KR20080028247A - Production method of methane gas from olive mill waste - Google Patents

Abstract

A production method of methane gas from waste olive mill waste is provided to produce methane gas at a high yield by subjecting an olive mill waste to anaerobic digestion without performing a pre-treatment process. A production method of methane gas from waste olive mill waste comprises the steps of: (a) optionally culturing a second sludge of a municipal wastewater treatment plant containing a nitrogen supply source at anaerobic conditions to produce an anaerobic microorganism-enriched sludge; (b) injecting an olive mill waste and the second sludge of the municipal wastewater treatment plant containing the nitrogen supply source into the anaerobic microorganism-enriched sludge to mix the second sludge and the olive mill waste with the anaerobic microorganism-enriched sludge: and (c) anaerobic digesting the mixture of the step(b) to generate methane gas and effluent. The production method further comprises the step of agitating the olive mill waste with the second sludge of the municipal wastewater treatment plant containing the nitrogen supply source prior to the step(b) of injecting an olive mill waste and the second sludge of the municipal wastewater treatment plant containing the nitrogen supply source into the anaerobic microorganism-enriched sludge. The production method further comprises the step of returning a portion of the effluent of the step(c) to the step of agitating the olive mill waste with the second sludge of the municipal wastewater treatment plant containing the nitrogen supply source.

Description

Production method of methane gas from olive mill waste}

1 is a process chart showing one example of the present invention.

2 is a graph showing the amount of methane generated according to the operation time according to an example of the present invention.

The present invention relates to a methane gas production method using an olive waste liquid, and more particularly, can be anaerobic digestion of olive waste liquid without pretreatment, can produce methane gas in high yield, and to simultaneously process the olive waste liquid and secondary sludge It relates to a methane gas production method using olive waste oil.

Around 98% of the world's requirements are produced on the Mediterranean coast, which is about 1.77 million tons per year. About twice as much olive oil is produced as waste, and the region produces about 3.5 million tons of waste. The largest regions of olive oil production are Spain (602,000 ton), Italy (451,000 ton), Greece (332,000 ton), Tunisia (173,000 ton), Turkey (92,000 ton), Syria (81,000 ton) and Morocco (46,000 ton) ) Is a major producer. In addition, small quantities are produced in Australia, the United States, and Lebanon. Olive-producing areas generally have a desert climate, characterized by very low rainfall and high temperatures. Olive oil from this region is exported to countries around the world, and its production is expected to increase.

Olive oil is harvested from olives and crushed under high pressure to extract oil and water and recovered through high-speed centrifugation. The solid waste produced in this process is not a problem because it is used as a camel or sheep food, but olive mill wastewater (OWM) is the main waste generated in the olive oil extraction process, and the disposal of this waste is a big problem. . Olive waste liquid has an organic content of 150,000mg / L based on CODcr and a polyphenol concentration of about 10,000mg / L. The organic content of olive waste liquor is quite high and energy production by anaerobic digestion can be a solution, but catechol, 4-hydroxybenzoic acid, 2- (3,4-dihydroxy) phenylethanol, 3,4-di Since polyphenols such as hydroxyphenyl acetic acid are contained, it is difficult to perform anaerobic digestion without pretreatment.

Therefore, pretreatment is carried out by UV, fenton oxidation, ozone treatment, electrolysis, etc. However, this method removes not only toxic substances but also non-toxic organic substances. There was a problem that the gas production is reduced and the cost is expensive. In addition, the method of using the residue as fuel after the long-term evaporation of waste liquid in a large pond was the most commonly used method. However, this pond storage method (Lagoon) is odorous, especially penetrates into the soil and may cause groundwater contamination. There was this.

Therefore, the technical problem to be achieved by the present invention is to provide a methane gas production method using the olive waste liquid that can be produced in a high yield by performing anaerobic digestion of olive waste liquid without pretreatment.

