Description

APPARATUS AND METHOD FOR TREATMENT OF FOOD

WASTE

Technical Field

[1] The embodiments of the present invention relate to an apparatus and a method for the treatment of food waste. Particularly, the embodiments of the present invention relate to an apparatus and a method for the treatment of food waste by degrading organic materials of food waste under both anaerobic and aerobic conditions, separating the treated food waste into a precipitate and a supernatant, and chemically treating the supernatant, wherein denitrification of nitrate nitrogen (NO -N) is conducted before and after the anaerobic degradation. Background Art

[2] The world population has drastically increased throughout the years. With such increase, the amount of food waste generated has also significantly increased. Currently, the food waste accounts for approximately 22.5% of the entire household waste.

[3] During the 1960's (prior to the industrialization age in Korea), the food waste was typically fed to livestock such as dogs, pigs, chickens and the like. However, due to the rapidly growing population and productivity, the amount of food waste significantly increased over the years, thereby fast becoming a tremendous social problem.

[4] Reclamation and incineration are typical methods for treating food waste.

However, the food waste generally tends to be soggy. This causes incomplete combustion during incineration and decreases incineration efficiency, thus resulting in high operational costs due to the large use of fuel to facilitate incineration. Further, the reclamation of food waste can lead to environmental pollution caused by landfill leachate (e.g., groundwater contaminations, noxious odors, etc.). Thus, the reclamation method has been banned in Korea since 2005.

[5] Therefore, there is a strong need for alternative approaches to reducing, treating and recycling food waste. Despite such need, no satisfactory approaches have yet been introduced. Disclosure of Invention

Technical Problem

[6] Therefore, in order to address and resolve the above-described problem, the present invention seeks to provide an apparatus and method for the treatment of food waste by converting such waste into a sludge with reduced weight and an effluent having

suitable quality for discharge, generating methane gas used as an energy source and maximizing the denitrification efficiency of nitrate nitrogen (NO -N).

Technical Solution

[7] According to one embodiment of the present invention, there is provided a method for treating food waste, comprising:

[8] (1) pre-treating a food waste by pulverizing the same and adding water thereto;

[9] (2) degrading organic materials of the pre-treated food waste under an anaerobic condition and collecting a methane gas generated therefrom;

[10] (3) concentrating and dehydrating the resulting material passed through the step (2);

[11] (4) denitrifying nitrate nitrogen included in a sludge, which is fed through a return line in the following steps (6) and (7), by using the organic materials remaining in the resulting material passed through the step (3) as a carbon source; [12] (5) degrading the organic materials remaining in the resulting material passed through the step (4) under an aerobic condition by using aerobic microorganisms and oxygen; [13] (6) denitrifying nitrate nitrogen (NO -N) included in the resulting material passed through the step (5) by using short-chain organic acids as a carbon source, which is fed through an inflow line; [14] (7) separating the resulting material passed through the step (6) into a precipitate and a supernatant; and [15] (8) transferring the precipitate separated in the step (7) to the step (4) through a return line and chemically treating the supernatant to remove non-biodegradable materials. [16] According to another embodiment of the present invention, there is provided an a pparatus for treating food waste, comprising: [17] an anaerobic digester wherein organic materials of food waste are degraded under an anaerobic condition and a methane gas is generated; [18] an anaerobic tank wherein nitrate nitrogen included in a sludge, which is fed through a return line, is subjected to denitrification by using the organic materials remaining in the resulting material passed through the anaerobic digester as a carbon source; [19] an aeration tank wherein the organic materials remaining in the resulting material passed through the anaerobic tank are degraded under an aerobic condition; and [20] a denitrification tank wherein the nitrate nitrogen remaining in the resulting material passed through the aeration tank is subjected to denitrification, [21] wherein the anaerobic and denitrification tanks are placed forward and behind the aeration tank, respectively, and the denitrification tank is connected to an inflow line

