CN109082446B - Method for improving anaerobic digestion gas production performance of straws through photocatalytic pretreatment - Google Patents

Abstract

A method for improving anaerobic digestion gas production performance of rice straw by photocatalytic pretreatment is characterized in that rice straw with certain mass is weighed according to 50gTS/L load, and the load is calculated by the TS of the rice straw; adding titanium dioxide into water to dissolve, adding the titanium dioxide into a glass container, adding a certain mass of straws after uniformly stirring, continuously uniformly stirring, then putting the mixture into a photocatalytic reactor, enabling the surface of the solution to be 40-50cm away from a lamp source, starting a mercury lamp to irradiate for 1-8 h, and stirring by using a stirrer all the time in the illumination process; the temperature of the reaction solution is kept at 47 +/-2 ℃; mixing the pretreated straw stalks with an inoculum, wherein the inoculum is biogas slurry subjected to anaerobic digestion, the pH is 7.0-8.0, the ammonia nitrogen is 200-1500 mg/L, the alkalinity is 2000-6000 mg/L, and the inoculum size is 20g MLSS/L; adding water, stirring uniformly, and fixing the volume and sealing to ensure an anaerobic environment; the mesophilic anaerobic digestion process is carried out in a thermostatic water bath box at 35 +/-1 ℃ for 25d, and the rocking is carried out for 1 time every day. The invention is non-toxic and harmless, the anaerobic digestion period is obviously shortened, and the methane yield per TS is improved by 12.87-56.98%.

Description

Method for improving anaerobic digestion gas production performance of straws through photocatalytic pretreatment

Technical Field

The invention belongs to the field of anaerobic digestion of organic solid wastes, and particularly relates to a method for improving gas production performance of straws through photocatalytic pretreatment.

Background

China is a big agricultural country, various crop straws reach 8 hundred million tons every year, and a large amount of straws are burned in the open air or are discarded at will, so that the ecological environment of China is seriously influenced. The method converts the straws into the biogas by the anaerobic digestion technology, and is an effective way for solving the environmental pollution of agricultural wastes and realizing the resource utilization of the wastes.

The straw is a typical lignocellulose biomass and mainly comprises lignin, cellulose and hemicellulose, wherein the anaerobic digestion efficiency and the gas production efficiency are low due to the existence of the cross-linked structure of the lignin, the cellulose and the hemicellulose, particularly the lignin on the surface structure of the straw. The lignin is a three-dimensional phenolic polymer, the complex structure causes the lignin to be difficult to degrade by microorganisms, and the microorganisms and enzymes are prevented from contacting and utilizing cellulose and cellulose wrapped by the lignin, so that the straws are generally required to be pretreated before anaerobic fermentation. The pretreatment method mainly includes physical, chemical, physicochemical, and biological methods. The physical method mainly destroys the crystal structure of lignin, but can not realize the conversion and utilization of lignin, and mostly adopts high-temperature and high-pressure conditions, and the operation and the device are complicated. During chemical pretreatment, chemicals escape into the environment, and thus there is a problem of contamination with chemical agents. The physicochemical methods have some common problems in the physical and chemical methods, although they are effective. And physical and chemical pretreatment means mainly focus on destroying the cross-linking structures of lignin and cellulose and hemicellulose, so that the cellulose and the hemicellulose are more easily contacted and utilized by microorganisms, but the degradation effect on the lignin is poor, and the lignin cannot be completely utilized in the anaerobic digestion process. Although the biological treatment method can degrade lignin, the lignin-degrading microorganisms are few in types, the enzyme activity of decomposition enzymes is low, and the treatment time is long. In the pretreatment methods, few methods based on oxidation are used for dissolving lignin, so that the stubborn organic part of the lignin is beneficial to biodegradation, therefore, the patent provides a method for improving the gas production performance of the straws by adopting photocatalytic pretreatment, the lignin is degraded by adopting a photocatalytic pretreatment technology, the cellulose in the lignin is released, and the degradation and utilization of the lignin are realized.

Previous researches find that photocatalysis can oxidize and degrade lignin to obtain small molecular substances such as vanillin, guaiacol and the like, but mainly carries out catalytic degradation on single lignin, and a pretreatment method aiming at crop straws is not adopted, so that the subsequent research on anaerobic digestion performance is improved.

The literature: chenyuping, nano TiO₂Study on photocatalytic degradation of alkali lignin [ J]The research of biomass chemical engineering, 2009,43(6): 31-35, finds that: using nano TiO₂As a catalyst, alkali lignin is degraded by catalytic oxidation under ultraviolet light, and the degradation rate can reach more than 70% when the lignin is 5g, the dosage of the catalyst is 0.75g/L, the illumination time is 2.5h and the pH value is 10, and micromolecular substances such as syringyl derivatives, vanillin, guaiacyl derivatives and the like are obtained after degradation.