The present invention to achieve the above technical problem,

(a) selective culture of secondary sludge in an urban sewage treatment plant including a nitrogen source under anaerobic conditions to produce anaerobic microorganism concentrated sludge;

(b) injecting and mixing the secondary sludge and the olive waste solution of the municipal sewage treatment plant including the nitrogen supply source to the anaerobic microorganism concentrated sludge; And

(c) providing a methane gas production method using an olive waste liquid comprising the step of anaerobic digestion of the mixture of step (b) to generate methane gas and effluent.

According to an embodiment of the present invention, step (a) may be performed for 20 to 32 days.

According to another embodiment of the present invention, the total sludge content of the sludge in the municipal sewage treatment plant including the nitrogen source of steps (a) and (b) may be 1.5 to 15% by weight based on the solid content. .

According to another embodiment of the present invention, the secondary sludge and olive of the municipal sewage treatment plant including the nitrogen source before injecting the second sludge and the olive waste liquid in the municipal sewage treatment plant including the nitrogen source of step (b) The method may further include stirring the waste liquid.

According to another embodiment of the present invention, the method may further include the step of returning a portion of the effluent of step (c) to the step of stirring the secondary sludge and the olive waste liquid of the municipal sewage treatment plant including the nitrogen source. have.

According to another embodiment of the present invention, the secondary sludge of the municipal sewage treatment plant including the nitrogen source of steps (a) and (b) may be liquid sludge or dry sludge.

According to another embodiment of the present invention, the injection ratio of the secondary sludge: olive waste solution of the municipal sewage treatment plant including the nitrogen source of step (b) may be 8.5: 1 ~ 10.5: 1 by volume ratio.

According to another embodiment of the present invention, the steps (a), (b) and (c) may be performed by a sequencing batch reaction process.

According to another embodiment of the present invention, the anaerobic digestion of step (c) is 8-12 days of hydraulic retention time (HRT), Mixed Liquor Suspended Solid (MLSS) 20,000-30,000mg / L, pH 7-8 and temperature 25-35 degreeC can be performed.

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

In the methane gas production method using the olive waste liquid according to the present invention, the anaerobic microorganism concentrated sludge is produced by selectively cultivating the secondary sludge of the municipal sewage treatment plant including the nitrogen source indicated in solid line under anaerobic conditions as shown in FIG. Making; (b) injecting and mixing the secondary sludge and the olive waste solution of the municipal sewage treatment plant including the nitrogen source to the anaerobic microorganism concentrated sludge; And (c) anaerobic digestion of the mixture of step (b) to generate methane gas and effluent.

Municipal sewage treatment consists of (1) screens for filtering out relatively large solids in the wastewater, (2) sedimentation for sedimenting and removing grit, a mixture of sand and dirty mass, and (3) sedimentable solids in the wastewater. Primary sedimentation cell for sedimentation removal, (4) Aeration tank where organic material that does not precipitate in primary sedimentation basin is synthesized into cells of microorganism, and the microorganism can be precipitated well. Secondary sedimentation battery, (6) mainly through the disinfection step of killing pathogenic microorganisms by injecting chlorine, sludge precipitated in the secondary sedimentation basin is called secondary sludge, mainly composed of microorganisms. Secondary sludge produced during activated sludge treatment is also called activated sludge. Since the secondary sludge mainly consists of microorganisms, the composition thereof may be represented by C ₅ H ₇ O ₂ N or the like. That is, the secondary sludge may act as a nitrogen source for anaerobic bacteria at the time of anaerobic digestion, and the secondary sludge may act as a spawn for the anaerobic reaction because the secondary sludge itself is composed of various microorganisms.