that feeds short chain organic acids thereinto. [22] A representative example of the apparatus according to the present invention is described in Fig. 1. Referring to Fig. 1, the apparatus for the treatment of food waste in accordance with the present invention may comprise: [23] an anaerobic digester 2 wherein organic materials of food waste are degraded under an anaerobic condition and a methane gas is generated; [24] a concentration tank 3 wherein the resulting material passed through the anaerobic digester 2 is concentrated and dehydrated; [25] an anaerobic tank 4 wherein nitrate nitrogen included in a sludge, which is fed through a return line, is subjected to denitrification by using the organic materials included in the resulting material passed through the concentration tank 3 as a carbon source; [26] an aeration tank 6 wherein the organic materials remaining in the resulting material passed through the anaerobic tank 4 are degraded under an aerobic condition; [27] a denitrification tank 7 wherein the nitrate nitrogen remaining in the resulting material passed through the aeration tank 6 is subjected to denitrification; [28] a precipitation tank 8 wherein the resulting material passed through the denitrif ication tank 7 is separated into a precipitate and a supernatant; [29] a chemical treatment tank 9 wherein the precipitate separated in the precipitation tank 8 is transferred to the anaerobic tank 4 through a return line, and wherein the supernatant is chemically treated to remove non-biodegradable materials; [30] a microorganism activation tank 5 wherein aerobic microorganisms are activated and transferred to the aeration tank 6 through an inflow line; [31] a gas collector 10 connected to the anaerobic digester 2 and adapted to collect the methane gas generated in the anaerobic digester 2; [32] a return line 16 which transfers the nitrate nitrogen generated in the denitrification tank 7 to the anaerobic tank 4, and a return line 17 that transfers the nitrate nitrogen generated in the precipitation tank 8 to the anaerobic tank 4; [33] a return line 18 adapted to continuously feed a sludge into the microorganism activation tank 5; [34] an inflow line 21 that feeds short chain organic acids into the denitrification tank 7; and

[35] a waste sludge line that discharges the sludge from the precipitation tank 8.

[36]

[37] Hereinafter, the present invention will be explained in more detail.

[38] Referring to Fig. 1, there is provided a method for treating food waste in accordance with the present invention. [39] The step (1) is a process for pre-treating food waste by pulverizing the same and

adding water thereto.

[40] Food waste is mainly composed of organic materials such as carbohydrates, fats, proteins and the like. Thus, it requires a relatively long period of time for hydrolysis due to the various particle sizes and types of said constituents. As such, the food waste must be finely pulverized by means of a mechanical method and water must be added thereto in an appropriate amount, which facilitates the smooth transfer of food waste to the following process. At this time, it is preferable to add water in a volume ratio of 1:1 to 1:1.5 based on the amount of food waste.

[41] The step (2) is a process for degrading the organic materials of pre-treated food waste under an anaerobic condition and collecting methane gas generated therefrom.

[42] The term "anaerobic degradation" used herein refers to a process in which anaerobic microorganisms metabolize organic materials included in the food waste by using them as a nutrient source, thereby producing methanol. The anaerobic degradation is composed of two successive steps: acid degradation and methane fermentation. The acid degradation step degrades carbohydrates, proteins and fats into alcohol or short- chain organic acids, while the methane fermentation step produces methane (CH ) by the action of methane forming microbes from the degraded organic acids. Said process takes place in the anaerobic digester 2 of the apparatus for the treatment of food waste in accordance with the present invention. Further, the anaerobic digester 2 may comprise: a gas collector 10 for collecting methane gas generated by the anaerobic degradation; a temperature controller 11 for regulating temperature inside the anaerobic digester 2; and a mixer 12 for stirring the mixture.

[43] During the anaerobic degradation process of organic materials, carbohydrates are degraded into glucose followed by finally being degraded into CH and CO , as shown by the following Reaction Scheme 1 :

[44] <Reaction Scheme 1>

[45] C 6 H 12 O 6 → 3CO 2 + CH 4

[46]

[47] Proteins and fats function to inhibit the decrease in pH within the anaerobic digester by inducing alkalization during the process of anaerobic degradation. The degradation reactions for proteins and fats are represented by the following Reaction Schemes 2 and 3, respectively:

[48] <Reaction Scheme 2>

[49] HOOCCH 2 CH2 CHNH2 COONa + 3H 2 O → CO 2 + 2CH4 + NH4 HCO3 + NaHCO 3

[50] <Reaction Scheme 3>

[51] CH 3 CH2 CH2 COONa + 2H 2 O → CO 2 + 2CH4 + NaHCO 3

[52]

[53] At this time, methane gas generated in the anaerobic degradation process may be

collected and used as an energy source in the form of a fuel.

[54] When hydraulic retention time (HRT) of the anaerobic digester 2 is adjusted to 80 days, food waste is preferably fed into the anaerobic digester 2 in an amount ranging from 600 to 650 WIt per day, more preferably about 625 WIt per day.

