阅读说明：本技术 以畜禽粪污为原料两阶段发酵生产中链脂肪酸的方法 (Method for producing medium-chain fatty acid by taking livestock and poultry manure as raw material through two-stage fermentation ) 是由 董红敏 张万钦 尹福斌 朱志平 曹起涛 陈永杏 于 2019-10-31 设计创作，主要内容包括：本发明属于农业废弃物资源化循环利用领域,具体涉及一种以畜禽粪污为原料两阶段发酵生产中链脂肪酸的方法,包括如下步骤：A、预先将污泥进行热处理；B、一级发酵阶段生产短链脂肪酸；C、二级发酵阶段生产中链脂肪酸。本发明还提供一种利用畜禽粪污生产短链脂肪酸的方法,包括如下步骤：①、预先将污泥进行热处理；②、发酵阶段生产短链脂肪酸。本发明生产短链脂肪酸的方法不仅发酵前热处理污泥降低了有机酸甲烷化,发酵系统控制为碱性强化了持续酸化过程,大幅度提高了短链脂肪酸的产量。本发明两阶段发酵的方法使约60％的短链脂肪酸转化为高附加值的中链脂肪酸,为畜禽粪污的资源化利用提供一条新途径。(The invention belongs to the field of resource recycling of agricultural wastes, and particularly relates to a method for producing medium-chain fatty acid by using livestock and poultry manure as a raw material through two-stage fermentation, which comprises the following steps: A. carrying out heat treatment on the sludge in advance; B. producing short chain fatty acids in a primary fermentation stage; C. medium chain fatty acids are produced in the secondary fermentation stage. The invention also provides a method for producing short-chain fatty acid by using the livestock and poultry manure, which comprises the following steps: firstly, performing heat treatment on sludge in advance; ② short chain fatty acid is produced in the fermentation stage. The method for producing the short-chain fatty acid not only reduces the methanation of the organic acid by heat-treating the sludge before fermentation, but also strengthens the continuous acidification process by controlling the fermentation system to be alkaline and greatly improves the yield of the short-chain fatty acid. The two-stage fermentation method of the invention converts about 60% of short-chain fatty acid into medium-chain fatty acid with high added value, and provides a new way for the resource utilization of livestock and poultry feces.)

1. A method for producing medium-chain fatty acid by two-stage fermentation with livestock and poultry manure as a raw material is characterized by comprising the following steps:

A. carrying out heat treatment on the sludge in advance;

B. producing short chain fatty acids in a primary fermentation stage; the initial pH value is 10, and the pH value is controlled to be 9.0-10.0 in the fermentation process;

C. production of medium-chain fatty acids in the secondary fermentation stage: n-hexanoic acid, n-heptanoic acid, n-octanoic acid.

2. A method for producing short-chain fatty acid by using livestock and poultry manure is characterized by comprising the following steps:

firstly, performing heat treatment on sludge in advance;

② short chain fatty acid is produced in the fermentation stage, the initial pH value is 10, and the pH value is controlled to be 9.0-10.0 in the fermentation process.

Technical Field

The invention belongs to the field of resource recycling of agricultural wastes, and particularly relates to a method for producing medium-chain fatty acid by using livestock and poultry manure as a raw material through two-stage fermentation, and a method for producing short-chain fatty acid by using the livestock and poultry manure.

Background

The rapid development of animal husbandry generates a large amount of livestock and poultry manure, and the anaerobic digestion technology is one of the effective ways for treating the livestock and poultry manure at present. The anaerobic digestion process of the livestock and poultry manure can generate two products of volatile fatty acid and methane, and previous researches are focused on how to efficiently generate methane from the livestock and poultry manure. However, in recent years, researches show that the problem of high ammonia nitrogen inhibition of methanogen metabolic activity is easy to occur in the single-phase anaerobic digestion process due to the low C/N ratio of the livestock and poultry manure, so that the operation stability of an anaerobic digestion system is poor, and the methane yield is low. Compared with methane, the volatile fatty acid, an intermediate metabolite in the anaerobic digestion process of livestock and poultry manure, has higher value and wider application approaches, such as being used for synthesizing products with high added values, such as Polyhydroxyalkanoate (PHA), medium-chain fatty acid and the like.

The anaerobic digestion system usually contains two functional floras of acid-producing bacteria and methanogenic bacteria, so how to reduce the metabolic activity of the methanogenic bacteria in the system, block the methanation process of the livestock and poultry manure, enable the anaerobic digestion to stay in the acid-producing stage, and realize the oriented organic acid conversion of organic matters with creativity. In recent years, the related inventors have conducted studies on anaerobic acid production of organic wastes using an anaerobic acidification process; for example, patent CN102583917B discloses a pretreatment method for enhancing anaerobic acid production of municipal sludge, CN105132475A discloses a method for producing acid by anaerobic fermentation after steam explosion pretreatment of excess sludge, CN102586344B discloses a method for efficiently producing volatile fatty acid by anaerobic fermentation of heating circulating sludge, and CN100526469C discloses a method for realizing directional acetic acid production of sludge by adding methanogen inhibitor; CN103923951A discloses a method for enhancing directional anaerobic acid production of kitchen waste by adopting an ultrasonic/acid pretreatment method, CN103509829A discloses a method for preparing acetic acid and butyric acid by combining kitchen waste with excess sludge fermentation, and CN105603011A discloses a method for preparing acetic acid by utilizing kitchen waste fermentation and a device used by the same. In conclusion, the existing acidification process of organic matters is developed for municipal sludge and kitchen waste, and the anaerobic directional acidification process for livestock and poultry manure is not reported.

