WO2020000372A1

WO2020000372A1 - Combined treatment method for sorghum bicolor (linn.) moench plants rich in heavy metals

Info

Publication number: WO2020000372A1
Application number: PCT/CN2018/093681
Authority: WO
Inventors: 李十中; 李纪红; 薛忠财; 仉磊
Original assignee: 清华大学
Priority date: 2018-06-29
Filing date: 2018-06-29
Publication date: 2020-01-02

Abstract

A combined treatment method for Sorghum bicolor (Linn.) Moench plants rich in heavy metals: first fermenting Sorghum bicolor (Linn.) Moench stalks by using a solid state fermentation technology to produce ethanol with an economic value, wherein specific Saccharomyces cerevisiae TSH2 is selected to ensure that the fermentation time is further shortened while the ethanol yield is more than 90%; and then performing combustion treatment on a large quantity of cadmium-rich fermentation slag of the Sorghum bicolor (Linn.) Moench stalks generated after fermentation, controlling the combustion temperature to recycle fly ash generated after combustion and cadmium in furnace slag to the greatest extent, and moreover, generate heat energy with an economic value for ethanol production, power generation, or heat supply. By effectively integrating the solid state fermentation technology and the combustion technology, the problem on safe treatment of remediation plants can be effectively solved, and the economy and environmental protection properties can be achieved.

Description

Method for jointly treating sweet sorghum plants rich in heavy metals

Technical field

The invention relates to the field of environmental restoration of heavy metal polluted farmland, in particular to a method for jointly treating sweet sorghum plants rich in heavy metals, and belongs to the field of comprehensive recovery and utilization of plant resources and environmental protection.

Background technique

Phytoremediation refers to the use of plants with strong ability to accumulate heavy metals. The heavy metals are transferred and stored in the above-ground part of the plant through absorption and transport. Finally, the purpose of reducing the heavy metal content in the soil is achieved by harvesting the above-ground part. There are two main methods: Extract the heavy metals from the soil by using the superabsorbent capacity of the super-accumulating plants. Second, select non-super-accumulating plants that grow rapidly, have large biomass, and have a relatively strong ability to accumulate heavy metals.

Researchers have proposed planting energy plants with high biological yields on heavy metal-contaminated land, on the one hand, to achieve comprehensive utilization of heavy metal-polluted farmland, expand the planting area of energy plants, and on the other hand produce biomass energy (such as biogas, bioethanol, etc.) It can generate certain economic benefits, and at the same time, it can extract and repair heavy metals in the soil to achieve the purpose of multi-effects. It has positive effects on the agricultural structure of farmland polluted by heavy metals, increasing farmers' income, increasing the significance of restoration and extension. Role.

Sweet sorghum (Sorghum bicolor (Linn.) Moench), as an important energy plant, has the characteristics of high photosynthetic efficiency, high biological yield, strong resistance to stress, wide adaptability, etc., and it is very useful for heavy metals such as zinc, arsenic, copper, and cadmium. Strong absorption capacity and tolerance, can produce 5-6 tons of stalks with sugar content of 12-14% per mu. Therefore, the production of ethanol from sweet sorghum is considered to be one of the potential alternatives to petroleum. Its mature fermentation process, short production cycle, and relatively low production cost have the advantages.

Although sweet sorghum can be planted on heavy metal-contaminated farmland, if a large amount of sweet sorghum stalk fermentation residues rich in heavy metals such as cadmium cannot be disposed of as quickly and reasonably as possible, it will probably return to the soil. High activity increases its harmfulness and causes secondary pollution. At present, the disposal methods for rehabilitated plants are mainly used as waste or as resources, mainly including incineration, composting, compression landfilling, pyrolysis, plant metallurgy, spices extraction, and bioenergy.

