KR100973349B1 - Enzymatic hydrolysis of food waste and methane fermentation by UASB bioreactor - Google Patents

Abstract

The present invention relates to a methane production method using food waste, and more specifically, in the methane production method, 0.2 to 0.4 parts by weight of mixed enzyme per 100 parts by weight of ground food waste is added at a temperature of 45 to 55 ° C. Reaction for 10 hours to obtain a hydrolysis solution (S10); Collecting the supernatant by centrifuging the hydrolysis solution at 3500 to 4500 rpm for 5 to 15 minutes (S20); Diluting the supernatant with distilled water 5 to 6 times to use the influent of the UASB reactor (S30); And obtaining methane using the UASB reactor (S40), wherein the mixed enzyme is carbohydrase: protease: lipase in a ratio of 1: 2: 1, and the mixture of the UASB reactor The temperature relates to a methane production method using food waste, characterized in that 35 ~ 40 ℃.

Food waste, enzymes, hydrolysis, UASB, methane fermentation

Description

Production method of methane using food waste {Enzymatic hydrolysis of food waste and methane fermentation by UASB bioreactor}

The present invention relates to a method of producing methane using food waste, and more particularly, by hydrolyzing food waste by a mixed enzyme to obtain a hydrolysis solution having the highest VSS reduction rate and SCOD growth rate, The present invention relates to a method of producing methane using food waste which obtains methane of high purity and efficiency by using an enzyme hydrolyzate as an influent of a UASB reactor for methane production.

Food waste is easily polluted, odorous, and causes high-salt disease-causing diseases. It has been recognized as an environmental pollutant that must be disposed of in an appropriate manner. On the other hand, food waste contains high concentrations of organic compounds such as soluble sugars, starch, fats, proteins, cellulose, etc., and when used as fermentation substrates in biological processes, it not only reduces treatment costs and prevents environmental pollution but also recycles resources. Has great meaning. Therefore, methane fermentation using food waste has received much attention in recent years in terms of production of renewable energy that can replace fossil fuels, reduction of global warming gas, and resource recycling.

  In order to use solid wastes such as food waste as methane fermentation substrates, efficient hydrolysis of solids is essential as a precondition. In the existing solid waste methane fermentation process, the hydrolysis reaction of particulate organic matter acts as a rate-limiting step of the entire fermentation process, which is an important factor in determining the decomposition rate of organic components and the hydraulic residence time of the digester. . In addition, since food waste is composed of various organic compounds such as starch, protein, and fat, organic acid according to the difference in the content of the three components, the decomposition rate and biodegradability of the three components during hydrolysis and acid fermentation, In the operation of the fermenter by the accumulation of various problems have been revealed. In order to efficiently methanize biomass containing such high concentration solids, studies have been actively conducted for spatial separation of acid fermentation tanks and methane fermentation tanks and optimization of various methane fermentation processes.

Conventionally, since biodegradability of starch, protein and cellulose components in food waste is determined by the pH, residence time and environmental conditions of the acid fermentation tank, the result of adjusting the appropriate dilution ratio in the acid fermentation step (3.0-1.0 / d), food It was found that the efficiency of acid fermenter increased with increasing hydrolysis of cellulose and protein in the waste. In addition, considering that about 50% of food waste is a cellulose-based vegetable, about 1.2 times as much as the efficiency of conventional mesophilic fermentation bacteria (59.5%) using lumen microorganisms having excellent cellulose resolution as a seed germ. Improved acid efficiency (71.2%) has been reported. In addition, in order to utilize food waste as an external carbon source of Biological Nutrient Removal (BNR), an enzyme pretreatment was attempted to increase the efficiency of acid fermentation. However, studies on the enzymatic hydrolysis that can replace the hydrolysis and acid fermentation of food waste for high efficiency methane fermentation are insignificant.

Recently, high-efficiency upflow anaerobic sludge bed (UASB) has been widely applied to various kinds of industrial wastewater treatment. Particularly, granular granular sludge, which is agglomerates of high density anaerobic bacteria formed by the microbial magnetization flocculation process, maintains high density methane bacteria in the UASB reactor. And because it can secure a long residence time, it is recognized as a process excellent in response to high organic loading rate (OLR: Organic Loading Rate).

