KR101340059B1 - Reduction Method Of Excess Sludge - Google Patents

Abstract

The present invention relates to a method for reducing excess sludge, comprising the steps of reacting waste activated sludge and acid catalyst methanol generated in an activated sludge process through an aeration tank and a settling tank, and solidifying the reactants of the waste activated sludge and acid catalyst methanol. Recovering the excess sludge, extracting the fatty acid methyl ester from the liquid phase obtained through the solid-liquid separation, recovering methanol by extracting the fatty acid methyl ester and remaining liquid portion, the methanol obtained through the distillation Including the step of reacting the waste activated sludge with the acid catalyst methanol and the step of recovering the methanol and supplying the liquid portion containing the remaining solubilized sludge decomposition product to the aeration tank of the activated sludge process 60 Can be reduced by more than% and bio di The can get.

Description

Reduction Method Of Excess Sludge

In the present invention, waste activated sludge is solubilized using acid catalyst methanol without any additional pretreatment process at the place where biodiesel can be obtained and at the same time, the amount of excess sludge generated can be reduced by more than 60% and waste gas can be obtained by obtaining biogas. The present invention relates to a method for reducing excess sludge that can reduce sludge treatment costs.

Currently, wastewater, such as municipal sewage, livestock wastewater and organic factory wastewater, is mostly treated by activated sludge methods (anaerobic, aerobic and anaerobic / aerobic, etc.).

In this activated sludge process, biodegradable organic matter is converted to carbon dioxide, which is an inorganic material, and removed, but a part of the biodegradable organic matter is converted into a surplus microorganism by microbial growth and accumulated in the form of sludge.

The accumulated sludge is mainly treated by landfilling, fertilization, incineration, ocean dumping, and the like, and may cause environmental pollution when treated in the same manner as described above.

In addition, the cost of treating sludge is a significant burden that amounts to about 30 to 60% of the total cost of the biological sewage treatment process.

Therefore, various efforts have been made to reduce the excess sludge.

Conventional sewage water treatment process is a biodegradation tank consisting of anaerobic tank, aerobic tank, etc., the biologically decomposed treated water is transferred to the settling tank and the solid-liquid separation. The supernatant is then recovered, some of the precipitated sludge is returned to the bioreactor to maintain the proper microbial concentration in the bioreactor, and the remaining excess sludge is concentrated through the sludge thickening tank and dehydrated after the chemicals are added in the chemical mixing tank. Dehydrated through the tank. This dewatered cake (waste) is landfilled or incinerated.

However, the wastewater treatment process as described above has a problem in that it takes too much cost for the treatment of excess sludge.

In order to solve this problem, Korean Patent No. 0413593 discloses a sludge reduction and recycling system that reduces sludge generation by adding ozone to a portion of sludge to be returned.

However, in the above technology, when excessively large amount of sludge is transported by ozone treatment, the sedimentation of microorganisms is lowered and a serious problem occurs in the quality of treated water, so that it may not be possible to treat the entire amount of excess sludge by such a method. Accordingly, if only a part of the excess sludge is treated with ozone to reduce the sludge, the sludge reduction rate may be insignificant because only the sludge for some surplus sludge is reduced.

Therefore, there is a need for a method of reducing excess sludge that has no problem in water quality and has a high reduction rate of excess sludge.

It is an object of the present invention to solubilize waste activated sludge at the place of its production using acid catalyst methanol without any pretreatment process and at the same time to obtain biodiesel, as well as to reduce excess sludge by 60% or more. To provide.

Excess sludge reduction method of the present invention for achieving the above object is the step of reacting the waste activated sludge and acid catalyst methanol generated in the activated sludge process made through the aeration tank and the settling tank, the solid-liquid separation of the reactant of the waste activated sludge and acid catalyst methanol Recovering the precipitated excess sludge, extracting the fatty acid methyl ester from the liquid phase obtained by the solid-liquid separation, recovering methanol by extracting the fatty acid methyl ester and remaining liquid portion, obtained through the distillation And injecting methanol into the step of reacting the waste activated sludge with the acid catalyst methanol, and recovering the methanol and supplying a liquid part including the remaining solubilized sludge decomposition product to an aeration tank of the activated sludge process.

Recovering the methanol further comprises adding water to the liquid phase containing the solubilized sludge decomposition product remaining and distilling to recover the methanol.

The recovery of the methanol is repeated 2 to 4 times.

The distillation step is carried out for 0.5 to 2 hours.

The water content of the waste activated sludge generated in the activated sludge method is 60 to 90% by weight.

5 to 200 parts by weight of acid catalyst methanol is added to 1 part by weight of the waste activated sludge.

