阅读说明：本技术 一种皂化预处理提高废油脂厌氧消化产甲烷的方法 (Method for improving methane production by anaerobic digestion of waste oil through saponification pretreatment ) 是由 吴坤 何霞 郝家厚 于 2020-12-16 设计创作，主要内容包括：本发明涉及一种利用皂化预处理提高废油脂厌氧消化产甲烷的方法,具体为先将废油脂与钙离子在室温且碱性条件下按照钙/油摩尔比为0.25-1的范围内进行皂化反应,再将生成的钙皂加入厌氧消化反应器中,然后加入接种物,使钙皂与接种物的比值为0.5(gVS/gVS),在温度为35-37℃和转速为150rpm的条件下进行厌氧消化,促进了油脂中的长链脂肪酸的降解,提高了产甲烷量。与现有技术相比,本发明使得废油脂产甲烷速率提升、缓解长链脂肪酸的抑制作用、提高厌氧消化产甲烷菌的活性,且实施容易。(The invention relates to a method for improving methane production of waste oil anaerobic digestion by saponification pretreatment, which comprises the steps of firstly carrying out saponification reaction on waste oil and calcium ions at room temperature and under an alkaline condition according to a calcium/oil molar ratio of 0.25-1, then adding the generated calcium soap into an anaerobic digestion reactor, then adding an inoculum to enable the ratio of the calcium soap to the inoculum to be 0.5(gVS/gVS), and carrying out anaerobic digestion under the conditions of a temperature of 35-37 ℃ and a rotating speed of 150rpm, so that the degradation of long-chain fatty acids in the oil is promoted, and the methane production amount is improved. Compared with the prior art, the method has the advantages of improving the methane production rate of the waste oil, relieving the inhibition effect of long-chain fatty acid, improving the activity of anaerobic digestion methanogens, and being easy to implement.)

1. A method for improving methane production by anaerobic digestion of waste oil and fat through saponification pretreatment is characterized by comprising the following steps:

(1) saponification pretreatment: mixing and stirring waste oil and fat and calcium ions under alkaline conditions (sodium hydroxide is used, and the pH value is 11) so as to generate calcium soap;

(2) anaerobic digestion for methane production: adding the calcium soap generated in the step (1) into an anaerobic digestion reactor, then adding the inoculum to ensure that the ratio of the calcium soap to the inoculum is 0.5(gVS/gVS), and carrying out anaerobic digestion under the conditions of temperature of 35-37 ℃ and rotating speed of 150rpm to produce methane.

2. The method for improving methane production by anaerobic digestion of waste oil and fat through saponification pretreatment according to claim 1, wherein the saponification pretreatment comprises the following steps: the calcium soap in the step (1) is prepared at normal temperature.

3. The method for improving methane production by anaerobic digestion of waste oil and fat through saponification pretreatment according to claim 1, wherein the saponification pretreatment comprises the following steps: the calcium soap in the step (1) is Ca²⁺the/LCFA is generated by reacting a calcium source with waste oil and fat in the proportion of 0.25, 0.5 and 1(mol/mol), and the waste oil and fat is firstly hydrolyzed in sodium hydroxide solution (1mol/L) for 10 minutes, and then the two types of calcium sources with corresponding amount are added and mixed.

4. The calcium soap according to claim 1, characterized in that: a small amount of generated samples are taken and scanned by a Fourier infrared spectrometer, so that obvious characteristic peaks of the calcium soap can be observed, and the characteristic peaks are distributed in four regions: region 1: 4000-3000cm^-1Calcium soap is 3400cm^-1The left side and the right side have wide absorption peaks; region 2: 1800 plus 1350cm^-1After the calcium ions react with the carboxylate radical, the carbonyl group generates stretching vibration at 1745cm-1, and the carboxylic acid radical generates tensile vibration at 1577 cm and 1541cm respectively^-1And 1468, 1435 and 1422cm^-1Forming a characteristic peak; region 3: 1350 and 1180cm^-1And 720cm^-1Nearby; region 4: 665cm^-1Calcium-oxygen bond of 665cm^-1Has stronger characteristic peak.