In the step (a), the secondary sludge of the municipal sewage treatment plant is mainly composed of aerobic bacteria or random bacteria (microorganisms growing with or without oxygen), and by anaerobic digestion without injecting air, To anaerobic organic acid bacteria and methane bacteria. The breeding process is a process of transition of the ecosystem, using a process in which a suitable microorganism occupies the dominant species as it maintains the anaerobic environment. That is, the secondary sludge in the city sewage treatment plant is a predominant aerobic bacteria, but if the oxygen supply to maintain the anaerobic state without aeration or aeration, suitable anaerobic bacteria will be the dominant species. Looking at this process in detail, anaerobic digestion is caused by various kinds of bacteria, and is largely divided into organic acid bacteria and methane bacteria. Random to anaerobic organic acid bacteria decompose organic materials to produce organic acids and alcohols, where a small amount of CO ₂ , acetone, H _2, etc. are generated. The reaction of this stage is called the first stage digestion, and methane bacteria classified in the fourth genus of Methanobacterium, Methanococcus , Methanosarcina , and Methanospirillium decompose the organic acid generated in the first stage digestion, such as CH ₄ and CO ₂ . Generates gaseous substances, and some NH ₃ , H ₂ S, mercaptan, etc. are also generated. The conversion of organic matter to gas requires the proper activity of organic acids and methane. That is, in the first stage digestion, an organic acid that is a nutrient necessary for the second stage digestion is generated, and in the second stage digestion, the organic acid is decomposed to prevent the pH from being lowered by the accumulation of the organic acid. In addition, organic acids produce nutrients for methane, as well as consume oxides to form a reducing agent, creating a completely anaerobic state. Through the above step (a), the secondary sludge of the municipal sewage treatment plant including the nitrogen source becomes an anaerobic microorganism concentrated sludge such as methane, and the secondary sludge of the municipal sewage treatment plant including the nitrogen source in step (b). And when the olive waste solution is injected, anaerobic microorganisms such as methane bacteria are the dominant species, so that anaerobic digestion of step (c) occurs smoothly, and as a result, the generation of methane gas increases.

The physical properties of olive waste are reported to be pH 4.5-5.9, COD (Chemical Oxygen Demand) 40-200 (g / L), BOD (Biochemical Oxygen Demand) 20-110 (g / L), P 800-1,100 ( mg / L), K 7,200 (mg / L), Ca 700 (mg / L), Mg 400 (mg / L), Na 900 (mg / L), Fe 70 (mg / L), Cl 300 (mg / L), 1-8% by weight of total carbohydrates (based on dry weight), 0.28-2% by weight of organic nitrogen (based on dry weight), 0.5-1% by weight of organic acid (based on dry weight), 1-1.5% by weight of polyalcohol (dry) By weight), tannins 0.37-1% by weight (dry weight), polyphenols 0.5-2.4% by weight (dry weight), grease (0.03-1% by weight).

As a result, the olive waste liquid has 150g / L of CODcr, which is enough carbon for the growth of anaerobic microorganisms, but lacks nitrogen as 0.16% by weight (dry weight) of organic nitrogen, and it is a toxic polyphenol (catechol, 4). Hydroxybenzoic acid, 2- (3,4-dihydroxy) phenylethanol, 3,4-dihydroxyphenyl acetic acid, and the like) are present in large amounts at 10 g / L. In step (b), by supplying the secondary sludge of the municipal sewage treatment plant including the nitrogen source to the anaerobic microorganism concentrated sludge together with the olive waste liquid, nitrogen necessary for the growth of the anaerobic microorganism can be supplied to the olive waste liquid. . In addition, by the action of diluting a high concentration of polyphenols by a large amount of water contained in the secondary sludge of the municipal sewage treatment plant including the nitrogen source, the concentration is such that microorganisms can be decomposed or contained in the secondary sludge. Polyphenol decomposition by denitrification microorganisms or desulfurization microorganisms, or a combination of the above actions can inhibit the toxic effects of polyphenols, and various microorganisms are present in the secondary sludge of the municipal sewage treatment plant. Can be used as That is, the secondary sludge of the municipal sewage treatment plant including a nitrogen source may be used for the anaerobic digestion of olive waste. In addition, the secondary sludge of the municipal sewage treatment plant can be decomposed by anaerobic digestion, so that the secondary sludge itself of the municipal sewage treatment plant can be treated. Therefore, according to the present invention, not only the olive waste liquid, but also secondary sludge, which can be referred to as waste in urban sewage treatment plants, can be treated. As a result, it will be possible to anaerobic digestion of the olive waste liquid will be able to produce methane gas using the olive waste liquid.

Step (a) may be carried out for 20 to 32 days, less than 20 days may be insufficient anaerobic digestion of olive waste liquid to form methane bacteria to produce methane gas, methane if more than 32 days Unnecessary period of time for the formation of germs may occur, which may adversely affect the operating conditions.