The acid catalyst methanol is added in an amount of 10 times or more (based on the weight ratio) of the water content contained in the waste activated sludge.

The acid catalyst methanol is included in 0.1 to 5 parts by weight of the acid catalyst based on 100 parts by weight of methanol.

The acid catalyst of the acid catalyst methanol is 1 to 5% (V / V) sulfuric acid.

The excess sludge reduction rate by the method for reducing excess sludge is 60 to 90%.

Excess sludge reduction method of the present invention can reduce the amount of excess sludge generated by 60% by using cryptic growth (growth using the decomposition of other cells).

In addition, since the amount of sludge generated is reduced by 60% or more, the cost of treating excess sludge is greatly reduced and economical.

In addition, the method of reducing excess sludge of the present invention can obtain biodiesel and / or biogas, which is an environmentally friendly fuel, thereby reducing the amount of excess sludge and reducing the cost of treating excess sludge.

1 is a view showing a process for reducing excess sludge in accordance with an embodiment of the present invention,
2 is a flowchart illustrating a method of reducing excess sludge in accordance with an embodiment of the present invention.
3 is a view showing the measured values of MLSS, emission COD, discharge TSS obtained according to the examples and comparative examples of the present invention in order to measure the reduction rate of the excess sludge.

The present invention not only can solubilize waste activated sludge using acid catalyst methanol at the place of its production without additional pretreatment process and at the same time obtain biodiesel, and can reduce the cost of high waste activated sludge, which can reduce the amount of surplus sludge by more than 60%. The present invention relates to a method for reducing excess sludge that can be reduced.

Hereinafter, the present invention will be described in detail.

Excess sludge reduction method of the present invention is the step of reacting the waste activated sludge and acid catalyst methanol generated in the activated sludge process made through the aeration tank and the settling tank (S110), the excess precipitate precipitated by solid-liquid separation of the reactants of the waste activated sludge and acid catalyst methanol Recovering the sludge (S120), extracting the fatty acid methyl ester from the liquid phase obtained through the solid-liquid separation (S130), extracting the fatty acid methyl ester and recovering methanol by distilling the remaining liquid portion (S140); Supplying the methanol obtained through the distillation to the step of reacting the waste activated sludge with the acid catalyst methanol (S150) and supplying an aeration tank roll of the activated sludge process to recover the methanol and the liquid part including the remaining solubilized sludge decomposition products. (S160).

The excess sludge reduction method will be described with reference to FIGS. 1 and 2.

First, in step S110, fatty acid methyl ester (FAME) is produced by solubilizing and transesterifying waste activated sludge generated in the activated sludge process (110).

The waste activated sludge is subjected to solubilization and transesterification using acid catalyst methanol to produce fatty acid methyl ester (FAME).

The waste activated sludge is obtained through the aeration tank 120 and the settling tank 130 in the activated sludge process (110).

The waste activated sludge discharged from the settling tank 130 is moved to the acid catalyst methanol reactor 140, and the acid catalyst methanol is added to the waste activated sludge in the acid catalyst methanol reactor 140 to 40 to 80 ° C., preferably 50 to 70 ° C. The solubilized waste activated sludge is solubilized by stirring for 1 to 10 hours, preferably 2 to 6 hours.

First, in step S110, fatty acid methyl ester (FAME) is produced by solubilizing and transesterifying waste activated sludge generated in the activated sludge process (110).

The waste activated sludge is subjected to solubilization and transesterification using acid catalyst methanol to produce fatty acid methyl ester (FAME).

The waste activated sludge is obtained through the aeration tank 120 and the settling tank 130 in the activated sludge process (110).

The waste activated sludge discharged from the settling tank 130 is moved to the acid catalyst methanol reactor 140, and the acid catalyst methanol is added to the waste activated sludge in the acid catalyst methanol reactor 140 to 40 to 80 ° C., preferably 50 to 70 ° C. The solubilized waste activated sludge is solubilized by stirring for 1 to 10 hours, preferably 2 to 6 hours.

If the temperature is less than the lower limit, solubilization rate of the waste activated sludge may be low. If the temperature is above the upper limit, solubilization may not be further promoted even if the temperature is high, and only the installation cost and energy cost for heating may increase.

The waste activated sludge contains 60 to 90% by weight of water based on the total weight of the waste activated sludge, and is added in an amount of 5 to 200 parts by weight, preferably 20 to 100 parts by weight of acid catalyst methanol, based on 1 part by weight of waste activated sludge. . More preferably, acid catalyst methanol of 10 times or more (by weight ratio), more preferably 10 to 50 times, even more preferably 10 to 20 times of the water content contained in the waste activated sludge is added.