An object of the present invention is to investigate the applicability of industrial enzyme hydrolysis as an efficient pretreatment process of organic solids containing food wastes. It is intended to produce methane of high purity and high efficiency using the mixed enzyme ratio, the amount of addition, and the reaction time, and the food waste medium liquid subjected to the enzymatic hydrolysis as the substrate of the UASB reactor.

Methane production method using the food waste of the present invention for achieving the above object, in the methane production method, adding 0.2 to 0.4 parts by weight of mixed enzyme per 100 parts by weight of ground food waste, and at a temperature of 45 ~ 55 ℃ Reaction for 10 hours to obtain a hydrolysis solution (S10); Collecting the supernatant by centrifuging the hydrolysis solution at 3500 to 4500 rpm for 5 to 15 minutes (S20); Diluting the supernatant with distilled water 5 to 6 times to use the influent of the UASB reactor (S30); And obtaining methane using the UASB reactor (S40).

At this time, the mixed enzyme is mixed by adding carbohydrase: protease: lipase in a ratio of 1: 2: 1, the temperature of the UASB reactor is preferably 35 ~ 40 ℃.

In the methane production method using food waste according to the present invention, as a pretreatment step for the production of methane, by adding an appropriate amount to the food waste, an enzyme mixed with carbohydrase: protease: lipase in a ratio of 1: 2: 1 to 8 ~ By hydrolysis for 10 hours, not only high VSS reduction rate and SCOD increase rate were obtained, but also high efficiency and high purity methane could be obtained using the above mixed enzyme hydrolysis solution as a substrate of the UASB reactor.

Hereinafter, the present invention will be described in detail.

Food waste used in the present invention was collected in the cafeteria of Gyeonggi-do Small and Medium Business Center, the composition of the collected food waste was 49% by weight of vegetables, 31% by weight of grains, 17% by weight of fish and meat, and 3% by weight of other ingredients.

The food waste thus collected was pulverized using a grinder (AM-11, ACE, Nissei, Japan), filtered through a metallic sieve (1800-2200 μm mesh), and used as a raw material for the enzymatic hydrolysis experiment.

The characteristics of the food waste pulverized as described above are shown in Table 1 below.

division shame Moisture content (wt%) 81.5 Solid content (% by weight) 18.5 Volatile solids (% by weight) of solids 95.7 Ash content in solids content (% by weight) 4.3 Volatile Float (g / L) 91.0 pH 4.3 TCOD (mg / L) 263.5 SCOD (mg / L) 127.4 Viscosity (g / cm ³ ) 1.048

As can be seen in Table 1, the crushed food waste already had an acid fermentation during the harvesting process, the pH was 4.3, and exhibited a high water content (81.5 wt%) and a solid content (18.5 wt%). The solids contained about 95% by weight of volatile solids and 4.3% by weight of ash, and the total COD was 263.5 g / L and the dissolved COD was 127.4 g / L.

In addition, the enzymes used in the present invention are industrial enzymes, carbohydrase, protease, and lipase, which were used to perform individual and mixed enzyme hydrolysis of food waste. Among them, Carbohyrases is a multiple complex enzyme derived from Aspergillus aculeatus, arabanase (arabanase), cellulase (cellulase), beta-glucanase (β-glucanase) ), One of a broad range of carbohydrases, including hemicellulase, xylanase and the like, was purchased from Novozymes. In addition, the protease is a protease derived from Aspergillus oryzae, and is mainly used in the food industry, particularly the meat processing industry, and the lipase is Candida rugos. It is a lipase derived from, and is a long chain, heavy chain, or short chain lipase. The protease and lipase enzymes were purchased from Amano.

1. Enzymatic Hydrolysis of Food Waste

In order to find out the optimal amount of enzyme addition and mixing ratio for the hydrolysis of food waste, individual and mixed enzyme hydrolysis using food waste was performed.

In order to perform the enzymatic hydrolysis experiment, the crushed food waste and distilled water were mixed at a weight ratio of 1: 1 to prepare a sample.

1-1. Individual enzyme hydrolysis

First, in the individual enzymatic hydrolysis experiment, 500 g of the sample prepared above was put in a 1 L Erlenmeyer flask, the pH of the sample was adjusted to 4.5 with 3N NaOH, and carbohydrase, protease and lipase per 100 parts by weight of crushed food waste. After adding 0.02, 0.05, 0.1, 0.2 and 0.4 parts by weight, the individual enzyme hydrolysis was performed for 24 to 26 hours at a stirring speed of 130 to 170 rpm in an incubator at 45 to 55 ° C (DSK 512, Daeil Engineering, Korea). Was carried out.

