KR20040110145A - Foodwaste recycling process exploiting decomposed manure - Google Patents

Abstract

PURPOSE: A method for composting food leftovers is provided to solve problems of conventional composting methods for example, complex pretreatment, high cost, long composting period and wastewater, by using decomposed compost as a water content modifier instead of saw dust. CONSTITUTION: The method for composting food leftovers comprises: sorting out impurities or foreign materials from food leftovers; grounding it; dehydrating it; mixing it with a water content modifier, that is decomposed compost; and stirring with a stirrer(7) and fermenting the mixture, wherein the mixing ratio of the food leftovers to the decomposed compost is 70:30 by weight. The method further comprises an anaerobic digestion process in which wastewater from the dehydration step of an aerobic composting process is mixed with a part of food leftovers, so as to generate methanol, which can be used as an energy source.

Description

Foodwaste recycling process exploiting decomposed manure}

The present invention relates to a composting method of food waste, and more particularly, in the composting process of food waste by the high operating cost and prolongation and dilution of the composting period by the complicated pre-treatment for the water control and the addition of a large amount of sawdust for water control It is related with the composting method of food waste for solving problems, such as the treatment of the wastewater which arises.

In the conventional food waste composting process, a composting method is performed by adding sawdust as a moisture control agent to food waste.

In Korean Patent Laid-Open Publication No. 2002-0031910, a method of composting by mixing sawdust as a moisture control agent in food waste is known. In Korean Patent Laid-Open Publication No. 2001-0017779, a mixture of sawdust and rice husk in food waste is used as a moisture control agent. Methods for composting are known.

When sawdust is added to the composting process, about 30% of the sawdust is added by weight (Ji et al., 1996), and about 40% of the food waste composting operation cost is used for the purchase of sawdust. Because it is composed of hardly decomposable substances, it does not decompose even after a long composting period, which leads to a prolonged maturity period.In addition, it may require long time for these decomposition and large facility area because it may contain growth inhibitory substances. Since there is a problem that affects the compost production cost, it is necessary to develop an alternative moisture control agent that can minimize the input of the moisture control agent.

In addition, the wastewater generated by washing water used for desalination during the composting process of food waste is processed in connection with the sewage treatment plant, but the wastewater generated in the composting process contains high organic matter concentration and low concentration of nitrogen and phosphorus. As a result, when the wastewater is discharged directly into the sewage treatment plant, there is a problem that an overload of the sewage treatment plant occurs.

The present invention has been proposed to solve the problems of the prior art as described above, the object of the present invention is to add a moisture control agent that can replace the sawdust which is a moisture control agent when composting food waste as described above To provide a composting method, and to provide a food waste composting method that can utilize the waste water generated during the composting process as an energy source.

The above object of the present invention was achieved by mixing the home compost as a moisture control agent to the food waste, and by mixing the waste water generated during the composting process with some food waste using an anaerobic digestion process to produce methane.

1 is a cross-sectional view showing a composting reactor used in the Lab Test according to a preferred embodiment of the present invention,

2 is a cross-sectional view showing a fermentor apparatus of a pilot scale for the composting experiment according to a preferred embodiment of the present invention,

Figure 3 is a graph showing the temperature change during the composting period in the Pilot Test according to a preferred embodiment of the present invention,

Figure 4 is a graph showing the decomposition of organic matter during the composting period in the Pilot Test according to a preferred embodiment of the present invention,

Figure 5 is a graph showing the pH change during the composting period in the Pilot Test according to a preferred embodiment of the present invention,

Figure 6 is a graph showing the salinity change during the composting period in the Pilot Test according to a preferred embodiment of the present invention,

7 is a graph showing how the salt affects the decomposition of SCOD components in the anaerobic digestion process according to a preferred embodiment of the present invention,

8 is a graph showing how salt affects gas generation in an anaerobic digestion process according to a preferred embodiment of the present invention.

9 is a graph showing the SCOD removal rate while changing the SCOD in HRT conditions of 2 (R1), 4 (R2), 6 (R3), 8 days (R4) according to a preferred embodiment of the present invention,

10 illustrates the relationship between SCOD removal rate, gas generation rate and pH change while changing SCOD under HRT conditions of 2 (R1), 4 (R2), 6 (R3), and 8th (R4) according to a preferred embodiment of the present invention. The graph shown.

