Lactic acid type denitrification carbon source for biotransformation of kitchen waste as well as preparation method and application of lactic acid type denitrification carbon source

Abstract

The invention provides a lactic acid type denitrification carbon source for kitchen waste biotransformation and a preparation method and application thereof, and belongs to the technical field of sewage treatment. According to the preparation method provided by the invention, the kitchen waste is taken as a substrate, indigenous flora and exogenous lactic acid bacteria are combined to realize directional lactic acid biotransformation, and the sewage denitrification external liquid carbon source is prepared. The method has the beneficial effects that (1) the problem of low COD / TN (Chemical Oxygen Demand / Total Nitrogen) in the sewage denitrification process is solved, and the treatment cost of per ton of water of a sewage treatment plant is reduced while the kitchen waste is efficiently recycled; (2) stable and efficient directional lactic acid bioconversion of the kitchen waste is realized, and a single high-quality liquid denitrification carbon source with stable components is obtained; and (3) the negative influence of grease and the like on anaerobic fermentation is effectively reduced, the directional biotransformation effect of the kitchen waste is enhanced, different resource recovery treatment modes are adopted for different components, the utilization efficiency is improved, and full-amount recycling of the kitchen waste is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a lactic acid type denitrification carbon source for bioconversion of kitchen waste, and a preparation method and application thereof. Background Art

[0002] The amount of food waste produced worldwide is huge and is increasing year by year. According to the Food and Agriculture Organization (FAO) of the United Nations, by 2025, the world will generate about 2.2 billion tons of food waste. In my country, food waste accounts for about 50% of the total domestic waste, which is in a dominant position. Although the implementation of the garbage classification system in my country in recent years has enabled food waste to be collected and processed in a centralized manner, facing a large amount of food waste with complex components and characteristics, reasonable deep and high-value disposal and utilization is still a difficulty and challenge that needs to be solved urgently.

[0003] The composition of food waste is complex, with high water content, high organic matter content, high salt content, high oil content, easy biodegradation, carrying pathogenic microorganisms, easy to rot and deteriorate, thus breeding mosquitoes and flies and producing unpleasant odors. Traditional methods for treating food waste include incineration and landfill. Incineration has a high degree of reduction, but due to the low calorific value of food waste, it consumes a lot of energy for incineration, and produces harmful substances such as dioxins, causing secondary pollution. Sanitary landfill is the simplest treatment method, with a large treatment volume and low cost, but the excessive land occupation, difficult-to-treat leachate and large amounts of greenhouse gases are disappointing. At present, the main way to treat food waste in my country is to use anaerobic digestion to generate biogas with methane as the main component, and realize in-situ heat circulation supply through combustion. Its main drawback is that the remaining biogas residue and liquid are difficult to treat. In addition, there are more and more studies on the use of microorganisms to transform food waste to obtain specific chemicals, such as ethanol, lactic acid and volatile organic acids. However, it takes a lot of time and purification costs to extract the target product from the complex and low-concentration fermentation broth, the production cycle is long and the controllability is poor, and the market competitiveness is far lower than direct chemical synthesis. Therefore, it is necessary to develop a highly controllable, economical and environmentally friendly resource recovery pathway based on the characteristics of food waste itself.

[0004] Urban and rural sewage is an important source of nitrogen load in water bodies. In order to avoid excessive nitrogen discharge into natural water bodies and thus cause eutrophication problems, the discharge standards for nitrogen-containing pollutants in the effluent of sewage treatment plants are becoming increasingly stringent. However, urban and rural sewage in my country generally has the problem of low COD / TN. The microorganisms in the activated sludge cannot obtain sufficient carbon sources to support the denitrification process, making it difficult for sewage treatment plants to achieve ideal sewage treatment effects through the current biological denitrification technology. A simple solution is to add an external carbon source to compensate for the lower COD value in the influent. Currently, the commonly used external carbon sources are sugars, methanol and sodium acetate. Among them, sugars such as glucose are difficult to control in amount, and will cause sludge to swell violently, resulting in additional sludge disposal costs; methanol has certain biological toxicity, and there are also safety risks in transportation and use; although sodium acetate has a good effect, the cost is too high. Therefore, it is necessary to find a low-cost, high-denitrification efficiency and stable external carbon source.

