Method for reducing sludge moisture content and greenhouse gas emission in biological drying process

Abstract

The invention discloses a method for reducing sludge moisture content and greenhouse gas emission in a biological drying process, which comprises the following steps: preparing sludge, biomass, biochar and calcium oxide into a mixed material, carrying out biological drying on the mixed material, and in the biological drying process, after 25 hours, adding magnesium chloride to complete biological drying treatment on the sludge. According to the method disclosed by the invention, calcium oxide and magnesium chloride are sequentially added in the biological drying process, and moisture in the sludge can be efficiently removed and the yield of greenhouse gases can be remarkably reduced under the combined action of calcium oxide and magnesium chloride, so that the moisture content of the sludge and the emission of the greenhouse gases in the biological drying process can be effectively reduced; the method has the advantages of being simple in process, convenient to operate, low in cost, high in drying efficiency, small in pollution gas emission amount, environmentally friendly and the like, not only can effectively solve the problem of greenhouse gas emission reduction in the sludge biological drying process, but also can achieve rapid sludge reduction, and is high in use value and good in application prospect.

Description

Technical Field

[0001] The invention belongs to the field of organic solid waste disposal, relates to a sludge biological drying method, and specifically relates to a method for reducing the sludge water content and greenhouse gas emissions during the biological drying process. Background Art

[0002] With the acceleration of my country's urbanization process, the amount of sewage treatment is increasing, and the output of sludge is also increasing. Sludge contains a large amount of organic matter, heavy metals and pathogens. If it is not properly treated, it will pollute the soil and water sources, posing a threat to the ecosystem and human health. In addition, the high water content of sludge (usually above 80%) increases the cost of treatment and transportation, and also limits the resource utilization of sludge. Therefore, it is necessary to efficiently dehydrate the sludge and reduce greenhouse gas emissions during the dehydration process, so as to obtain a dry product with stable properties and environmental friendliness in a short time.

[0003] As a low-cost, environmentally friendly and resource-saving drying technology, biological drying has attracted much attention in recent years. Through the metabolism of microorganisms, biological drying technology converts organic matter in sludge into the biological heat of the microorganisms themselves, while releasing water, thereby achieving the purpose of reducing the moisture content of sludge. Although biological drying has many advantages, it also encounters some problems in practical applications, such as the great influence of environmental conditions on microbial activity, long treatment cycle, and strict requirements on operating conditions. Not only that, the biological drying process will also produce odor and greenhouse gas emissions. Specifically, the metabolic activities of microorganisms will inevitably produce greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Especially under anaerobic conditions, the amount of methane produced is large, and its greenhouse effect is about 25 times that of carbon dioxide. It can be seen that the reduction of moisture content and greenhouse gas emissions in the biological drying process cannot be ignored. To this end, the inventors of the present application have proposed a method for biological drying of sludge, which comprises first baking the biomass material, then mixing the baking product, sludge, biochar material and a conditioning agent to form a mixed material for biological drying. However, further improvements are still needed in the following aspects: (1) The reproduction and growth of microorganisms, especially thermophilic microorganisms, start slowly, resulting in a slow heating rate of the biological drying system, making it difficult to efficiently remove moisture from the sludge, wherein the moisture content of the sludge can only be reduced to about 30% within 11 days; (2) It is difficult to effectively control the absorption and bioavailability of nutrients (such as carbon sources and nitrogen sources) by microorganisms by improving the structure and nutrient composition of the pile, and by changing the porosity and increasing the surface area of ​​the reactor space, and thus it is difficult to effectively regulate the production of pollutant gases, especially oxygen-containing greenhouse gases (such as CO2 and N2O). Not only is it difficult to regulate the production of pollutant gases, but the emission of pollutant gases is still relatively high. Therefore, obtaining a sludge biological drying method that can quickly reduce the moisture content of sludge and effectively reduce greenhouse gas emissions is of great significance for effectively reducing the moisture content of sludge and greenhouse gas emissions during the biological drying process and realizing the resource utilization of sludge. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for reducing the moisture content of sludge and greenhouse gas emissions during biological drying in view of the deficiencies in the prior art. The method can not only efficiently remove moisture from the sludge, but also significantly reduce greenhouse gas emissions.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for reducing sludge moisture content and greenhouse gas emissions during biological drying, comprising the following steps:

[0007] S1. Mix sludge A, biomass A, biochar A and calcium oxide to obtain a mixed material A;

[0008] S2. The mixed material A obtained in step S1 is subjected to biological drying. During the biological drying process, magnesium chloride is added to the mixed material A after 25 hours to complete the biological drying treatment of the sludge.

[0009] The above method is further improved in that in step S2, during the biological drying process, magnesium chloride is added to the mixed material A during the period of 25h to 50h.

[0010] The above method is further improved in that in step S1, the amount of calcium oxide added is 1% to 4% of the dry weight of the mixed material A.