Disclosure of Invention

Therefore, the invention is provided for solving the problems that lignin is difficult to degrade and digest and the anaerobic digestion efficiency is low in the anaerobic fermentation process. The invention aims to provide a method for improving anaerobic digestion gas production performance of straw stalks by photocatalytic pretreatment, which has the following characteristics:

the technical scheme of the invention comprises the following contents:

(1) raw materials and reagents

Raw materials: preparing straw raw materials, namely cutting air-dried straw stalks into 3-4 cm, and crushing, drying and storing for later use by using a crusher with a 40-mesh screen;

reagent: TiO 2₂。

(2) Pretreatment method

Weighing a certain mass of straw stalks, and calculating the load by using the TS of the straw stalks; adding 0.2 g-2 g of titanium dioxide into a glass container by adding water for dissolving, adding a certain mass of straws after uniformly stirring, continuously uniformly stirring, then putting into a photocatalytic reactor, adopting a long-arc mercury lamp as a light source in the reactor, keeping the surface of the solution at a certain distance from the light source, starting the long-arc mercury lamp to respectively irradiate for 1 h-8 h, and continuously stirring by adopting a stirrer in the illumination process. In this process, since the semiconductor particles have an energy band structure, when the semiconductor is irradiated with light having an energy equal to or greater than the forbidden band width, electrons in the valence band are excited to transit to the conduction band, and electron-hole pairs having strong oxidation and reduction properties can be generated, but due to TiO₂Has a wide band gap (about 3.2eV), and thus, irradiation with ultraviolet light generates strong oxidative photogenerated holes, thereby initiating a series of redox reactions and generating hydroxyl radicals, which are considered as driving forces for degradation of oxidized organic matter. Research shows that the strong oxidative hydroxyl free radical can destroy the carbonyl and double bond on the side chain of lignin to further generate small molecular substances. After the pretreatment, the mixture was stored in a refrigerator at 4 ℃ for further use.

(3) Anaerobic digestion

Mixing the pretreated straw stalks with an inoculum, wherein the inoculum is biogas slurry subjected to anaerobic digestion, the pH is 7.0-8.0, the ammonia nitrogen is 200-1500 mg/L, the alkalinity is 2000-6000 mg/L, and the inoculum size is 20g MLSS/L; adding water, stirring uniformly, and fixing the volume and sealing to ensure an anaerobic environment; the mesophilic anaerobic digestion process is carried out in a thermostatic water bath box at 35 +/-1 ℃ for 25d, and the rocking is carried out for 1 time every day.

And (3) measuring the percentage content of methane and the daily biogas yield in the anaerobic digestion process, wherein the data is used for evaluating the anaerobic digestion effect of the straw stalks after photocatalytic pretreatment.

The method comprises the following specific steps:

weighing 15.98g of straw stalks according to 50g of TS/L load, wherein the load is calculated by the TS of the straw stalks; respectively adding 0.2g, 1g and 2g of titanium dioxide into a glass container by adding water for dissolving, uniformly stirring, then adding weighed straws and carrying out constant volume to 200ml, then putting into a photocatalytic reactor, wherein a long-arc mercury lamp is adopted as a light source in the reactor, the surface of the solution is 41cm away from a lamp source, the long-arc mercury lamp is started to respectively irradiate for 1h, 2h, 4h and 8h, an external illumination type strip-shaped lamp tube is adopted in the experiment, and the lamp source is a 500W long-arc mercury lamp with the main wavelength of 365 nm; stirring by using a magnetic stirrer all the time in the illumination process, wherein the stirrer adopts a Shanghai Si le 85-2 type constant-temperature magnetic stirrer, and the temperature of the reaction solution is kept at 47 +/-2 ℃; after the pretreatment, the mixture was stored in a refrigerator at 4 ℃ for further use.

The catalyst is VK-T06S type white powdery high-activity nano titanium dioxide purchased from Shaoxing photocatalytic air purification center, the particle size is 20 +/-5.60 nm, and the specific area is 70-120 m²The crystal form is a rutile and anatase mixed crystal form. Mixing the pretreated straw stalks with an inoculum, wherein the inoculum is biogas slurry obtained after anaerobic digestion of pig manure, the pH is 7.0-8.0, the ammonia nitrogen is 200-1500 mg/L, the alkalinity is 2000-6000 mg/L, and the inoculum size is 20g MLSS/L; adding water, stirring uniformly, fixing the volume to 0.3L, and sealing to ensure an anaerobic environment; the mesophilic anaerobic digestion process is carried out in a thermostatic water bath box at 35 +/-1 ℃ for 25d, and the rocking is carried out for 1 time every day.