[0005] Similar to the supernatant of sludge hydrolysis, food waste can also be hydrolyzed and acidified to generate liquid containing a variety of volatile organic acids (VFA) as an additional carbon source for denitrification, but its fermentation cycle is long and the product composition is difficult to control, and the denitrification effect is unstable. Therefore, it is of great practical significance to develop a cheap, efficient and stable liquid carbon source for sewage denitrification using food waste as a substrate. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a lactic acid-type denitrification carbon source for the biological transformation of food waste and its preparation method and application. The preparation method provided by the present invention realizes the lactic acid-type directional high-quality resource utilization of food waste by inoculating high-yield lactic acid bacteria, thereby providing a stable carbon source supply for denitrification and denitrification in sewage treatment plants.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a lactic acid-type denitrification carbon source for food waste bioconversion, the preparation method using food waste as a substrate, combining indigenous bacterial flora with exogenous lactic acid-producing bacteria to achieve directional lactic acid bioconversion, and preparing a wastewater denitrification additional liquid carbon source; the method comprises the following steps:

[0009] (1) sorting the food waste, removing the materials that are not easily crushed and fermented, preliminarily crushing and grinding, and adding water to make food waste slurry;

[0010] (2) After the food waste slurry is boiled and oil is extracted, it is separated into liquid phase, solid residue and crude oil by a three-phase separation machine, wherein the solid residue and crude oil are recycled and reused, and the liquid phase is reserved;

[0011] (3) injecting the unsterilized liquid phase into a batch anaerobic fermentation tank, inoculating lactic acid-producing bacteria at a ratio of 5% to 10% (v / v), maintaining a pH value of 6.0 to 7.2, a fermentation temperature of 30° C. to 45° C., stirring under sealed anaerobic conditions, and directing biotransformation for 3 days to 5 days; the lactic acid-producing bacteria is Enterococcus mundtii, with a deposit number of CGMCC No. 22227;

[0012] (4) Take the product after the bioconversion is completed, centrifuge it at 3000 rpm to 10000 rpm for 10 min to 30 min, and the supernatant obtained by centrifugation is the lactic acid type denitrification carbon source.

[0013] In the present invention, the indigenous flora is the original microorganisms in the food waste. The present invention prepares the food waste into a food waste slurry with higher biodegradability by pretreatment means such as grinding and solid-liquid ratio adjustment. In accordance with the open natural fermentation lactic acid production characteristics of food waste, the slurry is not sterilized, and the hydrolysis and acidification effect is enhanced by using a large number of indigenous microorganisms in the food waste. On this basis, high-yield lactic acid bacteria are additionally added, and the temperature and pH of the fermentation process are adjusted to promote the production of high-concentration and high-proportion lactic acid, which is used as a liquid denitrification carbon source with stable performance and good performance.

[0014] The invention sorts the restaurant kitchen waste, removes the substances which are not easy to be crushed and fermented, preliminarily crushes and grinds the waste, and adds water to prepare the restaurant kitchen waste slurry.

[0015] In the present invention, the materials that are not easily broken and fermented in step (1) preferably include but are not limited to shells, bones, plastics, and metals.

[0016] In the present invention, the preliminary crushing and grinding in step (1) is preferably performed by using a crushing pulper to grind the food waste into a uniform slurry.

[0017] In the present invention, the water content of the food waste slurry in step (1) is preferably 70% to 90%.

[0018] After the cooking and oil extraction of the kitchen waste slurry, the present invention is separated into a liquid phase, solid residue and crude oil by a three-phase separation machine, wherein the solid residue and crude oil are recycled and reused, and the liquid phase is reserved. The nitrogen-containing solid residue after the three-phase separation of the present invention can be used to produce insect protein feed, and the crude oil can be sold or used to produce biodiesel, thereby realizing the full resource utilization of kitchen waste.

[0019] In the present invention, the cooking and oil extraction in step (2) is performed by heating at 70° C. to 80° C. for 60 min to 120 min, with continuous stirring during the process.

[0020] The invention injects a liquid phase which has not been sterilized into a batch anaerobic fermentation tank, inoculates lactic acid-producing bacteria at a ratio of 5% to 10% (v / v), maintains a pH value of 6.0 to 7.2, a fermentation temperature of 30° C. to 45° C., stirs under sealed anaerobic conditions, and performs directional biotransformation for 3d to 5d; the lactic acid-producing bacteria is Enterococcus mundtii, and the preservation number is CGMCC No. 22227.

[0021] In the present invention, the lactic acid-producing bacteria need to be activated and enriched before inoculation; the activation conditions are: MRS culture medium, inoculation ratio (v / v) 10% to 25%, temperature 30°C to 45°C, activation time 9h to 12h; the enrichment conditions are: MRS culture medium, inoculation ratio (v / v) 10% to 25%, temperature 30°C to 45°C, enrichment time 12h to 36h.

[0022] In the present invention, the concentration of lactic acid producing bacteria in step (3) during inoculation is 1×10 7 ~1×10 10 CFU / mL.

