A method for reducing sludge moisture content and greenhouse gas emissions in a biological drying process

Abstract

The application discloses a method for reducing the moisture content of sludge and the amount of greenhouse gas emission in a biological drying process, which comprises the following steps: preparing a mixture of sludge, biomass, biochar and calcium oxide, and performing biological drying on the mixture; during the biological drying process, magnesium chloride is added after 25 hours, and the biological drying treatment of the sludge is completed. In the method, calcium oxide and magnesium chloride are added in sequence in the biological drying process, and water in the sludge can be efficiently removed and the production of greenhouse gas can be significantly reduced under the joint action of calcium oxide and magnesium chloride, so that the moisture content of the sludge and the amount of greenhouse gas emission in the biological drying process can be effectively reduced. The method has the advantages of simple process, convenient operation, low cost, high drying efficiency, small amount of pollution gas emission, environmental friendliness and the like, can not only effectively solve the problem of greenhouse gas emission reduction in the biological drying process of sludge, but also can realize rapid reduction of the sludge, has high use value and good application prospect.

Description

Technical Field

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

[0002] With the rapid urbanization in my country, the volume of wastewater treated is constantly increasing, leading to a corresponding increase in sludge production. Sludge contains large amounts of organic matter, heavy metals, and pathogens. If not properly treated, it can pollute soil and water sources, posing a threat to ecosystems and human health. Furthermore, the high water content of sludge (typically above 80%) increases treatment and transportation costs and limits its resource utilization. Therefore, it is necessary to efficiently dewater sludge, reduce greenhouse gas emissions during the dewatering process, and obtain stable, environmentally friendly dried products in a short time.

[0003] Biological drying, as a low-cost, environmentally friendly drying technology with high resource recovery potential, has attracted much attention in recent years. Biological drying technology uses the metabolism of microorganisms to convert organic matter in sludge into bioheat for the microorganisms themselves, while releasing moisture, thereby reducing the water content of the sludge. Despite its many advantages, biological drying also encounters some problems in practical applications, such as the significant influence of environmental conditions on microbial activity, long processing cycles, and strict requirements for operating conditions. Furthermore, the biological drying process also generates odors and greenhouse gas emissions. Specifically, the metabolic activities of microorganisms inevitably produce greenhouse gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Especially under anaerobic conditions, methane production is significant, with a greenhouse effect approximately 25 times that of carbon dioxide. Therefore, the reduction of water content and greenhouse gas emissions during the biological drying process cannot be ignored. To this end, the inventors of this application have proposed a biological drying method for sludge. First, the biomass material is baked, and then the baked product, sludge, biochar material, and conditioner are mixed to form a mixture for biological drying. However, further improvements are still needed in the following aspects: (1) The reproduction and growth of microorganisms, especially thermophilic microorganisms, are slow, resulting in a slow heating rate of the biological drying system, making it difficult to efficiently remove water from the sludge. The water content of the sludge can only be reduced to about 30% within 11 days; (2) By improving the structure and nutrient composition of the pile, and by changing the porosity and increasing the surface area of ​​the reactor space, it is difficult to effectively control the absorption and bioavailability of nutrients (such as carbon source and nitrogen source) by microorganisms, and thus it is difficult to effectively regulate the generation of polluting gases, especially oxygen-containing greenhouse gases (such as CO2 and N2O). Not only is it difficult to regulate the production of polluting gases, but the emission of polluting gases is still too high. Therefore, obtaining a sludge biological drying method that can rapidly reduce sludge moisture content and effectively reduce greenhouse gas emissions is of great significance for effectively reducing sludge moisture content and greenhouse gas emissions during biological drying, as well as realizing the resource utilization of sludge. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing a method for reducing the moisture content of sludge and greenhouse gas emissions during the biological drying process. This method can not only efficiently remove moisture from sludge, but also significantly reduce greenhouse gas emissions.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for reducing sludge moisture content and greenhouse gas emissions during bio-drying includes the following steps:

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

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

[0009] In a further improvement to the above method, in step S2, during the biological drying process, magnesium chloride is added to the mixture A during the period from 25 to 50 hours.

[0010] In a further improvement to the above method, in step S1, the amount of calcium oxide added is 1% to 4% of the dry weight of the mixture A.

[0011] In a further improvement to the above method, in step S2, the amount of magnesium chloride added is 1% to 4% of the dry weight of the mixture A.

[0012] In a further improvement to the above method, in step S1, the amount of calcium oxide added is 2% to 3% of the dry weight of the mixture A.