1-2. Mixed Enzyme Hydrolysis

In addition, the mixed enzyme hydrolysis experiment was carried out by mixing the mixing ratio (carbohydrase: protease: lipase) of each of the enzymes at 1: 1: 1, 2: 1: 1, 1: 2: 1 and 1: 1: 2 The sample was added to the sample, and the mixed enzyme injection amount was constant at 0.4 parts by weight per 100 parts by weight of food waste, and was carried out under the same conditions as the individual enzyme hydrolysis experiment.

Such individual and mixed hydrolysis experiments were repeated three times.

1-3. By individual enzymatic hydrolysis VSS  Reduction

First, the hydrolytic ability of the enzyme was evaluated by the rate of decrease of suspended solids (VSS) in the food waste by individual enzyme hydrolysis.

As shown in FIG. 2, the decrease in VSS was increased in a hyperbolic form with an increase in the injection amount of each enzyme.

When the lipase was added as an enzyme, the VSS reduction rate increased to 22% by 0.1 parts by weight, but no increase in VSS was observed at the addition amount. Indeed, the fats and oils in the food waste were effectively removed in the lipase experiments, but they did not significantly affect the increase in the VSS reduction rate. In addition, in the hydrolysis experiment using carbohydrase as an enzyme, the VSS reduction amount increased to 0.2 parts by weight, showing a VSS reduction rate of about 43%. However, when the protease was added as an enzyme, the decrease in VSS was continuously increased up to 0.2 parts by weight, showing an increase rate of about 51%, the highest decrease in VSS.

1-4. By mixed enzyme hydrolysis VSS  Reduction rate and SCOD  Increase

Next, the hydrolysis capacity of the enzyme was evaluated by the rate of decrease of suspended solids (VSS) and the rate of increase of the eluted SCOD by the mixed enzyme hydrolysis in which each enzyme was mixed at various mixing ratios.

Table 2 below shows the amount of enzyme injected at 0.4 parts by weight per 100 parts by weight of food waste, and shows the rate of VSS decrease and the rate of eluted SCOD at various mixing ratios of each enzyme.

Mixing ratio (C: P: L) VSS Reduction (%) % SCOD Growth 1: 1: 1 58 51 2: 1: 1 56 50 1: 2: 1 62 56 1: 1: 2 53 49

C: carbohydrase P: protease L: lipase

As can be seen in Table 2, the highest VSS reduction rate and SCOD increase rate were observed at high protease addition ratio of C: P: L = 1: 2: 1, and the VSS reduction rate of the individual protease enzymatic hydrolysis experiment (43%). VSS reduction was much higher than). These results indicate that the lectin-like protein of food waste biopolymers is hydrolyzed by proteases, and other polysaccharides and oils and fats are degraded by carbohydrases and lipases, rather than individual protease hydrolysis. We believe this is a high rate of VSS reduction.

1-5. Mixed enzyme addition and reaction time measurement

When the mixing ratio of carbohydrase: protease: lipase is 1: 2: 1 in the results of the individual and mixed enzyme hydrolysis experiments, the hydrolysis ratio of food waste was the highest. The optimum ratio was selected and the mixed enzyme addition amount determination experiment was performed.

Experiment to determine the amount of mixed enzyme added for the hydrolysis of food waste was performed by mixing the control group without adding enzyme with 0.02, 0.05, 0.1, 0.2, 0.3, 0.4 parts by weight per 100 parts by weight of food waste, respectively. The experimental group to which the enzyme was added was carried out under the same conditions as the individual and mixed enzyme hydrolysis experiments, and samples were periodically taken to evaluate the rate of hydrolysis by analyzing the VSS reduction rate and SCOD increase rate.

Figure 3 shows the VSS concentration of each mixed enzyme addition over time. As can be seen in Figure 3, the VSS concentration was sharply reduced with the increase in the amount of the mixed enzyme, in particular, the amount of VSS was significantly decreased according to the amount of the enzyme added up to 0.1 part by weight, but the difference was 0.2 to 0.4 parts by weight. It was insignificant. At 0.4 parts by weight, the lowest VSS concentration of about 16,000 mg / L was observed.

