阅读说明：本技术 一种低返料比下提高餐厨垃圾批式干发酵系统稳定性和产气量的方法 (Method for improving stability and gas production rate of kitchen waste batch dry fermentation system under low material return ratio ) 是由 袁海荣 包蕊 李秀金 于 2021-07-27 设计创作，主要内容包括：一种低返料比下提高餐厨垃圾批式干发酵系统稳定性和产气量的方法属于有机固体废物厌氧消化领域。本发明针对易酸化原料在批式厌氧干法发酵时容易失稳导致系统崩溃的问题,提出一种在批式厌氧中低返料比条件下提高餐厨垃圾等易酸化物料干法厌氧发酵系统稳定性并提高产气量的方法,主要包括原料的准备、青稞秆的预处理和预处理青稞秆添加方式和厌氧消化4部分。本发明通过在餐厨垃圾中加入不同比例的预处理青稞秆,可有效改善餐厨垃圾厌氧消化的产气性能,厌氧消化周期明显缩短,系统稳定性明显提高。(A method for improving the stability and the gas production rate of a kitchen waste batch dry fermentation system under a low material return ratio belongs to the field of organic solid waste anaerobic digestion. The invention provides a method for improving the stability of a kitchen waste and other easily-acidified materials dry anaerobic fermentation system and improving the gas yield under the condition of low-medium material return ratio in batch anaerobic aiming at the problem that the easily-acidified materials are easy to destabilize to cause system collapse during batch anaerobic dry fermentation, which mainly comprises 4 parts of raw material preparation, highland barley stalk pretreatment, a pretreated highland barley stalk adding mode and anaerobic digestion. According to the invention, the pretreated highland barley stalks with different proportions are added into the kitchen waste, so that the gas production performance of anaerobic digestion of the kitchen waste can be effectively improved, the anaerobic digestion period is obviously shortened, and the system stability is obviously improved.)

1. A method for improving the stability and the gas production rate of a kitchen waste batch dry fermentation system under the condition of low material return ratio is characterized in that,

comprises the following contents:

(1) preparation of the raw materials

The raw materials comprise kitchen waste, highland barley straw, CaO and biogas slurry; taking the kitchen waste back, removing impurities, crushing the kitchen waste into slurry, and storing the slurry in a refrigerator at the temperature of-20 ℃ for later use; taking the highland barley stalks back, naturally airing and drying the highland barley stalks, and crushing the highland barley stalks for later use; the biogas slurry is a liquid part discharged after anaerobic digestion, and the biogas slurry is discharged after anaerobic digestion by taking straws or kitchen waste as a raw material; if the biogas slurry is the biogas slurry of other raw materials except the straws or the kitchen waste, the straws or the kitchen waste are required to be added for acclimation for more than one month and then used; the total solid content in the biogas slurry is controlled to be 2% -5%, and if the total solid content is higher than the range, the solid content needs to be reduced;

(2) pretreatment of highland barley stalk raw material

Performing combined pretreatment on the highland barley stalks by using CaO and biogas slurry; firstly, weighing a certain mass of highland barley stalks and placing the highland barley stalks in a self-sealing bag, evacuating air in the self-sealing bag, and uniformly spreading the highland barley stalks on the self-sealing bag; weighing CaO, firstly, uniformly scattering CaO on the surface of highland barley stalks in a self-sealing bag, fully mixing the CaO and the highland barley stalks, then pouring weighed biogas slurry into the self-sealing bag, fully mixing the CaO, the biogas slurry and the highland barley stalks uniformly, sealing the self-sealing bag, wherein the addition amount of the CaO is 4-8% of the total dry solid weight (TS) of the highland barley stalks, the moisture content in a pretreatment system is ensured to be 70% in the pretreatment process, the moisture content in the pretreatment system is adjusted by the amount of the biogas slurry added into the system, the solid content of the added biogas slurry is 2-5%, the temperature is controlled to be 35 ℃, and the pretreatment time is 48 hours; the raw materials of the pretreatment system comprise highland barley stalks, CaO and biogas slurry;

(3) highland barley stalk adding mode

Mixing the pretreated highland barley stalks with kitchen waste, wherein the mixing ratio by mass is highland barley stalks: fully mixing the kitchen waste equal to 0.2-5;