When the amount of the acid catalyst methanol is less than the lower limit with respect to 1 part by weight of the waste activated sludge, the amount of the acid catalyst methanol is insignificant, so that the solubilization rate of the waste activated sludge is low and the biodiesel production is lowered. When the content is above the upper limit, methanol recovery is performed. The distillation process time is increased and methanol removal is not easy, so the biodegradability may be high.

The acid catalyst methanol used in the present invention consists of methanol and an acid catalyst such as 1 to 5% (v / v) sulfuric acid. The methanol breaks down the cell membrane by destroying the phospholipid bilayer structure of the microbial cell membrane, and the acid catalyst solubilizes the waste activated sludge by hydrolyzing the sludge floc structure with water formed by the reaction of free fatty acids and methanol present in the microorganism. do.

In addition, the acid catalyst can obtain biodiesel in addition to cell membrane decomposition by performing a transesterification reaction in which a lipid component composed of triglyceride and free fatty acid contained in the microbial cell membrane in the sludge is converted into methane ester.

The acid catalyst methanol is composed of 0.1 to 5 parts by weight of the acid catalyst based on 100 parts by weight of methanol. If the content of the acid catalyst is less than the lower limit for 100 parts by weight of methanol, solubilization is not properly hydrolyzed due to the hydrolysis of the sludge floc structure, biodiesel is not obtained, and if the acid catalyst is higher than the upper limit, the facility cost due to increased methanol recovery And operating costs may increase.

In addition, when the concentration of sulfuric acid used as the acid catalyst is less than 1% (v / v), the sludge floc structure is not hydrolyzed, solubilization is not properly achieved, biodiesel is not obtained, the concentration is 5% (v / v) ), The pH is lowered and a separate neutralization process may be required.

The methanol used in the acid catalyst methanol may be anhydrous methanol or methanol aqueous solution mixed with 0.01 to 20% of water.

The activated sludge method 110 consists of an aeration tank 120 and a settling tank 130, the aeration tank 120, aeration for 8 to 25 hours by mixing inlet water and activated sludge, such as waste water introduced, and stirred to aerobic bacteria Adsorption and oxidative decomposition of organic matter are performed. In addition, the settling tank 130 is separated into the waste activated sludge and the supernatant by leaving the fluid passed through the aeration tank 120 for 30 to 70 minutes. The separated waste activated sludge and the supernatant are discharged for 5 to 15 minutes, and the discharged waste activated sludge is mostly used for solubilizing with acid catalyst methanol, but part is returned to the aeration tank.

In the activated sludge method 110, the hydraulic residence time is fixed to 10 to 35 hours.

Next, in step S120, the waste sludge solubilized by methanol is left in the step S110 for 30 to 70 minutes to solid-liquid separation into sludge decomposed products containing solubilized organic matter and precipitated excess sludge.

The excess sludge may be recovered and sent to the anaerobic fermentation tank, or may be transferred to the dehydration tank (170).

The excess sludge transferred to the anaerobic fermentation tank may be anaerobic fermented to produce biogas under pH 7.0 to 8.0, and the biogas (methane gas) thus obtained may be collected through a separate gas storage means. In addition, the excess sludge that is not anaerobic fermentation is discharged to the outside and concentrated and discarded.

In addition, the excess sludge passed through the dehydration tank 170 is separated into a dewatering cake and a dehydration filtrate, and the dewatering filtrate is returned to the methanol extraction tank 160.

Next, in step S130, the fatty acid methyl ester is extracted from the liquid phase obtained in step S120.

Since the fatty acid methyl ester formed by the transesterification reaction of the waste activated sludge and the acid catalyst methanol in step S110 is present in the liquid phase during solid-liquid separation in step S120, the liquid phase is transferred to the separation tank 150 and then hexane, ketone and supercritical carbon dioxide Extracted into one species selected from the group consisting of to obtain a fatty acid methyl ester from the liquid portion. Thus, the yield of biodiesel obtained in the process of reducing excess sludge of the present invention is about 8 to 15%.

Next, in step S140, the fatty acid methyl ester is extracted in step S130, and the remaining sludge decomposition product and the liquid part containing methanol are distilled to recover only methanol.

Extracting the fatty acid methyl ester in step S130, the remaining liquid portion is sent to the methanol extraction tank 160 is distilled to recover the methanol. The recovered methanol is added to the step of reacting the waste activated sludge and the acid catalyst methanol (step S110) (S150) and reused. At this time, since only the methanol is not mixed with the catalyst may be added sulfuric acid separately.

