KR20180011405A - Preparation method of biodiesel using waste water sludge - Google Patents

Abstract

The present invention provides a preparation method of biodiesel using waste sludge, which comprises the following steps: (1) mixing alcohol and an acid catalyst in the waste sludge to perform an esterification conversion reaction; (2) cooling the mixture to room temperature after completion of the reaction and performing centrifugation; (3) collecting a supernatant solution obtained through a centrifugation process; (4) adding hexane to the collected supernatant solution to perform layer separation; (5) separating the hexane layer, washing the hexane layer with distilled water to remove impurities, and adding a moisture scavenger to remove residual moisture; and (6) recovering hexane using an evaporator to obtain residual biodiesel. According to the present invention, the yield of the esterification reaction is improved by using waste sludge having high moisture content.

Description

[0001] The present invention relates to a method for producing biodiesel using waste sludge,

The present invention relates to a method for producing biodiesel using waste sludge, and more particularly, to a method for producing biodiesel using waste sludge, in which an esterification reaction is effectively carried out using sludge having a high moisture content or a high oil content and a positive effect on a subsequent anaerobic digestion process The present invention relates to a method for producing biodiesel using waste sludge, which can provide biodiesel having an improved efficiency compared to conventional methods.

In Korea, energy imports are highly dependent on the importance of bio-energy in terms of energy security, but stable supply and demand of raw materials should be solved first. The domestic bio-energy technology level is estimated to be 75.7% of the US as of 2013, and bio-diesel is the closest among the related technologies. Looking at domestic biodiesel producers, SK Chemicals is the largest with 120,000 tons / year, commercializing biodiesel in the Danseok, Aekyung, and M energy industries. On the other hand, the energy technology of sewage sludge has been developed and applied mainly for anaerobic digestion and dry fuel conversion, and a total of 68 sites of anaerobic digestion tanks are currently in operation, including the digestion tanks applying the combined digestion. In the case of anaerobic digestion technology, there are limitations in the hydrolysis and methane generation stages, and efforts to develop technologies to overcome these limitations have been made steadily. However, in most of the anaerobic digestion facilities, Along with the dissemination of anaerobic digesters, we are carrying out a project to improve digesters to improve efficiency. In the case of dry fueling technology, the infrastructure for sludge solidification facilities for the sake of the sewage sludge power plants is established and operated nationwide, and the utilization rate of sludge as a raw material for the power plant is about 45% nationwide. However, in the case of drying fuel, it is necessary to solve the problem of odor generated in the process of excessive use of energy and drying during drying due to excessive amount of moisture.

Development of sludge biodiesel production technology is limited because it is a wet raw material with very high moisture content along with impurities (bacterial maintenance, wax, steroid, etc.) when compared to other raw materials. The moisture contained in the sludge is a major cause of the biodiesel yield and quality deterioration due to the reverse reaction in the esterification reaction as well as the ionization of the alcohol and the activation of the catalyst. Conventional sludge biodiesel technology requires freezing and drying pretreatment of raw materials in order to minimize moisture disturbance, but it is a major cause of increasing the cost of biodiesel production by consuming excessive energy, which accounts for more than 30% of total biodiesel production process . Therefore, it is necessary to overcome these problems, so that the biodiesel produced from sludge biomass can secure competitiveness with petroleum diesel. Therefore, efficient water exclusion technology should be developed during the esterification reaction.

On the other hand, even if the above-mentioned technologies are developed, the unconditional exclusion of moisture may lead to a decrease in the hydrolysis efficiency upon anaerobic digestion in the treatment of the biodiesel extract residue, which may significantly degrade the biogas quality. Specifically, water in the production of biodiesel acts as a factor for inhibiting the esterification reaction, but acts as a positive factor for hydrolysis of the organic matter in the anaerobic digestion, so that the unconditional elimination of water lowers the biogas production efficiency, There is a problem that the connection with the anaerobic digestion process is deteriorated.

Therefore, it is necessary to develop sewage sludge reduction / energy reduction technology that integrates the optimization of the catalyst from the non-drying high moisture sludge and the efficient water exclusion system during the esterification reaction and the recovery of the biofuel of the biodiesel extraction residue. .

DISCLOSURE Technical Problem The present invention has been made to solve the problems of the prior art as described above, and it is an object of the present invention to provide a method and apparatus for efficiently performing an esterification reaction using a waste sludge having a high water content, The present invention also provides a method of manufacturing biodiesel using waste sludge which can provide biodiesel with an improved efficiency compared with the conventional biodiesel.

The technical problem of the present invention as described above is achieved by the following means.

1. (1) mixing alcohol and an acid catalyst to waste sludge to perform an esterification conversion reaction; (2) cooling to room temperature after completion of the reaction and centrifuging; (3) collecting the supernatant obtained through the centrifugation process; (4) adding hexane to the collected supernatant to perform layer separation; (5) separating the hexane layer, washing it with distilled water to remove impurities, and removing moisture to remove residual water; And (6) recovering hexane by using an evaporator to obtain residual biodiesel.