[0011] The above method is further improved in that in step S2, the amount of magnesium chloride added is 1% to 4% of the dry weight of the mixed material A.

[0012] The above method is further improved in that in step S1, the amount of calcium oxide added is 2% to 3% of the dry weight of the mixed material A.

[0013] The above method is further improved, in step S2, the amount of magnesium chloride added is 2% to 3% of the dry weight of the mixed material A; and the magnesium chloride is anhydrous magnesium chloride.

[0014] The above method is further improved in that step S1 further comprises adding domesticated sludge; the amount of the domesticated sludge added is 20% to 25% of the weight of the sludge A.

[0015] The above method is further improved, wherein the domesticated sludge is prepared by domesticating sludge B, biomass B, and biochar B, comprising the following steps:

[0016] (1) mixing sludge B, biomass B, and biochar B to obtain a mixed material B;

[0017] (2) The mixed material B is subjected to acclimation treatment to obtain acclimated sludge.

[0018] The above method is further improved, in step (1), the biomass B is at least one of wheat straw, camellia oleifera cake, camellia oleifera shell, and reed; the amount of biomass B added is 35% to 40% of the weight of the sludge B; the wheat straw is in powder form with a particle size of 4 mm to 5 mm; the camellia oleifera cake is in powder form with a particle size of 20 mesh to 50 mesh; the biochar B is at least one of bamboo charcoal, stalk biochar, peanut shell biochar, sludge biochar, and manure biochar; the amount of biochar B added is 5% of the total dry weight of the sludge B and biomass B; the particle size of the biochar B is 60 mesh to 80 mesh.

[0019] The above method is further improved, in step (2), the acclimation treatment is carried out under aerobic conditions; during the acclimation treatment, the compost is turned at 0, 1, 3, 5, 8, 11, 15 and 21; the acclimation treatment time is 21 days; after the acclimation treatment is completed, the following treatment is also included: placing the material obtained after the acclimation treatment in a bacterial culture room at 60°C for 24 hours.

[0020] The above method is further improved in that in step S1, the moisture content of the mixed material A is 55% to 60%.

[0021] The above method is further improved, wherein the biomass A is at least one of wheat straw, camellia oleifera cake, camellia oleifera shell, and reed; the amount of biomass A added is 35% to 40% of the weight of the sludge A; the wheat straw is in powder form with a particle size of 4 mm to 5 mm; the camellia oleifera cake is in powder form with a particle size of 20 mesh to 50 mesh; the biochar A is at least one of bamboo charcoal, stalk biochar, peanut shell biochar, sludge biochar, and manure biochar; the amount of biochar A added is 5% of the total dry weight of the domesticated sludge, sludge A, and biomass A; the biochar A is in powder form with a particle size of 60 mesh to 80 mesh.

[0022] The above method is further improved, in step S2, the biological drying time is 6 days to 21 days.

[0023] The above method is further improved, in step S2, the biological drying time is 6 days to 11 days.