[0013] In a further improvement to the above method, in step S2, the amount of magnesium chloride added is 2% to 3% of the dry weight of the mixture A; and the magnesium chloride is anhydrous magnesium chloride.

[0014] In a further improvement to the above method, step S1 further includes adding acclimatized sludge; the amount of acclimatized sludge added is 20% to 25% of the weight of sludge A.

[0015] A further improvement to the above method, wherein the acclimated sludge is prepared by acclimation of sludge B, biomass B, and biochar B, and includes the following steps:

[0016] (1) Mix sludge B, biomass B and biochar B to obtain mixture B;

[0017] (2) The mixture B is subjected to acclimatization treatment to obtain acclimatized sludge.

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

[0019] In a further improvement to the above method, in step (2), the acclimatization treatment is carried out under aerobic conditions; during the acclimatization treatment, turning treatment is performed at 0, 1, 3, 5, 8, 11, 15 and 21; the acclimatization treatment lasts for 21 days; after the acclimatization treatment is completed, the following treatment is also included: the material obtained after acclimatization treatment is placed in a bacterial culture room and placed at 60°C for 24 hours.

[0020] In a further improvement to the above method, in step S1, the moisture content of the mixture A is 55% to 60%.

[0021] In a further improvement to the above method, the biomass A is at least one of wheat straw, camellia oil cake, camellia oil shell, and reed; the amount of biomass A added is 35% to 40% of the weight of sludge A; the wheat straw is in powder form with a particle size of 4 mm to 5 mm; the camellia oil 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, straw biochar, peanut shell biochar, sludge biochar, and fecal biochar; the amount of biochar A added is 5% of the total dry weight of the acclimatized sludge, sludge A, and biomass A; the biochar A is in powder form with a particle size of 60 mesh to 80 mesh.

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

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

[0024] In a further improvement to the above method, step S2 of the biological drying process further includes the following treatment: aerating and turning the mixture A, aerating the mixture A on day 0, aerating the mixture A three times, controlling the aeration rate at 0.4 L / min kg, and aerating for 30 min for each aeration treatment, and turning the mixture once on days 1, 3, 5, 8, 11, 15 and 21.