The secondary sludge of the municipal sewage treatment plant including the nitrogen source of steps (a) and (b) may be 1.5 to 15 wt% based on solid content, and less than 1.5 wt% of anaerobic microorganisms. There is a concern that it may not be suitable for growth, and even if it exceeds 15% by weight, there is a fear that it may not be suitable for anaerobic microbial growth.

As shown in the dotted box of Figure 1, the secondary sludge and olive of the municipal sewage treatment plant including the nitrogen source before injecting the second sludge and the olive waste solution of the municipal sewage treatment plant including the nitrogen source of step (b) The method may further include stirring the waste liquid, and injecting the secondary sludge and the olive waste liquid from the municipal sewage treatment plant including the nitrogen source into the anaerobic microorganism concentrated sludge, which may cause a uniform reaction to anaerobic digestion. Can be stabilized.

As shown in the dotted line of Figure 1, the step of returning a portion of the effluent of step (c) to the step of stirring the secondary sludge and olive waste liquid of the municipal sewage treatment plant including the nitrogen supply source have. Since the effluent contains various organic substances and microorganisms necessary for anaerobic digestion through anaerobic digestion, the effluent is returned to the step of stirring the secondary sludge and the olive waste liquid in the municipal sewage treatment plant including the nitrogen source, and then the olive waste liquid. Has the effect of helping anaerobic digestion.

Secondary sludge of the municipal sewage treatment plant including the nitrogen source of steps (a) and (b) may be liquid sludge or dry sludge. Since the normal secondary sludge exhibits a high value of about 95 to 99% of moisture, dry sludge can be used for convenience of use, and the dry sludge is sludge dried in a sludge dry phase or the like. It means sludge in which 20 to 90% of the water content is removed.

Secondary sludge of the municipal sewage treatment plant including the nitrogen source of step (b): the injection ratio of the olive waste liquid may be 8.5: 1 ~ 10.5: 1 by volume ratio, the secondary of the municipal sewage treatment plant for one volume of olive waste liquid If the sludge is less than 8.5 volume, the concentration of olive waste liquid is high, which may limit the growth of anaerobic microorganisms due to the toxicity of polyphenols or the lack of nitrogen source, and more than 10.5 volume of secondary sludge in urban sewage treatment plant for 1 volume of olive waste liquid In the case of, the olive waste liquid is diluted, which may limit the growth of anaerobic microorganisms due to the lack of a carbon source necessary for the growth of anaerobic microorganisms, and there is a concern that the volume of the reactor becomes larger than necessary.

Steps (a), (b) and (c) can be performed by a sequencing batch reaction process. The continuous batch reaction process includes (1) wastewater inflow (fill), (2) reaction, (3) sediment, and (4) continuous process of draw. Can be. That is, in the step (a) of the present invention, the secondary sludge of the municipal sewage treatment plant including the nitrogen supply source is not supplied with oxygen and introduced into a continuous batch reaction tank satisfying anaerobic conditions, and reacted by stirring or the like. After a certain period of time, the sediment is discharged into the effluent and the methane gas is collected in a continuous batch reactor to continuously maintain the hydraulic retention time (HRT) of the secondary sludge in the municipal sewage treatment plant. The anaerobic microorganisms in which the anaerobic microorganisms, such as bacteria, are predominant, can produce sludges in which the anaerobic microorganisms are concentrated. By making the anaerobic microorganism concentrated sludge, the secondary sludge and olive waste solution of the municipal sewage treatment plant including a nitrogen source may be injected into the continuous batch reactor in the future to generate an anaerobic reaction to generate methane gas. In addition, the inflow, anaerobic reaction, precipitation, discharge in one reactor has the advantage that the space can be used economically. In the continuous batch reactor, the anaerobic microorganism concentrated sludge is injected and mixed with the secondary sludge and the olive waste solution of the municipal sewage treatment plant including a nitrogen source, followed by step (c). By passing through a continuous batch reactor, inflow of secondary sludge and olive waste liquor in an urban sewage treatment plant containing a certain amount of nitrogen source in one reactor, anaerobic reaction of the mixed liquid with the anaerobic digestion, and anaerobic reaction Precipitation of anaerobic microorganism group, discharge of effluent, which is the supernatant after the precipitation, occur continuously, maintain a constant flow rate in the reaction tank, increase the amount of precipitation of anaerobic microorganisms such as methane bacteria in the reaction tank, the system allows the formation of methane You can increase it to a level that does.