[0024] The above method is further improved, in step S2, the biological drying process also includes the following treatment: aerating and turning the mixed material A, aerating the mixed material A on day 0, the number of aeration treatments is 3 times, the aeration volume is controlled to be 0.4L / min kg during the aeration treatment, the aeration time of a single aeration treatment is 30min, and the compost is turned once on days 1, 3, 5, 8, 11, 15 and 21.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] (1) In view of the problems of low drying efficiency and large emission of polluting gases in the existing sludge biological drying methods, the present invention creatively proposes a method for reducing the moisture content of sludge and the emission of greenhouse gases during the biological drying process. By successively adding calcium oxide and magnesium chloride during the biological drying process, the moisture in the sludge can be efficiently removed under the combined action of calcium oxide and magnesium chloride, and the production and emission of greenhouse gases can be significantly reduced. The details are as follows: (a) The calcium oxide added first accelerates the evaporation of water through an exothermic reaction, and the magnesium chloride added later further reduces the moisture content of the sludge through hygroscopic action. In addition, magnesium chloride, as a strong hygroscopic agent, can absorb free water in the sludge. The addition of magnesium chloride can significantly improve the dehydration efficiency of sludge, and can also change the surface tension of sludge, reduce the adhesion between water molecules and sludge particles, and make it easier to separate water from sludge. Therefore, under the synergistic effect of calcium oxide and magnesium chloride, the dehydration speed of sludge is accelerated, thereby shortening the entire drying cycle and improving the drying efficiency. In particular, the water content of sludge treated with calcium oxide and magnesium chloride is greatly reduced, making it more suitable for resource utilization, such as fertilizer, soil conditioner or building material. In addition, this treatment method can also reduce microbial activity and reduce the risk of transmission of pathogens and harmful substances. (b) In terms of affecting the internal environment of sludge, adding calcium oxide first can increase the pH value of sludge, help inhibit microbial activity and reduce the decomposition of organic matter, while the subsequent addition of magnesium chloride can help form a stable sludge structure, regulate the osmotic pressure of sludge and promote the degradation of organic matter. In addition, calcium oxide can neutralize acidic substances in sludge and reduce the generation of odorous gases, while the hygroscopic effect of magnesium chloride can help control the humidity of sludge and further reduce odor. (c) By adding calcium oxide and magnesium chloride successively, the growth conditions and treatment environment of microorganisms can be controlled to ensure the stability and safety of the treatment process and provide favorable conditions for the growth environment of microorganisms. Specifically, on the one hand, calcium oxide, as an alkaline substance, can neutralize the acidic substances in the sludge and increase the pH value of the sludge. The adjustment of this pH value helps to create an environment suitable for the growth and metabolism of microorganisms. In addition, the chemical reaction of calcium oxide and magnesium chloride can generate calcium hydroxide and calcium chloride. These compounds can provide certain microorganisms with the necessary calcium and magnesium nutrients and promote their growth and metabolic activities. On the other hand, adding calcium oxide first can increase the temperature of the sludge, provide a suitable growth environment for certain thermophilic microorganisms, and accelerate the metabolic rate of microorganisms. The magnesium chloride added later can reduce the moisture content of the sludge due to its hygroscopic effect, reduce the inhibitory effect of moisture on microbial metabolism, thereby promoting the metabolic activities of microorganisms, and further improving the drying effect of the sludge.(d) In terms of the physical and chemical properties of sludge, the addition of calcium oxide and magnesium chloride can improve the physical structure of sludge, increase porosity, provide more oxygen, and reduce certain substances in the sludge that inhibit the growth of microorganisms, such as heavy metals and toxic organic compounds, thereby improving the activity of microorganisms and enhancing their tolerance to environmental changes. Moreover, the addition of calcium oxide and magnesium chloride can change the chemical environment of sludge, which may promote the formation and stability of different microbial communities, increase the diversity of microbial communities, and thus improve the drying effect of sludge and reduce the generation of pollutant gases. (e) Adding calcium oxide and magnesium chloride successively can not only ensure efficient water removal effect, but also reduce energy loss in the biological drying process. Specifically, in general, biological drying requires a large amount of energy to achieve material drying and processing. In the present invention, after calcium oxide and magnesium chloride are added successively, the situation has undergone a positive change. Calcium oxide has strong water absorption and can react chemically with water in the material to generate calcium hydroxide and release heat. This part of heat can accelerate the evaporation of water and reduce the energy required for external heating. At the same time, calcium hydroxide can adjust the pH value of the material, optimize the living environment of microorganisms, promote the metabolic activity of microorganisms, and improve Drying efficiency. Further, the magnesium chloride added later can form crystalline hydrates under certain conditions, absorb moisture in the material, and thus reduce the moisture content. In addition, magnesium chloride can also affect the cell osmotic pressure of microorganisms, regulate the metabolic process of microorganisms, and enhance the ability of microorganisms to decompose organic matter to generate heat, which helps to reduce the input of external energy. It can be seen that under the joint action of the unique chemical properties of calcium oxide and magnesium chloride, the chemical reactions in the biological drying process can be effectively promoted, thereby reducing dependence on external energy, not only reducing energy input, but also optimizing the energy utilization efficiency of the entire biological drying process, so that the original high energy consumption process has been significantly improved. (f) By adding calcium oxide and magnesium chloride in sequence, greenhouse gas emissions during the biological drying of sludge can be reduced. Specifically, calcium oxide will form calcium hydroxide after dissolving in water, which can increase the pH value of the system. This alkaline environment helps to inhibit the growth of anaerobic microorganisms and reduce the production of greenhouse gases such as methane. In addition, calcium oxide reacts with water to form calcium hydroxide, which further reacts with carbon dioxide to form calcium carbonate, thereby reducing the concentration of carbon dioxide in the atmosphere. More importantly, magnesium chloride can act as a catalyst to promote the decomposition and conversion of organic matter and reduce the emission of greenhouse gases (such as methane and carbon dioxide) produced under anaerobic conditions. Moreover, after adding calcium oxide and magnesium chloride, the dried biomass can be used as a fertilizer to improve the quality of sludge, reduce the release of volatile organic matter, and increase the carbon storage capacity of sludge, thereby indirectly reducing greenhouse gas emissions.Therefore, the method of the present invention successively adds calcium oxide and magnesium chloride during the biological drying process, and can effectively remove moisture from the sludge and significantly reduce the production of greenhouse gases under the joint action of calcium oxide and magnesium chloride, thereby effectively reducing the moisture content of the sludge and the greenhouse gas emissions during the biological drying process. It has the advantages of simple process, convenient operation, low cost, high drying efficiency, low pollutant gas emissions, and environmental friendliness. It can not only effectively solve the problem of greenhouse gas emission reduction during the sludge biological drying process, but also is conducive to achieving rapid sludge reduction, high use value, and good application prospects.