Scholars at home and abroad have also carried out relevant researches on the aspect of preparing the medium-chain fatty acid with high added value by utilizing the organic waste anaerobic process. For example, the citrus chentaimen and the like take excess sludge as a raw material, and the anaerobic fermentation liquid of the citrus chentaimen and the like is subjected to chain extension reaction to obtain caproic acid (citrus chentaimen, research on medium-chain fatty acid produced by excess sludge based on anaerobic fermentation, university of Hunan, 2018); it has also been shown that high-concentration caproic acid can be produced by a two-stage anaerobic fermentation process using food waste and municipal organic domestic waste as raw materials. In the prior art, municipal sludge, food waste and municipal organic domestic garbage are mostly adopted as raw materials to prepare high value-added products, but the research of producing medium-chain fatty acid by using livestock and poultry manure is not reported.

The invention takes the livestock and poultry excrement with complex components as the raw material, produces the medium-chain fatty acid with high added value by a two-stage anaerobic digestion process, and particularly produces the heptanoic acid with high industrial application value in the medium-chain fatty acid, thereby providing a new idea for the resource utilization of the livestock and poultry excrement. The method has simple production process and good economic, social and environmental benefits.

Disclosure of Invention

The invention aims at the technical problems, provides a method for producing medium-chain fatty acid by using livestock and poultry manure as a raw material through two-stage fermentation, and provides a new idea for realizing resource utilization of the livestock and poultry manure.

The invention provides a method for producing medium-chain fatty acid by taking livestock and poultry manure as a raw material through two-stage fermentation, which comprises the following steps:

A. carrying out heat treatment on the sludge in advance;

B. producing short chain fatty acids in a primary fermentation stage; the initial pH value is 10, and the pH value is controlled to be 9.0-10.0 in the fermentation process;

C. production of medium-chain fatty acids in the secondary fermentation stage: n-hexanoic acid, n-heptanoic acid, n-octanoic acid.

Wherein the heat treatment in the step A is carried out in water bath at 70-90 ℃ for 3-5h, preferably in water bath at 85 ℃ for 3 h.

B, a primary fermentation stage, namely mixing the sludge subjected to heat treatment and the livestock and poultry manure to form an anaerobic fermentation system, and adjusting the initial pH value of the anaerobic fermentation system to 10.0; carrying out medium-temperature anaerobic fermentation to produce short-chain volatile fatty acid.

Wherein, in the primary fermentation stage in the step B, the fermentation concentration is 2% VS-6% VS.

Wherein, in the first-stage fermentation stage of the step B, the sludge is subjected to VS_{Sludge treatment}：VS_{Livestock and poultry excrement}1: (2-10) mixing with livestock and fowl feces, preferably VS_{Sludge treatment}：VS_{Livestock and poultry excrement}＝1：(2-5)。

Wherein, the secondary fermentation stage in the step C comprises the following specific steps: adding ethanol as electron donor to drive carbon chain extension reaction, and controlling pH value of the system to 5.0-8.0, preferably pH value to 6.5-7.0.

Wherein in the secondary fermentation stage of step C, the amount of ethanol added is determined based on the molar ratio ethanol/short chain fatty acid (2-10):1, preferably in a ratio of 2: 1.

Wherein, the livestock and poultry manure is preferably pig manure.

Considering that the short-chain fatty acid obtained in the primary fermentation stage has wide application value in industry, the invention also provides a method for producing the short-chain fatty acid by using the livestock and poultry manure, which comprises the following steps:

firstly, performing heat treatment on sludge in advance;

② short chain fatty acid is produced in the fermentation stage, the initial pH value is 10, and the pH value is controlled to be 9.0-10.0 in the fermentation process.

Wherein, the heat treatment in the step (i) is carried out in 70-90 ℃ water bath for 3-5h, preferably 85 ℃ water bath for 3 h.

Wherein, the short-chain fatty acid is produced in the fermentation stage, specifically, the inoculated sludge after heat treatment is mixed with the livestock and poultry manure, the initial pH value of anaerobic fermentation is adjusted to 10.0, and the pH value is controlled to 9.0-10.0 in the anaerobic fermentation process.

Wherein the inoculated sludge is mixed with the livestock and poultry manure, and the sludge is in accordance with VS_{Sludge treatment}：VS_{Livestock and poultry excrement}1: (2-10) mixing with livestock and fowl feces, preferably VS_{Sludge treatment}：VS_{Livestock and poultry excrement}＝1：(2-5)。

Wherein the fermentation concentration is 2% VS-6% VS.

Wherein, the livestock and poultry manure is preferably pig manure.

The invention has the beneficial effects that:

the invention provides a method for producing medium-chain fatty acid by utilizing a two-stage anaerobic digestion process of livestock and poultry manure, wherein a fermentation substrate is the livestock and poultry manure, an inoculum is anaerobic digestion sludge, the raw material source is wide, the operation cost is low, the product added value is high, and the harmless treatment and high-value utilization of the livestock and poultry manure can be effectively realized. The method has the advantages of simple process operation, easy control of anaerobic fermentation conditions, low economic cost and good application prospect.

Drawings

FIG. 1 is a bar graph of the volatile fatty acid production per VS of pig manure at various pH conditions in example 1 of the present invention.

FIG. 2 is a bar graph of the concentrations of short and medium chain fatty acids after the end of secondary fermentation at different pH conditions in example 2 of the present invention.

FIG. 3 is a bar graph of the concentrations of short-chain and medium-chain fatty acids after the end of secondary fermentation at different pig manure fermentation concentrations in example 2 of the present invention.

Detailed Description

The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.