The technology for producing ethanol by using sweet sorghum fermentation has been relatively mature, mainly including liquid fermentation method and direct solid-state fermentation method of crushing stalks and squeezing juice. Although liquid fermentation is the most commonly used method for biofuel ethanol, the liquid fermentation process of sweet sorghum stalks has the disadvantages of difficult juice extraction and serious water pollution problems, and basically cannot control the discharge of trace heavy metals in wastewater. For sweet sorghum solid fermentation, the stalk is pulverized. Under the premise that the moisture content of the sweet sorghum crushed material is within a certain range, the fermented seed liquid is mixed and mixed to produce ethanol. Compared with liquid fermentation, solid-state fermentation technology improves sugar utilization, simplifies the process, reduces production costs, and avoids the generation of a large amount of wastewater.

In summary, the energy utilization of the repaired sweet sorghum can be achieved through the production of ethanol, but how to properly handle the large amount of cadmium-rich sweet sorghum stalk fermentation residues produced after fermentation has become a key issue, and the economics of the processing technology And environmental protection is also of great significance to the development of this phytoremediation technology. Therefore, based on the principles of reduction, harmlessness and recycling, incineration is considered to be the most feasible technology.

Therefore, there is a need for a combined treatment method for heavy sorghum plants rich in heavy metals that can effectively solve the problem of safe disposal of rehabilitative plants, and is both economical and environmentally friendly.

Summary of the invention

In order to solve the above problems, the purpose of the present invention is to provide a combined treatment method for sweet sorghum plants rich in heavy metals, which uses solid-state fermentation technology to treat the stalks to produce fuel ethanol, and then uses combustion technology to treat the heavy metal-rich fermentation residues produced after fermentation. , Generates heat energy and heavy metal-rich residues and fly ash, and finally collects the residues and fly ash for heavy metal recovery. Through the effective combination and integration of the two technologies, the resource utilization and energy utilization of sweet sorghum plants rich in heavy metals were realized. At the same time, the reduction and harmless treatment of sweet sorghum stalks were achieved.

The solid-state fermentation technology is used to produce ethanol fuel from the stalks of sweet sorghum as raw materials. The specific steps are as follows:

1. Plant sweet sorghum in soil contaminated by heavy metals, and obtain sweet sorghum aerial parts after maturity;

2. The fresh sweet sorghum stalk is peeled and pulverized and mixed uniformly, preferably, the stalk is pulverized to a diameter of 1-5 mm and a length of less than 50 mm;

3. Weigh the crushed material and insert the cultivated seed liquid according to the inoculation amount of 5-15% of the mass of the crushed material. Among them, the inoculation amount is determined according to the growth and fermentation efficiency of the bacteria.

Preferably, the seed liquid is Saccharomyces cerevisiae Hansen TSH2. The Saccharomyces cerevisiae TSH2 is a special strain that has been specially domesticated and genetically modified. TSH2 can withstand high temperatures under solid fermentation conditions and absorb fermentable sugars. The rate is high, so the solid fermentation efficiency is significantly higher than other industrial yeasts. It is a high-yield ethanol yeast strain, which effectively solves the problems of the previous strains for solid fermentation fermentation heat accumulation (high temperature) and poor mass transfer effect. The Saccharomyces cerevisiae TSH2, the deposit number: CGMCC 14223, the deposit unit is the General Microbiology Center of the China Microbial Strain Collection Management Committee, and the deposit date is June 06, 2017.

4. Under the condition of 30 ° C, directly perform the solid fermentation in the solid fermenter, that is, ferment in the drum fermenter, the inoculation amount is 10% of the stalk mass, and the fermentation time is 24h. The stirring speed was controlled at 0.08 rpm.

5. Ethanol is obtained after distillation of crudely distilled ethanol, and the ethanol yield reaches more than 90%, which further effectively shortens the fermentation time from 24 hours to 20 hours in the prior art.

The combustion technology is used to treat sweet sorghum stalk fermentation residues and waste. The combustion technology uses a tube furnace combustion technology. The combustion system includes a gas distribution system, a tube furnace, a fly ash collection system, and flue gas absorption. System composition

The gas distribution system includes a gas bottle, a valve, and a gas flow meter for controlling the gas flow rate.

Preferably, the tube furnace uses a SK2-4-10 high temperature tube furnace as a burner, and the furnace temperature can be arbitrarily set at 500-1200 ° C according to the needs of the experiment.