The percentage content of methane and the daily biogas yield in the anaerobic digestion process are measured in the experimental process, and the data are used for evaluating the anaerobic digestion effect of the straw stalks after photocatalytic pretreatment.

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

(1) compared with the prior pretreatment method, the photocatalysis technology can be carried out under mild conditions, namely room temperature and normal pressure, the operation is simple, the engineering popularization is easy, and the technology is nontoxic and harmless and has important significance for protecting the environment.

(2) The anaerobic digestion period is significantly shortened compared to the blank (22d)Each pretreatment test group T₈₀The time is shortened by 1-4 days and is shortened by 5-18%.

(3) The anaerobic digestion efficiency of the experimental groups is obviously reduced after 25d, and in the anaerobic fermentation of 25d, compared with a blank group, the unit TS gas production of each experimental group is improved by 11.07-38.86%, and the unit TS methane production is improved by 12.87-56.98%.

(4) The pretreatment time is significantly shortened. The pretreatment time of the invention is only 1-8 h, when TiO is used₂The addition amount is 1g, and when the illumination time is 1h, the pretreatment effect is best, compared with the previous pretreatment time, the pretreatment time is greatly saved, and the time cost is saved.

(5) Compared with the blank group, the lignin degradation rate of each experimental group is 13.59-22.41%.

Detailed Description

Weighing 15.98g of straw stalks according to 50g of TS/L load, wherein the load is calculated by the TS of the straw stalks; 0.2g, 1g and 2g of titanium dioxide are respectively added with water to be dissolved and added into a glass container, after the mixture is uniformly stirred, weighed straws are added, the volume is constant to 200ml, then the mixture is placed into a photocatalytic reactor, a long-arc mercury lamp is adopted as a light source in the reactor, the distance between the surface of the solution and a lamp source is 41cm, the long-arc mercury lamp is started to respectively irradiate for 1h, 2h, 4h and 8h, an external illumination type strip-shaped lamp tube is adopted in the experiment, a 500W long-arc mercury lamp is adopted as the lamp source, and the main wavelength is 365 nm. And in the illumination process, a magnetic stirrer is used for stirring all the time, the stirrer adopts a Shanghai Si le 85-2 type constant-temperature magnetic stirrer, and the temperature of the reaction solution is kept at 47 +/-2 ℃. After the pretreatment, the mixture was stored in a refrigerator at 4 ℃ for further use.

Mixing the pretreated straw stalks with an inoculum, wherein the inoculum is biogas slurry obtained after anaerobic digestion of pig manure, the pH is 7.0-8.0, the ammonia nitrogen is 200-1500 mg/L, the alkalinity is 2000-6000 mg/L, and the inoculum size is 20g MLSS/L; adding water, stirring, diluting to 0.3L, and sealing; the mesophilic anaerobic digestion process is carried out in a thermostatic water bath box at 35 +/-1 ℃ for 25d, and the rocking is carried out for 1 time every day.

In the experimental process, the percentage content of methane and the daily biogas yield in the anaerobic digestion process are measured, the contents of cellulose, hemicellulose and lignin after pretreatment are measured, and the data is used for evaluating the anaerobic digestion effect of the straw stalks after photocatalytic pretreatment.

In all the following experiments, the anaerobic digestion experimental device is formed by connecting a 1L blue-cap bottle, a 1L wide-mouth bottle, a water collecting tank, a glass tube and a latex tube. The straw is straw crushed by a 40-mesh screen crusher, and the addition amount is 50g TS. The inoculum is biogas slurry of a pig manure anaerobic digestion tank which normally runs, and the addition amount of the inoculum is 20g MLSS/L.

Example 1

Taking 39 parts of 15.98g of straw stalks by weight; respectively adding 0.2g, 1g and 2g of titanium dioxide solid catalyst, adding water to dissolve the titanium dioxide solid catalyst, adding the titanium dioxide solid catalyst into a glass container, uniformly stirring, then adding weighed straws, carrying out constant volume to 200ml, then placing the mixture into a photocatalytic reactor, adopting a long-arc mercury lamp as a light source in the reactor, enabling the surface of the solution to be 41cm away from a lamp source, starting the long-arc mercury lamp to respectively irradiate for 1 hour, 2 hours, 4 hours and 8 hours, wherein an external illumination type strip-shaped lamp tube is adopted in the experiment, and a 500W long-arc mercury lamp is adopted as the lamp source, and the main wavelength is 365 nm. And in the illumination process, a magnetic stirrer is used for stirring all the time, the stirrer adopts a Shanghai Si le 85-2 type constant-temperature magnetic stirrer, and the temperature of the reaction solution is kept at 47 +/-2 ℃. After the pretreatment, the mixture was stored in a refrigerator at 4 ℃ for further use.