[55] Further, the anaerobic digester 2 of the present invention is capable of conducting all types of normothermic digestion, hypothermic digestion, mesophilic digestion and thermophilic digestion, and heated by a heating coil connected to a temperature controller 11. It is preferable that the reaction in the anaerobic digester 2 in the step (2) is carried out according to mesophilic digestion at a temperature ranging from 30 to 4O ⁰ C, more preferably at a temperature of about 35 ⁰ C. In addition, food waste and anaerobic microorganisms introduced into the anaerobic digester 2 are stirred by means of a mixer 12 to achieve homogeneously mixing.

[56] There is no limitation as to the anaerobic microorganisms employable in the present invention so long as they can grow under an anaerobic condition. The representative examples thereof may include Bacteroides succinogenes, Acetobacterium woodii, Methanobacterium formicicum, Methanocuccus vannielii and the like, but are certainly not limited thereto.

[57] The step (3) is a process for concentrating and dehydrating the resulting material passed through the anaerobic degradation step.

[58] The concentration and hydration process is for lowering the concentration of suspended materials, which is relatively high in the resulting material passed through the step (2). Such a process takes place in the concentration tank 3 of the apparatus adapted to treat food waste in accordance with the present invention. Since the raw water of food waste contains a large quantity of suspended materials, the effluent discharged from the anaerobic digester 2 also contains a high concentration of suspended materials. If the resulting material in which a concentration of suspended materials is high is introduced into the aeration tank 6, then it is very difficult to maintain a proper concentration of mixed liquor suspended solid (MLSS) in the aeration tank. However, the method of the present invention can remove the resulting material as a sludge cake after the concentration and dehydration in this step. This makes it possible to reduce the load factor of suspended materials in the aeration tank and maintain a proper concentration of MLSS.

[59] Preferable examples of the concentration method may include gravity concentration, centrifugation concentration, floating concentration and the like. The dehydration method may be exemplified by natural drying, mechanical dehydration and the like. Further, the representative examples of the mechanical dehydration may include vacuum dehydration, pressure dehydration, centrifugation dehydration, a belt press, a screw press and the like. In one preferred embodiment of the present invention,

the treated food waste may be concentrated by gravity and dehydrated using a belt press.

[60] The step (4) is a process for denitrifying nitrate nitrogen included in a sludge, which is transferred through a return line, by using the organic materials remaining in the resulting material passed through the concentration and dehydration step as a carbon source.

[61] In this step, nitrate nitrogen included in the sludge, which is transferred to the anaerobic tank 4 through the return line 16 from the denitrification tank 7 and through the return line 17 from the precipitation tank 8, is subjected to denitrification under an anaerobic condition. The denitrification is performed by using the organic materials remaining in the resulting material passed through the concentration and dehydration step as a carbon source. Phosphorous is also eluted in this step. When there is little dissolved oxygen in the anaerobic tank, energy is obtained by using a nitrogen-oxygen complex in the form of NO and NO as an electron acceptor. Further, nitrate nitrogen is converted into nitrogen gas (N ) by the action of denitrifying microorganisms (denitrifiers) and liberated into the air, as represented by the following Reaction Scheme 4:

[62] <Reaction Scheme 4>

[63] NO 3 → NO 2 → NO → N 2O → N 2

[64]

[65] The denitrification process takes place in the anaerobic tank 4 of the apparatus adapted to treat food waste in accordance with the present invention. Further, the anaerobic tank 4 may be equipped with a mixer 13 so as to homogeneously mix the denitrifying microorganisms, carbon sources and nitrate nitrogen. The denitrifying microorganisms employable in this process may include all types of bacteria, which are known in the art as those capable of producing nitrogen gas through the reduction of nitrate or nitrite. The representative examples thereof may include Pseudomonas sp., Micrococcus sp., Archromobacter sp., Bacillus sp. and the like, but are certainly not limited thereto.

[66] Since organic acids used as an electron donor in the denitrification process are plentiful in the resulting material passed through the anaerobic tank 2, the method for treating food waste in accordance with the present invention can effectively perform the denitrification process without adding an external carbon source.

[67] The step (5) is a process for degrading the organic materials remaining in the resulting material passed through the step (4) under an aerobic condition by using aerobic microorganisms and oxygen.