Anaerobic digestion of step (c) is 8-12 days of hydraulic retention time (HRT), Mixed Liquor Suspended Solid (MLSS) 20,000-30,000mg / L, pH 7-8 and temperature 25 It can carry out at -35 degreeC. The operating conditions for anaerobic digestion of step (c) may be equally applicable to the production of anaerobic microorganism concentrated sludge by selectively cultivating the secondary sludge of the municipal sewage treatment plant including the nitrogen source of step (a) under anaerobic conditions. have.

If the hydraulic retention time is less than 8 days, the anaerobic digestion period is short, and there is a fear that the olive waste liquid may not be sufficiently decomposed, and if it is more than 12 days, the operation period may be unnecessarily longer.

When the mixed liquor suspended solids (MLSS) is less than 20,000 mg / L, the amount of anaerobic microorganisms such as methane is low, so that anaerobic digestion may be insufficient, and in the case of more than 30,000 mg / L, This is because the amount of anaerobic microorganisms may increase, which may adversely affect the growth of microorganisms.

If the pH is less than 7 or more than 8, growth of anaerobic microorganisms such as methane bacteria may be difficult. The reason is that methane is sensitive to pH, and in order to increase the production of methane gas, it is necessary to perform anaerobic digestion in an appropriate pH range.

Even when the temperature is less than 25 ℃ or above 35 ℃, growth of anaerobic microorganisms such as methane bacteria may be difficult.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments, but the present invention is not limited thereto.

Example 1

Sewage sludge (Second activated sludge collected from Jungnang Sewage Treatment Plant, Korea) at 570 mL / day in a sequencing batch anaerobic digester with a 10-hour, 24-hour operation cycle of hydraulic retention time (HRT) Injected for 28 days, the sewage sludge was selectively cultured under anaerobic conditions to produce anaerobic microorganism concentrated sludge. The sewage sludge was injected for about 12 hours while the continuous batch anaerobic digester was being mixed and remixed for 6 hours after the injection was completed. Thereafter, it was precipitated for 6 hours. The injection was made by injecting 30 minutes and repeating the rest for 2 hours 30 minutes. The amount of methane gas discharged from the continuous batch anaerobic digester was measured, and 30 ml / d of the olive waste liquor was mixed in the sewage sludge 570 mL / d and the stirred tank from 29 to 50 days of the elapsed operation. The reaction was carried out in a sequencing batch anaerobic digester with a 10-day, 24-hour operating cycle of hydraulic retention time (HRT). The mixed solution was injected for about 12 hours while the continuous batch anaerobic digester was being mixed, and remixed for 6 hours after the injection was completed. Thereafter, it was precipitated for 6 hours. The injection of the olive waste solution and sewage sludge was made for 30 minutes and repeated for 2 hours and 30 minutes. After that, the amount of olive waste was increased to 40 ml / d until the elapsed operating time of 51 to 70 days, and to 60 ml / d until 71 to 90 days. As a result, the amount of influent sludge was increased by measuring gas generation daily for a total of 90 days, including the production period of 20 days of anaerobic microorganism concentrated sludge. The olive waste solution was 9.5: 1 in volume ratio at 60 mL / d. In addition, the operating conditions for each period are shown in Table 1, and the operating conditions of the continuous batch anaerobic reactor were MLSS 24,000 mg / L, pH 7.6, and temperature 35 ° C after 90 days of operation.

