阅读说明：本技术 一种利用橘子皮生产挥发性脂肪酸的方法 (Method for producing volatile fatty acid by using orange peel ) 是由 罗景阳 邵钱祺 方心阳 鲍星辰 林丽芳 方世玉 黄文轩 于 2021-09-07 设计创作，主要内容包括：本发明公开了一种利用橘子皮生产挥发性脂肪酸的方法,以橘子皮粉末作为厌氧发酵底物,以污水处理厂污泥作为接种物,将发酵底物和接种物混合进行厌氧发酵产酸。橘子皮和污泥的质量比为0.1～1:1,厌氧发酵的pH为4～9,温度为15～55℃,厌氧发酵的天数为6～16天。本发明的方法能同步实现废弃橘子皮和剩余污泥的减量化和资源化,生产具有高市场价值和广阔市场需求的挥发性脂肪酸,且能够提高VFAs的生成速率和产量,本发明VFAs产量在较优条件下可高达11718.1mg COD/L,其中乙酸和丙酸的比例高达85％以上。(The invention discloses a method for producing volatile fatty acid by using orange peel, which takes orange peel powder as an anaerobic fermentation substrate and sludge of a sewage treatment plant as an inoculum, and mixes the fermentation substrate and the inoculum for anaerobic fermentation to produce acid. The mass ratio of the orange peel to the sludge is 0.1-1: 1, the pH value of anaerobic fermentation is 4-9, the temperature is 15-55 ℃, and the number of days of anaerobic fermentation is 6-16. The method can synchronously realize the reduction and the resource utilization of the waste orange peel and the residual sludge, produce the volatile fatty acid with high market value and wide market demand, and can improve the generation rate and the yield of the VFAs, the yield of the VFAs can reach 11718.1mg COD/L under better conditions, wherein the proportion of the acetic acid to the propionic acid is up to more than 85 percent.)

1. A method for producing volatile fatty acid by using orange peel is characterized in that the orange peel and sludge are mixed and then are subjected to anaerobic fermentation, so that organic matters in the sludge are converted into the volatile fatty acid.

2. The method for producing the volatile fatty acid by using the orange peel as claimed in claim 1, wherein the mass ratio of the orange peel to the sludge is 0.1-1: 1.

3. The method for producing the volatile fatty acid by using the orange peel as claimed in claim 1, wherein the mass ratio of the orange peel to the sludge is 0.2-0.5: 1.

4. The method for producing volatile fatty acid by using orange peel as claimed in claim 1, wherein the pH of the anaerobic fermentation is 4-9.

5. The method for producing volatile fatty acid by using orange peel as claimed in claim 1, wherein the pH of the anaerobic fermentation is 6-8.

6. The method for producing the volatile fatty acid by using the orange peels as claimed in claim 1, wherein the temperature of the anaerobic fermentation is 15-55 ℃.

7. The method for producing volatile fatty acid by using orange peel as claimed in claim 1, wherein the temperature of the anaerobic fermentation is 20-35 ℃.

8. The method for producing volatile fatty acid by using orange peel as claimed in claim 1, wherein the number of days of anaerobic fermentation is 6-16 days.

9. The method for producing volatile fatty acid by using orange peel as claimed in claim 1, wherein the sludge concentration is 10-20 g/L.

10. The method for producing volatile fatty acid by using orange peel as claimed in claim 1, wherein the sludge is sludge in a secondary sedimentation tank in a sewage treatment process.

Technical Field

The invention relates to a method for producing fatty acid, in particular to a method for producing volatile fatty acid by using orange peel.

Background

Volatile Fatty Acids (VFAs) are important intermediate products which are widely concerned in the anaerobic fermentation process, have wide application range and are important raw materials for synthesizing paints, coatings, biodegradable plastics and the like. Taking the acetic acid and the propionic acid which account for relatively high proportion in the VFAs as an example (the total amount of the acetic acid and the propionic acid generally accounts for more than 70 percent of the VFAs), the acetic acid (400-.

At present, anaerobic fermentation mostly has the problems of low organic matter content of substrates (such as sludge), unbalanced carbon-nitrogen ratio, difficult accumulation of products VFAs (consumption and utilization of methanogens and the like), and the like.