[0027] (2) In the present invention, by optimizing the amount of calcium oxide added to 1% to 4% of the dry weight of the mixture A, especially when the amount of calcium oxide added is 2% to 3% of the dry weight of the mixture A, not only can the pH value of the pile (mixed material A) be adjusted to a suitable range, but also the composition and richness of the microorganisms in the pile can be optimized, so that the moisture in the pile can be removed more quickly and efficiently. When the dosage of calcium oxide is too low, it is not conducive to the regulation of the pH value of the pile, and it is difficult to obtain a suitable pH. When the dosage of calcium oxide is too high, it will seriously stress the microbial community structure, making it difficult to use microbial heat to improve the drying effect. In addition, in the present invention, by optimizing the amount of magnesium chloride added to 1% to 4% of the dry weight of the mixture A, especially when the amount of magnesium chloride added is 2% to 3% of the dry weight of the mixture A, the mineralization rate of organic matter in the pile can be effectively promoted, and a weakly acidic pH value can be provided for the pile microorganisms.

[0028] (3) In the present invention, the biological drying system also includes: adding domesticated sludge, wherein the domesticated sludge is prepared by domesticating sludge, biomass, and biochar. By adding domesticated sludge, efficient inoculation of microorganisms in sludge biological drying can be achieved, which is not only beneficial to improving the quality of sludge, but also can significantly improve the efficiency and effect of sludge treatment. In addition, the sludge biological drying technology of adding domesticated products in the present invention also has the following advantages: it can accelerate the decomposition of organic matter and improve sludge stability; reduce odor and reduce greenhouse gas emissions; improve resource utilization potential and reduce the use of chemical additives; enhance sludge biological activity and increase calorific value; promote harmless treatment and improve treatment flexibility; reduce energy consumption and promote ecological circulation; improve safety. These advantages show that adding domesticated sludge has important application value and prospects in the process of sludge biological drying. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0030] Figure 1 This is a process flow chart for reducing sludge moisture content and greenhouse gas emissions during biological drying in Example 1 of the present invention.

[0031] Figure 2 This is a diagram showing changes in system temperature during the bio-drying process of Example 1 of the present invention and Comparative Examples 1-4.

[0032] Figure 3 This is a diagram showing changes in the moisture content of the system during the biological drying process of Example 1 of the present invention and Comparative Examples 1-4.

[0033] Figure 4 This is a diagram showing changes in greenhouse gas potential values ​​of the system during the biological drying process of Example 1 of the present invention and Comparative Examples 1-4. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0035] The materials and instruments used in the following examples are all commercially available.

[0036] Embodiment 1:

[0037] A method for reducing the moisture content of sludge and greenhouse gas emissions during biological drying, the process flow chart of which is as follows Figure 1 As shown, the following steps are included:

[0038] (1) preparing domesticated sludge, which is obtained by domesticating sludge B, biomass B, and biochar B, specifically:

[0039] (1.1) Bamboo charcoal, wheat straw and camellia oleifera cake are dried, crushed and sieved respectively to obtain bamboo charcoal powder with a particle size of 60 to 80 mesh, wheat straw with a particle size of 4 to 5 mm and camellia oleifera cake powder with a particle size of 20 to 50 mesh.

[0040] (1.2) According to the addition amount of wheat straw and camellia oleifera cake being 20% ​​and 16.67% of the sludge weight, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, 94.6g of bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly to obtain a mixed material B.

[0041] (1.2) The mixed material B is subjected to a 21-day acclimation treatment. During the acclimation treatment, the compost is turned on days 0, 1, 3, 5, 8, 11, 15 and 21. After 21 days of acclimation, the material is placed in a bacterial culture room at 60°C for 24 hours to obtain an acclimation product, namely, acclimated sludge.

[0042] (2) According to the addition amount of domesticated sludge, wheat straw and camellia oleifera cake being 21%, 20% and 16.67% of the weight of the sludge, 630g of domesticated sludge, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total weight of the semi-mixed material, bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly, and the moisture content of the material was adjusted to 55% to obtain a mixed material A; according to the addition amount of calcium oxide being 2.5% of the dry weight of the mixed material A, calcium oxide was added to the mixed material A for biological drying treatment for 21 days. During the biological drying process, anhydrous magnesium chloride was added to the mixed material A at 48h (the second day), wherein the addition amount of anhydrous magnesium chloride was 2.5% of the dry weight of the mixed material A.

[0043] The biological drying process of step (2) also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, aerating the mixed material A three times, controlling the aeration volume (air) to 0.4 L / min kg during the aeration process, and turning the compost once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying of the sludge.

[0044] Comparative Example 1:

[0045] A biological drying method for sludge is basically the same as Example 1, except that in Comparative Example 1, calcium oxide and magnesium chloride are not added.