[0023] The present invention takes the product after the biological transformation, centrifuges it at 3000rpm to 10000rpm for 10min to 30min, and the supernatant obtained by centrifugation is the lactic acid type denitrification carbon source.

[0024] In the present invention, the solid residue remaining after centrifugation can be collected and reused.

[0025] The present invention also provides a denitrified carbon source prepared by the preparation method described in the above technical scheme.

[0026] In the present invention, the denitrification carbon source also includes but is not limited to acetic acid, propionic acid, butyric acid, and ethanol.

[0027] The present invention also provides an application of the denitrification carbon source described in the above technical solution in sewage treatment, wherein the denitrification carbon source is added and used in a denitrification section of sewage treatment.

[0028] In the present invention, COD / TN needs to be adjusted to 5-10.

[0029] Beneficial technical effects: The present invention provides a lactic acid-type denitrification carbon source for food waste bioconversion and its preparation method and application. The preparation method of the present invention uses food waste as a substrate, combines indigenous bacteria with exogenous lactic acid bacteria to achieve directional lactic acid bioconversion, and prepares a wastewater denitrification plus liquid carbon source. Compared with the prior art, the beneficial effects of the present invention are:

[0030] (1) The present invention utilizes food waste to produce liquid carbon sources to solve the problem of low COD / TN in the process of sewage denitrification, and effectively utilizes food waste as a resource while reducing the per-ton water treatment cost of the sewage treatment plant.

[0031] (2) The present invention adopts the method of adding high-yield lactic acid bacteria to achieve stable and efficient directional lactic acid bioconversion of food waste, thereby obtaining a high-quality liquid denitrification carbon source with stable and single components.

[0032] (3) The present invention utilizes a quality-separation and phase-separation pretreatment method to effectively reduce the negative effects of oil and fat on anaerobic fermentation, enhance the directional biotransformation effect of food waste, adopt different resource recovery and disposal methods for different components, improve utilization efficiency, and realize the full resource utilization of food waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a process flow chart of the present invention;

[0034] Figure 2 This is a graph showing changes in carbon source concentration during open batch lactic acid fermentation in Example 1;

[0035] Figure 3 This is a graph showing the change in nitrogen concentration during biological treatment of sewage in Experimental Example 1 (with the addition of a lactic acid-based denitrification carbon source from food waste);

[0036] Figure 4 This is a graph showing the change in nitrogen concentration during biological wastewater treatment in Comparative Example 1 (with the addition of commercially available sodium acetate carbon source). DETAILED DESCRIPTION

[0037] In order to better understand the present invention, the content of the present invention is further explained in conjunction with the following examples, but the content of the present invention is not limited to the following examples. The materials, reagents, etc. used in the examples and test examples of the present invention, unless otherwise specified, can be obtained from commercial channels; the methods used in the examples and test examples of the present invention, unless otherwise specified, are conventional methods.

[0038] Enterococcus monteri, with a deposit number of CGMCC No. 22227, has been disclosed in patent CN113493809A.

[0039] Example 1

[0040] The kitchen waste from a university cafeteria in Beijing was taken, sorted to remove metals, plastics, etc., and then mixed with water at a solid-liquid ratio of 2:1 (v / v). The water content was 84.5%, and then injected into a grinder for crushing and refining. The kitchen waste slurry was injected into a cooking tank, heated to 80°C for 120 minutes, and 72% of the waste oil in the kitchen waste was extracted and recovered through a three-phase separator. The liquid phase obtained by three-phase separation was directly injected into an anaerobic fermentation tank without sterilization (open), and the activated and enriched Enterococcus montegrioides was inoculated at an inoculation ratio of 10% (v / v). Anaerobic fermentation was carried out at a pH of 6.8 and a fermentation temperature of 43°C for 4 days. The pH value during the fermentation process was adjusted and maintained with a 10M sodium hydroxide solution. The fermentation results are shown in Figure 2 The fermented material was centrifuged at 7000rpm for 10min to achieve solid-liquid separation. The supernatant is the lactic acid denitrification carbon source for kitchen waste, which is mainly composed of lactic acid and can be directly used as a liquid carbon source for denitrification. The HPLC test showed that the lactic acid concentration exceeded 100g / L and the SCOD reached 139895mg / L.