With the development of economic society, the proportion of fruit and vegetable garbage represented by orange peel in urban garbage components is gradually increased. Although the orange peel has high organic matter content, contains rich trace elements, orange oil and other high-value products, more than 99 percent of the orange peel is not effectively utilized at present and is generally treated by a direct landfill mode. This not only causes the very big waste of resource, and the great amount of tangerine peel that abandons simultaneously will cause serious environmental pollution because of being difficult to decompose fast.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a method for producing volatile fatty acid by utilizing orange peel, which can synchronously realize reduction and resource utilization of waste orange peel and excess sludge.

The technical scheme is as follows: the method for producing the volatile fatty acid by using the orange peel disclosed by the invention is characterized in that the orange peel and the sludge are mixed and then are subjected to anaerobic fermentation, so that organic matters in the sludge are converted into the volatile fatty acid.

The mass ratio of the orange peel to the sludge is 0.1-1: 1, if the mass ratio is too low, the acid production amount is small due to insufficient substrate concentration, if the mass ratio is too high, mass transfer is affected and energy consumption is increased, meanwhile, the pH is reduced due to accumulation of VFAs, the metabolic activity of microorganisms is reduced, the acid production amplification is greatly reduced, and the efficiency is reduced; more preferably, the mass ratio is 0.2-0.5: 1; within this range, the fermentation substrate and microorganism count are co-balanced, which is more conducive to the accumulation of VFAs.

The pH value of the anaerobic fermentation is 4-9, and when the pH value is too high or too low, the activity of microorganisms such as acid-producing bacteria in the system can be inhibited, so that the anaerobic fermentation efficiency is limited; more preferably 6-8, and in the range, microorganisms such as acid-producing bacteria and the like can keep higher activity, and more favorable for VFAs accumulation.

Wherein the temperature of the anaerobic fermentation is 15-55 ℃, if the fermentation temperature is too high, the reaction energy consumption is greatly increased, the yield of VFAs is increased less, the fermentation efficiency is reduced, if the pH value is too low, the microbial activity in a fermentation system is influenced, and the reaction rate is reduced, so that the fermentation is not facilitated; more preferably 20-35 ℃, and in the range, the microbial activity is higher, the actual operation energy consumption is lower, and the resource extraction of VFAs is more facilitated.

The number of days of anaerobic fermentation is 6-16 days, if the fermentation time is too long, the activity of methanogenic bacteria is facilitated, so that the product VFAs in the acid production stage is further converted into methane, the accumulation of the VFAs is not facilitated, meanwhile, the running cost is further increased by prolonging the fermentation time, and if the fermentation time is too short, the dissolving and hydrolyzing process of the fermentation is incomplete, and the accumulation amount of the VFAs is low; more preferably 8-12 days, in the range, the method is not only favorable for the full dissolution and hydrolysis of the organic substrate, but also can limit the subsequent consumption of the VFAs to a certain extent, and is more favorable for the accumulation of the VFAs.

Wherein the sludge concentration is 10-20 g/L, and if the sludge concentration is too low, anaerobic fermentation microorganisms are insufficient, and substrate fermentation is insufficient; if the sludge concentration is too high, the reaction substances are too thick, the mass transfer speed among the substances is influenced, and the fermentation acid production rate is further influenced.

Wherein, the sludge is the sludge in a secondary sedimentation tank in the sewage treatment process, and compared with primary sedimentation sludge, the secondary sedimentation sludge has higher microorganism content and activity and is more beneficial to the production of VFAs.

Citrus essence in orange peelThe oil contains one particular substance: d-limonene can inhibit methanogenic bacteria in anaerobic digestion system, and acid-producing bacteria are less affected by the d-limonene, so that VFAs in the system are changed into CH₄The conversion rate is slowed, namely the acid production rate is far greater than the gas production rate, and the VFAs are continuously accumulated, so that the yield of the VFAs is improved.

The traditional anaerobic fermentation system is often lack of trace elements, and orange peel contains various trace elements such as potassium, calcium, iron, zinc and the like. On one hand, the trace elements can be used as nutrient substances to supply to anaerobic microorganisms, so that the activity of a plurality of key enzymes and functional microorganisms in the acid production stage is effectively improved; on the other hand, the trace elements can be used as electron donors to participate in electron transfer in the microbial metabolism process, so that the metabolic activity of the microbes is promoted, the substrate hydrolysis acidification rate is accelerated, the generation of VFAs is promoted, and the yield of the VFAs is finally and greatly increased.