(4) anaerobic fermentation

Mixing highland barley stalks: transferring the mixed material with the kitchen waste equal to 0.2-5 into an anaerobic reaction bottle, adding an inoculum, and then fully and uniformly mixing, wherein the inoculum is discharged after straw or kitchen waste is used as a raw material for anaerobic digestion, and if the original biogas slurry except the straw or kitchen waste is used as the inoculum, the straw or kitchen waste needs to be added for acclimation for one month and then is used; the addition amount of the inoculum is 2 times of the TS of the mixed material, the system of the anaerobic reaction bottle is ensured to comprise the pretreated highland barley stalks, the kitchen waste and the inoculum, the total TS of the mixture is 20 percent, the pH value is measured after the mixture is fully mixed, if the pH value is lower than 7.5, the pH value of the mixture needs to be uniformly adjusted to 7.5-8.0, and the reaction bottle is sealed; meanwhile, adding pure highland barley stalks, pure kitchen waste groups and inocula as blank controls, and deducting a background value; the fermentation temperature is 35 ℃, and the anaerobic fermentation period is 40 d; and arranging a plurality of parallel samples in each group, and taking an average value to analyze and calculate.

Technical Field

The invention belongs to the field of anaerobic digestion of organic solid wastes, and particularly relates to a method for improving the stability of a kitchen waste dry-process anaerobic digestion system, relieving acidification and improving gas production under the condition of low material return ratio.

Background

The anaerobic digestion technology is an important method for effectively obtaining biomass energy, has the advantages of low energy consumption, high capacity and the like, and is widely applied to industrialization and large-scale demonstration in China at present. The dry anaerobic fermentation technology is an effective way for the energy regeneration and disposal of organic solid wastes, and has gradually become a hot spot of the research on the agricultural solid waste resource technology of various countries in the world in recent years. Compared with wet anaerobic digestion, dry anaerobic digestion has the advantages of small fermentation volume, low reaction water demand, less biogas slurry and the like, but has a plurality of problems in actual operation. Firstly, the starting is difficult and the fermentation period is long; and secondly, metabolite inhibition, wherein the concentration of a substrate of a dry fermentation system is much higher than that of wet fermentation in the reaction process, so that the transfer and diffusion of reaction intermediate products and energy in a medium are difficult, and intermediate metabolites in partial areas are excessively accumulated, so that the acidification and instability of the system are caused, and the system start failure is caused. In order to enable a system to start quickly and to keep the system stable, it is often necessary to increase the amount of inoculation and the feed back ratio at each feeding, which greatly increases the running cost.

Due to the large difference of physicochemical properties of different raw materials, the addition amount of the inoculum for anaerobic dry fermentation is also different. Generally, the inoculation amount of the dry fermentation system is about 30% of the raw material. When the pig manure is used as a raw material, the starting is fastest when the inoculation is 50%. But for easily acidified domestic garbage, kitchen and other raw materials, in the dry anaerobic digestion process, the inoculation ratio at the start of the system accounts for 80-100% of the effective volume of the fermentation tank. The higher the inoculation ratio, the less organic matter will be treated and the less efficient its anaerobic digestion will be. Otherwise, acidification and instability of the system may result. The Wang research finds that: under the conditions that the TS of a dry fermentation system is 29 percent and the inoculation ratio is 0.6(VS ratio) (corresponding to the ratio of inoculum to raw material is 2:1), when the content of the cucumber residues is more than 30 percent for 5 pig manures or 50 percent for 3 pig manures, the TVFA/alkalinity value of the system is between 0.58 and 0.85, and the system is in an unstable state. When the mixing ratio of the pig manure to the corn straws to the cucumbers is 5:2:3, the methane yield is up to 305.4mL/g VS (Wang Y, et al. effects of co-differentiation of cucumber metabolites to corn stock and pig management ratio of methane production in soluble state and biological chemistry [ J ]. 2017,250,328 and 336.). The maximum methane yield of the mixed raw material is 246.9mg/L VS (Xiaoang, Chen X., et al. Cooperation of high-solids to liquid and biological co-diagnostic of food and green water [ J ]. Bioresource Technology 2014,154,215- & 221.) under the condition that the TS of the system is 20% and the ratio of kitchen waste to fallen grass leaves is 2: 3.

