KR970006146B1 - Treatment method for waste-water from reclaimed land - Google Patents

Abstract

The leaching water generated from the wastes removed land is treated biologically first, and then it is treated secondly with the chemical and biological method such as a fenton oxidation method etc. after the original leaching water of 1~15% is added to the discharged water which was treated first. Therefore, the treating water reduces a pollutant without generating sludge.

Description

How to Treat Leachate from Landfills

1 is a graph showing the results of experiments while varying the concentration ratio of Fe ²⁺ to a certain amount of hydrogen peroxide.

Figure 2 is a graph showing the treatment effect according to the change in drug dosage.

3 is a graph showing the results of experiments varying hydrogen peroxide and Fe ²⁺ from 1000 mg / L to 18000 mg / L, respectively.

4 is a graph showing the results of experiments with varying amounts of Fe ²⁺ .

5 is a graph showing the treatment effect according to the reaction pH.

6 is a graph showing the treatment effect according to the change of reaction time.

7 is a graph showing the treatment effect according to the change in the stirring speed.

8 is a graph showing the results of two fenton oxidation.

9 is a graph showing the Fenton treatment effect after mixing the leachate source water and landfill treatment water.

The present invention relates to a method for treating leachate generated in a landfill, and more specifically, by adding a small amount of raw leachate to biologically treated water prior to chemical treatment after treating the leachate biologically. Is about the way.

Recently, the amount of general wastes is increasing rapidly due to economic growth and urban concentration. Most of the general waste is disposed of in landfills. Since leachate from landfill contains high concentrations of organic materials, groundwater pollution and secondary cold pollution are greatly raised. Therefore, it is urgently needed to discharge leachate properly. .

Leachate water quality from landfills is reported to be high in organic, inorganic and nitrogen compounds, while low in phosphorus and heavy metals. The existing post-treatment methods for activated sludge treated water include flocculation sedimentation, activated carbon adsorption, and chemical oxidation. However, flocculation sedimentation is not effective for COD removal and activated carbon adsorption is not easily removed by activated carbon. It was found to be not very effective. In addition, the disadvantage of the chemical oxidation method is that a high cost occurs because a large amount of oxidizing agent is administered when treating a high concentration of wastewater, especially biodegradation when using chemical oxidation as a pre-treatment of the post-biological treatment of landfill treated water treated with biological treatment There is a disadvantage that the performance is not improved much. Chemical treatment methods are known as ozone treatment, UV treatment and Fenton oxidation.

Among chemical treatment methods, the Fenton oxidation method is known to be the most efficient. Here, a method using a small amount of Fe ²⁺ as a catalyst and using an amount similar to hydrogen peroxide is known.

Much research has been done on the biological treatment of landfill leachate, and anaerobic, aerobic and a combination of anaerobic and aerobic are used as biological treatment methods. The biological treatment methods commonly used in Korea are the anaerobic digester as the first biological treatment and the lagoon during the aeration as the second biological treatment.

It has been shown that the aerobic biological treatment efficiency of leachate with a COD concentration of less than 1,000 mg / L produced from older landfills is very low. The COD removal rate is only 43% even though the COD loading rate was operated at 0.1Kg / m ³ -day. The organic material in the leachate is mainly composed of hardly decomposable material, so that the leachate with 0.03 BOD / COD ratio of 0.03 each shows no decrease of COD concentration even after 7.7 days of aeration. Trickling filters and RBC are not shown to be as effective as the activated sludge process for treating leachate in older landfills.

Under these circumstances, most of the leachate from our landfill is discharged to the water source through the first and second biological treatments, so the CODmn is over 400, and the current emission standard is less than 100mg / L and BOD The environmental standard value of 80 mg / L or less is not achieved.

In addition, the BOD / COD ratio was not more than 0.3 even when the chemical oxidation treatment was performed. Already, almost no BOD source was already removed from the biological treatment of the advanced acupuncture water (anaerobic digester and aeration type lagoon). This is because there is a small amount of substance that can be converted into a BOD source.

Accordingly, an object of the present invention is to provide a method of lowering residual BOD and COD concentrations within an emission limit by oxidizing hardly decomposable organic components in leachate activated sludge treated water. In the study on leachate treatment, the present inventors have obtained a effluent that satisfies the emission limit by biologically treating the leachate raw water with a small amount of leachate and then treating the leachate. It was found that it can. This is a result of the high BOD in the leachate, so that after chemical oxidation, COD decreases while BOD improves. That is, when the raw leachate is mixed and chemically treated, the hardly decomposable substance in the treated water and the hardly decomposable substance in the leachate are changed to degradable, and since the BOD component in the leachate is retained in a substantial amount, the microorganism grows vigorously. Not only does it lower the BOD, but it also lowers the COD.