5. The anaerobic digestion reaction system according to claim 1, wherein: the calcium soap according to claim 3 was added to the anaerobic digestion system as a reaction substrate, and the ratio of the calcium soap to the inoculum was 0.5 (gVS/gVS).

6. The anaerobic digestion reaction system according to claim 5, wherein: the ratio of the working volume of the anaerobic digestion reactor to the volume of inoculum was 10: 1.

7. The anaerobic digestion reaction system according to claim 5, wherein: in order to keep the anaerobic condition in the anaerobic digestion bottles, introducing nitrogen into all the groups of sealed anaerobic digestion bottles for 5 minutes; anaerobic digestion was then carried out at 35-37 ℃ and 150rpm, with periodic measurements of methane content.

Technical Field

The invention belongs to the field of anaerobic digestion of organic wastes, and particularly relates to a method for improving the methane production performance of anaerobic digestion of waste oil and fat by using saponification pretreatment to prepare calcium soap

Background

With the global energy crisis and the greenhouse effect becoming more severe, there is a great deal of interest in finding clean, sustainable, renewable energy sources. Under the trend, the waste oil and fat has higher methane production potential which is 2.4 times higher than carbohydrate and 2 times higher than protein, so the treatment mode of the waste oil and fat is transferred to anaerobic digestion technology which can convert organic waste into methane from traditional landfill and incineration.

Anaerobic digestion is a promising technology for recovering biological energy from biomass or biosolid waste, and is one of the more effective waste oil treatment methods at present. The technology can be applied toPeranaerobic microbial communities convert biodegradable substrates into biogas (about 55-70% CH)₄And 30% -45% of CO₂Mixture of) is used for combustion or power generation, wherein the combustion product of methane is CO₂And H₂O, it is nontoxic and has good economic benefits, and the greenhouse effect is far lower than that of nitrogen oxides.

The waste oil and fat are degraded into long-chain fatty acid after being hydrolyzed, the enrichment of the long-chain fatty acid is the main reason for inhibiting anaerobic digestion, the long-chain fatty acid is adsorbed to the surface of biomass, further accumulates on the cell surface of bacteria and archaea, and limits the transportation of a substrate, and then the flotation and scouring of sludge are caused, so that the contact and the utilization rate of microorganisms to the substrate are reduced, and the methane yield is finally influenced; in addition, long chain fatty acids have toxic effects on different microbial communities (synbiotics and methanogens), eventually leading to a reduced methanogenesis rate.

Disclosure of Invention

The invention aims to overcome the problems in the anaerobic digestion process of the waste oil and fat, and provides a method for preparing calcium soap by saponification reaction of the waste oil and fat and calcium ions so as to slow down the inhibition effect of long-chain fatty acid on the anaerobic digestion of the waste oil and fat, improve the activity of microorganisms and improve the methane production rate and the methane yield.

In order to achieve the purpose, the invention is implemented according to the following technical scheme:

a method for improving the methane production performance of anaerobic digestion of waste oil by saponification pretreatment comprises the following steps:

(1) determination of the ratio of calcium ions to Long chain fatty acids

Design Ca²⁺The three ratios to LCFAs were 0.25, 0.5, 1(mol/mol), respectively. It is also noted that the fat is three times (based on molar mass) the long chain fatty acid, from which Ca is calculated²⁺The addition amount of (A) produces 6 kinds of calcium soaps.

(2) Preparation of calcium soap

Step A: low erucic acid rapeseed oil is used as waste grease material.

The oil component in rapeseed oil generally consists of C16 and C18.

And B: two types of calcium sources are commonly used: (a) anhydrous calcium sulfate (CaSO)₄) (ii) a (b) Calcium hydroxide (Ca (OH)₂)。

And C: preparing an alkaline solution: deionized water and solid sodium hydroxide (Na (OH)₂96.0% or more and 40(MW)) to prepare a sodium hydroxide solution having a concentration of 1 mol/L.

Step D: the calcium soap substrate is produced by using waste grease and calcium source materials under the alkaline and normal-temperature conditions.

(3) Determination of calcium soap formation

A small number of the resulting samples were taken at intervals and scanned by Fourier Infrared Spectroscopy (FTIR-HATR) until a distinct peak of calcium soap appeared, and stirring was stopped.