The fly ash collection system includes a filter cartridge support and a glass fiber filter cartridge arranged in the support; the glass fiber filter cartridge in the filter cartridge support is used to filter and collect fly ash generated by combustion.

The flue gas absorption system includes a series of absorption bottles, and the absorption bottle contains a mixed solution of 5% HNO ₃ + 10% H ₂ O ₂ for absorbing gaseous heavy metals.

Among them, the combustion technology is used to burn the sweet sorghum stalk fermentation residue and waste at a combustion temperature of 900 ° C to recover cadmium. The specific operation method is:

Accurately weigh the sweet sorghum stalk fermentation slag, set the combustion temperature at 900 ° C, and heat the tube furnace according to the set program; when the furnace temperature reaches the set temperature, air is passed in and the gas flow is 5L / min; The corundum boat with the reaction sample was pushed in and left for 30 minutes to make it fully react. After the system was cooled, the slag, fly ash and flue gas absorption liquid were collected separately. When the combustion temperature is 900 ° C, the cadmium content in the fly ash is the highest. At this time, only the burned part and the fly ash in the glass fiber filter can be recovered to achieve the complete recovery of cadmium, while maximizing energy savings.

In actual production, a circulating fluidized bed boiler can be used for combustion treatment of sweet sorghum rod fermentation slag, and the combustion residues and fly ash are collected at a combustion temperature of 900 ° C to maximize the recovery of cadmium; Before the combustion treatment, the sweet sorghum stalk fermentation residue also needs to be dehydrated. The water content in the sweet sorghum stalk fermentation residue after distillation is about 80%. The sweet sorghum is combined with solar energy and heat generated by the combustion of a circulating fluidized bed boiler. The straw fermentation residue is dried to reduce the water content to below 50%.

The invention provides a combined treatment method for sweet sorghum plants rich in heavy metals, which uses solid state fermentation technology to ferment sweet sorghum stalks to produce economically valuable ethanol. The selected Saccharomyces cerevisiae TSH2 is used to guarantee an ethanol yield of more than 90% At the same time, the fermentation time is further shortened; a large amount of cadmium-rich sweet sorghum stalk fermentation slag produced after fermentation is treated by using combustion technology, and the combustion temperature is controlled to maximize the recovery of cadmium in burned fly ash and slag At the same time, thermal energy with economic value is generated. Through the effective integration of solid-state fermentation technology and incineration technology, the present invention effectively solves the problem of safe disposal of repaired plants, and is both economical and environmentally friendly.

It should be understood that the foregoing general description and the subsequent detailed description are exemplary descriptions and explanations, and should not be used as a limitation on the claimed content of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the accompanying drawings, further objects, functions and advantages of the present invention will be clarified by the following description of the embodiments of the present invention, in which:

FIG. 1 is a flow chart of specific steps of a combined treatment method for sweet sorghum plants rich in heavy metals according to the present invention.

FIG. 2 is a combustion curve of sweet sorghum stalk fermentation residue at a temperature rising rate of 30 ° C / min.

Figure 3 shows the change in the mass of the residue and fly ash (Figure 3a) and its percentage of the total mass (Figure 3b) after combustion at different temperatures.

Figure 4 shows the migration and transformation characteristics of cadmium during the combustion process, of which Figure 4a is the mass of cadmium in the residue, fly ash and smoke; Figure 4b is the normalized distribution of cadmium in the residue, fly ash and smoke; Figure 4c is Cadmium content in residues and fly ash.

detailed description

The objects and functions of the present invention and methods for achieving the objects and functions will be clarified by referring to the exemplary embodiments. However, the present invention is not limited to the exemplary embodiments disclosed below; it can be implemented in different forms. The essence of the description is merely to help those skilled in the relevant art to comprehensively understand the specific details of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

FIG. 1 is a flow chart of specific steps of a combined treatment method for sweet sorghum plants rich in heavy metals according to the present invention. Referring to FIG. 1, the present invention provides a combined treatment method for sweet sorghum plants rich in heavy metals. The stalks are treated by wastewater-free solid-state fermentation technology, and crude ethanol is distilled to obtain fuel ethanol. Combustion technology is used to treat the rich Heavy metal fermentation slag produces economical thermal energy and heavy metal-rich residues and fly ash for heavy metal recovery. Through the effective combination and integration of the two technologies, the resource utilization and energy utilization of sweet sorghum plants rich in heavy metals were realized. At the same time, the reduction and harmless treatment of sweet sorghum stalks were achieved.