[0041] Test Example 1

[0042] In the denitrification batch experiment, the working volume of the conical flask was 500mL, and the activated sludge from the sewage treatment plant was inoculated. The sludge concentration MLSS was controlled at about 3000mg / L. The initial nitrate nitrogen concentration in the reactor was about 45mg / L. The addition of lactic acid-type denitrification carbon source from food waste made the influent COD concentration reach 315mg / L, that is, the COD / TN ratio was 7, and anoxic denitrification experiments were carried out. During the denitrification process, the nitrate nitrogen concentration gradually decreased, and after 2h, the nitrate nitrogen in the water was basically degraded completely; the nitrite nitrogen concentration gradually increased, and accumulated to the maximum value in 1h, and then gradually decreased. After 2.5h, the reaction was basically over, and no nitrite nitrogen was detected. The changes in the concentrations of different forms of nitrogen during the reaction can be seen in Figure 3 Specific denitrification rate V DN Up to 4.6mgNO x - N / (gMLSS·h), the calculation formula is as follows:

[0043]

[0044] Where V DN is the specific denitrification rate, mg NO x - -N / (g MLSS·h); MLSS is sludge concentration, g / L; Δt is denitrification time, h; NO x - -N(mg / L)=NO3 - -N+0.6NO2 - N; ΔNO x - -N,mg / L.

[0045] Comparative Example 1

[0046] In the denitrification batch experiment, the working volume of the conical flask was 500mL, and the activated sludge from the sewage treatment plant was inoculated. The MLSS was controlled at about 3000mg / L. The initial nitrate nitrogen concentration in the reactor was about 45mg / L. Sodium acetate carbon source was added to make the influent COD concentration reach 315mg / L, that is, the COD / TN ratio was 7, and anoxic denitrification experiments were carried out. During the denitrification process, the nitrate nitrogen concentration gradually decreased, and after 1.5h, the nitrate nitrogen in the water was basically degraded completely; the nitrite nitrogen concentration gradually increased, and accumulated to the maximum value in 40min, and then gradually decreased. After 4.5h, the reaction was basically over, and no nitrite nitrogen was detected. The changes in the concentrations of different forms of nitrogen during the reaction are shown in Figure 4 Specific denitrification rate V DN 2.4mgNO x - -N / (gMLSS·h).

[0047] Compared with the lactic acid liquid carbon source provided in Experimental Example 1, the sodium acetate in Comparative Example 1 showed a lower V DN This is related to the high accumulation of nitrite nitrogen, which leads to a slow denitrification process. This shows that the food waste bioconversion lactic acid liquid denitrification carbon source provided by the present invention has excellent denitrification performance and can be used as an external carbon source for strengthening sewage denitrification.

[0048] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a lactic acid-type denitrification carbon source for bioconversion of food waste, characterized in that: The preparation method uses kitchen waste as a substrate, combines indigenous bacterial flora with exogenous lactic acid-producing bacteria to achieve directional lactic acid bioconversion, and prepares wastewater denitrification and liquid carbon source; and comprises the following steps: (1) sorting the food waste, removing the materials that are not easily crushed and fermented, preliminarily crushing and grinding, and adding water to make food waste slurry; (2) After the food waste slurry is boiled and oil is extracted, it is separated into liquid phase, solid residue and crude oil by a three-phase separation machine, wherein the solid residue and crude oil are recycled and reused, and the liquid phase is reserved; (3) injecting the unsterilized liquid phase into a batch anaerobic fermentation tank, inoculating lactic acid-producing bacteria at a ratio of 5% to 10% (v / v), maintaining a pH value of 6.0 to 7.2, a fermentation temperature of 30° C. to 45° C., stirring under sealed anaerobic conditions, and directing biotransformation for 3 days to 5 days; the lactic acid-producing bacteria is Enterococcus mundtii, with a deposit number of CGMCC No. 22227; (4) Take the product after the bioconversion is completed, centrifuge it at 3000 rpm to 10000 rpm for 10 min to 30 min, and the supernatant obtained by centrifugation is the lactic acid type denitrification carbon source.

2. The preparation method according to claim 1, characterized in that: The water content of the kitchen waste slurry in step (1) is 70% to 90%.

3. The preparation method according to claim 1, characterized in that: The steaming and oil extraction in step (2) is performed by heating at 70°C to 80°C for 60min to 120min, with continuous stirring during the process.

4. The preparation method according to claim 1, characterized in that: The concentration of lactic acid bacteria in step (3) during inoculation is 1×10 7 CFU / mL~1×10 10 CFU / mL.

5. A denitrified carbon source prepared by the preparation method according to any one of claims 1 to 5.

6. The denitrification carbon source according to claim 5, characterized in that The denitrification carbon source also includes but is not limited to acetic acid, propionic acid, butyric acid, and ethanol.

7. Use of the denitrification carbon source according to any one of claims 5 to 6 in sewage treatment, characterized in that: The denitrification carbon source is added and used in the denitrification section of sewage treatment.

8. The use according to claim 7, characterized in that: COD / TN needs to be adjusted to 5-10.

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