[0046] In Comparative Example 1, the biological drying method of sludge comprises the following steps:

[0047] (1) preparing domesticated sludge, which is obtained by domesticating sludge B, biomass B, and biochar B, specifically:

[0048] (1.1) Bamboo charcoal, wheat straw and camellia oleifera cake are dried, crushed and sieved respectively to obtain bamboo charcoal powder with a particle size of 60 to 80 mesh, wheat straw with a particle size of 4 to 5 mm and camellia oleifera cake powder with a particle size of 20 to 50 mesh.

[0049] (1.2) According to the addition amount of wheat straw and camellia oleifera cake being 20% ​​and 16.67% of the sludge weight, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, 94.6g of bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly to obtain a mixed material B.

[0050] (1.2) The mixed material B is subjected to a 21-day acclimation treatment. During the acclimation treatment, the compost is turned on days 0, 1, 3, 5, 8, 11, 15 and 21. After 21 days of acclimation, the material is placed in a bacterial culture room at 60°C for 24 hours to obtain an acclimation product, namely, acclimated sludge.

[0051] (2) According to the addition amount of domesticated sludge, wheat straw and camellia oleifera cake being 21%, 20% and 16.67% of the sludge weight, 630g of domesticated sludge, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total weight of the semi-mixed material, bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly, and the moisture content of the material was adjusted to 55% to obtain a mixed material A; the mixed material A was subjected to a biological drying treatment for 21 days.

[0052] The biological drying process of step (2) also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, aerating the mixed material A three times, controlling the aeration volume to be 0.4 L / min kg during the aeration process, and turning the compost once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying of the sludge.

[0053] Comparative Example 2:

[0054] A biological drying method for sludge is basically the same as Example 1, except that in Comparative Example 2, calcium oxide is not added, and magnesium chloride is directly added to the mixed material A.

[0055] In Comparative Example 2, the biological drying method of sludge comprises the following steps:

[0056] (1) preparing domesticated sludge, which is obtained by domesticating sludge B, biomass B, and biochar B, specifically:

[0057] (1.1) Bamboo charcoal, wheat straw and camellia oleifera cake are dried, crushed and sieved respectively to obtain bamboo charcoal powder with a particle size of 60 to 80 mesh, wheat straw with a particle size of 4 to 5 mm and camellia oleifera cake powder with a particle size of 20 to 50 mesh.

[0058] (1.2) According to the addition amount of wheat straw and camellia oleifera cake being 20% ​​and 16.67% of the sludge weight, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, 94.6g of bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly to obtain a mixed material B.

[0059] (1.2) The mixed material B is subjected to a 21-day acclimation treatment. During the acclimation treatment, the compost is turned on days 0, 1, 3, 5, 8, 11, 15 and 21. After 21 days of acclimation, the material is placed in a bacterial culture room at 60°C for 24 hours to obtain an acclimation product, namely, acclimated sludge.

[0060] (2) According to the addition amount of domesticated sludge, wheat straw and camellia oleifera cake being 21%, 20% and 16.67% of the weight of the sludge, 630g of domesticated sludge, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total weight of the semi-mixed material, bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly, and the moisture content of the material was adjusted to 55% to obtain a mixed material A; according to the addition amount of anhydrous magnesium chloride being 5% of the dry weight of the mixed material A, anhydrous magnesium chloride was added to the mixed material A for biological drying treatment for 21 days.

[0061] The biological drying process of step (2) also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, aerating the mixed material A three times, controlling the aeration volume to be 0.4 L / min kg during the aeration process, and turning the compost once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying of the sludge.

[0062] Comparative Example 3:

[0063] A biological drying method for sludge is basically the same as Example 1, except that in Comparative Example 3, magnesium chloride is not added.

[0064] The biological drying method of sludge used in Comparative Example 3 comprises the following steps:

[0065] (1) preparing domesticated sludge, which is obtained by domesticating sludge B, biomass B, and biochar B, specifically:

[0066] (1.1) Bamboo charcoal, wheat straw and camellia oleifera cake are dried, crushed and sieved respectively to obtain bamboo charcoal powder with a particle size of 60 to 80 mesh, wheat straw with a particle size of 4 to 5 mm and camellia oleifera cake powder with a particle size of 20 to 50 mesh.

[0067] (1.2) According to the addition amount of wheat straw and camellia oleifera cake being 20% ​​and 16.67% of the sludge weight, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, 94.6g of bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly to obtain a mixed material B.

[0068] (1.2) The mixed material B is subjected to a 21-day acclimation treatment. During the acclimation treatment, the compost is turned on days 0, 1, 3, 5, 8, 11, 15 and 21. After 21 days of acclimation, the material is placed in a bacterial culture room at 60°C for 24 hours to obtain an acclimation product, namely, acclimated sludge.

[0069] (2) According to the addition amount of domesticated sludge, wheat straw and camellia oleifera cake being 21%, 20% and 16.67% of the weight of the sludge, 630g of domesticated sludge, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total weight of the semi-mixed material, bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly, and the moisture content of the material was adjusted to 55% to obtain a mixed material A; according to the addition amount of calcium oxide being 5% of the dry weight of the mixed material A, calcium oxide was added to the mixed material A for biological drying treatment for 21 days.