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

[0026] (1) In view of the problems of low drying efficiency and large emissions of pollutants in existing sludge biological drying methods, this invention creatively proposes a method to reduce the moisture content of sludge and greenhouse gas emissions during biological drying. By adding calcium oxide and magnesium chloride sequentially during the biological drying process, the water in the sludge can be efficiently removed and the production and emission of greenhouse gases can be significantly reduced under the combined action of calcium oxide and magnesium chloride. Specifically, (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 effect. In addition, magnesium chloride, as a strong hygroscopic agent, can absorb free water in the sludge. The addition of magnesium chloride, combined with the dehydrating effect of calcium oxide, significantly improves the dewatering efficiency of sludge. Furthermore, the addition of magnesium chloride alters the surface tension of the sludge, reducing the adhesion between water molecules and sludge particles, making it easier for water to separate from the sludge. Thus, the synergistic effect of calcium oxide and magnesium chloride accelerates the dewatering speed of the sludge, shortening the entire drying cycle and improving drying efficiency. In particular, sludge treated with calcium oxide and magnesium chloride has a significantly reduced moisture content, making it more suitable for resource utilization, such as as fertilizer, soil conditioner, or building material. This treatment method also reduces microbial activity, decreasing the risk of pathogen and harmful substance transmission. (b) Regarding the impact on the internal environment of the sludge, the initial addition of calcium oxide increases the pH value of the sludge, helping to inhibit microbial activity and reduce the decomposition of organic matter. The subsequent addition of magnesium chloride helps form a stable sludge structure, regulates the osmotic pressure of the sludge, and promotes the degradation of organic matter. Moreover, calcium oxide neutralizes acidic substances in the sludge, reducing the generation of malodorous gases, while the hygroscopic effect of magnesium chloride helps control the moisture content of the sludge, further reducing odor. (c) By adding calcium oxide and magnesium chloride sequentially, 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 of microorganisms. Specifically, calcium oxide, as an alkaline substance, can neutralize the acidic substances in the sludge and increase the pH value of the sludge. This pH adjustment helps to create a suitable environment for the growth and metabolism of microorganisms. Moreover, the chemical reaction between calcium oxide and magnesium chloride can generate calcium hydroxide and calcium chloride. These compounds can provide essential calcium and magnesium nutrients for certain microorganisms, promoting their growth and metabolic activities. On the other hand, adding calcium oxide first can increase the temperature of the sludge, providing a suitable growth environment for certain thermophilic microorganisms and accelerating the metabolic rate of microorganisms. The subsequently added magnesium chloride can reduce the moisture content of the sludge due to its hygroscopic effect, reducing the inhibitory effect of moisture on microbial metabolism, thereby promoting the metabolic activities of microorganisms and improving the drying effect of the sludge.(d) In terms of the physicochemical 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 sludge that inhibit microbial growth, 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 stabilization of different microbial communities, increase the diversity of microbial communities, and thus improve the drying effect of sludge and reduce the amount of polluting gases produced. (e) The sequential addition of calcium oxide and magnesium chloride not only ensures efficient dehydration but also reduces energy loss during the biological drying process. Specifically, biological drying typically requires a large amount of energy to dry and process materials. In this invention, the sequential addition of calcium oxide and magnesium chloride leads to a positive change. Calcium oxide has strong hygroscopic properties and can react chemically with moisture in the material to generate calcium hydroxide, releasing heat. This heat accelerates moisture evaporation, reducing the energy required for external heating. Simultaneously, calcium hydroxide regulates the pH of the material, optimizes the microbial environment, promotes microbial metabolic activity, and improves... Furthermore, the added magnesium chloride can form crystalline hydrates under certain conditions, absorbing moisture from the material and thus reducing the moisture content. In addition, magnesium chloride can affect the osmotic pressure of microbial cells, regulate the metabolic processes of microorganisms, and enhance their ability to decompose organic matter and generate heat, which helps to reduce the input of external energy. It can be seen that the unique chemical properties of calcium oxide and magnesium chloride can effectively promote the chemical reactions in the biological drying process, thereby reducing the dependence on external energy. This not only reduces energy input but also optimizes the energy utilization efficiency of the entire biological drying process, significantly improving the originally high-energy-consuming process. (f) By adding calcium oxide and magnesium chloride sequentially, greenhouse gas emissions during the bio-drying process of sludge can be reduced. Specifically, calcium oxide dissolves in water to form calcium hydroxide, which increases the pH of the system. This alkaline environment helps inhibit the growth of anaerobic microorganisms and reduces the production of greenhouse gases such as methane. Furthermore, after calcium oxide reacts with water to form calcium hydroxide, it 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 transformation of organic matter, reducing 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 fertilizer, improving sludge quality, reducing the release of volatile organic compounds, and increasing the carbon storage capacity of sludge, thereby indirectly reducing greenhouse gas emissions.Therefore, the method of this invention, by adding calcium oxide and magnesium chloride sequentially during the biological drying process, can efficiently remove moisture from sludge and significantly reduce greenhouse gas emissions under the combined action of calcium oxide and magnesium chloride. This effectively reduces the sludge moisture content and 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 greenhouse gas emission reduction problem during sludge biological drying, but also help to achieve rapid sludge reduction. It has high use value and good application prospects.

[0027] (2) In this invention, by optimizing the amount of calcium oxide added to 1% to 4% of the dry weight of mixture A, especially when the amount of calcium oxide added is 2% to 3% of the dry weight of mixture A, not only can the pH value of the pile (mixture A) be adjusted to a suitable range, but the composition and abundance of microorganisms in the pile can also be optimized, thereby enabling faster and more efficient removal of moisture from the pile. When the amount of calcium oxide is too low, it is not conducive to the adjustment of the pH value of the pile, making it difficult to obtain a suitable pH. When the amount of calcium oxide is too high, it will severely stress the microbial community structure, making it difficult to utilize microbial heat generation to improve the drying effect. In addition, in this invention, by optimizing the amount of magnesium chloride added to 1% to 4% of the dry weight of mixture A, especially when the amount of magnesium chloride added is 2% to 3% of the dry weight of 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 microorganisms in the pile.

[0028] (3) In this invention, the biological drying system also includes the addition of acclimated sludge, wherein the acclimated sludge is prepared by acclimation of sludge, biomass, and biochar. By adding acclimated sludge, efficient inoculation of microorganisms in sludge biological drying can be achieved, which not only helps to improve the quality of sludge but also significantly improves the efficiency and effect of sludge treatment. In addition, the sludge biological drying technology of this invention with added acclimated products has the following advantages: it can accelerate the decomposition of organic matter and improve sludge stability; reduce odor and reduce greenhouse gas emissions; improve the potential for resource utilization and reduce the use of chemical additives; enhance the biological activity of sludge and increase its calorific value; promote harmless treatment and improve treatment flexibility; reduce energy consumption and promote ecological cycle; and improve safety. These advantages indicate that the addition of acclimated sludge has important application value and prospects in the process of sludge biological drying. Attached Figure Description

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

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

[0031] Figure 2 The graph shows the temperature changes of the system during the bio-drying process in Examples 1 and 1-4 of the present invention.