[68] The term "aerobic degradation" used herein refers to a process in which aerobic microorganisms take in organic materials included in food waste, use them as a nutrient

source for survival, and then degrade them into carbon dioxide, ammonia, water and the like. At this time, the produced ammonia in such a process binds to oxygen and is oxidized into nitrate (NO ) nitrogen by way of nitrite (NO ) nitrogen. Such an aerobic degradation takes place in the aeration tank 6 of the apparatus adapted to treat food waste in accordance with the present invention. At this time, the concentration of MLSS in the aeration tank 6 is preferably maintained in the range of 9,000 to 12,000 WIL

[69] There is no limitation as to the aerobic microorganisms employable in the present invention so long as they can grow under an aerobic condition. The representative examples thereof may include Bacillus megaterium, rotifers, stalked ciliates and the like, but are certainly not limited thereto. The aerobic degradation is preferably carried out at a room temperature for 10 to 15 days.

[70] The aeration tank 6 is divided into a number of compartments by means of a plurality of membranes. The amount of dissolved oxygen (DO) in each compartment is differently maintained in a graduate manner. In the preferred embodiment of the present invention, the aeration tank 6 may be divided into three compartments. Here, a first compartment of the aeration tank is designed to effectively degrade organic materials in waster water by maintaining a high DO concentration through the inflow of external air. Further, ammonia nitrogen is oxidized into nitrate (NO ) nitrogen via nitrite (NO ) nitrogen by the action of denitrifying microorganisms in this compartment. In a third compartment of the aeration tank, the supply of oxygen is discontinued so as to maintain a low DO concentration. The treated food waste is stirred by using a mixer 14 equipped at the upper part of the aeration tank, which makes it easy to perform the denitrification reaction in the following step. It is preferable that the DO concentration of the first compartment is maintained in the range of 0.5 to 1.0 WIl, while that of the second compartment is maintained in the range of 0.3 to 0.5 WIL Further, it is preferred that the DO concentration of the third compartment is maintained at 0.1 WIl or below.

[71] Microorganisms participating in the aerobic degradation are activated under an aerobic condition in the microorganism activation tank 5 and then transferred to the aeration tank 6 through an activated microorganism aeration tank inflow line 22. At this time, the inside of the microorganism activation tank 5 is kept under an aerobic condition by introducing external air. Thus, the aerobic microorganisms can be selectively activated in the microorganism activation tank 5 under such a condition. Particularly, it is preferable to use the aerobic microorganism in the form of a colony prepared by selectively isolating the microorganisms from soli and culturing the same. Further, the microorganism activation tank 5 is designed to continuously supply a sludge through the return line 18, which results in the successive activation of mi-

croorganisms eluted from the microorganism colony and those included in the introduced sludge. [72] The step (6) is a process for denitrifying nitrate nitrogen (NO -N) remaining in the resulting material passed through the aerobic degradation step by using short-chain organic acids as a carbon source, which is fed into a denitrification tank through an inflow line.

[73] Said process takes place in the denitrification tank 7 of the apparatus adapted to treat food waste in accordance with the present invention. Under an anaerobic condition, nitrate nitrogen is used as an oxygen source for denitrifying microorganisms and is converted into N gas (said process is referred to as denitrification). At this time, the denitrification efficiency can be maximized by using short-chain organic acids introduced into the denitrification tank though the denitrification inflow line 21 as a carbon source.

[74] The step (7) is a process for separating the resulting material passed through the denitrification step into a precipitate and a supernatant.

[75] Said process is carried out in the precipitation tank 8 of the apparatus adapted to treat food waste in accordance with the present invention. The food waste treated in the denitrification step is subjected to solid-liquid separation by means of gravity, thereby being separated into a precipitate and a supernatant. The separated supernatant is transferred to the next step for chemical treatment. On the other hand, the precipitated sludge is transferred to the anaerobic tank 4 through a return line 17, while nitrate nitrogen included therein is subjected to denitrification.

[76] Thereafter, some of the sludge falls into disuse through a sludge line 19, while the rest is transferred to the microorganism activation tank 5 through a return line 18 and subjected to microorganism activation.

[77] The step (8) is a process for transferring the precipitated sludge separated in said step to a chemical treatment tank through a return line and chemically treating the supernatant to remove non-biodegradable materials.