 Driving time  0-28 days  29-50 days  51-70 days  71-90 days  Injection material  Sludge 570ml / d  Sludge570ml / d + OMW 30ml / d  Sludge570ml / d + OMW 40ml / d  Sludge570ml / d + OMW 60ml / d Load capacity (kg COD / m ³ / d)  0.6  1.0  1.1  1.3

Test Example 1

Generated gas composition analysis

Gas generation amount was measured by gas chromatography (Shimazue, Japan) for methane, carbon dioxide, hydrogen, nitrogen, hydrogen sulfide in the 71-90 days, the stable generation of methane gas of Example 1, the average generated gas It has a volume ratio of 65% of methane, 31% of carbon dioxide, 3.6% of hydrogen, 0.3% of nitrogen, and 0.06% of hydrogen sulfide. From the above results, the methane gas production method according to the present invention can produce methane gas in high yield.

Test Example 2

Methane gas analysis

The amount of methane gas generated over the entire operation period of Example 1 was measured by gas volume measurement method and the results are shown in FIG. 2. In the acclimatization phase, methane gas generation tends to decrease after 20 days and 28 days. This phenomenon is believed to be due to the depletion of organic materials, especially carbon sources, as methane bacteria thrive. As shown in FIG. 2, by increasing the amount of olive waste solution injected at 50 days and 70 days when methane generation rate does not increase, methane gas production can be increased, and methane gas is generated stably after 90 days. Seems to do. The time when the methane gas generation rate does not increase is also considered to be due to the depletion of organic matter, especially carbon sources, as methane bacteria thrive. It is determined that can be generated. It can be seen from the above results that the methane gas production method according to the present invention can stably produce methane gas.

As described above, the methane gas production method using the olive waste liquid according to the present invention can be anaerobic digestion of olive waste liquid without pretreatment, can produce methane gas in high yield, and simultaneously process the olive waste liquid and the secondary sludge can do. In addition, it is possible to anaerobic digestion in one reactor, spatially advantageous, and the effluent produced after anaerobic digestion can be used for agriculture by removing toxic substances.

Claims (9)

(a) selective culture of secondary sludge in an urban sewage treatment plant including a nitrogen source under anaerobic conditions to produce anaerobic microorganism concentrated sludge; (b) injecting and mixing the anaerobic microbial concentrated sludge with a secondary sludge and an olive waste solution of an urban sewage treatment plant including the nitrogen source; And (c) anaerobic digestion of the mixture of step (b) to produce methane gas and effluent water. According to claim 1, wherein the step (a) methane gas production method using an olive waste liquid, characterized in that performed for 20 to 32 days. The olive according to claim 1, wherein the secondary sludge of the municipal sewage treatment plant including the nitrogen source of steps (a) and (b) has a total nitrogen content of 1.5 to 15 wt% based on the solid content. Methane gas production method using waste liquid. The method according to claim 1, wherein the secondary sludge and the olive waste solution of the municipal sewage treatment plant including the nitrogen source are stirred before injecting the secondary sludge and the olive waste liquid from the municipal sewage treatment plant including the nitrogen source of step (b). Methane gas production method using the olive waste liquid, characterized in that it further comprises a step. 5. The olive according to claim 4, further comprising the step of returning a part of the effluent of step (c) to the step of stirring the secondary sludge and the olive waste liquid of the municipal sewage treatment plant including the nitrogen source. Methane gas production method using waste liquid. The method of claim 1, wherein the secondary sludge of the municipal sewage treatment plant including the nitrogen source of step (a) and (b) is a liquid sludge or dry sludge, methane gas production method using an olive waste liquid. The method of claim 1, wherein the injection ratio of the secondary sludge: olive waste solution of the municipal sewage treatment plant including the nitrogen source of step (b) is 8.5: 1 ~ 10.5: 1 by volume ratio of methane using the olive waste solution Gas production method. The method of claim 1, wherein the steps (a), (b) and (c) is a methane gas production method using an olive waste liquid, characterized in that carried out by a sequencing batch reaction (Sequencing Batch Reaction) process. According to claim 1, wherein the anaerobic digestion of step (c) is a hydraulic retention time (HRT) 8-12 days, Mixed Liquor Suspended Solid (MLSS) 20,000 ~ 30,000mg / L, pH Methane gas production method using an olive waste liquid, characterized in that carried out at 7 ~ 8 and the temperature 25 ~ 35 ℃.

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