(4) Anaerobic digestion treatment mode

Step A: the ratio of calcium soap to inoculum was 0.5(gVS/gVS), wherein the inoculum was selected from Yanjing beer (Guilin Liquan) Inc. for anaerobic digestion of the beer wastewater.

And B: according to the ratio of the working volume of the anaerobic digestion reactor to the volume of the inoculum of 10:1, the reaction substrate and the inoculum are transferred to an anaerobic digestion bottle with the working volume of 150mL, and ultrapure water (which reduces the influence of calcium ions in water on the experiment) is added to the anaerobic digestion bottle to achieve the constant volume of 150 mL.

And C: in order to maintain anoxic conditions in the anaerobic digestion bottles, nitrogen is introduced into all the groups of sealed anaerobic digestion bottles for 5 minutes. Anaerobic digestion was then carried out at a temperature of 35-37 ℃ and a rotational speed of 150rpm, with periodic measurements of methane content.

Drawings

FIG. 1 Fourier infrared spectrum detection of three calcium sources (a) CaSO₄、(b)Ca(OH)₂Calcium soap spectrogram generated from waste oil

FIG. 2(a) type calcium soap cumulative methane production and rate of daily methane production

FIG. 3(b) type calcium soap cumulative methane production and rate of daily methane production

FIG. 4 is a flow chart of a saponification pretreatment process for improving anaerobic digestion of waste oil and fat to produce methane

Detailed Description

The following embodiments of the present invention are provided, and it should be noted that the present invention is not limited to the following embodiments, and all equivalent changes based on the technical solutions of the present invention are within the protection scope of the present invention.

The following is a detailed description of the process for preparing calcium soap and the method for improving anaerobic methanogenesis of waste oil and fat according to the embodiment of the present invention.

Example 1

The embodiment provides a method for preparing calcium soap and improving anaerobic methanogenesis of waste oil, which specifically comprises the following steps:

CaSO is used in this example₄As a calcium source, Ca is used²⁺Three ratios with LCFAs, 0.25, 0.5, 1(mol/mol), respectively, produce calcium soaps.

At room temperature, 5mL of sodium hydroxide solution (1mol/L) is added into a 100mL beaker, 5g of rapeseed oil is added to hydrolyze at 200rpm for 10min, and then a corresponding amount of CaSO is added into the beaker₄Wherein Ca is²⁺The set of LCFAs 1 was supplemented with 5ml of ultrapure water (easy to stir), and finally the beaker mouth was sealed with tinfoil paper and stirred at 450 rpm.

A small amount of the resulting sample was scanned at intervals by Fourier Infrared Spectroscopy (FTIR-HATR) until a distinct peak of calcium soap was observed, and stirring was stopped to produce calcium soap. (a) The spectrum of the type calcium soap is shown in FIG. 1 (a).

In this example, 3 sets of anaerobic digestion bottles with a total volume of 150mL are provided, and each set includes 3 parallel samples, i.e., CaSO₄-0.25、CaSO₄-0.5 and CaSO₄-1 group. In the initial stage of the reaction, the ratio of substrate to inoculum was 1: 2(gVS/gVS) after 15mL of inoculated sludge was added to each anaerobic digestion bottle, a corresponding amount of calcium soap substrate (a) (as shown in Table 1) was added, and 5min of nitrogen was passed through each anaerobic digestion bottle, air was vented, and anaerobic conditions were maintained.

All anaerobic digestion bottles were subjected to anaerobic digestion at a temperature of 35-37 ℃ and a rotational speed of 150rpm, and the methane content was measured periodically. After 38 days of anaerobic digestion reaction，CaSO₄-0.25、CaSO₄-0.5 and CaSO₄The cumulative methane production and methane production rate for the-1 group are shown in FIG. 2.

Example 2

The embodiment provides a method for preparing calcium soap and improving anaerobic methanogenesis of waste oil, which specifically comprises the following steps:

this example uses Ca (OH)₂As a calcium source, Ca is used²⁺Three ratios with LCFAs, 0.25, 0.5, 1(mol/mol), respectively, produce calcium soaps.