In the conventional biological treatment method, BOD is almost eliminated while COD treatment efficiency is low, and the effluent is present as a hardly decomposable substance having a low BOD / COD ratio. Symons was BOD ₅ / were CODcr using a non-classifying the biodegradation potential of the waste water, whereby BOD ₅ / CODcr If the ratio is 0.6 or more waste can be easily treated in the biological, 0.4 processable waste water biologically, and 0.2 is treated in the biological Is classified as a toxic environment that does not allow for volatility (0.04) .APPCedure for Determination of the Biological Treatability of Industrial wastes, J. WPCF, Vol. 32, Leachate from Current Landfills Commonly used methods for the treatment of the following are: treatment in an anaerobic digester for several days and then in an aeration lagoon, after which the microorganism and the supernatant are separated from the settling tank and the microorganisms are returned to the aeration lagoon. If the discharged water satisfies the discharge limit, discharge it to the water source. If it does not is further subjected to chemical treatment and biological treatment.

However, when considering the classification based on the classification of Symons, the BOD / COD ratio is obtained even if the biochemical treatment, the chemical treatment, and the post-biological treatment are carried out by the above-mentioned general methods currently performed on the leachate generated in domestic landfills. Since is almost 0.2, it is currently difficult to pass the current COD standards of 100mg / L or less under any chemical and biological treatment as a post-treatment.

This will be described with reference to the accompanying drawings. Here, the Fenton oxidation method is described as an example of the chemical oxidation method, and even if other chemical oxidation methods are used, the results will not be better. That is, the Fenton oxidation method is the most efficient chemical treatment method currently implemented, so it is only representative of this example, and it is clear that it is not intended to limit the idea of the present invention for any reason.

FIG. 1 shows the results of experiments in which the amount of hydrogen peroxide was fixed at 300 mg / L and the amount of Fe ²⁺ was changed from 60 mg / L to 420 mg / L. As shown in the figure, landfill water with CODcr of 430mg / L is reduced to 289mg / L-150mg / L and Fe ²⁺ shows almost constant CODcr value from 300mg / L. CODmn also decreases as Fe ²⁺ increases, indicating that CODcr tends to be almost the same. BOD ₅ showed a similar overall value at about 30 mg / L, which was about three times increased from 10 mg / L to landfill. The BOD ₅ / CODcr ratio, a measure of biodegradability, increased from 0.02 to 0.24 before treatment, but did not increase to 0.6 for the BOD ₅ / CODcr ratio, which Symson said. In this experiment, the BOD ₅ / CODcr ratio was selected as the pretreatment condition of the fixed phase biology reactor by selecting the hydrogen peroxide: Fe2 + ratio, 300: 300 (mg / L), which is the minimum drug value of more than 0.2. However, during the operation of the reactor, the treated water of the leachate treatment plant in the field is gradually weakened, so there is a need to determine a new chemical injection amount.

2 shows the results of experiments in which the concentration of hydrogen peroxide and the concentration of Fe 2+ (mg / L) were varied from 100: 100 to 40000: 4000. As shown in the figure, CODcr decreases from 584mg / L to 102mg / L and CODmn decreases from 374mg / L to 72mg / L as the concentration of hydrogen peroxide and Fe ²⁺ increases. From the graph, if more Fenton reagent is injected, CODmn can be lowered to 50mg / L, but it is certainly not uneconomical to treat wastewater with chemical treatment using such a large amount of chemicals. It can be seen that the BOD ₅ value increased by about 3.5 times from 40 mg / L to 40 mg / L as a whole to 40 mg / L as a whole at 14 mg / L before treatment. Applying the classification of symons to the graph of Figure 2, it can be seen that the amount of hydrogen peroxide and Fe ²⁺ with a BOD ₅ / CODcr ratio of 0.2 or more should be at least 1000 mg / L, respectively.