* Description of the main parts of the drawings *

1. Air pump 2. Air flow control device

3. Compost 4. Reactor

5. Thermal cover 6. Perforated plate

7. Auger stirrer 8. Ammonia and humidity sensor

9. Roller 10. Pressure gauge

11. Intake / Exhaust Pump 12. Odor Suction Pipe

13. Reactor 14. Valve

The present invention for realizing this

In the aerobic composting method of food waste comprising the steps of bringing in and storing food waste, discharging the enamel by the sorting process, crushing, dehydrating, mixing sawdust with a moisture control agent, stirring and fermentation In

It is characterized by putting the composting compost as a moisture control agent.

Aerobic composting of organic wastes basically increases the internal temperature (60 ~ 70 ℃) by oxidative heat generated by decomposing organic matters by aerobic microorganisms, decomposes organic matters, reduces water by evaporating moisture, and stabilizes residues. It is used as compost.

TABLE 1

Table 1 shows a schematic process flow chart of the aerobic composting process, the aerobic composting process comprising the steps of importing and storing food waste;

Selecting the stored food waste and discharging the colloid;

Crushing the discharged food waste into a predetermined size;

Dehydration of the crushed food waste and dehydration by sludge centrifugation;

Injecting a moisture control agent for controlling the moisture of the dehydrated food waste;

Mixing the added moisture control agent with food waste;

Fermenting the mixed food waste and the moisture control agent by stirring;

The fermented compost is selected and discharged or returned.

As can be seen from Table 1, the moisture control agent is added through the storage step, the screening / discharging step, and the dehydration step. In the conventional aerobic composting process, the sawdust is added as a moisture control agent, but the composting process according to the present invention controls water. Zero home compost.

The use of low moisture content (less than 50%) may cause an increase in the amount of non-composting compost, which is added according to the present invention. Therefore, it is preferable to use low moisture content as much as possible. In the case of adding a large amount of home compost, it is preferable not to add a large amount because the air permeability is lowered and the salt concentration may increase.

In addition, in the present invention, as shown in Table 1, the leachate (wastewater) generated by the washing water for removing salt in the dehydration step during the aerobic composting process is mixed with a part of the food waste used for the composting to generate methane It is configured to further include an anaerobic digestion process that can be used as a source.

Anaerobic digestion is a process in which high concentrations of organic solids and organic polymers are converted into more stable low molecular materials such as gases, liquids, and inorganics by anaerobic conditions.

The anaerobic digestion process digests organic wastes containing soluble organic matters into VFA (Volatilefatty acid) by using a reaction tank in the operation of a digester for high-purity methane recovery, and converts VFA, a byproduct produced therein, into CO Methane is produced by a process that causes the reaction to switch to ₂ and CH ₄ .

Hereinafter, the specific configuration and operation of the present invention will be described with reference to Examples, but the scope of the present invention is not limited only to these Examples.

Example 1: Lab. For the development of a composting process that does not use sawdust. Test

1 is Lab. It is a composting reactor used for the test, and the reactor supplies oxygen (air) to the inside of the reaction tank using an air pump (1), and the amount of air flowing into the reaction tank through the air flow control device (2) is 0.2 L / min. Adjusted to / kg, and covered with a thermal cover (5) to keep the heat of fermentation during the composting progress, to facilitate the inflow of air into the compost and to separate the leachate was installed perforated plate.

Using the reactor, food waste was fixed at a wet weight ratio of 70%, and used compost as a moisture control agent instead of sawdust. The optimal amount of home compost was determined by adjusting the rate of home compost to 10-40%. The C / N ratio was not controlled at the beginning of composting. The progress of composting was investigated by changing the temperature, pH, water content, C / N ratio, organic matter content and salinity.

In the change of temperature, it was confirmed that the reaction rate of the high temperature zone proceeded rapidly by mixing the composting compost. The maximum temperature reached during the composting period showed the fastest composting reaction rate of 0.03d-1 / ℃ up to 76 ℃ when 30% of mixed compost was mixed.

No composting initial pH drop was found in compost with 30% and 40% mixed compost. Since the stabilized home compost was mixed, the organic matter content did not decrease significantly while the hot zone was maintained, but the organic compost was reduced by about 10% in the reactor where the home compost was mixed with 10% and 30%. There was no significant difference during the composting process because water was supplied for controlling the initial moisture content of composting.

The best ratios of water content and organic decomposition rate were 70%: 30% of food waste: home compost. By adding 30% of home compost in composting without sawdust, it was possible to achieve the first composting period by 9 to 10 days compared to the conventional sawdust addition composting.