Therefore, in order to solve the problem of anaerobic dry fermentation acidification, the invention mixes the kitchen waste with the highland barley stalks according to a certain proportion, and adopts methods such as pretreatment and the like under the condition of lower return ratio, thereby effectively improving the buffer capacity of the system and further improving the anaerobic digestion efficiency and the gas production rate.

Disclosure of Invention

The invention provides a method for improving the stability of a kitchen waste and other easily-acidified materials dry anaerobic fermentation system and improving the gas yield under the condition of low-medium material return ratio in batch anaerobic aiming at the problem that the easily-acidified materials are easy to destabilize to cause system collapse during batch anaerobic dry fermentation, which mainly comprises 4 parts of raw material preparation, highland barley stalk pretreatment, a pretreated highland barley stalk adding mode and anaerobic digestion.

The technical scheme of the invention comprises the following contents:

(1) preparation of the raw materials

The raw materials comprise kitchen waste, highland barley straw, CaO and biogas slurry. Taking the kitchen waste back, removing impurities, crushing the kitchen waste into slurry, and storing the slurry in a refrigerator at the temperature of-20 ℃ for later use; taking the straws as the highland barley straws, naturally airing and drying the highland barley straws, and crushing the highland barley straws for later use; CaO is analytically pure or industrially available; the biogas slurry is a liquid part discharged after anaerobic digestion, and the biogas slurry is preferably discharged after anaerobic digestion by taking straws or kitchen waste as a raw material. If the biogas slurry is the biogas slurry of other raw materials, straws or kitchen waste are added for domestication for one month and then are used. The total solid content in the biogas slurry is controlled to be 2-5%, and if the total solid content is higher than the range, the solid content needs to be reduced by adopting a filtration or centrifugation mode and the like.

(2) Pretreatment of highland barley stalk raw material

And performing combined pretreatment on the highland barley stalks by using CaO and biogas slurry. Firstly, weighing a certain mass of highland barley stalks and placing the highland barley stalks in a self-sealing bag, evacuating air in the self-sealing bag, and uniformly spreading the highland barley stalks on the self-sealing bag. Weighing CaO with corresponding mass, firstly uniformly scattering the CaO on the surface of highland barley stalks in a self-sealing bag, fully mixing the CaO and the highland barley stalks, then pouring the weighed biogas slurry into the self-sealing bag, fully mixing the CaO, the biogas slurry and the highland barley stalks uniformly, sealing the self-sealing bag, wherein the addition amount of the CaO is 4-8% of the total dry solid weight (TS) of the highland barley stalks, the moisture content in a pretreatment system is ensured to be 70% in the pretreatment process, the moisture content in the pretreatment system is adjusted by the amount of the biogas slurry added into the system, the solid content of the added biogas slurry is 2-5%, no additional water is needed, the temperature is controlled at 35 ℃, and the pretreatment time is 48 hours.

(3) Highland barley stalk adding mode

A large container, such as a large beaker, or a basin with a large opening is prepared, so that materials can be mixed and stirred sufficiently. Mixing the highland barley stalks pretreated for 48 hours with the kitchen waste, wherein the mixing ratio is highland barley stalks: and (3) putting the kitchen waste equal to 0.2-5 into a large container for fully mixing.

(4) Anaerobic fermentation

Uniformly mixing the materials, namely the highland barley stalks: transferring the material with the kitchen waste equal to 0.2-5 into an anaerobic reaction bottle, adding an inoculum, and then fully and uniformly mixing, wherein the inoculum can be anaerobic digestion biogas slurry or anaerobic digestion sludge of various raw materials, preferably, straw or kitchen waste is used as the discharge material of the raw materials after anaerobic digestion, and if biogas slurry of other raw materials is used as the inoculum, the straw or kitchen waste needs to be added for acclimation for one month and then be used. The addition amount of the inoculum is 2 times of the TS of the mixed material, the system of the anaerobic reaction bottle is ensured to comprise the pretreated highland barley stalks, the kitchen waste and the inoculum, the total TS of the mixture is 20%, the pH value is measured after the mixture is fully mixed, if the pH value is lower than 7.5, the pH value of the mixture needs to be uniformly adjusted to 7.5-8.0, and the reaction bottle is sealed well. Meanwhile, pure highland barley stalks, pure kitchen waste groups and inocula are added as blank controls, and background values are deducted. The fermentation temperature is 35 ℃, and the anaerobic fermentation period is 40 d. Each group was set with 3 replicates and the average of the three replicates was taken for analytical calculation. And (3) measuring the daily gas production by using a drainage method in the fermentation process, measuring the percentage content of methane, and calculating the daily methane production. The bottle weight, pH value after discharging, TS, VS, ammonia nitrogen, alkalinity, VFA and other properties of the discharged materials are weighed for evaluating the anaerobic digestion performance.