Has the advantages that: compared with the prior art, the invention has the following remarkable effects: 1. the waste orange peel and excess sludge are used as raw materials to produce VFAs, so that the reduction and the resource utilization of the waste orange peel and the excess sludge can be synchronously realized, the pollution to the environment can be reduced by preparing the VFAs through anaerobic fermentation, and an economic, effective, green and environment-friendly method is provided for organic waste treatment. 2. The sludge and orange peel co-fermentation acid production can adjust the C/N balance of a fermentation substrate, enhance the buffer performance of a fermentation system, weaken the inhibition of toxic substances on fermentation microorganisms, synergistically promote anaerobic metabolic processes such as dissolution, hydrolysis and acidification of organic matters, and improve the generation rate and the yield of VFAs, wherein the yield of the VFAs can reach 11718.1mg COD/L under better conditions, and the proportion of acetic acid and propionic acid is higher than 85%; 3. effectively shortens the time of fermentation acid production, reduces the volume of a treatment system, reduces the operation cost, and is safe and efficient.

Detailed Description

The present invention is described in further detail below.

Example 1

(1) Orange peel powder and 300mL of residual sludge sample are added into an organic glass reactor with the working volume of 600mL, and the mixing ratio is 0.1g/g, wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be about 7, and the fermentation reaction temperature is controlled to be 35 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 8 based on the chemical oxygen demand, and that the VFAs content was 1117.0 mg/L. Wherein the accumulated amount of acetic acid is 98.9mg/L, which accounts for 8.85% of the total amount of acid produced; the accumulation amount of propionic acid is 786.1mg/L, which accounts for 70.38% of the total amount of acid produced.

Example 2

(1) Orange peel powder and 300mL of residual sludge sample are added into an organic glass reactor with the working volume of 600mL, and the mixing ratio is 0.2g/g, wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be about 7, and the fermentation reaction temperature is controlled to be 35 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 6 based on the chemical oxygen demand, and that the VFAs content was 4141.7 mg/L. Wherein the accumulated amount of acetic acid is 2398.4mg/L, which accounts for 57.91% of the total amount of acid produced; the accumulation amount of propionic acid is 1117.2mg/L, which accounts for 26.97% of the total amount of acid produced.

Example 3

(1) Orange peel powder and 300mL of residual sludge sample are added into an organic glass reactor with the working volume of 600mL, and the mixing ratio is 0.5g/g, wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be about 5, and the fermentation reaction temperature is controlled to be 35 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 10 based on the chemical oxygen demand, and that the VFAs content was 11718.1 mg/L. Wherein the accumulated amount of acetic acid is 6647.5mg/L, which accounts for 56.73% of the total amount of the acid produced; the accumulation amount of propionic acid is 3366.3mg/L, which accounts for 28.73% of the total amount of acid produced.

Example 4

(1) Orange peel powder and 300mL of residual sludge sample are added into an organic glass reactor with the working volume of 600mL, and the mixing ratio is 1g/g, wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be about 5, and the fermentation reaction temperature is controlled to be 35 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 10 based on the chemical oxygen demand, and that the VFAs content was 11996.3 mg/L. Wherein the accumulated amount of acetic acid is 4754.1mg/L, which accounts for 39.63% of the total amount of acid produced; the accumulation amount of the propionic acid is 3860.8mg/L, which accounts for 32.18 percent of the total amount of the acid produced.

Example 5

(1) Adding orange peel powder and 300mL of residual sludge sample into an organic glass reactor with a working volume of 600mL, mixing the orange peel powder and the residual sludge sample at a ratio of 0.2g/g, and adjusting the pH value to 4; wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be 4, and the fermentation reaction temperature is controlled to be 35 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized at day 14 based on the chemical oxygen demand, and that the VFAs content was 1976.4 mg/L. Wherein the accumulated amount of acetic acid is 942.3mg/L, which accounts for 47.68% of the total amount of acid produced; the accumulation amount of propionic acid is 389.5mg/L, which accounts for 41.34% of the total amount of acid produced.

Example 6

(1) Adding orange peel powder and 300mL of residual sludge sample into an organic glass reactor with a working volume of 600mL, mixing the orange peel powder and the residual sludge sample at a ratio of 0.2g/g, and adjusting the pH value to 5; wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be 5, and the fermentation reaction temperature is controlled to be 35 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 8 based on the chemical oxygen demand, and that the VFAs content was 2872.4 mg/L. Wherein the accumulated amount of acetic acid is 1634.7mg/L, which accounts for 56.91% of the total amount of acid produced; the accumulation amount of propionic acid is 385.6mg/L, which accounts for 13.43% of the total amount of acid produced.