2. The method for producing biodiesel using waste sludge according to claim 1, wherein the concentration of the acid catalyst is 4-6% (v / v) based on the volume of alcohol.

3. The method for producing biodiesel using waste sludge according to claim 1, wherein the reaction temperature is 55 to 65 ° C.

4. The method for producing biodiesel using waste sludge according to claim 1, wherein the reaction time is 6 to 8 hours.

5. The method for producing biodiesel using waste sludge according to claim 1, wherein the mixing ratio of alcohol and sludge in step (1) is 5 to 15 (v / w).

6. The method for producing biodiesel using waste sludge according to claim 6, wherein n-hexane is recovered at 30 to 50 ° C and 150 to 200 rpm using a rotary evaporator.

7. The method for producing biodiesel using waste sludge according to claim 1, wherein in step (1), the alcohol is methanol, the acid catalyst is sulfuric acid, and the reaction is maintained at a pH of 1-2.

8. The method for producing biodiesel using waste sludge according to claim 1, wherein the moisture content of the dried sludge is 30 to 50%.

According to the present invention, it is possible to improve the yield of the esterification reaction using waste sludge having a high water content, and to provide a positive effect on the subsequent anaerobic digestion process, Can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram of a biodiesel production process according to an embodiment of the present invention; FIG.
FIG. 2 is a graph showing an experimental result showing the yield of biodiesel according to the change of the acid catalyst concentration. FIG.
FIG. 3 is a graph showing an experimental result showing biodiesel yield (H ₂ SO ₄ concentration 5%) by reaction time.
FIG. 4 is a graph showing an experimental result showing the yield of biodiesel according to the amount of the solvent.
FIG. 5 is a graph showing experimental results showing the yield of biodiesel according to the reaction temperature.
FIG. 6 is a graph showing experimental results showing changes in yield of biodiesel according to the methanol: sludge ratio.
FIG. 7 is a graph showing the results of a comparison of yields of biodiesel according to the catalyst concentration of dehydrated caked (dairy product).
FIG. 8 is a graph showing the results of biodiesel production according to dehydration CAKE (dry) reaction time of food (dairy product).
9 is a graph showing experimental results showing the yield of biodiesel according to reaction time of crude sludge pressurized with food (dairy product).

The method for producing biodiesel according to the present invention comprises the steps of: (1) performing an ester conversion reaction by mixing alcohol and an acid catalyst in waste sludge; (2) cooling to room temperature after completion of the reaction and centrifuging; (3) collecting the supernatant obtained through the centrifugation process; (4) adding hexane to the collected supernatant to perform layer separation; (5) separating the hexane layer, washing it with distilled water to remove impurities, and removing moisture to remove residual water; And (6) recovering hexane using an evaporator to obtain residual biodiesel.

The alcohol and the acid catalyst are mixed to perform the ester conversion reaction to the waste sludge in the step (1). The reason for using the acid catalyst is that since the content of free fatty acid (FFA) in the waste sludge is high, the saponification reaction can proceed when the base catalyst is used. Examples of the alcohol include methanol, ethanol, propanol, butanol, and amyl alcohol. Of these, methanol and ethanol are preferable, and methanol is more preferable. As the acid catalyst, sulfuric acid, nitric acid, phosphoric acid, acetic acid, formic acid and the like can be used, and sulfuric acid is preferable.

At this time, the mixing ratio of the alcohol and sludge is 5 to 15 (v / w), preferably 10 (v / w), the concentration of the acid catalyst is 4 to 6% (v / v) Is preferably 5% (v / v).

The ester conversion reaction is preferably carried out at a reaction temperature of 55 to 65 ° C, preferably 60 ° C, and a reaction time of 6 to 8 hours, preferably 7 hours, after mixing the reactants. At this time, it is preferable to perform the reaction under conditions where the pH of the reactant is fixed at 1.0 to 2.0, preferably at pH 1.0.

Conventionally, a technique of adding a co-solvent (hexane, etc.) having a low boiling point at the time of the reaction to increase the efficiency of the ester reaction has been disclosed. However, in this case, since the reaction temperature must be lower than 50 ° C, And the co-solvent evaporates at about 60 ° C in order to increase the yield of biodiesel in about 20 minutes, so that it can not be used. In this case, toluene and xylene having a high boiling point can be used as co-solvents. However, in this case, an increase in the unit price of the product leads to an economical problem, and it is difficult to remove it in the refining process.

In the present invention, as described above, it is possible to increase the production yield of biodiesel by a simple process by controlling reaction variables such as temperature condition, addition ratio of reactant and acid catalyst, and reaction time.

When the esterification conversion reaction of the step (1) is completed, the reaction mixture is cooled to room temperature and a centrifugation process is performed. In the present invention, centrifugation is preferably performed at 2000 to 4000 rpm for 5 to 10 minutes in order to minimize the influence of the solid content of the sludge in the recovery of biodiesel.