Example 2 Pilot Test for Development of Composting Process without Sawdust

Based on the experimental results in Example 1, the present invention was installed on a pilot scale composting device in the field to perform an experiment for composting without using sawdust.

The food waste used in the present invention was produced at the time of S and used a solid component which had undergone the adsorbate removal step, crushing and dehydration.

The water content of the initial food waste was 70-75%, the salinity was 0.6-1.2%, pH 4-6, and the food waste used in the experimental seeds was 15-25% of the animal input during the experiment. It was found to remain as a component that was not crushed by the seeds of plants and plants, and experiments were conducted without removing the remaining non-fragmentable components to make the initial properties the same as those of the actual treatment plant.

The composting compost used as a sawdust substitute was added to produce 30% of the total weight produced in S. Initial moisture content was adjusted to 55-65%.

Figure 2 is a cross-sectional view showing a pilot scale fermenter device for the composting experiment, made of SUS 304 material of 1m in width, 4m in length, 1m in height and inside the stand auger (7), composting is in progress Ammonia and humidity sensors (8) for measuring the moisture content of odors and composting stages generated during operation, rollers (9) for smooth movement in the reaction tank of auger type agitators and ammonia and humidity sensors, Pressure gauge (10), three intake / exhaust pumps (11) to minimize the anaerobic in the fermentation tank during the fermentation period, odor suction pipe (12) for outflow of the odor generated during the composting period outside the compost site and seasonal external temperature Air heaters were installed in the primary fermenter to minimize the effects of

In addition, the inlet air was supplied using a downward nozzle to prevent clogging of the air supply nozzle, and the top of the nozzle covered about 20 cm of rice husk, and SUS 304 having a width of 5 cm and a length of 1 cm to prevent mixing between the chaff and the reactants. A perforation was used to serve as the valve 14.

In order to measure the physicochemical changes during the fermentation period, CO ₂ , O ₂ , humidity and temperature sensors were manufactured and installed.

The conditions of the experimental system are RUN-1 for food waste + home compost, RUN-2 for food waste + sewage sludge + home compost, and RUN-3 for food waste + sewage sludge + sawdust.

Figure 3 is a Pilot according to the present invention. It is a graph showing the temperature change during the composting period in the test, and as a result of the experiment, the experimental system using the composting compost in the temperature evaluation that can indirectly estimate the composting rate from FIG. While showing a rapid temperature rise close to 70 ℃, it can be seen that the experimental system using sawdust showed only a temperature rise of about 36 ℃.

4 is a pilot according to the present invention. It is a graph showing the decomposition of organic matter during the composting period in the test, and it can be seen from FIG. 4 that the rate of decomposition of organic matter is much faster than that of sawdust in terms of the rate of decomposition of organic matter.

5 is a pilot according to the present invention. It is a graph showing the pH change during the composting period in the test, the experimental system using the home compost from Figure 5 shows that the accumulation of organic acid due to the fast composting reaction did not show a large neutralization, but the rapid neutralization, the experimental system using sawdust It can be seen that a significant drop in pH due to the accumulation of organic acids was observed in the initial reaction.

On the other hand, Figure 6 is a graph showing the change in salinity concentration during the composting period in Pilot.Test according to the present invention, it can be seen from the Figure 6 that no significant difference is observed in the evaluation by the change in salinity concentration.

Example 3 Development of Washing Water Treatment Process for Desalination of Food Wastes by Methanogenic Anaerobic Wastewater Treatment

Reducing the high concentration of salt in food waste is a major challenge in domestic composting. In order to reduce the concentration of these salts, a method of washing with water is mostly used. Currently, in most cases, the wastewater generated in the composting process contains high organic matter concentrations and low concentrations of nitrogen and phosphorus, which is directly discharged to the sewage treatment plant. Is likely to cause overload problems.

In order to solve the above problems, the present invention has developed a process for the treatment of food waste washing water by anaerobic digestion using the characteristics of waste water containing high organic matter concentration and low phosphorus and nitrogen concentration.

In the present invention, by the basic concept that all wastes or waste water generated in the composting process should be treated in the process by the anaerobic digestion process using the characteristics of the food waste washing water containing a lot of organic matter generated in the dehydration step by the aerobic composting process. A part of the food waste used in composting and the washing water were mixed to establish a system that can simultaneously achieve the reuse and desalination as energy due to methane generation.

To this end, in the present invention, the optimum ratio of food waste and washing water to remove methane generation and salt was determined.

In the present invention, a 4L capacity CSTR (continuous stir tank reactor) type reactor was used. Food waste and washing water were introduced from the bottom of the reactor, and the gas from the reactor was collected from the inlet installed on the top of the reactor for analysis.