[0070] The biological drying process of step (2) also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, aerating the mixed material A three times, controlling the aeration volume to be 0.4 L / min kg during the aeration process, and turning the compost once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying of the sludge.

[0071] Comparative Example 4:

[0072] A biological drying method for sludge is basically the same as Example 1, except that in Comparative Example 4, the order of adding calcium oxide and magnesium chloride is reversed.

[0073] The biological drying method of sludge used in Comparative Example 3 comprises the following steps:

[0074] (1) preparing domesticated sludge, which is obtained by domesticating sludge B, biomass B, and biochar B, specifically:

[0075] (1.1) Bamboo charcoal, wheat straw and camellia oleifera cake are dried, crushed and sieved respectively to obtain bamboo charcoal powder with a particle size of 60 to 80 mesh, wheat straw with a particle size of 4 to 5 mm and camellia oleifera cake powder with a particle size of 20 to 50 mesh.

[0076] (1.2) According to the addition amount of wheat straw and camellia oleifera cake being 20% ​​and 16.67% of the sludge weight, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, 94.6g of bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly to obtain a mixed material B.

[0077] (1.2) The mixed material B is subjected to a 21-day acclimation treatment. During the acclimation treatment, the compost is turned on days 0, 1, 3, 5, 8, 11, 15 and 21. After 21 days of acclimation, the material is placed in a bacterial culture room at 60°C for 24 hours to obtain an acclimation product, namely, acclimated sludge.

[0078] (2) According to the addition amount of domesticated sludge, wheat straw and camellia oleifera cake being 21%, 20% and 16.67% of the weight of the sludge, 630g of domesticated sludge, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total weight of the semi-mixed material, bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly, and the moisture content of the material was adjusted to 55% to obtain a mixed material A; according to the addition amount of anhydrous magnesium chloride being 2.5% of the dry weight of the mixed material A, anhydrous magnesium chloride was added to the mixed material A for biological drying treatment for 21 days. During the biological drying process, calcium oxide was added to the mixed material A at 48h (the second day), wherein the addition amount of calcium oxide was 2.5% of the dry weight of the mixed material A.

[0079] The biological drying process of step (2) also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, aerating the mixed material A three times, controlling the aeration volume to be 0.4 L / min kg during the aeration process, and turning the compost once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying of the sludge.

[0080] During the biological drying process of Example 1 and Comparative Examples 1-4, the temperature, moisture content and greenhouse gas potential (GWP) in the system were monitored in real time. The results are as follows: Figures 2 to 4 shown.

[0081] Depend on Figure 2It can be seen that in Comparative Example 1, when calcium oxide and magnesium chloride were not added, no stress was exerted on the pile, and the temperature of the biological drying system could rise to 59.0°C at the highest, but there was still a defect of low biological drying temperature. In Comparative Example 2, when magnesium chloride was added alone, no stress was exerted on the pile, and the temperature of the biological drying system could rise to 59.6°C at the highest, but there was still a defect of low biological drying temperature. In Comparative Example 3, when calcium oxide is added alone, the temperature of the bio-drying system can rise to a maximum of 51.2°C on the 2nd to 3rd day, and there are defects of slow heating rate and low bio-drying temperature. The reasons are: on the one hand, although calcium oxide has an exothermic effect after absorbing water, this effect has an immediate effect, so the temperature will drop quickly, and in a larger bio-drying system, this heat is relatively small; on the other hand, calcium oxide has a bactericidal effect and will destroy the community structure of microorganisms in the pile, and the temperature of the pile is mainly generated by the metabolism of microorganisms, so adding calcium oxide in the early stage of bio-drying is not conducive to the heating of the pile. In particular, the calcium oxide added in Comparative Example 3 is 5% of the dry weight of the mixed material. Excessive calcium oxide has a stronger stress effect on the pile, which is not conducive to improving the metabolic rate of alkaliphilic thermophilic microorganisms, so the heating is slower and the maximum temperature is lower. In comparative example 4, magnesium chloride is added first, and then calcium oxide is added. On the 1st to 2nd day, the temperature of the biological drying system can rise to a maximum of 53.7°C. There are defects of slow heating rate and low biological drying temperature. The reason is that the calcium oxide is added at the heating stage of the biological drying system. The calcium oxide added at this time will destroy the bacterial community structure and inhibit the heating process of the pile body because calcium oxide itself has a bactericidal effect. At the same time, although the pile body will restore part of the bacterial community after adding calcium oxide, this time point has missed the optimal heating period of the biological drying system. Therefore, the order of adding magnesium chloride first and then calcium oxide is not conducive to improving the drying effect. Completely different from them, in Example 1, calcium oxide is added first and then magnesium chloride, and the biological drying temperature can rise to a maximum of 63.28°C within the 1st to 2nd day. In addition, in the existing conventional sludge biological drying method, it takes at least 2 to 4 days to heat up to the highest temperature, that is, the system temperature can be raised to the highest after 2 to 4 days of biological drying, and there is also a defect of slow heating rate. It can be seen that compared with the conventional sludge biological drying method, the present invention successively adds calcium oxide and magnesium chloride in the biological drying system. Under the joint action of calcium oxide and magnesium chloride, it is beneficial to quickly increase the temperature of the sludge, thereby facilitating the effective removal of water in the sludge.