Compared with the prior art, the invention has the following beneficial effects:

(1) the gas production rate is obviously improved

By adding the pretreated highland barley stalks in different proportions into the kitchen waste, the method can be used for preparing the foodEffectively improve the gas production performance of kitchen garbage anaerobic digestion, wherein 1 part of pretreated highland barley stalk is added in 3 parts of kitchen garbage, namely the kitchen and highland barley stalk TS is 3: the methane yield is highest in anaerobic digestion at 1 hour, the methane yield is highest at 407.93mL/g VS after anaerobic digestion for 40 days, and the methane yield is 140.84 percent and 97 percent higher than that of pure highland barley stalks and pure kitchen waste at 40 days respectively. In the whole anaerobic digestion period, the kitchen waste and the pretreated highland barley stalks 3:1 group reaches 80 percent of total gas production rate, namely T₈₀The yield of the methane is 342.60mL/g VS, which is improved by 555.46% compared with the yield of pure kitchen methane. Anaerobic digestion of the kitchen waste and the pretreated highland barley stalks 3 in 25 days: the yield of methane of 1 group is 240.77mL/g VS, which is improved by 839.09% compared with the yield of pure kitchen methane.

(2) The anaerobic digestion period is obviously shortened

After the highland barley stalks pretreated by combining 6 percent of TSCAO and biogas slurry are added into the kitchen waste, the acidification phenomenon of the kitchen waste can be obviously improved, and the anaerobic digestion period is obviously shortened. The mixing ratio of the kitchen waste, CaO with different concentrations and biogas slurry in combined pretreatment of the highland barley stalks is 3:1 hour, T₈₀Is 29-30 days, is shortened by 26.7-31.0 percent compared with a pure kitchen waste group (38d), greatly saves the operation cost and is more suitable for industrial production.

(3) The system stability is obviously improved

The system stability of the batch anaerobic dry fermentation of the kitchen waste and the pretreated highland barley stalks under the conditions of different mixing ratios is obviously better than that of a pure kitchen waste batch anaerobic dry fermentation reaction system, when the proportion of the kitchen waste is more than or equal to 5, acidification and severe acidification phenomena occur in the system with a low material return ratio (inoculum to raw material ratio is 2:1), and when the proportion of the kitchen waste is less than 5, the acidification phenomenon does not occur in the system.

Drawings

FIG. 1 is a methane yield graph

Detailed Description

(1) Raw material collection

Crushing the kitchen waste into slurry by using a crusher, and storing the slurry in a refrigerator at the temperature of-20 ℃ for later use; naturally drying the highland barley stalks, crushing the highland barley stalks into 20 meshes, and standing and storing the highland barley stalks at normal temperature for later use; and collecting a discharged liquid part obtained by anaerobic digestion of kitchen waste serving as a raw material in a kitchen waste treatment plant as an inoculum and biogas slurry, and storing the inoculum and biogas slurry at normal temperature for later use.

(2) Pretreatment of highland barley stalk raw material

The highland barley stalks are jointly pretreated by CaO and biogas slurry, the addition amounts of the CaO are respectively 4%, 6% and 8% of dry basis of the highland barley stalks, the total water content in a pretreatment system is 70%, wherein the water content is adjusted by the biogas slurry without adding water, the temperature is controlled to be about 35 ℃, and the pretreatment is carried out for 48 hours. The specific operation is as follows:

firstly, 100g of highland barley stalks are weighed and put into a self-sealing bag, and 9 bags are weighed together. Weighing 4%, 6% and 8% (namely 4g, 6g and 8g) CaO, uniformly scattering the weighed CaO on the surface of the highland barley straw in the self-sealing bag, fully mixing the CaO and the highland barley straw, pouring biogas slurry into the self-sealing bag, fully mixing the CaO, the biogas slurry and the highland barley straw, sealing the self-sealing bag, sealing, ensuring that the moisture content in the pretreatment system is 70% (namely 30% of highland barley straw TS), adjusting the moisture content by the biogas slurry without additionally adding water, controlling the temperature to be about 35 ℃, performing anaerobic digestion on the pretreated raw materials after 48 hours of pretreatment, measuring the biogas yield and the methane content every day, and determining the optimal pretreatment parameters by using the methane yield.