However, when the amount of hydrogen peroxide and Fe ²⁺ is more than 2000 mg / L, hydrogen peroxide is not economical due to the chemical cost of Fenton's reagent itself, as well as the amount of NaOH used to raise the pH for coagulation and the amount of precipitated sludge. ^The experiment was performed by changing the concentration (mg / L) ratio of ²⁺ from 1000: 1000 to 1800: 1800 and to select the optimal drug ratio therefrom. From Table 1, it can be seen that TKN NH ₃ -N and NO ₃ -N are not changed by the high concentration of Fenton reagent injection. However, as the amount of hydrogen peroxide and Fe ²⁺ increases, the amount of TDS and FDS increases, which means that a large amount of Fenton's reagent lowers the pH after the Fenton's oxidation reaction. It is seen as a result of consuming.

In addition, the TP value of Table 2 shows that the TP value existing in the leachate treated water at a low concentration of 2.1 mg / L is lowered to about 1 mg / L after the Fenton oxidation treatment. It can be seen that it is necessary.

3 is hydrogen peroxide and Fe The results of experiments varying from 100mg / L to 1800mg / L, respectively. You can see that the value is showing. However, the amount of fenton reagent injected (mg / L)

Sludge was not precipitated well and floated below 1200: 1200, and the absorbance value exceeded 0.09 and color was not removed. At this time, the BOD / CODcr ratio was 0.19, which did not have good biodegradability, but at higher doses of the drug, the biodegradability did not become better and there was no economic feasibility.

4 is hydrogen peroxide: Fe In order to check whether the ratio of 1 to 1 is a suitable value, It is the result of experiment by changing the value. As shown in the figure, both CODcr and CODmn are Fe It can be seen that the amount of continues to decrease until 1400 mg / L, but there is little change. The BOD value is approximately 65 mg / L as a whole It can be seen that the BOD / CODcr ratio is about 0.29 at the amount of 1400 mg / L. It can be seen that the value is higher than the BOD / CODcr ratio in FIG. 3, which seems to be due to the residual BOD remaining as the leachate treatment in the field is worse than before.

From the above experimental results, hydrogen peroxide and Fe As the amount of is increased, it can be seen that the points such as CODcr, CODmn, and TOC are gradually reduced, and the BOD / CODcr ratio is gradually increased. However, it is impossible to reduce CODmn below 50mg / L by pentanolation alone, and it is economical and suitable amount of hydrogen peroxide and Fe As a result, the BOD / CODcr ratio could not be increased to the point where biodegradability was extremely high. However, since the removal of COD is more than 60% after Fenton's oxidation treatment, the BOD / CODcr value does not improve more than three times. Therefore, the biodegradability can be greatly improved if it is added that can be provided as BOD during Fenton's oxidation treatment. It seems to be.

Figure 5 shows the results of the experiment by changing the pH to 2-7 to find the best pH conditions. At this time, hydrogen peroxide and Fe The injection amount of was 1400 mg / L, respectively. In general, the optimum pH of the oxidation reaction is known as 3-5. As shown in the figure, CODcr was treated at 670mg / L at 202mg / L and CODmn at 340mg / L at 104mg / L. At pH2, the value is similar to that of pH3, while the pH of Fenton's oxidation rapidly deteriorates as the pH is higher than 4.

However, the BOD value at pH 3 is better than that at pH 2, and the BOD / CODcr ratio is more advantageous at pH 3. The remaining fruit water was also 124 mg / L, 234 mg / L, and 410 mg / L at pH 4-7, respectively. As the pH is higher, the decomposition of hydrogen peroxide does not occur and the oxidation of organic matters is less.

Hydrogen Peroxide and Fe Were injected at a constant 1400mg / L, respectively, and the reaction time was increased to 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours to perform the fenton oxidation reaction. As a result, as shown in FIG. 6, it can be seen that the oxidation reaction continues to occur in less than 1 hour, and the CODcr and CODmn were not changed after 1 hour.

7 shows a reaction time of 1 hour, sorghum and Fe In order to investigate the effect of stirring speed on Fenton's reaction with the amount of 1400mg / L, respectively, the rapid stirring speed of Jar-tester was changed to 50rpm, 100rpm, 200rpm, 300rpm, 400rpm and the fenton oxidation reaction was performed. The results are shown. As a result, it can be seen that sufficient Fenton oxidation reaction did not occur at 50 rpm at 1 hour of reaction time, and sufficient decomposition reaction occurred at 100 rpm. That is, the decomposition reaction of Fenton's reagent occurs at an early stage, but the time varies according to the reacting material, and the decomposition reaction rate is also affected by the stirring speed.