The biodiesel is contained in the supernatant obtained through centrifugal separation as described above. Only the supernatant is collected and the solvent is added to perform the layer separation. In the present invention, hexane (n-hexane) is used as the solvent. Biodiesel is dissolved in the layered hexane layer. As described above, in the present invention, hexane does not participate in the reaction as a conventional solvent as in the prior art (in this case, the reaction temperature is limited), and is used as a solvent for dissolving biodiesel to increase the yield of final biodiesel . At this time, the addition ratio of alcohol and hexane is preferably 10 to 60 (v / v). When the addition ratio is less than 10, the yield is very low. When the addition ratio is more than 60, the yield is increased, but when the addition ratio is more than 60, the yield is lowered. Separate the hexane layer separately and rinse with distilled water 2-3 times to remove impurities to increase the purity.

Thereafter, residual water is removed by adding anhydrous sodium sulfate to the hexane layer from which the impurities have been removed, as a water removing agent, preferably anhydrous sodium sulfate. The n-hexane recovered at 30 to 50 ° C and 150 to 200 rpm using a rotary evaporator can be recovered and the residual biodiesel can be obtained.

The dried sludge used in the step (1) of the present invention may be a sludge having a moisture content of 80% or more (sewage sludge, food wastewater sludge, dehydrated sludge generated in an automobile part production process, or food wastewater sludge) Is adjusted to a water content of 60% or less, preferably 30 to 50%, which can improve the decomposition efficiency of the organic matter in the anaerobic digestion tank while enhancing the ester conversion efficiency of the subsequent reaction. When the esterification reaction using the acid catalyst is performed using the dried sludge prepared by pretreating the water content to 30 to 50% as described above, the saponification reaction is inhibited to maximize the ester conversion efficiency, and the subsequent anaerobic digestion process So that it is possible to maintain the required moisture content required by the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, these Examples are presented for the purpose of illustrating the present invention, and the scope of the present invention is not limited to these Examples.

[Experimental Example]

In this experiment, first, second and dehydrated sludge samples were collected from A sewage treatment plant and S sewage treatment plant in Chungnam for biodiesel production from sludge. In case of primary and secondary sludge, in order to check the effect of coagulant during the production of biodiesel, coagulation sedimentation was carried out by jar-test, followed by centrifugation and drying at 60 ° C for about 2 days together with dehydrated sludge. Dry sludge was made into powder form with a mixer and tested. A sewage treatment plant is a facility that operates digesters unlike S sewage treatment plants for sludge treatment.

In order to confirm the effect of biodiesel yield due to the influence of oils and fats on the production of biodiesel, pressurized floating sludge, transport sludge, and dewatered sludge (dry / non-dried) of Y food wastewater (oil industry) , And the dehydrated sludge was dried / non-dried, and the pressurized floating sludge was used with 60 ° C dry sludge and gravity concentration. Activated sludge was collected by centrifugation, dried at 60 ℃, and sludge was pulverized into powder form.

Food wastewater was collected at the resource facility in Chungnam. The wastewater from the food wastewater was obtained by three-phase centrifugation (water, oil, sludge).

[Experimental Process]

Experiments were carried out in the same order as in Fig. 1 in order to find optimum biodiesel conversion conditions from the conditions presented using sewage sludge samples. In this case, as the sludge, there are (1) primary sludge, (2) secondary sludge, (3) secondary sludge and organic polymer coagulant, (4) secondary sludge and inorganic coagulant (ferric chloride), (5) dehydrated sludge, (Dry / non-dried), ⑦ food wastewater dehydrated sludge, ⑨ drinking water (water separation from food wastewater), and ⑧ automobile parts production process wastewater sludge.

In order to derive optimal reaction conditions for the production of biodiesel from the above-mentioned sludge, various reaction conditions were set as shown below. In the case of the catalyst, since the free fatty acid (FFA) is generally high in the sludge, the acid catalyst H ₂ SO ₄ is fixed in consideration of the saponification reaction through the base catalyst. The setting conditions for biodiesel conversion are as follows.

- Catalyst concentration: 0.25, 1, 5, 7, 10% (catalyst / methanol, Volume / Volume)

- Reaction time: 3, 5, 7, 10 hr

- Reaction temperature: 40, 50, 60, 70 ℃

- Methanol and dry sludge ratio: 10, 15, 20 (Volume / Weight)

- methanol and normal hexane: 10, 20, 40, 60 (Volume / Volume)

(1) ester conversion reaction

The prepared sludge and waste oil were weighed (10 g) according to the conditions and injected into a 500 mL round bottom flask. Methanol was then added to the reaction mixture to adjust the pH to 1 by the addition of 5 mL of H ₂ SO ₄ as an acid catalyst. The flask was connected to a cooling device, water was added at a set temperature, and the mixture was stirred.

(2) Extraction of FAME components

After the reaction was completed, the flask was removed from the cooling apparatus after cooling to room temperature. In order to minimize the influence of sludge solids during biodiesel recovery, the supernatant was collected by centrifugation at 3000 rpm for 5 minutes, and the solvent was distilled off by adding hexane (n-hexane) as a solvent to the 1 L fractionation funnel.