Example 1 Solid-state fermentation technology of sweet sorghum stalks

The sweet sorghum used in the experiment was grown in a cadmium-contaminated farmland in Shaoguan, Guangdong. The cadmium concentration in the soil was 7.93 mg / kg, the effective cadmium content was 2.89 mg / kg, the sugar content of the stalk was 11.3%, and the fresh weight was 750 g / plant. Adopt advanced solid fermentation (ASSF) technology and a unique high temperature resistant, high metabolic efficiency strain (Saccharomyces cerevisiae Hansen TSH2), the main fermentation time is completed within 20 hours, the ethanol yield is more than 90%, and the entire process It produces almost no waste water and effectively reduces secondary pollution of heavy metals.

The specific operation method is as follows: the fresh sweet sorghum stem is peeled and pulverized and mixed uniformly (1-5 mm in diameter and less than 50 mm in length), 10 kg of crushed material is weighed, and the cultivated seed liquid is inserted according to 10% of the inoculation amount ( The strain is Saccharomyces cerevisiae Hansen (TSH2). The initial fermentation temperature is 25-35 ° C. The fermentation is carried out in a drum fermentation tank with a capacity of 50L. The stirring speed is controlled at 0.08 rpm, and the fermentation is performed for 20 hours. Ethanol is obtained after distillation. The theoretical yield of ethanol is over 90%, and the fermentation time is shortened from 24 hours to 20 hours in the prior art.

The strains used in this embodiment are obtained after screening, domestication and genetic modification, and can tolerate the characteristics of high temperature and low mass transfer rate under solid fermentation, further reducing the fermentation time from 24h to 20h in the prior art, thereby improving Fermentation efficiency and ethanol yield. The strain is Saccharomyces cerevisiae TSH2, and the deposit number is CGMCC 14223, and the deposit unit is: General Microbial Center of China Microbial Strain Collection Management Committee, and the deposit date is June 6, 2017.

Example 2 Combustion technology of sweet sorghum stalk fermentation residue and waste

Using tube furnace combustion technology, the combustion system consists of gas distribution system, tube furnace, fly ash collection system and flue gas absorption system. The gas distribution system consists of gas bottles, valves and gas flow meters to control the gas flow rate. The tube furnace uses SK2-4-10 high temperature tube furnace as the burner, and the furnace temperature can be arbitrarily set at 500-1200 ° C according to the needs of the experiment. The fly ash produced by the combustion is collected by filtering through the glass fiber filter cartridge in the cartridge holder. The flue gas absorption system is composed of a series of absorption bottles containing a mixed solution of 5% HNO ₃ + 10% H ₂ O ₂ for absorbing gaseous heavy metals.

The specific operation method is: accurately weigh 4.000g sweet sorghum stalk fermentation slag, and study the migration and transformation of cadmium at different combustion temperatures, and set the combustion temperature to 600 ° C, 700 ° C, 800 ° C, 900 ° C, and 1000 ° C for 5 combustion temperatures. According to the set program, the tube furnace is heated up. When the furnace temperature reaches the set temperature, air is passed in and the gas flow rate is 5 L / min. Then, the corundum boat containing the reaction sample is pushed in, and it is left for 30 minutes to make it Complete reaction. After the system cools down, collect slag, fly ash and flue gas absorption liquid.

The content of cadmium was determined by inductively coupled plasma emission spectrometer (Agilent 7700X, Agilent Technologies, USA). Fly ash sweet sorghum stem after fermenting sludge and co-firing, the residue microwave digestion were digested (CEM-MARS) method, acid digestion system of _{_{HNO 3 -HClO 4 -HF (2:}} 2: 1), the digestion solution volume . For the sample of smoke absorption liquid, transfer two bottles of 5% HNO ₃ + 10% H ₂ O ₂ absorption liquid to a 500ml volumetric flask according to the EPA METHOD 29 method, and use a constant volume.