The results show that: when the water content of the pretreatment is 70 percent, and the addition amount of CaO is 4 percent, 6 percent and 8 percent of the dry basis of the highland barley stalks, the methane yield of the pretreated highland barley stalks is 148.06mL/gVS, 171.25mL/gVS and 158.00mL/gVS respectively, and is improved by 20.38 percent, 39.23 percent and 28.45 percent respectively compared with the methane yield of the non-pretreated highland barley stalks (123.01mL/gVS), so that the pretreatment conditions of the optimal methane production group are 70 percent of water content and 6 percent of CaO. The results are shown in table 1:

TABLE 1 pretreatment Condition parameter screening

(3) Method for adding highland barley stalks

A larger container, which can be a large beaker, or a container with a larger opening of a basin, is prepared, so that the materials are conveniently and fully mixed and stirred. The pretreated highland barley stalks (6% CaO and 70% pretreated water content, both calculated as highland barley stalks TS) and the kitchen waste are put into a larger container for fully mixing according to the TS ratio of 1:1, 1:3, 1:5, 3:1 and 5:1, and the amount of the specifically weighed highland barley stalks and the amount of the kitchen waste are shown in Table 2.

(4) Anaerobic fermentation

And (3) transferring 5 groups of the uniformly mixed materials 1:1, 1:3, 1:5, 3:1 and 5:1 into an anaerobic reaction bottle with an effective volume of 400mL, adding an inoculum, and then fully and uniformly mixing, wherein the inoculum is a liquid part discharged after anaerobic digestion by taking kitchen waste as a raw material, the addition amount of the inoculum is 2 times of the TS of the mixed material, the specific addition amount is shown in Table 2, the total TS of the mixture in the anaerobic reaction bottle is ensured to be 20%, and the total mass of the materials in the bottle is kept to be 600 g. After mixing well, the pH value is measured, if the pH value is lower than 7.5, the pH value of the mixture needs to be uniformly adjusted to 7.5-8.0, and the reaction bottle is sealed. Meanwhile, pure highland barley stalks, pure kitchen waste groups and inocula are added as blank controls, and background values are deducted. The fermentation temperature is 35 ℃, and the anaerobic fermentation period is 40 days. Each group was set with 3 replicates and the average of the three replicates was taken for analytical calculation. And (3) measuring the daily gas production by using a drainage method in the fermentation process, measuring the percentage content of methane, and calculating the daily methane production. The bottle weight, pH value after discharging, TS, VS, ammonia nitrogen, alkalinity, VFA and other properties of the discharged materials are weighed for evaluating the anaerobic digestion performance.

TABLE 2 Loading data

And (3) measuring the daily gas production by using a drainage method in the fermentation process, measuring the percentage content of methane, and calculating the daily methane production. Discharging after fermenting for 40 days, wherein the bottle weight, the pH value after discharging, TS, VS, ammonia nitrogen, alkalinity, VFA and other properties are required for discharging.