Example 7

(1) Adding orange peel powder and 300mL of residual sludge sample into an organic glass reactor with a working volume of 600mL, mixing the orange peel powder and the residual sludge sample at a ratio of 0.2g/g, and adjusting the pH value to 6; wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be 6, and the fermentation reaction temperature is controlled to be 35 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 10 based on the chemical oxygen demand, and that the VFAs content was 3736.0 mg/L. Wherein the accumulated amount of acetic acid is 1814.6mg/L, which accounts for 48.57% of the total amount of acid produced; the accumulation amount of propionic acid is 893.5mg/L, which accounts for 23.92% of the total amount of acid produced.

Example 8

(1) Adding orange peel powder and 300mL of residual sludge sample into an organic glass reactor with a working volume of 600mL, mixing the orange peel powder and the residual sludge sample at a ratio of 0.2g/g, and adjusting the pH value to 7; wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be 7, and the fermentation reaction temperature is controlled to be 35 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 6 based on the chemical oxygen demand, and that the VFAs content was 3210.269 mg/L. Wherein the accumulated amount of acetic acid is 1704.1mg/L, which accounts for 53.08% of the total amount of acid produced; the accumulation amount of propionic acid is 587.3mg/L, which accounts for 18.30% of the total amount of acid produced.

Example 9

(1) Adding orange peel powder and 300mL of residual sludge sample into an organic glass reactor with a working volume of 600mL, mixing the orange peel powder and the residual sludge sample at a ratio of 0.2g/g, and adjusting the pH value to 8; wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be 8, the fermentation reaction temperature is controlled to be 35 +/-1 ℃, and the result shows that the accumulation amount of the VFAs reaches the maximum value on the 8 th day by the chemical oxygen demand, and the content of the VFAs is 4868.5 mg/L. Wherein the accumulated amount of acetic acid is 3077.5mg/L, which accounts for 63.21% of the total amount of acid produced; the accumulation amount of propionic acid is 779.5mg/L, which accounts for 16.01% of the total amount of acid produced.

Example 10

(1) Adding orange peel powder and 300mL of residual sludge sample into an organic glass reactor with a working volume of 600mL, mixing the orange peel powder and the residual sludge sample at a ratio of 0.2g/g, and adjusting the pH value to 9; wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be 9, and the fermentation reaction temperature is controlled to be 35 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized at day 14 based on the chemical oxygen demand, and that the VFAs content was 3121.8 mg/L. Wherein the accumulated amount of acetic acid is 1599.4mg/L, which accounts for 51.23% of the total amount of the acid produced; the accumulation amount of propionic acid is 760.7mg/L, which accounts for 24.37% of the total amount of acid produced.

Example 11

(1) Adding orange peel powder and 300mL of residual sludge sample into an organic glass reactor with a working volume of 600mL, mixing the orange peel powder and the residual sludge sample at a ratio of 0.2g/g, and adjusting the pH value to 8; wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be 8, and the fermentation reaction temperature is controlled to be 15 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 10 based on the chemical oxygen demand, and that the VFAs content was 2765.8 mg/L. Wherein the accumulated amount of acetic acid is 1743.6mg/L, which accounts for 63.04% of the total amount of acid produced; the accumulation amount of propionic acid is 443.6mg/L, which accounts for 16.04% of the total amount of acid produced.

Example 12

(1) Adding orange peel powder and 300mL of residual sludge sample into an organic glass reactor with a working volume of 600mL, mixing the orange peel powder and the residual sludge sample at a ratio of 0.2g/g, and adjusting the pH value to 8; wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be 8, and the fermentation reaction temperature is controlled to be 55 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 8 based on the chemical oxygen demand, and that the VFAs content was 5654.2 mg/L. Wherein the accumulated amount of acetic acid is 3723.8mg/L, which accounts for 65.86% of the total amount of acid produced; the accumulation amount of the propionic acid is 904.3mg/L, which accounts for 15.99 percent of the total amount of the acid produced.

Example 13

(1) Adding orange peel powder and 300mL of residual sludge sample into an organic glass reactor with a working volume of 600mL, mixing the orange peel powder and the residual sludge sample at a ratio of 0.2g/g, and adjusting the pH value to 8; wherein the sludge concentration is 10g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be 8, and the fermentation reaction temperature is controlled to be 55 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 8 based on the chemical oxygen demand, and that the VFAs content was 5654.2 mg/L. Wherein the accumulated amount of acetic acid is 3723.8mg/L, which accounts for 65.86% of the total amount of acid produced; the accumulation amount of the propionic acid is 904.3mg/L, which accounts for 15.99 percent of the total amount of the acid produced.