In order to maintain the constant temperature of the reactor, a water jacket (water-jaket) was used to maintain a temperature of 35 ℃ while operating the reactor.

7 is a graph showing the effect of salinity on the decomposition of SCOD components in the anaerobic digestion process, the result of the examination of how the salt affects the gas generated by the SCOD component and anaerobic digestion process, as shown in FIG. When the SCOD concentration was about 4500 mg / L, the salinity concentration of 2g / L (R1) was obtained more than 96% of SCOD removal after about 90 hours of operation, and at 7g / L (R2) and 12g / L (R3). It can be seen that a removal rate of about 70% is obtained.

From the above results, it was estimated that the anaerobic digestion efficiency drops sharply at a salt concentration of 7 g / L or more. In other words, when the ratio of food waste and washing water is more than 1: 2 (w / v), it is estimated that there will be a sharp inhibition on anaerobic digestion.

This fact can be seen more clearly from the results of gas generation by anaerobic digestion. FIG. 8 is a graph showing the effect of salinity on gas generation in the anaerobic digestion process. From FIG. 8, when the salinity of 2g / L was obtained, a gas generation amount of more than about 5000mL was obtained after 3 days of operation, whereas 7g / L And 12g / L, gas generation after 3 days was 1800-2200mL.

From the above results, the optimum ratio (w / v) of food waste and washing water in anaerobic treatment by salt concentration and gas generation amount was found to be 1: 3.

The SCOD removal rate and gas generation rate were examined by continuous operation experiments at HRT conditions of 2 (R1), 4 (R2), 6 (R3) and 8 (R4) days. In order to prevent the sudden overload of SCOD concentration in the reactor, the experiment was conducted slowly increasing to 3000 mg / L up to 3 days of operation, about 8000-9000 mg / L up to 10 days, and about 12000 mg / L after 10 days.

9 is a graph showing the SCOD removal rate when the SCOD is changed in HRT conditions of 2 (R1), 4 (R2), 6 (R3), and 8 (R4), and FIG. 10 is 2 (R1) and 4 (R2). , 6 (R3), 8 (R4) is a graph showing the pH change at this time, showing the SCOD removal rate and gas generation when changing the SCOD under HRT conditions.

From Figure 9 it can be seen that the high SCOD concentration of about 8.2g / L up to 75-95% was removed in a short hydraulic residence time (HRT) of 2-4 days compared to the conventional anaerobic digestion process, It can be confirmed that pH control is not necessary because it maintains a stable operation even in relatively acid (pH 4-5) influent from 10.

Example 4: determination of maturity of production compost

To determine the maturity of compost of food waste, food waste + dust, food waste + sewage sludge, which is produced using saw compost as a moisture control agent without using sawdust, and to determine the physical and chemical characteristics of each compost. The changes in soil physicochemical properties and the effects of crops such as cabbage and lettuce were compared.

As a result, the compost produced from food waste, food waste + flakes, food waste + sewage sludge showed the most dominant growth. In particular, compost produced from food waste + sewage sludge showed an average higher growth than commercial compost.

The present invention is to control the anaerobic phenomenon of the compost by the high moisture content in the early stage of composting by using sawdust compost without using any sawdust as a moisture control agent to maintain the aerobic condition through improving the ventilation line to the high temperature step during the composting process Shorten the first fermentation time, improve the rate of decomposition of organic matters, shorten the period of staying, prevent the accumulation of organic acids to prevent the pH decrease due to the accumulation of organic acids, and operating cost is reduced by not using sawdust This is a very beneficial invention for the fertilizer and environmental industry because it produces an excellent effect of treating organic waste and making it available as an energy source by utilizing wastewater generated during the composting process.

Claims (4)

In the aerobic composting method of food waste consisting of bringing in and storing food waste, discharging the enamel by the sorting process, crushing, dehydration, mixing the moisture control agent, stirring and fermentation, Composting method of food waste composting, characterized in that the use of ripening compost as the moisture control agent. The food waste composting method according to claim 1, wherein the mixing ratio of the input food waste and home compost is 70%: 30%. According to claim 1, Food waste characterized in that it comprises an anaerobic digestion process that can be used as an energy source by mixing the wastewater generated in the dehydration step of the aerobic composting process with a portion of the food waste used for the composting to generate methane Composting method. The food waste composting method according to claim 3, wherein the ratio (w / v) of the food waste to the wastewater is 1: 3.