(3) Evaporation of normal hexane using a rotary evaporator

At this time, the layered hexane (n-hexane) layer of the upper layer contains biodiesel. The hexane layer was separated, washed several times with distilled water to remove impurities, and then anhydrous sodium sulfate was added to remove residual water. Then, n-hexane was recovered at 40 ° C and 150 ~ 200 rpm using a rotary evaporator, and residual biodiesel was analyzed. The following formula was used for biodiesel yield analysis.

In order to evaluate the FAME content of the produced biodiesel, the biodiesel produced from the sludge was analyzed by applying the method of "Fat and oil derivative-fatty acid methyl ester (FAME) -ester and linolenic acid methyl ester content analysis method" and analyzed using a chromatograph Flame ionization Dectecter (GC-FID, YL6500 GC system, Youngin Instrument). Methyl heptadecanoate as an internal standard substance was dissolved in heptane and used. Analytical column was Agilent HP-1 (30m × 0.32mm × 0.25um, USA) and N ₂ gas was used as carrier gas. The oven temperature was maintained at 60 캜 for 2 minutes, then heated to 310 캜 at 5 캜 / min and held for 5 minutes. Sample injection volume was analyzed with 1 uL and split less conditions.

[Experiment result]

1. Biodiesel conversion experiment from sewage sludge

(1) Effect of catalyst type

In this experiment, in order to investigate the reduction of biodiesel yield due to the saponification phenomenon due to the presence of a high proportion of free fatty acid (FFA) in the reaction with the base catalyst, KOH and H ₂ SO ₄ as a base catalyst were added to methanol in an amount of 5% , And the biodiesel conversion experiment was carried out at a reaction temperature of 60 ° C, a methanol / sludge ratio (v / w) of 10, and a reaction time of 3 hours. Base catalyst and the result of comparing the biodiesel yield of the acid catalyst, a base catalyst (KOH) and acid catalyst (H ₂ SO ₄₎ respectively the biodiesel yield of the acid catalyst to an average of 0.9% and an average 2.2% (H ₂ SO ₄₎ from about 2 times or more High biodiesel yield was obtained. In this experiment, the optimal catalyst for the conversion of biodiesel to sludge was assumed to be acid catalyst, and all biodiesel conversion experiments proceeded with acid catalyst (H ₂ SO ₄ ).

(2) Effect of catalytic reaction

It was also observed that white crystals were formed when the biodiesel product was left at room temperature for a long time. These white crystals were caused by white lattice elements in the sludge feedstock that could not be converted to biodiesel due to insufficient catalytic amount during the transesterification reaction for biodiesel conversion. It is considered that the addition of an appropriate amount of catalyst to cause a sufficient reaction in the conversion of biodiesel from sludge acts as an important influential factor.

(3) Effect of catalyst concentration

The results of the previous experiments confirm that sufficient catalyst should be present in the reaction for the sufficient biodiesel conversion of the lipid component during biodiesel conversion. Since biodiesel conversion reaction temperature to derive the optimum condition for the catalyst concentration 60 ℃, methanol and sludge ratio (v / w) 100: 10 , the reaction time 3hr, the acid catalyst _{(H 2 SO 4) 0.25,} 1, 5, 7 , And 10%, respectively.

Experimental results show that the biodiesel yield tends to increase with increasing catalyst concentration and the average yield of biodiesel is 3.9% at the concentration of 5% of acid catalyst (H ₂ SO ₄ ). Acid catalyst showed a tendency to decrease in the yield of biodiesel (H ₂ SO ₄₎ concentration of 5% or more, an acid catalyst (H ₂ SO ₄₎ in a concentration of 10% biodiesel is Yield The results of 3.4%. These results suggest that the carbon bond of the substance to be converted into biodiesel in the sludge is disassembled due to the excess supplied acid catalyst.

In addition, it was confirmed that the biodiesel product formed by the reaction in the presence of a sufficient catalyst does not form white crystals due to the presence of the lipid component even if left at room temperature for a long time. Figure 2 shows the concentrations of biodiesel yield of the acid catalyst (H ₂ SO _4).

(4) Biodiesel yield by reaction time with optimum catalyst concentration

Reaction time in biodiesel conversion is an important influence factor. In this experiment, biodiesel conversion experiment was performed by changing the reaction time to evaluate the biodiesel yield change according to the reaction time during biodiesel conversion. Biodiesel conversion conditions were as follows: 5% of acid catalyst (H ₂ SO ₄ ), 60 ° C of reaction temperature, 100:10 of methanol and sludge ratio (v / w), 100% of methanol and N-hexane ratio, 10, and reaction times 3, 5, 7, and 10 hr. As a result of the experiment, the yield of biodiesel increased to 4.0% until 7 hours of reaction, and the yield of biodiesel decreased to 3.3% after 10 hours of reaction. The optimal reaction time was determined to be 7 hr, and the yield of biodiesel by reaction time was shown in FIG.