As a result, it was found that: the pure kitchen waste is treated in an acidification state all the first 15 days, and the methane yield of the pure kitchen waste is 18.20mL/g VS all the time at 5-15 days (as shown in figure 1), which indicates that under the condition of low material return ratio, the kitchen waste laboratory set system is always in acidThe chemical state does not enter a methanation fermentation stage, normal gas production is started until 20 days later, and normal gas production can be realized within the first 20 days by adding the highland barley straw groups pretreated according to different proportions, namely 1:1, 1:3, 1:5, 3:1 and 5:1, which shows that the acidification phenomenon of the pure kitchen waste can be effectively relieved by adding the pretreated highland barley straws into the easily-acidified kitchen waste under the condition of low material return ratio. The methane yield of the pure highland barley stalks is 169.38mL/g VS, and after the highland barley stalks with different proportions are added, the methane yields of the kitchen waste materials of 1:1, 1:3, 1:5, 3:1 and 5:1 are 358.91, 407.93, 383.39, 258.70 and 242.81mL/g VS respectively, which are improved by 111.89%, 140.83%, 126.34%, 52.73% and 43.35% respectively and are improved by 73.33%, 97.00%, 85.15%, 24.93% and 17.26% respectively compared with the methane yield of the pure highland barley stalks. Wherein, the kitchen waste and the pretreated highland barley stalks 3: the highest methane yield of the group 1 in anaerobic digestion 40 days is 407.93mL/g VS, which is 140.84 percent and 97 percent higher than the methane yield of pure highland barley stalks and pure kitchen waste in 40 days respectively. In the whole anaerobic digestion period, the kitchen waste and the pretreated highland barley stalks 3:1 group reaches 80 percent of total gas production rate, namely T₈₀The yield of the methane is 342.60mL/g VS, which is improved by 555.46% compared with the yield of pure kitchen methane. Anaerobic digestion of the kitchen waste and the pretreated highland barley stalks 3 in 25 days: the yield of methane of 1 group is 240.77mL/g VS, which is improved by 839.09% compared with the yield of pure kitchen methane. Specific data are shown in table 3:

TABLE 3 methane yield (mL/g VS) at different stages during anaerobic fermentation

In anaerobic fermentation, T₈₀To reach 80% time of total gas production. As can be seen from Table 4, the time for the pure kitchen waste to reach 80% of the total gas production is 38 days, which is 9 days later than the time for the pure kitchen waste to reach 80% of the total gas production, because the acidification phenomenon occurs in the pure kitchen waste, the system needs a longer buffer recovery time. The ratio of the pretreated highland barley stalks to the kitchen waste is 1:1, 1:3, 1:5, 3:1, 5: 1T₈₀The time is 29-30 days, which indicates that a certain proportion of water is addedThe acidification phenomenon of pure kitchen waste can be relieved by treating the highland barley stalks, the anaerobic fermentation period is shortened, and the highland barley stalks have great application value in practical engineering.

TABLE 4 anaerobic fermentation reaction T₈₀

VFAs are intermediates in anaerobic digestion processes and include primarily acetic, propionic, butyric, isobutyric, valeric and isovaleric acids. As can be seen from Table 5, the proportion of the highland barley straw to the kitchen waste is 1:5, the propionic acid content in the pure kitchen waste is 13472.50 mg/L and 15126.50mg/L respectively, the butyric acid content is 669.25 mg/L and 2950.80mg/L respectively, and the propionic acid content is very high, so that the instability phenomenon of the system occurs. And a large amount of propionic acid is not accumulated under the condition of proportioning other materials, and the system is kept in a stable state.

TABLE 5 analysis of VFAs

Ammonia nitrogen, alkalinity and pH are important indexes for investigating the stability of an anaerobic digestion system. The ammonia nitrogen, alkalinity and pH at different mixing ratios are listed in table 6. The pH after discharge was within the normal range. The ammonia nitrogen content in the pure kitchen waste and the pure highland barley stalk anaerobic fermentation system is 5476 mg/L and 3755mg/L respectively, and the ammonia nitrogen content in the anaerobic fermentation system with different mixing ratios is in the range of 3000-5000 mg/L. The alkalinity and the pH value of the system are kept in a higher range, and the system belongs to the range of normal anaerobic fermentation parameters. The stability of the fermentation system is guaranteed.

TABLE 6 stability index of dry anaerobic fermentation system

When the ratio of VFAs to alkalinity (TVFAs/TAC) is less than 0.2 of TVFAs/TAC which is one of indexes reflecting the stability of the fermentation system, the system is stable; when TVFAs/TAC is more than 0.2 and less than 0.4, the system is more stable; when TVFAs/TAC is more than 0.4 and less than 0.8, the system begins to generate an unstable phenomenon; when VFAs/TAC is more than 0.8, the fermentation system is seriously unstable, and VFA in the system is accumulated, the buffer capacity of the system is insufficient, and the acidification phenomenon is generated. As can be seen from Table 7, the instability phenomenon occurred in the pure kitchen waste and the system of 1:5 of the highland barley straw and the kitchen waste, and a large amount of propionic acid was accumulated. And the material ratio is 1:3, the system is stable, single kitchen waste acidification can be relieved, and the gas production rate is improved.

TABLE 7 System stability analysis