 1,000 mg / L, respectively, the COD removal rate (%) of the fenton oxidation reaction and the fenton oxidation reaction using ultrasound was 72.57% and 74.78%, respectively.

In addition, when the injection amounts of hydrogen peroxide and iron salt were 500 mg / L and 1,500 mg / L, respectively, the COD removal rate (%) of the fenton oxidation reaction and the fenton oxidation reaction using ultrasonic wave was 76.55% and 83.63%, respectively.

From this, it can be expected that the COD removal rate of the ultrasonic oxidation reaction is about 10% higher than the Fenton oxidation reaction, and the consumption of hydrogen peroxide can be reduced by the synergistic effect, thereby saving the cost of difficult-decomposable wastewater treatment.

The present invention can suppress the use of expensive hydrogen peroxide by irradiating the treated water of the reaction vessel with ultrasonic waves to further improve the COD removal rate of the treated water, thereby providing the effect of reducing the cost of difficult-decomposable wastewater treatment.

Claims (1)

In the hardly decomposable wastewater treatment method in which the hardly decomposable wastewater is oxidized with iron salt and hydrogen peroxide in an oxidation reaction tank (3), and then solid-liquidly separated into sludge and supernatant while passing through a neutralization coagulation tank (5) and a precipitation tank (6). Ultra-degradable wastewater treatment method using ultrasonic waves, characterized in that for irradiating the hard-decomposable wastewater oxidized by iron salt and hydrogen peroxide in the oxidation reaction tank (3).