(5) Solvent effect

It has been reported that biodiesel yield is improved by solubility enhancement of lipid according to addition of solvent in the reaction process during biodiesel conversion. Based on the results, we conducted a biodiesel conversion experiment according to the amount of solvent added to determine the yield change of biodiesel depending on the amount of solvent added. The experimental conditions for biodiesel conversion were as follows: acid catalyst (H ₂ SO ₄ ) 5%, reaction temperature 60 ° C, reaction time 7 hr, methanol and sludge ratio (v / w) (100: 10, 100: 20, 100: 40, 100: 60) of methanol and solvent N-Hexane ratio (v / v) And the biodiesel was extracted. As a result, the yield of biodiesel was found to be 6.2% in solvent 100: 60, and the yield of biodiesel increased with increasing amount of solvent. FIG. 4 shows the yield of biodiesel according to the amount of the solvent added.

(6) Effect of reaction temperature

The reaction temperature during biodiesel conversion is a major influencing factor in relation to the yield of biodiesel product. Using the dewatered sludge drying in order to assess the effect of the reaction temperature the acid catalyst _{(H 2 SO 4) 5%} , methanol and sludge ratio (v / w) 100: 10 , of methanol and N-Hexane ratio of 10: 1, reaction time 7 hr, and reaction temperatures of 40, 50, 60, and 70 ° C. As a result, the biodiesel yield was 4.0% at the reaction temperature of 60 ℃. The yield of biodiesel was improved up to 60 ℃ and the yield of biodiesel was decreased at over 60 ℃. At temperatures above 60 ℃, it is considered that the carbon bonds affecting the yield of biodiesel conversion in sludge components are disassembled. FIG. 5 shows the yield of biodiesel according to the reaction temperature.

(7) Effect of Methanol and Sludge Ratio

The mixing ratio of methanol and sludge, which is the main material used for biodiesel conversion, is an important factor in the conversion process of biodiesel. In this experiment, 5% of acid catalyst (H ₂ SO ₄ ), 10: 1 of methanol and N-hexane ratio, 7 hr of reaction time were used to derive the optimal mixing ratio of methanol and sludge ratio , And a methanol and sludge volume (weight: 100: 20, 100: 5, 100: 10, 100: At the ratio of 100: 15 and 100: 20 in the experimental procedure, the dried sludge absorbed methanol and the fluidity was decreased. As a result, it was confirmed that proper mixing was not achieved during the biodiesel conversion process. Experimental results showed that the yield of biodiesel increased with increasing methanol and sludge ratio, and the highest biodiesel yield was 4.0% at methanol and sludge ratio of 100: 10, and the methanol and sludge ratio increased above 100: 10 The yield of biodiesel was decreased (see FIG. 6). The reason for the decrease in the yield of biodiesel due to the increase of the sludge ratio is that a high proportion of the sludge absorbs excess methanol in the process of biodiesel conversion and forms into an emulsion form which adversely affects the biodiesel extraction process of the reaction product .

(8) Derivation of optimal reaction conditions for biodiesel conversion

Based on the results of the biodiesel yield evaluation, the optimal conditions for biodiesel conversion in sludge were derived. Biodiesel yields were different depending on the catalyst concentration, reaction temperature and time, and the mixing ratio (v / w) of methanol and sludge, and the yield of biodiesel was increased depending on the amount of solvent added. Optimum conditions for the conversion of biodiesel were 5% of H ₂ SO ₄ , 7 hr of reaction time, 60 ℃ of reaction temperature, and 100: 10 ratio of methanol to sludge (v / w) The yield of biodiesel increased. The table below shows the optimal conditions for biodiesel conversion.

Optimal reaction conditions for biodiesel conversion Acid catalyst concentration
(H ₂ SO ₄₎ Reaction temperature  Reaction time With methanol
Sludge mixing ratio Amount of solvent added 5% 60 ° C 7hr 100: 10
(volume: weight) more the better

(9) Effect of coagulant on biodiesel production

In order to investigate the effect of coagulant during the production of biodiesel, this experiment was divided into organic coagulant and inorganic coagulant. As an organic coagulant, a polymer used for improving the dewatering ability in a wastewater treatment facility was used. The effect of organic coagulant and inorganic coagulant on biodiesel yield was evaluated using ferric chloride (FeCl ₃ ) as an inorganic coagulant.

1) Effect of polymer (organic polymer flocculant)

Primary sludge and secondary sludge were used in the sewage treatment process to evaluate the effect of polymer (organic polymer flocculant) on biodiesel conversion. Polymer was prepared by using Kang Yang 's ionic polymer, and the yield of biodiesel before and after the coagulant application was evaluated. Biodiesel when switching experimental conditions an acid catalyst _{(H 2 SO 4) 5%} , methanol and sludge ratio (v / w) 10, of methanol and N-Hexane ratio of 10: 1, reaction time experiment set to 7hr, the reaction temperature 60 ℃ Respectively. The conversion of primary sludge to biodiesel showed 14.2% biodiesel yield. In the case of primary sludge injected with polymer, the yield of biodiesel increased by 16.7% due to coagulant.

In the case of secondary sludge, the biodiesel yield was 4.6% and the secondary sludge injected with polymer was 3.7%, indicating that the yield of biodiesel decreased due to the effect of coagulant. The results of application of coagulant of primary sludge and secondary sludge are shown in the figure below.