[0032] Figure 3 The graph shows the change in water content of the system during the biological drying process of Embodiment 1 and Comparative Examples 1-4 of the present invention.

[0033] Figure 4 This is a graph showing the changes in greenhouse gas potential values ​​of the system during the bio-drying process of Examples 1 and 1-4 of the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

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

[0036] Example 1:

[0037] A method for reducing sludge moisture content and greenhouse gas emissions during bio-drying is illustrated in the following process flow diagram: Figure 1 As shown, it includes the following steps:

[0038] (1) Preparation of acclimated sludge, which is obtained by acclimation of sludge B, biomass B, and biochar B, specifically as follows:

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

[0040] (1.2) Add 600g of wheat straw and 500g of camellia oil cake to 3000g of raw sludge (moisture content 80%), according to the addition amount of wheat straw and camellia oil cake being 20% ​​and 16.67% of the sludge weight, respectively, and mix evenly to obtain a semi-mixed material; add 94.6g of bamboo charcoal to the semi-mixed material according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, and mix evenly to obtain mixture B.

[0041] (1.2) The mixture B was acclimated for 21 days. During the acclimation process, the material was turned over on days 0, 1, 3, 5, 8, 11, 15 and 21. After acclimation for 21 days, the material was placed in a bacterial culture room at 60°C for 24 hours to obtain the acclimated product, which is the acclimated sludge.

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

[0043] The biological drying process in step (2) also includes the following treatments: aeration and turning of the mixture A, aeration treatment of the mixture A on day 0, aeration treatment 3 times, the aeration rate (air) is controlled at 0.4 L / min kg during the aeration treatment, the aeration time of each aeration treatment is 30 min, and turning of the mixture once each on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying treatment of the sludge.

[0044] Comparative Example 1:

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

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

[0047] (1) Preparation of acclimated sludge, which is obtained by acclimation of sludge B, biomass B, and biochar B, specifically as follows:

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

[0049] (1.2) Add 600g of wheat straw and 500g of camellia oil cake to 3000g of raw sludge (moisture content 80%), according to the addition amount of wheat straw and camellia oil cake being 20% ​​and 16.67% of the sludge weight, respectively, and mix evenly to obtain a semi-mixed material; add 94.6g of bamboo charcoal to the semi-mixed material according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, and mix evenly to obtain mixture B.

[0050] (1.2) The mixture B was acclimated for 21 days. During the acclimation process, the material was turned over on days 0, 1, 3, 5, 8, 11, 15 and 21. After acclimation for 21 days, the material was placed in a bacterial culture room at 60°C for 24 hours to obtain the acclimated product, which is the acclimated sludge.

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

[0052] The biological drying process in step (2) also includes the following treatments: aeration and turning of the mixture A, aeration treatment of the mixture A on day 0, aeration treatment 3 times, aeration rate of 0.4 L / min kg during aeration treatment, aeration time of 30 min for each aeration treatment, and turning of the mixture once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying treatment of the sludge.

[0053] Comparative Example 2:

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

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

[0056] (1) Preparation of acclimated sludge, which is obtained by acclimation of sludge B, biomass B, and biochar B, specifically as follows:

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

[0058] (1.2) Add 600g of wheat straw and 500g of camellia oil cake to 3000g of raw sludge (moisture content 80%), according to the addition amount of wheat straw and camellia oil cake being 20% ​​and 16.67% of the sludge weight, respectively, and mix evenly to obtain a semi-mixed material; add 94.6g of bamboo charcoal to the semi-mixed material according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, and mix evenly to obtain mixture B.

[0059] (1.2) The mixture B was acclimated for 21 days. During the acclimation process, the material was turned over on days 0, 1, 3, 5, 8, 11, 15 and 21. After acclimation for 21 days, the material was placed in a bacterial culture room at 60°C for 24 hours to obtain the acclimated product, which is the acclimated sludge.

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

[0061] The biological drying process in step (2) also includes the following treatments: aeration and turning of the mixture A, aeration treatment of the mixture A on day 0, aeration treatment 3 times, aeration rate of 0.4 L / min kg during aeration treatment, aeration time of 30 min for each aeration treatment, and turning of the mixture once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying treatment of the sludge.