At room temperature, 5mL of sodium hydroxide solution (1mol/L) was added to a 100mL beaker, 5g of rapeseed oil was added and hydrolyzed at 200rpm for 10min, and then the corresponding amount of Ca (OH) was added to the beaker₂Finally, the beaker mouth was sealed with tinfoil paper and stirred at 450 rpm.

A small amount of the resulting sample was scanned at intervals by Fourier Infrared Spectroscopy (FTIR-HATR) until a distinct peak of calcium soap was observed, and stirring was stopped to produce calcium soap. (b) The spectrum of the type calcium soap is shown in FIG. 1 (b).

In this example, 3 sets of 150mL anaerobic digestion bottles were installed, and each set was provided with 3 parallel samples, i.e., Ca (OH)₂-0.25、Ca(OH)₂-0.5 and Ca (OH)₂-1 group. In the initial stage of the reaction, the ratio of substrate to inoculum was 1: 2(gVS/gVS) after 15mL of inoculated sludge was added to each anaerobic digestion bottle, a corresponding amount of type (b) calcium soap substrate (shown in Table 1) was added, and 5min of nitrogen was passed through each anaerobic digestion bottle, air was vented, and anaerobic conditions were maintained.

All anaerobic digestion bottles were subjected to anaerobic digestion at a temperature of 35-37 ℃ and a rotational speed of 150rpm, and the methane content was measured periodically. After 38 days anaerobic digestion reaction, Ca (OH)₂-0.25、Ca(OH)₂-0.5 and Ca (OH)₂The cumulative methane production and methane production rate for the-1 group are shown in FIG. 3.

Comparative examples

The embodiment provides a method for anaerobic methane production by unsaponifiable pretreatment of waste oil, which specifically comprises the following steps:

in the embodiment, 1 group of anaerobic digestion bottles with the total volume of 150mL are arranged, and 3 parallel samples are arranged, namely the control group. In the initial stage of the reaction, the ratio of substrate to inoculum was 1: 2(gVS/gVS) after 15mL of inoculated sludge was added to the anaerobic digestion flask, the corresponding amount of unsaponifiable pretreated oil was added (as shown in Table 1), and the anaerobic digestion flask was purged with nitrogen for 5min to remove air and maintain anaerobic conditions. All anaerobic digestion bottles were subjected to anaerobic digestion at a temperature of 35-37 ℃ and a rotational speed of 150rpm, and the methane content was measured periodically.

At the end of anaerobic digestion, the comparative example reached a cumulative methane production of 689.6. + -. 116.6mL/gVS_addedCaSO of example 1₄-0.5 and CaSO₄The cumulative methane production in group-1 was inferior to that in the control group, but CaSO₄Cumulative methane production in the-0.25 group reached a maximum of 663.7. + -. 64.3mL/gVS_addedSimilar to the control group, and CaSO₄The daily methanogenesis rate of the-0.25 group reached a maximum at day 5 (average 75.0. + -. 3.8mL/gVS_addedD) the daily methanogenesis rate over the control group reached a maximum (average 64.0 mL/gVS) on days 7-10_addedD) 2-5 days earlier, the rate increases by 17.2%. While example 2 compares with comparative example, Ca (OH)₂Cumulative methane production for the-0.25 group was up to 791.5. + -. 46.6mL/gVS_addedThe increase is 14.8% compared with the control group. Ca (OH)₂Cumulative methane production for the-0.5 group 684.9. + -. 24.0mL/gVS_addedSimilar to the control group, if a longer digestion period is allowed, the control group will be exceeded, at higher calcium ion concentrations, Ca (OH)₂Anaerobic digestion of group-1 was inhibited, probably due to excess OH in calcium soaps^-Resulting in a too high pH in the system (pH 10.25). Ca (OH)₂-0.25、Ca(OH)₂-0.5 and Ca (OH)₂The daily methanogenesis rate of group-1 peaked at day 5, day 3 and day 3, respectively, 3-7 days earlier than the control group.

In conclusion, the saponification pretreatment has a remarkable promotion effect on the anaerobic digestion gas production performance of the waste oil.

TABLE 1 inoculum and substrate composition