2) Influence of ferric chloride (inorganic coagulant)

In order to evaluate the effect of inorganic coagulants on the conversion of biodiesel, ferric chloride was used as an inorganic coagulant to evaluate the yield of biodiesel before and after the coagulant application. For the application of inorganic flocculant, 38% aqueous solution of ferric chloride was injected into the secondary sludge of sewage treatment plant in Chungnam S with caustic soda, and the optimum amount of flocculant was set by jar test. Collected, centrifuged and dried.

Experiments were carried out under the conditions of 5% H2SO4, 10 methanol / sludge ratio (v / w), 10: 1 methanol / N-hexane ratio, . Experimental results show that the yield of biodiesel before and after applying the coagulant is 4.2% and 1.8%, respectively, and the yield of biodiesel is decreased due to the effect of ferric chloride.

2. Biodiesel conversion experiments from food (dairy) wastewater sludge

(1) Comparison of dried (non-dried) dehydrated cake of food (dairy product) wastewater

The yield of biodiesel was measured in the absence of drying of the food (dairy product) wastewater dehydrated cake with a moisture content of 81.8% in order to eliminate the cost of drying the dehydrated cake of the sewage sludge and wastewater sludge and the inconvenience of the drying process.

Food (dairy product) TS, VS test result and dehydrated cake moisture test result Name of sample TS (%) VS (%) Moisture content (%) Average(%) Food (dairy products)
Dehydrated cake
18.59 62.86 81.4 81.8 18.11 60.65 81.9 17.87 60.09 82.1

(2) Biodiesel conversion experiment according to catalyst concentration in food (dairy product) wastewater dehydrated cake

In order to investigate the yield of biodiesel according to the catalyst concentration, the experiment was carried out with varying catalyst concentration. Dehydration of food (dairy product) wastewater treatment process Drying of CAKE at 65 ℃ for 24hr, methanol and sludge ratio (v / w) 100: 10, methanol and N-hexane ratio 10: 1, reaction time 3hr, reaction temperature 60 ℃, (H ₂ SO ₄ ) were set to 0.25%, 1%, 3%, 5% and 10%, respectively. As a result, the yield of biodiesel at the concentration of 5% of acid catalyst (H ₂ SO ₄ ) was the highest at 10.7% (see FIG. 7).

(3) Biodiesel conversion experiment with food (dairy) wastewater sludge reaction time

The biodiesel yield from biodiesel production from sewage sludge is about 16% of the primary sludge. The primary sludge is known to show a large variation in biodiesel yield depending on the sewage inflow characteristics of the region. Only the primary sludge is selected It is practically difficult to apply a process of dehydration / drying. The secondary dewatered sludge, which is relatively easy to secure in the sewage treatment process, has a biodiesel yield of about 5.5%, which is lower than that of the primary sludge.

Therefore, in this experiment, biodiesel conversion experiment was carried out in food (dairy product) wastewater sludge because it contains a large amount of oil because of the nature of raw materials and it is considered that biodiesel yield will be higher than that of sewage sludge during biodiesel production.

In order to compare the biodiesel yields of the biodiesel conversion of food (dairy product) wastewater sludge, dehydrated CAKE in the food (dairy) wastewater treatment process was dried at 65 ° C for 24 hours to obtain 5% of acid catalyst (H ₂ SO ₄ ) The reaction conditions were set at a sludge ratio (v / w) of 100: 10, a methanol / N-hexane ratio of 10: 1, a reaction time of 3 hours, 5 hours, 7 hours and 10 hours. Experimental results showed the highest yield of biodiesel at 8.7% at 7 hr (see FIG. 8).

(4) Food (dairy) wastewater sludge Pressurized floating sludge Biodiesel yield comparison

In order to compare the yields of dewatered cake and pressurized floating sludge during biodiesel conversion of food (dairy) wastewater sludge, pressurized floating sludge was dried and biodiesel yield was measured. The pressurized floatation sludge in the food (dairy) wastewater treatment process was dried to obtain a mixture of 5% of acid catalyst (H2SO4), 100:10 of methanol and sludge ratio (v / w), 10: 1 of methanol and N-hexane ratio, , 7 hr, 10 hr. The reaction temperature was set to 60 ° C. Experimental results showed that the yield of biodiesel was the highest at 10.3% at reaction time 7 hr (see FIG. 9). It can be seen that the pressurized floating sludge is better suited for the biodiesel extraction condition because the biodiesel yield is about 1.6% higher than the dehydrated cake dry sludge.

After drying a conveying sludge and dehydrated sludge of dairy wastewater treatment processes in order to compare the biodiesel yield of the sludge during biodiesel conversion of dairy wastewater sludge acid catalyst _{(H 2 SO 4) 5%} , methanol and sludge ratio (v / w ) 100: 10, methanol and N-hexane ratio 10: 1, reaction time 7 hr, and reaction temperature 60 ° C. Experimental results showed that the primary diesel yield was 14.2% for primary sludge, 4.6% for secondary sludge, and 4.0% for dewatered sludge. In the case of sludge from the dairy wastewater process, the yield of biodiesel was 2.0% in transport sludge, 9.6% in dehydrated sludge, and 10.7% in pressurized floating sludge.