In addition, it was found that the hydrolysis of the solids in the food wastes occurred suddenly around 2 hours (the initial stage of the reaction) at the amount of each mixed enzyme added, and considering that the VSS concentration was insignificant after 6 to 8 hours, the food wastes It is judged that 8-10 hours are suitable as reaction time of the mixed enzyme of.

Therefore, as the optimum conditions for hydrolysis of food waste enzymes, the mixed enzyme ratio is carbohydrase: protease: lipase = 1: 2: 1, the mixed enzyme addition amount is 0.2-0.4%, and the enzyme hydrolysis time is 8-10. It turned out that time is preferable.

In the food waste enzyme hydrolysis experiment using the mixed enzyme as described above, the amount of increase of pure SCOD to the amount of pure VSS is shown in FIG. 4. As can be seen in FIG. 4, there was a high correlation coefficient (r ² ) of 0.9608 between the net SCOD increase to net VSS decrease, which is due to the hydrolysis of solids in food waste. I was able to know. In addition, the ratio of the pure VSS decrease amount and the pure SCOD increase amount was 1.29, and 1.29 g of pure SCOD was produced from 1 g of VSS in food waste by mixed enzyme hydrolysis. These results are slightly higher than the correlation coefficient (1.24) obtained in the enzymatic hydrolysis experiment of food waste as a substrate of a conventional biological nitrogen removal process (BNR).

2. Methane Fermentation

Based on the results of the mixed enzyme addition experiment conducted above, 0.2 to 0.4 parts by weight of the mixed enzyme mixed at a mixing ratio of carbohydrase: protease: lipase = 1: 2: 1 was added per 100 parts by weight of food waste. The reaction for ˜10 hours was selected as the optimal factor for the food waste enzyme hydrolysis experiment.

2-1. UASB  Methane Production Using Reactors

Centrifuged food waste hydrolyzate prepared under the above conditions at 3500-4500rpm for 5-15 minutes, and the supernatant was diluted 5-6 times with distilled water, and then the diluted solution was UASB (upflow anaerobic anaerobic) for methane fermentation experiment. Wastewater treatment method).

1, a UASB reactor is shown, and the UASB reactor is made of glass, and the reactor capacity is the main body (diameter (7 cm) x height (66 cm)) and the gas-liquid-solid separator (diameter (11 cm) x height (15 cm). )] And its capacity is 2.7dm ³ . In addition, by using a peristaltic pump circulating the internal water of about 92L / day to maintain the internal conveying speed (v _s ) 1m / h, using a heating jacket (heating jacket) to the temperature of the reactor to 35 ~ 40 ℃ Adjusted. The reactor influent was tested at various organic loading rates (OLR), 3.5, 4.9, 7.3, and 9.1 kg COD / m ³ d using a metering pump, and the pH of the influent was not controlled. In addition, the effluent line was made of U, and each part of the reactor was sealed to block the inflow of external air, and the 20L water-displace gas collector was made of acryl to improve the amount of generated gas and purity of CH ₄ . Measured.

2-2. Organic matter On load rate  Methane production

The seeded granular sludge was drawn from the UASB plant of the ethanol wastewater treatment plant, and the organic loading rate was increased over 60 days after the granulation sludge of about 25% by volume of the total reactor capacity was planted for methane fermentation. Organic Loading Rate) was conducted at 3.5, 4.9, 7.3 and 9.1 kgCOD / m ³ d, respectively. As a result, as shown in FIG. 5, the amount of methane was gradually increased as the organic loading rate was increased. That is, 2.3, 3.9, 5.9 and 7.8 L of pure methane were produced at organic loading rates of 3.51, 4.9, 7.3 and 9.1 kg COD / m ³ d, respectively.

2-3. methane Generation rate  And COD  Removal rate measurement

Total solids (TS), volatile solids (VS), and volatile suspended solids (VSS) of crushed food waste were quantified according to the standard method. Total chemical oxygen demand (TCOD) and soluble chemical oxygen demand (SCOD) were analyzed using a HACH DR / 2000 spectrophotometer (U.S.A). In addition, the methane purity was gas chromatography (Hewlett-Packard 6890 series) equipped with a flame ionization detector (FID), DB-TPH capillary column (30m x 0.32mm x 0.25) μm) was used. The temperature of the sample injection section and the detection section was set to 100 and 250 ° C., respectively, and helium and hydrogen-air flames were used as carrier gases.