In addition, almost all methanol remaining in the liquid phase is recovered by distillation by adding 10 to 30 times (by weight) water to the liquid portion including the sludge decomposed product from which methanol is extracted. This recollection process is preferably repeated 2 to 4 times.

At this time, the distillation to recover the methanol is distilled at low pressure and high temperature as compared to the distillation to recover the first methanol. Specifically, methanol is first distilled at a pressure of 300 to 400 mbar and a temperature of 60 to 75 ° C., but distillation is performed at a pressure of 120 to 180 mbar and a temperature of 80 to 95 ° C. for two or more distillations.

The time of one distillation in step S140 is carried out for 0.5 to 2 hours, preferably 0.5 to 1 hour. When the distillation time is below the lower limit, the removal of methanol is not sufficient, and when the distillation time is exceeded, the energy cost increases.

Next, in step S160, the liquid part including the remaining solubilized sludge decomposition product after methanol recovery in step S140 is returned and supplied to the aeration tank of the activated sludge method using a circulation pump (not shown).

The reduction rate of excess sludge reduced by this method is 60 to 90%, preferably 60%.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

Example 1.

Inlet water (wastewater) and activated sludge introduced into the aeration tank of the activated sludge process are aerated for 23 hours, transferred to the settling tank, and left for 50 minutes to be separated into waste activated sludge and supernatant. The supernatant and waste activated sludge are discharged for 10 minutes, and the waste activated sludge residence time is maintained at 14 days by discharging 100 ml / day of waste activated sludge in a mixed liqueur form. At this time, the dissolved oxygen concentration is maintained at 5 mg / l or more. After the discharged waste activated sludge was transferred to an acid catalyst methanol reactor, 50 g of acid catalyst methanol (0.2 parts by weight of 5% (v / v) sulfuric acid) based on 100 parts by weight of methanol was added to 5 g of waste activated sludge (water content of 4 g). The waste activated sludge is solubilized by addition and stirring at 65 ° C. for 2 hours. The solubilized waste sludge was extracted with hexane to obtain a fatty acid methyl ester, and methanol was recovered by extracting once at 75 ° C. at a pressure of 300 mbar using a rotary evaporator (Buchi R-205, Buchi Scientific). The recovered methanol is reused when solubilizing the waste activated sludge.

In addition, excess sludge obtained from the solubilized waste sludge is transferred to an anaerobic fermentation tank. The excess sludge transferred to the anaerobic fermentation tank was mixed with anaerobic microorganisms at 35 ° C. and increased to 0.7 ° C. per day for 15 days while maintaining pH 7.5. The remaining sludge that had not been fermented was discharged and discarded.

The COD of the influent is 357 mg O ₂ / l, the feed load is 0.25 kgCOD / ㎥day.

Example 2.

The same process as in Example 1 was carried out, but instead of extracting the solubilized waste sludge once at 75 ° C. for 1 hour to recover methanol, the process was performed by extracting methanol twice per hour. At this time, the extraction twice, methanol is extracted once, 100 ml of distilled water is added to the remaining waste sludge, and methanol is distilled off at a pressure of 150 mbar at 85 ° C.

Example 3.

The same procedure as in Example 1 was carried out, but instead of extracting the solubilized waste sludge once at 75 ° C. for 1 hour to recover methanol, the process was performed by extracting methanol three times per hour. At this time, two times and three times, 100 ml of distilled water was added, and methanol was distilled off at a pressure of 150 mbar at 85 ° C.

Comparative Example 1

In the same manner as in Example 1, instead of adding the acid catalyst methanol to the waste activated sludge, 7 g / l of sodium hydroxide was added and stirred at 121 ° C. for 30 minutes to proceed with the process.

The COD of the influent is 357 mg O ₂ / l, the feed load is 0.25 kgCOD / ㎥day.

Comparative Example 2

In the same manner as in Example 1, instead of adding 50 g of acid catalyst methanol to 5 g of waste activated sludge (water content of 4 g), 17 g was added to proceed the process.

Comparative Example 3

The process was carried out in the same manner as in Example 1, but using anhydrous methanol instead of the acid catalyst methanol.

Comparative Example 4

In the same manner as in Example 1, but using sulfuric acid / water instead of the acid catalyst methanol was carried out the process.