3. Production of biodiesel from wastewater sludge

In this experiment, we conducted biodiesel conversion experiment using dehydrated sludge containing waste oil in the production of automobile parts in order to confirm the possibility of applying various kinds of sludge in the production of biodiesel from sludge. (H ₂ SO ₄ ) 5%, methanol and sludge ratio (v / w) 100: 10, methanol and N-hexane ratio 10: 1, reaction time 7 hours, reaction And the temperature was set to 60 ° C. Experimental results showed a biodiesel yield of 9.8% and a yield of biodiesel similar to that of dairy wastewater sludge.

4. Comparison of biodiesel production according to the effect of digested sludge

In order to evaluate the yield of biodiesel due to the influence of digested sludge in the production of biodiesel from sewage sludge, two kinds of dehydrated sludge were operated by the digester operation and the non - operating sewage treatment plant.

In the case of a sewage treatment plant operating a digester, digested sludge is introduced during the dehydration process. (H ₂ SO ₄ ) 5%, methanol and sludge ratio (v / w) 100: 10, methanol and N-hexane ratio 10: 1, reaction time 7 hr, reaction temperature The experiment was conducted at 60 캜.

The yield of biodiesel converted from sludge affected by digester was 4.0%, and the yield of biodiesel converted from sludge not affected by digester was 5.6%, which is higher than that of sludge not affected by digested sludge It was confirmed that the biodiesel yield can be obtained.

5. Analysis of FAME content of biodiesel product

FAME content of biodiesel obtained instead of food wastewater sludge and food wastewater analysis was measured. (FAME) - ester and linolenic acid methyl ester content analysis method (KS M 2413: 2004) specified in the Korean industry standard for the evaluation of the FAME content of the biodiesel product produced from the sludge at optimum conditions. , And Methyl tetracosanoate (CH ₃ (CH ₂ ) ₁₂ COOCH ₃ ) and (CH ₃ (CH ₂ ) ₂₂ COOCH ₃ ) which are the C14: 0 and C24: 1 materials of Sigma- Respectively.

This method involves diluting the biodiesel product with methyl heptadecanoate (CH ₈ (CH ₂ ) ₁₅ COOCH ₃ ) as an internal standard sample in heptane (C ₇ H ₁₈ ) solution (solvent) , And the peak area of the internal standard sample is subtracted from the peak area of all the methyl esters detected to calculate the methyl ester content according to the internal standard method.

: C14의 메틸에스테르부터 C24:1까지의 메틸에스테르까지의 피크 전체 면적,

: 메틸 헵타데카노이트에 해당하는 피크 면적,

: 사용한 메틸 헵타데카노이트 용액의 농도(mg/mL),

: 사용한 메틸 헵타데카노이트 용액의 부피(mL), m : 시료의 무게(mg),
From here

: The total peak area from the methyl ester of C14 to the methyl ester of C24: 1,

: Peak area corresponding to methyl heptadecanoate,

: Concentration (mg / mL) of the methyl heptadecanoate solution used,

: Volume (ml) of the methyl heptadecanoate solution used, m: weight (mg) of the sample,

(1) Analysis of biodiesel FAME content

In order to evaluate the FAME content of the biodiesel produced from the sludge generated in the sewage treatment process, the dehydrated sludge generated in the primary sludge, the secondary sludge, the dehydrated sludge and the milk waste water process of the same sewage treatment plant was dried, Conversion experiments were performed. The FAME content of the biodiesel product converted to the optimum condition was analyzed using GC-FID. As a result, FAME contents were 66.56%, 44.84% and 40.37% for the primary sludge, secondary sludge and dehydrated sludge. The content of FAME in biodiesel produced from waste product sludge of dairy products was 48.33% of return sludge and 75.43% of dehydrated sludge, and the content of FAME was 56.79% in automobile production process wastewater sludge.

(2) Analysis of FAME content of biodiesel by coagulant effect

The FAME content of biodiesel produced from the optimum conditions was analyzed to evaluate the effect of FAME content on the effect of coagulant during the production of biodiesel from sludge. As a result, the amount of FAME increased from 66.56% to 98.38%, and the content of FAME in the secondary sludge increased from 44.84% to 43.17% without application of polymer in the primary sludge applied with organic coagulant polymer. There was no significant difference. In addition, the content of FAME in the secondary sludge containing ferric chloride, which is an inorganic coagulant, was reduced from 47.31% to 36.25% and 23%, respectively.

(3) Analysis of biodiesel FAME content according to the influence of digested sludge

The FAME content of biodiesel produced from the dehydrated sludge of the sewage treatment plant operated by the digester was 40.37%, and the amount of FAME from the sludge of the sewage treatment plant which does not operate the digestion tank The FAME content of the biodiesel produced was 55.49% and the biodiesel FAME content of the sewage treatment plant operating the digester was high.