[78] Said process takes place in the chemical treatment tank 9 of the apparatus adapted to treat food waste in accordance with the present invention. In this process, the nonbiodegradable materials such as phosphorus, suspended materials, color inducing materials and the like can be removed by adding a coagulant. At this time, the coagulant employable in the present invention may include Al-based coagulants, Fe- based coagulants and the like, but is certainly not limited thereto.

[79] Representative examples of the Al-based coagulant may include Alum (Al SO )-H

O, PAC (poly aluminum chloride) and the like. Those of the Fe-based coagulants may include FeSO 4 -H 2 O, FeCl 3 , Fe 2 (SO 4 ) 3 and the like. The chemical treatment is conducted while considering the effects of the type and inflow amount of coagulant, pH, turbidity

and the like. Further, a coagulant aid may be further employed in this step. Representative examples the coagulant aid may include a pH regulator such as calcium hydroxide (Ca(OH) ), calcium oxide (CaO), sodium hydroxide (NaOH) and sodium carbonate (Na CO ), as well as a turbidity enhancer such as bentonite, flay ash, activated silica and cement dust.

[80] Hydraulic retention time (HRT) of the object to be treated in each reaction tank of the apparatus adapted to treat food waste in accordance with the present invention may be regulated as follows: 70 to 80 days for the anaerobic digester 2; 4 to 5 days for the concentration tank 3; 8 to 8.5 days for the anaerobic tank 4; 1 to 1.5 days for the microorganism activation tank 5; 10 to 15 days for the aeration tank 6; and 8 to 8.5 days for the precipitation tank 8.

[81] As described above, the method of the present invention is devised to treat food waste by combining aerobic degradation with anaerobic degradation and progressively perform all the process according to the order, thereby increasing the treatment efficiency of food waste. According to the method of the present invention, food waste is degraded both aerobically and anaerobically, and is converted into a sludge with reduced weight and an effluent satisfying water quality suitable for discharging. During such a complex degradation process, methane gas that can be used as an energy source is generated. The sludge obtained in the final step of the method can be finally treated by reclamation or incineration, or be used as composts or raw materials for construction after undergoing a recycling process.

[82] Further, the method for treating food waste in accordance with the present invention exhibits a high efficiency for removing nitrogen, which acts as a pollutant inducing eu- trophication of a river and lake.

[83] In the present invention, nitrogen is removed by the following successive process: it converts into ammonia by means of biological degradation; the converted ammonia is changed into nitrate nitrogen through a nitrification process; and the nitrate nitrogen is turned into nitrogen gas through a denitrification process.

[84] At this time, the method for treating food waste in accordance with the present invention is characterized by performing the denitrification process twice before and after the aerobic degradation so as to maximize the denitrification efficiency. In particular, in the denitrification process before the aerobic degradation, nitrate nitrogen included in the sludge that is supplied through the return line is converted into the nitrogen gas and removed. In the denitrification process after the aerobic degradation, the efficiency of denitrifying nitrate nitrogen is maximized by supplying organic acids as a carbon source through the inflow line.

Advantageous Effects

[85] The apparatus and method for the treatment of food waste in accordance with the present invention can convert food waste into a sludge with reduced weight and an effluent satisfying water quality suitable for discharging, generate methane gas that can be used as an energy source, and maximize the denitrification efficiency of nitrate nitrogen.

Brief Description of the Drawings [86] The above and other objects and features of the instant invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which: [87] Fig. 1 is a diagram schematically illustrating an apparatus for the treatment of food waste, which is configured to produce biogas and purify sewage in accordance with the present invention.

Best Mode for Carrying Out the Invention

[88] The present invention provids a method for treating food waste, comprising:

[89] (1) pre-treating a food waste by pulverizing the same and adding water thereto;

[90] (2) degrading organic materials of the pre-treated food waste under an anaerobic condition and collecting a methane gas generated therefrom;

[91] (3) concentrating and dehydrating the resulting material passed through the step (2);