Figure 2 shows hydrogen peroxide and Fe It can be seen that as the amount of is increased, both CODcr and CODmn values are decreased. Iron at 1200mg / L, respectively, and hydrogen peroxide and Fe The concentration of (mg / L) was treated with 1) 300: 300, 2) 600: 600, 3) 1000: 1000, 4) 1200: 1200 and 5) 1400: 1400, and the results are shown in FIG. As shown in the figure, CODcr showed no change in both primary and secondary fenton oxidation, and in the case of CODmn, less than the primary CODmn value when secondary fenton oxidation. However, the combination of the two Fenton reagents in two doses did not seem to be as good as the one injected. In conclusion, CODmn value could not be lowered below 50mg / L even with two Fenton oxidation, and the BOD value was decreased during the second Fenton oxidation treatment, and the BOD / CODcr ratio tended to be lowered.

In summary, the experimental results of the Fenton oxidation reaction can be seen that CODcr and CODmn can be removed more than 60% and BOD is increased by 3 to 5 times. However, even after the Fenton oxidation treatment, the BOD / CODcr ratio does not exceed 0.3. As described above, the BOD source has already been almost eliminated in the biological treatment of the leachate (anaerobic digestion and aeration lagoons), and the BOD after the Fenton oxidation treatment in the leachate treatment water. This is because there are not many substances that can be changed into. Leachate raw water was divided into BOD4200mg / L, CODcr 7400mg / L, CODmn 840mg / L, and the leachate raw water was mixed with leachate treated water in the sense of providing BOD.

The mixing ratio of landfill treated water and leachate source water was set to 20: 1 by volume, and hydrogen peroxide and Fe The ratio of is fixed to 1: 1 and hydrogen peroxide and Fe Experiments were made by varying the dosage of. The result is shown in FIG. CODcr and CODmn can be seen to decrease similarly to Fenton-oxidized water only, whereas BOD decreases from 292mg / L to 150mg / L ~ 187mg / L. However, it can be seen that the BOD / CODcr ratio is all about 0.6, the B0D / CODcr ratio that Symons facilitates biological treatment. This later improved the biodegradability to the point where biological treatment is sufficient, and shows the possibility of reducing the injection amount of fenton reagent. In Table 3, TKN and NH-N are present at high values. When the flocculation settles at pH 8, this NH-N may cause sludge injury problems. . Absorbance and transmittance after Fenton's oxidation were determined by Fenton's oxidation

The value was similar to that shown.

In the above, only the result of mixing the landfill treated water with the leachate source water at a volume ratio of 20: 1 was shown, but according to the experiments of the present inventors, sufficient effects were obtained even when the leachate source water was reduced to 1%, and used up to 15%. It was also found that it worked. When the content of raw water was lowered below the lower limit, the content of BOD source in the mixed solution of landfill and leachate was not sufficient, and it was difficult to achieve the effect, and even above the upper limit, it was difficult to improve the BOD value and the COD value. And it was found.

As described above, none of all known techniques can reduce the COD and BOD values of the leachate generated in general landfills below the emission limit, but it can be realized by the present invention. As a result, groundwater contamination and secondary environmental pollution problems can be solved.

The present invention will be described in more detail with reference to the following examples. The analytical methods used in these examples were conducted in accordance with environmental pollution testing methods and standard methods. These examples are only intended to illustrate the invention and are not intended to limit the spirit of the invention.

Example 1

3000 tons of waste leachate from Gimpo landfill was digested for 10 days while avoiding contact with air in anaerobic digester. Thereafter, they stayed in the Foxy Lagoon for 3 days. The supernatant and the sludge were separated by standing for 7 hours in the settling tank. The sludge was automatically returned to the aeration lagoon with a pump. 1 liter of raw water was added to 20 liters of supernatant collected here. This mixture was taken and treated with 900 mg / L of Fenton's reagent. Post-biological treatments were performed using the fixed-phase biofilm method using media. Effluent was collected and analyzed after the post-biological treatment. The results are shown in Table 4.

Example 2

3000 tons of waste leachate was digested for 10 days in an anaerobic digester, avoiding contact with air. Thereafter, they stayed in the aeration lagoon for 3 days. The supernatant and the sludge were separated by standing for 7 hours in the settling tank. The sludge was automatically returned to the aeration lagoon with a pump. 1 L of raw water was added to 100 L of the supernatant water recollected here. Take this mixed solution and oxidize ozone with strong oxidizing power such as Fenton's reagent in ozone generator at 600mg / L-hr to remove color and hardly decomposable substance. Treatment was carried out. Biological treatments were used as the stationary biofilm method as in Example 1. The runoff was collected and analyzed. The results are shown in Table 5.