Example 14

(1) In an organic glass reactor having a working volume of 600mL, orange peel powder and 300mL of a sample of excess sludge (sludge concentration of 20g MLSS/L) were added at a mixing ratio of 0.2g/g, and pH was adjusted to 8.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by combined fermentation of excess sludge and orange peel powder. Wherein the pH is controlled to be 8, and the fermentation reaction temperature is controlled to be 55 +/-1 ℃. The results showed that the reaction was stopped by 16 days of fermentation based on the chemical oxygen demand and that the content of VFAs was 3430.0 mg/L. Wherein the accumulated amount of acetic acid is 1882.7mg/L, which accounts for 54.89% of the total amount of acid produced; the accumulation amount of propionic acid is 728.0mg/L, which accounts for 21.22% of the total amount of acid produced.

Comparative example 1

(1) Adding 300mL of excess sludge into an organic glass reactor with a working volume of 600mL, and taking the residual sludge without adding waste orange peel as a blank control; wherein the sludge concentration is 20g MLSS/L.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The organic matter is converted to VFAs by fermentation of the excess sludge. Wherein the pH is controlled to be about 7.6, and the fermentation reaction temperature is 35 +/-1 ℃. The results showed that the amount of VFAs accumulated was maximized on day 12 based on the chemical oxygen demand, and that the content of VFAs was 473.8 mg/L.

Comparative example 2

(1) In an organic glass reactor with a working volume of 600mL, a certain amount of waste orange peel powder and 300mL of water were added as a blank control without adding excess sludge.

(2) And (3) filling nitrogen into the reactor to remove oxygen for 10min, sealing the reactor, and uniformly mixing substances in the reaction system by using mechanical stirring. The accumulation of VFAs during anaerobic fermentation was always 0.

The results of anaerobic fermentation can be evaluated mainly by the accumulation of VFAs. The accumulated amounts of VFAs in examples 1-13 and comparative examples 1-2 are shown in Table 1 below, respectively.

TABLE 1 accumulated VFAs data for each of the examples and comparative examples

As can be seen from the data of comparative examples 1, 2 in Table 1 above, orange peel alone fermented without VFAs output; compared with comparative example 1, the accumulation amount of VFAs is gradually increased with the increase of the waste orange peel powder in examples 1-4, and is increased to 25 times at most, which also shows that the co-fermentation of orange peel and waste sludge has obvious promotion effect on acid production.

As can be seen from Table 1 above, in examples 5-10, the reaction pH was controlled to stabilize at 4, 5, 6, 7, 8, 9, respectively, and the incubation was performed under the same conditions, it can be seen that the accumulation of VFAs was much higher in example 9 than in example 5; the accumulation amount of VFAs was decreased by about 1/3 in example 10 as compared with example 9, and it was found that the accumulation of VFAs was more favorable in the more alkaline environment at a pH of about 8.

As can be seen from the comparison of example 9 with examples 11 and 12, the control of the reaction temperature at 35 ℃ gives better results than 15 ℃ and the best results are achieved at 55 ℃. However, 35 ℃ is preferred because it is considered that the energy consumption increases gradually with increasing temperature, the yield of VFAs increases slowly, and the practical economic benefit obtained by controlling the temperature at 55 ℃ is not as good as 35 ℃. Comparing example 9 with examples 13 and 14, it can be seen that when the reaction time exceeds a certain range, the accumulation of VFAs begins to decrease, and the VFAs produced in the acid production stage are further converted into methane, which also increases the energy consumption for operation; meanwhile, if the fermentation time is too short, the dissolution and hydrolysis of organic matters are insufficient, which is not beneficial to the generation of VFAs, so that the preferable fermentation time is 8-12 days.

In conclusion, the addition of the orange peel powder of the present invention can effectively promote the generation of acid in the anaerobic digestion process, and the optimal effect can be obtained when the reaction conditions are controlled to be the following parameters: the mass ratio of the substrate to the inoculum is 0.2-0.5: 1, the pH value of the anaerobic fermentation reaction is 6-8, the temperature of the anaerobic fermentation reaction is 34-36 ℃, and the anaerobic fermentation time is 8-12 days. The invention can realize the resource, harmless and reduction treatment of the waste orange peel. The method has the advantages that the economic benefit is obtained, meanwhile, the green and efficient treatment of the fruit and vegetable garbage and the excess sludge is realized, and the low-carbon transformation of the municipal sewage treatment industry is further promoted.