[0082] Depend on Figure 3It can be seen that in Comparative Example 1, when calcium oxide and magnesium chloride are not added, the final moisture content of bio-drying can reach 15.94%; in Comparative Example 2, when magnesium chloride is added alone, the final moisture content of bio-drying can reach 22.13%; in Comparative Example 3, when calcium oxide is added alone, the final moisture content of bio-drying can reach 25.27%; in Comparative Example 4, magnesium chloride is added first, and then calcium oxide is added. After 11 days of bio-drying, the moisture content of bio-drying is as high as 15% or more, and after 21 days of bio-drying, the final moisture content of bio-drying can reach 11.65%. Completely different from them, in Example 1, calcium oxide is added first, and then magnesium chloride is added. After 8 days of bio-drying, the moisture content of bio-drying can be reduced to 10%, and after 11 days of bio-drying, the moisture content of bio-drying can be kept within 10%, and the final moisture content of bio-drying can reach 7.76%. In addition, in the conventional sludge biological drying method, the moisture content of the biological drying can only be reduced to 26.9% after 11 days of biological drying. By comparison, compared with the conventional sludge biological drying method, the present invention adds calcium oxide and magnesium chloride in the biological drying system in sequence, and under the joint action of calcium oxide and magnesium chloride, the moisture in the sludge can be efficiently removed, thereby significantly reducing the moisture content of the sludge during the biological drying process.

[0083] Depend on Figure 4 It can be seen that in Comparative Example 1, when calcium oxide and magnesium chloride are not added, the greenhouse gas potential caused by greenhouse gas emissions during the biological drying process is 354.29 g / m 2 In Comparative Example 2, the greenhouse gas potential caused by the emission of greenhouse gases during the biological drying process when magnesium chloride was added alone was 186.22 g / m 2 In Comparative Example 3, when calcium oxide was added alone, the greenhouse gas potential caused by greenhouse gas emissions during the biological drying process was 340.14 g / m 2 In comparative example 4, magnesium chloride was added first and then calcium oxide. The greenhouse gas potential caused by greenhouse gas emissions during the biological drying process was 186.70 g / m 2 In contrast, in Example 1, calcium oxide was added first and then magnesium chloride. The greenhouse gas potential caused by greenhouse gas emissions during the biological drying process was 104.24 g / m 2. The emission of greenhouse gases in biological systems is mainly the result of microbial activities, and in the operation of reducing greenhouse gas emissions, the order of adding additives mainly reduces greenhouse gas emissions from two directions. The first aspect is to rely on the inherent chemical properties of calcium oxide. Since the emission of greenhouse gases has already begun in the initial stage of biological drying, adding calcium oxide first can reduce carbon dioxide emissions throughout the entire biological drying cycle, while in Example 4, calcium oxide is added on the second day, and it is difficult to rely on calcium oxide to absorb a large amount of carbon dioxide emitted during the heating and high temperature stages, so the overall emission reduction effect is weaker than Example 1. The second aspect is achieved by relying on the microbial community structure in the pile. By optimizing the order of adding calcium oxide and magnesium chloride, their stress effects on bacteria can be utilized to construct a suitable microbial community structure, thereby effectively improving the carbon dioxide emission reduction effect. Specifically, in Example 1, calcium oxide is added first, which can promote the growth and reproduction of thermophilic microorganisms, which is beneficial to improving the drying effect, while inhibiting the growth and reproduction of anaerobic microorganisms, which is beneficial to reducing the water production of greenhouse gases such as methane. By comparison, it can be seen that compared with the conventional sludge biological drying method, in the present invention, calcium oxide and magnesium chloride are added successively in the biological drying system. Under the joint action of calcium oxide and magnesium chloride, the emission of greenhouse gases in the biological drying process can be significantly reduced.