Example 3

3000 tons of waste leachate was digested for 10 days in an anaerobic digester, avoiding contact with air. Thereafter, they stayed in the aeration lagoon for 3 days. The supernatant and the sludge were separated by standing for 7 hours in the settling tank. The sludge was automatically returned to the aeration lagoon with a pump. 2 liters of raw water was added to 20 liters of supernatant collected here. The mixture was taken and in anticipation of a more effective oxidation reaction, ozone and hydrogen peroxide were injected together into the sample to decompose the hardly decomposable substance and then treated with activated sludge, which is one of the biological treatment methods. The runoff was collected and analyzed. The results are shown in Table 6.

As shown in the analysis results of the post-biological treatment effluent in Table 4, the ratio of BOD / CODcr after fenton oxidation is more than 0.6, which is suitable for biological treatment. Treatment efficiency of% showed an average of 98 mg / L of treated water. The CODmn of treated water averages 60mg / L, well below the 90mg / L emission limit. In this case, about 70% of CODcr was removed by Fenton treatment on the mixed solution of raw leachate and biologically treated supernatant, and 1.23g of hydrogen peroxide and Fe were removed to remove 1g of CODcr. Took. However, even if the Fenton oxidation treatment at a lower concentration of about 600 mg / L, the BOD / CODcr ratio value is more than 0.5, so a Fenton reagent of about 0.8 g is required to remove 1 g of CODcr. Fenton's oxidation reaction, on the other hand, requires a pH adjustment and a large amount of sludge occurs.

When ozone oxidation of the mixture of raw water and supernatant of Example 2 was carried out at the ratio of raw water 1: supernatant 100, the removal rate of CODmn by ozone oxidation was only about 25% and the removal rate of CODcr was about 40%. The BOD was only about 163 mg / L, a rise of about 50 mg / L, showing a BOD / CODcr ratio of only 0.31. As a result of treatment with 1-day residence time in the fixed bed biofilm reactor, CODer showed removal rate of 37-41%, and CODmn showed 28-40% removal rate. It became. The CODmn value of the treated water was 179-216 mg / L, well above the emission limit. Nevertheless, the ozone dose per 1 g of CODcr removed reached 5.2 g. Therefore, ozone oxidation was found to be unsuitable as a chemical treatment for lowering CODmn.

In the case of chemical oxidation by using ozone and hydrogen peroxide in Example 3, even in a mixed solution of raw water and supernatant mixed at 1: 10, about 64% of CODcr and about 55% of CODmn were removed and about 53% of BOD was removed. / CODcr ratio improved to 0.52 As shown in the biological treatment runoff analysis of Table 6, the treated water was treated with activated sludge method for 2 days of retention time, and the treated water of 183-204 mg / L for CODcr and 88-96 mg / L for CODmn was obtained. This CODmn concentration almost satisfies the emission limit of 90 mg / L. However, about 3 g of ozone and about 10 g of hydrogen peroxide were consumed per 1 g of CODcr removed. On the other hand, in the case of Example 2 and Example 3 there is an advantage that does not need to adjust the pH without the sludge generated during the chemical oxidation process.

As can be seen from the above, by adding a small amount of raw leachate to the supernatant after the first and second biological treatment of the leachate generated from the landfill, the chemical and biological treatment are further processed to obtain the effluent that satisfies the bleeding allowance standard. It can be seen that.

As will be claimed in the spirit of the present invention in the claims below, those skilled in the art will recognize that modifications and variations can be made to the present invention without departing from the spirit of the invention. . Therefore, such modifications and variations of the present invention will fall within the scope of the following claims.

Claims (3)

In the treatment of leachate generated from landfill, waste landfill is characterized by treating waste leachate by mixing a small amount of raw leachate with effluent that has undergone biological treatment and then proceeding chemical and biological treatment to the mixed solution. Treatment of leachate from The method of claim 1, wherein the leachate raw water is mixed in a volume ratio of 1% -15% with respect to the effluent. The method for treating leachate generated in landfills according to claim 1, wherein the Fenton oxidation method is used as a chemical treatment method.