Mixing the pretreated straw stalks with an inoculum, wherein the inoculum is biogas slurry obtained after anaerobic digestion of pig manure, the pH is 7.0-8.0, the ammonia nitrogen is 200-1500 mg/L, the alkalinity is 2000-6000 mg/L, and the inoculum size is 20g MLSS/L; adding water, stirring uniformly, fixing the volume to 0.3L, and sealing to ensure an anaerobic environment; the mesophilic anaerobic digestion process is carried out in a thermostatic water bath box at 35 +/-1 ℃ for 25d, and the rocking is carried out for 1 time every day.

And in the experimental process, the daily gas production is recorded by a drainage method, the percentage content of methane in the gas is measured every day, and the data is used for evaluating the anaerobic digestion effect of the straw stalks after the photocatalytic pretreatment. Calculating total gas production and methane production after the experiment is finished, and then calculating T₈₀And methane production improvement rates. The experimental results are shown in table 1 below.

TABLE 1 anaerobic fermentation 25d gas and methane production

Table 1 shows the gas and methane yields and T for anaerobic digestion for 25d₈₀In the 25 th day, the TS methane yield under different photocatalytic pretreatment conditions is 84.74-117.86 mL/gVS, which is 12.87% -56.98% higher than that of the untreated group (75.08mL/gVS), and T is 12.87% -56.98%₈₀Is 18-20 days, and is shortened by 5-18% compared with the non-pretreated group (22 d). Taken together, when TiO₂The addition amount is 1g, when the illumination time is 1h, the pretreatment effect is best, the anaerobic digestion TS methane production rate is 248.00mL/gVS, T₈₀It was 18.83 days. Therefore, the photocatalytic pretreatment can obviously shorten the anaerobic digestion time and improve the early-stage load methane production rate.

TABLE 2 straw Properties after pretreatment

Table 2 shows the mass of cellulose, hemicellulose and lignin after pretreatment, and compared with the mass of lignin (7.14%) of untreated straw, the lignin degradation rate of each experimental group is 13.59% -22.41%, which shows that the pretreatment technology can realize lignin degradation.

TABLE 3 discharge Properties

The experiment results in table 3 show that the pH, ammonia nitrogen and alkalinity of each group of discharged materials in the experiment are in the appropriate range (the ammonia nitrogen is less than 2000mg/L and the alkalinity is 3000-5000 mg/L) for anaerobic bacteria growth, the buffer capacity of a digestion system can be effectively improved, and the stability of the system is maintained.

Claims (3)

1. A method for improving anaerobic digestion gas production performance of rice straws by photocatalytic pretreatment is characterized by comprising the following steps:

(1) raw material and reagent preparation

Raw materials: preparing straw raw materials, namely cutting air-dried straw stalks into 3-4 cm, and crushing, drying and storing for later use by using a crusher with a 40-mesh screen;

reagent: TiO 2₂

(2) Pretreatment method

Weighing a certain mass of straw stalks according to 50gTS/L load, and calculating the load by using the TS of the straw stalks; adding titanium dioxide into a glass container in a water-soluble manner, stirring uniformly, adding a certain mass of straw, continuously stirring uniformly, and then putting into a photocatalytic reactor, wherein the mass ratio of the titanium dioxide to the straw is (0.2-2): (15-16); a long-arc mercury lamp is used as a light source in the reactor, the distance between the surface of the solution and the light source is 40-50cm, the mercury lamp is started to irradiate for 1-8 h, and a stirrer is used for stirring all the time in the illumination process; the temperature of the reaction solution is kept at 47 +/-2 ℃; after the pretreatment is finished, the mixture is stored in a refrigerator at 4 ℃ for later use;

(3) anaerobic digestion

Mixing the pretreated straw stalks with an inoculum, wherein the inoculum is biogas slurry subjected to anaerobic digestion, the pH is 7.0-8.0, the ammonia nitrogen is 200-1500 mg/L, the alkalinity is 2000-6000 mg/L, and the inoculum size is 20g MLSS/L; adding water, stirring uniformly, and fixing the volume and sealing to ensure an anaerobic environment; the mesophilic anaerobic digestion process is carried out in a thermostatic water bath box at 35 +/-1 ℃ for 25d, and the rocking is carried out for 1 time every day.

2. The method of claim 1, wherein: the lamp source was a 500W long arc mercury lamp.

3. The method of claim 1, wherein:

the surface of the solution was 41cm from the lamp source.