[0084] It can be seen from the above results that compared with conventional sludge biological drying, in the present invention, by successively adding calcium oxide and magnesium chloride during the biological drying process, the water in the sludge can be efficiently removed under the joint action of calcium oxide and magnesium chloride, and the emission of greenhouse gases can be significantly reduced, as follows: the calcium oxide added first can reasonably adjust the microbial community structure and richness inside the sludge, and screen out alkaliphilic and thermophilic microbial communities, especially in the early stage of biological drying, due to its screening and coercion effect on microorganisms, the activity of microorganisms is reduced, and the emission of greenhouse gases is also reduced accordingly. Then, when the pile body begins to heat up at the 25th hour of biological drying, the introduction of magnesium chloride can reduce the pH value of the pile body, provide a suitable living environment for microorganisms and extend the heating period and high temperature period of biological drying; in addition, the heating period and high temperature period of biological drying are the moments when the pile body emits the most greenhouse gases. The calcium oxide added first reacts with the water in the sludge to form calcium hydroxide and releases a large amount of heat, so the carbon dioxide generated during the heating period and high temperature period can be absorbed by calcium hydroxide to form calcium carbonate, thereby achieving greenhouse gas emission reduction. In addition, magnesium chloride can promote the oxidation of the surface area of ​​the dried material and achieve negative methane emissions in biological drying. It can be seen that in the present invention, different introduction strategies of calcium oxide and magnesium chloride are used in sludge biological drying for the first time, which can not only simplify the biological drying process, but also quickly achieve sludge dehydration and reduce greenhouse gas emissions in the biological drying process. It has the advantages of simple process, convenient operation, low cost, high drying efficiency, low pollutant gas emissions, and environmental friendliness. It can not only effectively solve the problem of greenhouse gas emission reduction in the sludge biological drying process, but also help to achieve rapid sludge reduction, high use value, and good application prospects.

[0085] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for reducing sludge moisture content and greenhouse gas emissions during biological drying, characterized in that: The following steps are involved: S1. Mix sludge A, biomass A, biochar A and calcium oxide to obtain a mixed material A; S2. The mixed material A obtained in step S1 is subjected to biological drying. During the biological drying process, magnesium chloride is added to the mixed material A after 25 hours to complete the biological drying treatment of the sludge.

2. The method according to claim 1, characterized in that In step S2, during the biological drying process, magnesium chloride is added to the mixed material A during the period of 25 hours to 50 hours.

3. The method according to claim 2, characterized in that In step S1, the amount of calcium oxide added is 1% to 4% of the dry weight of the mixed material A; In step S2, the amount of magnesium chloride added is 1% to 4% of the dry weight of the mixed material A.

4. The method according to claim 3, characterized in that In step S1, the amount of calcium oxide added is 2% to 3% of the dry weight of the mixed material A; In step S2, the amount of magnesium chloride added is 2% to 3% of the dry weight of the mixed material A; and the magnesium chloride is anhydrous magnesium chloride.

5. The method according to any one of claims 1 to 4, characterized in that: Step S1 also includes adding domesticated sludge; the amount of the domesticated sludge added is 20% to 25% of the weight of the sludge A.

6. The method according to claim 5, characterized in that The domesticated sludge is prepared by domesticating sludge B, biomass B, and biochar B, and comprises the following steps: (1) mixing sludge B, biomass B, and biochar B to obtain a mixed material B; (2) The mixed material B is subjected to acclimation treatment to obtain acclimated sludge.

7. The method according to claim 6, characterized in that In step (1), the biomass B is at least one of wheat straw, camellia oleifera cake, camellia oleifera shell, and reed; the amount of the biomass B added is 35% to 40% of the weight of the sludge B; the wheat straw is in powder form with a particle size of 4 mm to 5 mm; the camellia oleifera cake is in powder form with a particle size of 20 mesh to 50 mesh; the biochar B is at least one of bamboo charcoal, stalk biochar, peanut shell biochar, sludge biochar, and manure biochar; the amount of the biochar B added is 5% of the total dry weight of the sludge B and biomass B; the particle size of the biochar B is 60 mesh to 80 mesh; In step (2), the acclimation treatment is carried out under aerobic conditions; during the acclimation treatment, the compost is turned at 0, 1, 3, 5, 8, 11, 15 and 21; the acclimation treatment lasts for 21 days; and after the acclimation treatment is completed, the following treatment is also included: placing the material obtained after the acclimation treatment in a bacterial culture room at 60° C. for 24 hours.

8. The method according to claim 5, characterized in that In step S1, the moisture content of the mixed material A is 55% to 60%; the biomass A is at least one of wheat straw, camellia oleifera cake, camellia oleifera shell, and reed; the addition amount of the biomass A is 35% to 40% of the weight of the sludge A; the wheat straw is in powder form with a particle size of 4 mm to 5 mm; the camellia oleifera cake is in powder form with a particle size of 20 mesh to 50 mesh; the biochar A is at least one of bamboo charcoal, stalk biochar, peanut shell biochar, sludge biochar, and manure biochar; the addition amount of the biochar A is 5% of the total dry weight of the domesticated sludge, sludge A, and biomass A; the biochar A is in powder form with a particle size of 60 mesh to 80 mesh.

9. The method according to any one of claims 1 to 4, characterized in that: In step S2, the biological drying time is 6 to 21 days.

10. The method according to claim 9, characterized in that In step S2, the biological drying process also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, the number of aeration treatments is 3 times, the aeration volume is controlled at 0.4 L / min kg during the aeration treatment, the aeration time of a single aeration treatment is 30 min, and the compost is turned once on days 1, 3, 5, 8, 11, 15 and 21.

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