Test Example 1. Measurement of solubility of waste sludge

In Examples and Comparative Examples, solubilization (SCOD / TCOD) was measured by measuring TCOD (DR5000, Hach Company) and SCOD (DR5000, Hach Company) by diluting methanol solubilized waste sludge 100 times with distilled water. This is shown in Table 1 below.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 TCOD (mgO ₂ / ℓ) 664 ± 11 602 ± 11 597 ± 8 507 ± 2 666 ± 12 675 693 SCOD (mgO ₂ / ℓ) 414 ± 10 396 ± 11 390 ± 8 383 ± 8 381 ± 6 172 273 Solubility degree 0.62 0.66 0.66 0.76 0.57 0.26 0.39

As shown in Table 1, the solubilization of the solubilized sludge prepared by the production method of Examples 1 to 4 of the present invention was found to be 0.62 to 0.66. The solubility levels of 0.62 and 0.66 mean that 62% and 66% of the waste activated sludge was solubilized.

On the other hand, Comparative Examples 3 and 4 using anhydrous methanol or sulfuric acid / water instead of acid catalyst methanol were found to show low solubilization rate.

Test Example 2 Measurement of Reduction Rate of Excess Sludge

In the Examples and Comparative Examples, if the liquid portion containing sludge decomposed product was returned to the aeration tank, 180 mg (90 mg / lday of sludge loading per volume of the aeration tank) gradually increased MLSS (mg / l of the average suspended solid concentration of the mixed liquid in the aeration tank). After reaching the steady state, the MLSS, COD of discharged water and TSS (total suspended solids) (tested according to test standard method of water and wastewater) were measured and shown in Table 3 below.

The excess sludge generation rate is calculated by calculating [(MLSS * amount of waste activated sludge daily)-amount of returned sludge decomposition product].

division MLSS (mg / l) Emission Water COD
(MgO ₂ / ℓ) Emission water TSS (mg / L) Excess sludge generation rate (mg / day) Example 1 2588 34 42 79 Comparative Example 1 2017 29 43 202

As shown in Table 2 and FIG. 3, it can be seen that the generation rate of excess sludge according to Example 1 of the present invention has a excess sludge reduction rate of 60% since it is 79 mg / Lday.

On the other hand, Comparative Example 1 was confirmed that the excess sludge is not reduced because the rate of generation of excess sludge is 202 mg / lday.

Test Example 3 Production Yield of Biodiesel

In the Examples and Comparative Examples, the biodiesel extracted with hexane was evaporated for 20 minutes with a rotary evaporator set at a pressure of 320 mbar and a temperature of 60 ° C., and then the impurities were removed using nitrogen gas for 1 minute, and then the mass was measured. The yield of biodiesel from the content of waste activated sludge was obtained.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Biodiesel yield (%) 10.6 11.4 11.6 - 4.0 3.6 -

As shown in Table 3, the yield of the biodiesel produced according to the method according to Examples 1 to 3 of the present invention was 10% or more, but Comparative Examples 1 and 4 were confirmed that no biodiesel was produced.

In Comparative Examples 2 and 3, it was confirmed that biodiesel is produced at 4% or less.

100: continuous batch reactor 110: activated sludge method
120: aeration tank 130: sedimentation tank
140: acid catalyst methanol reactor 150: separation tank
160: methanol extraction tank 170: dehydration tank

Claims (8)

Reacting 1 part by weight of the waste activated sludge generated by the activated sludge method, which is formed through the aeration tank and the precipitation tank, with 5 to 200 parts by weight of the acid catalyst methanol;
Recovering the precipitated excess sludge by solid-liquid separation of the reactants of the waste activated sludge and the acid catalyst methanol;
Extracting the fatty acid methyl ester from the liquid portion obtained through the solid-liquid separation;
Extracting the fatty acid methyl ester and distilling the remaining liquid portion to recover methanol;
Adding methanol obtained by the distillation to reacting the waste activated sludge with the acid catalyst methanol; And
Recovering the methanol and supplying the liquid portion containing the remaining solubilized sludge decomposition product to the aeration tank of the activated sludge process, reducing the excess sludge generated in the activated sludge process. The method of claim 1, further comprising the step of adding water to the liquid portion containing the remaining solubilized sludge decomposition product after distillation of methanol and distillation to recover the methanol, the excess sludge is repeated 2 to 4 times. Reduction Method The method for reducing excess sludge according to claim 1 or 2, wherein the distillation step is performed for 0.5 to 2 hours. The method of claim 1, wherein the water content of the waste activated sludge generated by the activated sludge method is 60 to 90% by weight. delete The method of claim 1, wherein the acid catalyst methanol comprises 0.1 to 5 parts by weight of the acid catalyst based on 100 parts by weight of methanol. The method of claim 1, wherein the acid catalyst of methanol is 1 to 5% (V / V) sulfuric acid. The method for reducing excess sludge according to claim 1, wherein the reduction ratio of excess sludge reduced by the method for reducing excess sludge is 60 to 90%.

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