See Figures 2 to 4, Figure 2 is the combustion curve of sweet sorghum stalk fermentation residue at a temperature rise rate of 30 ° C / min, where: TGA represents the change in quality, and DTG represents the first-order differential of quality over time. DTA reflects the change of fuel energy during fuel combustion. It can be seen from the figure that the combustion of sweet sorghum stalk fermentation residue can be divided into four stages: preheating and drying, volatilization analysis, volatiles combustion, and coke burnout. The maximum weight loss rate occurs at about 350 ° C, that is, at Volatile combustion stage.

Figure 3 shows the changes in the quality of the residue and fly ash under different temperature combustion conditions. It can be seen from Figure 3a that as the temperature increases, the combustion is more sufficient, resulting in a decline in the quality of the residue and fly ash. From Figure 3b, The percentage of its solid sample decreased from 11.2% at 600 ° C to 6.00% at 900 ° C, which indicates that the quality of the sample was significantly reduced after combustion, effectively reducing the sweet sorghum residue and harmless treatment.

Figure 4 shows the migration and transformation characteristics of cadmium at different combustion temperatures. Cadmium has a low boiling point and is a volatile heavy metal.

Figure 4a is the mass curve of cadmium in slag, fly ash and flue gas at different combustion temperatures. It can be seen from the figure that the mass of cadmium in the residue decreases with increasing temperature, and the mass of cadmium in fly ash varies with As the temperature rises, it first rises and then decreases, and the mass in the flue gas remains unchanged.

Figure 4b is a normalized distribution diagram of the mass change of cadmium in slag, fly ash and flue gas at different temperatures. It can be seen from the figure that cadmium is mainly distributed in fly ash, but the mass in flue gas and residue is low. ; Although cadmium is distributed in bottom slag, fly ash, and flue gas, according to the theory of material balance, 100% recovery can be achieved at different temperatures, and it has no significant effect on the normalized distribution of cadmium.

Figure 4c shows the content of cadmium in the residue and fly ash. It can be seen from the figure that the content of cadmium in the residue and fly ash changes with increasing temperature. The content of cadmium in the residue at 900 ° C is 2.23 mg / kg. , And the content in fly ash can reach 63.3mg / kg.

In summary, it is known that when burning at 900 ° C, the cadmium content in fly ash is the highest. At this time, only the residue and fly ash after the combustion can be collected to achieve the recovery of cadmium. At the same time, it saves energy to the greatest extent and avoids burning at low temperatures. Dioxin problems.

In actual production, a circulating fluidized bed boiler can be used to comb the sweet sorghum rod fermentation slag. When the combustion temperature is 900 ° C, the residues and fly ash after combustion are collected to maximize the recovery of cadmium, while not recycling cadmium. Pollution to the environment again. The method for recovering cadmium is to realize the recovery of cadmium by a heap leaching method and an electrodeposition technology.

The combustion technology can effectively treat sweet sorghum stalk fermentation residues and wastes, generate thermal energy with economic value for ethanol production and power generation or heating, and the recovery rate of heavy metals in residues rich in heavy metals and fly ash can reach 100 %, In actual production, under the condition that the fermentation residues of sweet sorghum stalks are fully burned, when the combustion temperature is 900 ° C, cadmium is completely recovered, and energy is saved to the maximum; Harm treatment, while also realizing the resource utilization and energy utilization of sweet sorghum plants rich in heavy metals.

The invention is to provide a combined treatment method for sweet sorghum plants rich in heavy metals, to realize the safe disposal of sweet sorghum plants rich in heavy metals. The specific method is to use solid-state fermentation technology to treat the stalks to produce ethanol with economic value, and then burn them. The technology treats fermented slags rich in heavy metals produced after fermentation to generate thermal energy with economic value and residues and fly ash that can be used to extract heavy metals. Through the effective combination and integration of the two technologies, the resource utilization and energy utilization of sweet sorghum plants rich in heavy metals were realized. At the same time, the reduction and harmless treatment of sweet sorghum stalks were achieved.