Methane produced from the concentrations of influent and effluent, SCOD, and SCOD removal, purity and food waste volatile solids (VS) analyzed at the steady state of each organic loading rate (OLR) during the operation of the methane fermentor. The production rate is shown in Table 3 below.

Item Measures Influent
pH 4.5 ± 0.2 SCOD (g / L) 20.5 ± 0.3 Runoff
pH 7.7 ± 0.3 SCOD (g / L) 0.19 ± 0.03 Methane produced

SCOD removal rate (%) 99.0 ± 0.3 Methane Purity (%) 73.0 ± 1.0 Methane production rate (m ³ CH ₄ / kgVS) 0.372 ± 0.018

As can be seen in Table 3, SCOD (20.5 ± 0.3g / L) of the influent used by diluting the food waste hydrolyzate five times is consumed as most substrates in the methane fermentation process, resulting in a high of about 99.0 ± 0.3%. The SCOD removal rate was shown, and the methane purity of the produced gas was 73.0 ± 1.0%, resulting in high purity methane. In addition, on the basis of the SCOD consumed in the experiment, when the conversion from the VS content of food waste showed a high methane production rate of about 0.372 ± 0.018 m ³ CH ₄ / kgVS.

3. other With biomass  Methane Production Comparison

The production rate of methane produced in the present invention is compared with the production rate of methane produced from various biomass raw materials is shown in Table 4 below.

Kinds Methane production rate (m ³ CH ₄ / kgVS) Manure 0.252-0.348 Cow 0.252-0.323 Swine 0.320-0.348 Poultry 0.258-0.330 Agro-Industrial waste 0.310-0.390 Sugar beet 0.370 Tomato 0.320 Orange 0.330 Brew's grain 0.310 Sugar cane (sorghum) 0.390 Municipal solid waste 0.140-0.540 Yard wastes 0.140-0.209 Paper waste 0.215-0.369 Sewage sludge 0.225-0.320 European food waste 0.321-0.540 Korean food waste 0.356-0.440 Invention 0.353-0.390

As can be seen in Table 4, the amount of methane produced from food waste (0.372 ± 0.018 m ³ CH ₄ / kg VS) is livestock manure (0.252 ~ 0.348 m ³ CH ₄ / kg VS), such as livestock meal, pig meal, poultry meal, Agricultural residues (0.310 ~ 0.390m ³ CH ₄ / kgVS) such as sugar beet, tomato, orange, sugarcane and biomass derived from municipal solid waste (0.140 ~ 0.540m ³ CH ₄ / kgVS) such as garden waste, waste paper, sewage sludge Since the methane production rate is higher than), food waste is a biomass with high potential for high purity methane production. However, it was slightly lower than the methane yield (0.321 ~ 0.540 and 0.356 ~ 0.440m ³ CH ₄ / kgVS) produced from food waste in Europe and Korea using the conventional two-stage methane fermentation process. It is believed that this is due to the low hydrolysis rate of solids (VSS) in the food waste during the decomposition process.

1 is a view showing a UASB reactor used for the production of methane in the present invention.

FIG. 2 is a graph showing the decrease in suspended solids (VSS) in food wastes according to an increase in the amount of each enzyme injected in individual enzyme hydrolysis of food wastes.

Figure 3 is a graph showing the VSS concentration of each mixed enzyme addition over time in the mixed enzyme hydrolysis of food waste.

4 is a graph showing the pure SCOD increase with respect to the pure VSS decrease in the mixed enzyme hydrolysis of food waste.

5 is a graph showing the amount of methane produced by increasing the organic load.

Claims (4)

In the methane production method, Adding 0.2 to 0.4 parts by weight of mixed enzyme per 100 parts by weight of crushed food waste and reacting at a temperature of 45 to 55 ° C. for 8 to 10 hours to obtain a hydrolysis solution (S10); Collecting the supernatant by centrifuging the hydrolysis solution at 3500 to 4500 rpm for 5 to 15 minutes (S20); Diluting the supernatant with distilled water 5 to 6 times to use the influent of the UASB reactor (S30); And Obtaining methane using the UASB reactor (S40); Methane production method using food waste, characterized in that it comprises a. delete The method of claim 1, The mixed enzyme is a methane production method using food waste, characterized in that the carbohydrase: protease: lipase is added by mixing in a ratio of 1: 2: 1. The method of claim 1, The temperature of the UASB reactor is methane production method using food waste, characterized in that 35 ~ 40 ℃.

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