[92] (4) denitrifying nitrate nitrogen included in a sludge, which is fed through a return line in the following steps (6) and (7), by using the organic materials remaining in the resulting material passed through the step (3) as a carbon source; [93] (5) degrading the organic materials remaining in the resulting material passed through the step (4) under an aerobic condition by using aerobic microorganisms and oxygen; [94] (6) denitrifying nitrate nitrogen (NO -N) included in the resulting material passed through the step (5) by using short-chain organic acids as a carbon source, which is fed through an inflow line; [95] (7) separating the resulting material passed through the step (6) into a precipitate and a supernatant; and [96] (8) transferring the precipitate separated in the step (7) to the step (4) through a return line and chemically treating the supernatant to remove non-biodegradable materials. [97] Further, the present invention provids an apparatus for treating food waste, comprising: [98] an anaerobic digester wherein organic materials of food waste are degraded under an anaerobic condition and a methane gas is generated; [99] an anaerobic tank wherein nitrate nitrogen included in a sludge, which is fed

through a return line, is subjected to denitrification by using the organic materials remaining in the resulting material passed through the anaerobic digester as a carbon source; [100] an aeration tank wherein the organic materials remaining in the resulting material passed through the anaerobic tank are degraded under an aerobic condition; and [101] a denitrification tank wherein the nitrate nitrogen remaining in the resulting material passed through the aeration tank is subjected to denitrification, [102] wherein the anaerobic and denitrification tanks are placed forward and behind the aeration tank, respectively, and the denitrification tank is connected to an inflow line that feeds short chain organic acids thereinto.

Mode for the Invention [103] Each reactor used in the apparatus of the present invention was manufactured from acryl so as to easily allow the observation of their interior. Further, anaerobic reactors were heated by using a heating coil connected to a temperature controller, the accuracy of which has an error of less than I ⁰ C. [104] Table 1 shows the resource and size of each reactor in the apparatus of the present invention. A return line in the apparatus of the present invention was equipped with a transfer pump. Further, an aeration tank and a microorganism activation tank were equipped with a ventilator. [105] Table 1

[106] [107] Food waste used in the following experiment was collected from a refractory of Korea Institute of Science and Technology. It was then finely pulverized with a blender and stored in a cold chamber until use.

[108] HRT of each reactor was regulated to 80 days for an anaerobic digester, 4 days for a concentration tank, 8 days for an anaerobic tank, 1 day for a microorganism activation tank, 12 days for an aeration tank and 8 days for a precipitation tank.

[109] MLSS concentration of an aeration tank was maintained at 10,000 WIl. For maintaining such a concentration, a certain amount of surplus sludge was discarded from the precipitation tank. In addition, the apparatus was configured to transfer the object to be treated by a natural flowing method using gravity. The input and transfer of a sample was automatically controlled by using a quantitative pump equipped with a timer so as to ensure its accurate amount.

[HO] During the chemical treatment, ferric chloride (FeCl ) was employed as a coagulant in a concentration of 100 DFe/£ [111] After treating the food waste by using the apparatus of the present invention, chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solids (TSS), total Kjeldahl nitrogen (TKN) and a total amount of phosphorus (T-P) of effluents obtained in each step were measured, as shown in Table 2. At this time, the experimental data were represented as a mean value during the operation.

[112] Table 2

[113]

[114] As described in Table 2, the properties of raw water of the pulverized food waste were as follows: TSS/VSS concentration was 89,800/84,000 WIt; COD concentration was 110,000 ω/t; BOD concentration was 57,000 WIt; and T-P concentration was 480 WIt. Further, TKN concentration was 4,000 WIt and Nϋoncentration was 53 WIt. This

4 shows that NH out of TKN accounts for 1.3%.

4

[115] The ammonia concentration of effluent obtained from the anaerobic digester was significantly high compared to the raw water since organic nitrogen was subjected to ammonification in the anaerobic digester. It has been confirmed from these results that the high concentration of organic nitrogen included in the raw water is converted into ammonia nitrogen by undergoing the anaerobic digester.

[116] The water quality of the effluent obtained from the precipitation tank, which was regarded as a biological treatment process, was as follows: CODcr concentration was 342 WIt; BOD concentration was 57 WIt; TKN concentration was 74 WIt; and T-P concentration was 73 WIt. The water quality of the effluent obtained after the chemical treatment was as follows: CODcr concentration was 52 WIt; BOD concentration was 18 WIt; TSS concentration was 17 WIt; TKN concentration was 45 WIt; and TP concentration was 5 WIt. It has been confirmed that as the steps for treating food waste progressed, the water quality of effluent was improved to a level sufficient enough for discharge. Industrial Applicability

[117] As apparent from the foregoing, the apparatus and method for the treatment of food waste in accordance with the present invention can convert food waste into a sludge with reduced weight and an effluent satisfying water quality suitable for discharging, generate methane gas that can be used as an energy source and maximize the denitrifi cation efficiency of nitrate nitrogen (NO -N).