The results of the present invention were compared with those of biodiesel produced from food (dairy) wastewater sludge and food wastewater, and effects of biodiesel conversion by sludge coagulant addition in the water treatment process

The concentration of acid catalyst (H ₂ SO ₄ ), the reaction temperature and reaction time, the mixing ratio of methanol and sludge, the concentration of biodiesel due to addition of solvent, The optimum conditions for the conversion of biodiesel were obtained through the evaluation of yield. As a result, the yield of biodiesel was 5% at the concentration of acid catalyst (H ₂ SO ₄ ), the reaction temperature was 60 ℃, the reaction time was 7 hr and the mixing ratio of methanol and sludge was 100: The yield of biodiesel was high and the yield of biodiesel was higher as the amount of solvent added was larger in the reaction.

The biodiesel yield of the biodiesel conversion product was optimized by drying the sludge from the sludge and dairy product wastewater treatment process during the production of biodiesel from the sludge. As a result, the primary sludge produced in the sewage treatment process was 14.2% , Secondary sludge (4.6%) and dehydrated sludge (4.0%).

The conversion of biodiesel from food (dairy) wastewater sludge showed a yield of 9.6% biodiesel. The conversion of biodiesel from crude sludge with pressurized flooded wastewater from food (dairy product) resulted in a biodiesel yield of 10.7%.

In order to evaluate the effect of the coagulant on the biodiesel yield in the production of biodiesel from sludge, the yield of biodiesel was evaluated by using polymer as an organic coagulant and ferric chloride as an inorganic coagulant. As a result, Biodiesel yield increased about 2.5% in tea sludge and biodiesel yield decreased about 0.9% in secondary sludge. In the secondary sludge agglomerated with ferric chloride, which is an inorganic coagulant, the yield of biodiesel decreased by about 2.4%.

In order to evaluate the effect of yield on the production of biodiesel from sludge affected by digested sludge, the yield of biodiesel product converted into optimum conditions was evaluated by drying the sludge of sewage treatment plant operating the digester and the sludge of the sewage treatment plant not operating As a result, the yield of biodiesel in the sewage treatment plant sludge operated by the digester was 4.0%, the yield of biodiesel in the sewage treatment plant not operating the digestion tank was 5.6%, and the yield of the sludge in the sewage treatment plant, which is not affected by digested sludge, Respectively.

To evaluate the applicability of various wastewater sludge as a biodiesel production material, the yield of biodiesel from dehydrated sludge discharged from the automobile parts production process was 9.8%.

In order to evaluate the value of FAME from biodiesel produced from sewage sludge, the FAME content of primary sludge was 66.56 % In sewage sludge, and 44.84% and 40.37% in secondary sludge and dehydrated sludge, respectively.

The FAME content of biodiesel produced from the sludge of the sewage treatment plant operated by the digester was 40.37%, and the content of biodiesel produced from the sludge of the sewage treatment plant, which does not operate the digester, The content of FAME was 55.49%.

FAME content of biodiesel produced from food (dairy) wastewater sludge was 48.33% in secondary sludge, 75.43% in dehydrated sludge and 92.3% in pressurized floating sludge. The reason why the FAME content of the pressurized flotation tank is high is considered to be the effect of the untreated oil as the pretreatment concept in the treatment process.

The yield of biodiesel produced from the dehydrated sludge produced in the automobile parts production process was 9.8%, which was similar to that of dairy product wastewater sludge, but the FAME content was 56.79%, which was slightly higher than sewage. This is attributed to the influence of the waste oil generated due to the process characteristics.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. It can be understood that

Claims (8)

(1) mixing the waste sludge with an alcohol and an acid catalyst to effect an ester conversion reaction; (2) cooling to room temperature after completion of the reaction and centrifuging; (3) collecting the supernatant obtained through the centrifugation process; (4) adding hexane to the collected supernatant to perform layer separation; (5) separating the hexane layer, washing it with distilled water to remove impurities, and removing moisture to remove residual water; And (6) recovering hexane by using an evaporator to obtain residual biodiesel. 2. The method of claim 1, wherein in step (1)
Wherein the concentration of the acid catalyst is 4 to 6% (v / v) of the volume of the alcohol. 2. The method of claim 1, wherein in step (1)
Wherein the reaction temperature is 55 to 65 ° C. 2. The method of claim 1, wherein in step (1)
And the reaction time is 6 to 8 hours. The method according to claim 1, wherein in step (1), the mixing ratio of alcohol and sludge is 5 to 15 (v / w). The method of claim 1, wherein in step (6)
And recovering n-hexane at 30 to 50 ° C and 150 to 200 rpm using a rotary evaporator. 2. The method of claim 1, wherein in step (1)
Wherein the alcohol is methanol, the acid catalyst is sulfuric acid, and the reaction is carried out at a pH of 1 to 2. The method for producing biodiesel using the waste sludge according to claim 1, 2. The method of claim 1, wherein in step (1)
Wherein the moisture content of the dried sludge is 30 to 50%.

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