In conjunction with the description and practice of the invention disclosed herein, other embodiments of the invention will be readily conceivable and understood by those skilled in the art. The description and examples are to be considered exemplary only, with the true scope and spirit of the invention being defined by the claims.

Claims

A combined treatment method for sweet sorghum plants rich in heavy metals. The stalks are treated by solid-state fermentation technology without waste water. Crude steamed ethanol is rectified to obtain fuel ethanol. The heavy metal-rich ferment residues produced after fermentation are dehydrated and used. Combustion technology is used for processing to generate thermal energy and residues and fly ash containing heavy metals. The collected residues and fly ash are used for heavy metal recovery and extraction.
The combined treatment method according to claim 1, wherein the specific steps for treating the stalks by using wastewater-free solid state fermentation technology are:

Step 1: Plant sweet sorghum in soil contaminated by heavy metals, and obtain sweet sorghum aerial parts after maturity;

Step 2: The fresh sweet sorghum stem is peeled and pulverized and mixed uniformly, and the stem is pulverized to a diameter of 1-5 mm and a length of less than 50 mm;

Step 3: Weigh the crushed material, and insert the cultivated seed liquid according to the inoculation amount of 5-15% of the mass of the crushed material;

Step 4: Under the condition of 30 ° C, directly perform the solid fermentation in the solid fermenter, that is, ferment in the drum fermenter, the inoculation amount is 10% of the stem mass, and the fermentation time is 20h. , The stirring speed is controlled at 0.08rpm;

Step 5: Ethanol is obtained after crude distillation of ethanol, and the ethanol yield is above 90%.
The method of claim 2, in step 3, the seed liquid is Saccharomyces cerevisiae TSH2, the deposit number is CGMCC 14223, and the deposit unit is the Ordinary Microbiology Center of the China Microbial Strain Collection Management Committee, and the preservation date is 2017. June 06.
The combined processing method according to claim 1, wherein the combustion technology uses a tube furnace combustion technology, and the combustion system comprises a gas distribution system, a tube furnace, a fly ash collection system, and a flue gas absorption system;

The gas distribution system includes a gas bottle, a valve, and a gas flow meter for controlling a gas flow rate;

The tube furnace uses a SK2-4-10 high temperature tube furnace as a burner, and the furnace temperature can be arbitrarily set at 500-1200 ° C;

The fly ash collection system includes a filter cartridge support and a glass fiber filter cartridge arranged in the support; the glass fiber filter cartridge in the filter cartridge support is used to filter and collect fly ash generated by combustion;

The flue gas absorption system includes a series of absorption bottles, and the absorption bottle contains a mixed solution of 5% HNO 3 + 10% H 2 O 2 for absorbing gaseous heavy metals.
The combined treatment method according to claim 4, wherein the combustion technology is used to combust sweet sorghum stalk fermentation residue and waste at a combustion temperature of 900 ° C to recover cadmium, and the specific operation method is:

Accurately weigh the sweet sorghum stalk fermentation slag, set the combustion temperature at 900 ° C, and heat the tube furnace according to the set program; when the furnace temperature reaches the set temperature, air is passed in and the gas flow is 5L / min; The corundum boat with the reaction sample was pushed in and left to react for 30 minutes. After the system was cooled, the slag, fly ash and flue gas absorption liquid were collected separately. When the combustion temperature was 900 ° C, the cadmium content in the fly ash was the highest. Collect the residue and fly ash for heavy metal cadmium recovery and extraction.
The combined treatment method according to claim 1, wherein the combustion technology uses a circulating fluidized bed boiler to burn sweet sorghum rod fermentation slag, and collects burned residues and fly ash at a combustion temperature of 900 ° C to maximize cadmium Recycling.
The combined treatment method according to claim 6, before the combustion technology performs the combustion treatment, the sweet sorghum stalk fermentation residue is dehydrated by using solar energy and thermal energy generated by the combustion of a circulating fluidized bed boiler to reduce the water content from 80% To below 50%.
The method according to claim 5 or 6, wherein the method for recovering the heavy metal cadmium is a heap leaching method and an electrodeposition technology.