[0062] Comparative Example 3:

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

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

[0065] (1) Preparation of acclimated sludge, which is obtained by acclimation of sludge B, biomass B, and biochar B, specifically as follows:

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

[0067] (1.2) Add 600g of wheat straw and 500g of camellia oil cake to 3000g of raw sludge (moisture content 80%), according to the addition amount of wheat straw and camellia oil cake being 20% ​​and 16.67% of the sludge weight, respectively, and mix evenly to obtain a semi-mixed material; add 94.6g of bamboo charcoal to the semi-mixed material according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, and mix evenly to obtain mixture B.

[0068] (1.2) The mixture B was acclimated for 21 days. During the acclimation process, the material was turned over on days 0, 1, 3, 5, 8, 11, 15 and 21. After acclimation for 21 days, the material was placed in a bacterial culture room at 60°C for 24 hours to obtain the acclimated product, which is the acclimated sludge.

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

[0070] The biological drying process in step (2) also includes the following treatments: aeration and turning of the mixture A, aeration treatment of the mixture A on day 0, aeration treatment 3 times, aeration rate of 0.4 L / min kg during aeration treatment, aeration time of 30 min for each aeration treatment, and turning of the mixture once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying treatment of the sludge.

[0071] Comparative Example 4:

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

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

[0074] (1) Preparation of acclimated sludge, which is obtained by acclimation of sludge B, biomass B, and biochar B, specifically as follows:

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

[0076] (1.2) Add 600g of wheat straw and 500g of camellia oil cake to 3000g of raw sludge (moisture content 80%), according to the addition amount of wheat straw and camellia oil cake being 20% ​​and 16.67% of the sludge weight, respectively, and mix evenly to obtain a semi-mixed material; add 94.6g of bamboo charcoal to the semi-mixed material according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, and mix evenly to obtain mixture B.

[0077] (1.2) The mixture B was acclimated for 21 days. During the acclimation process, the material was turned over on days 0, 1, 3, 5, 8, 11, 15 and 21. After acclimation for 21 days, the material was placed in a bacterial culture room at 60°C for 24 hours to obtain the acclimated product, which is the acclimated sludge.

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

[0079] The biological drying process in step (2) also includes the following treatments: aeration and turning of the mixture A, aeration treatment of the mixture A on day 0, aeration treatment 3 times, aeration rate of 0.4 L / min kg during aeration treatment, aeration time of 30 min for each aeration treatment, and turning of the mixture once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying treatment of the sludge.

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

[0081] Depend on Figure 2It can be seen that in Comparative Example 1, without the addition of calcium oxide and magnesium chloride, no stress was exerted on the pile, and the temperature of the bio-drying system could rise to a maximum of 59.0℃, but the bio-drying temperature was still too low. In Comparative Example 2, with the addition of magnesium chloride alone, no stress was exerted on the pile, and the temperature of the bio-drying system could rise to a maximum of 59.6℃, but the bio-drying temperature was still too low. In Comparative Example 3, when calcium oxide was added alone, the temperature of the bio-drying system could reach a maximum of 51.2℃ on the 2nd to 3rd day. This resulted in a slow heating rate and a relatively low bio-drying temperature. The reasons are as follows: Firstly, although calcium oxide has an exothermic effect after absorbing water, this effect is immediate, so the temperature drops quickly, and in a larger bio-drying system, this heat is relatively small. Secondly, calcium oxide has a bactericidal effect, which can disrupt the community structure of microorganisms in the pile. Since the temperature of the pile mainly depends on the metabolic activity of microorganisms, adding calcium oxide in the early stage of bio-drying is not conducive to the temperature rise of the pile. In particular, in Comparative Example 3, the calcium oxide added was 5% of the dry weight of the mixture. Excessive calcium oxide exerts a stronger stress on the pile, which is not conducive to improving the metabolic rate of alkali-loving and thermophilic microorganisms, resulting in a slower heating rate and a lower maximum temperature. In Comparative Example 4, magnesium chloride was added first, followed by calcium oxide. On days 1-2, the temperature of the biological drying system reached a maximum of 53.7℃. This resulted in a slow heating rate and a relatively low biological drying temperature. The reason is that calcium oxide was added during the heating phase of the biological drying system. Since calcium oxide has a bactericidal effect, it disrupts the bacterial community structure and inhibits the heating process of the pile. Although the pile recovers some bacterial community after adding calcium oxide, this time has already missed the optimal heating period for the biological drying system. Therefore, adding magnesium chloride first and then calcium oxide is not conducive to improving the drying effect. In contrast, in Example 1, calcium oxide was added first, followed by magnesium chloride. The biological drying temperature could reach a maximum of 63.28℃ on days 1-2. Furthermore, in existing conventional sludge biological drying methods, it takes at least 2-4 days to reach the maximum temperature, meaning the system temperature can only be raised to its maximum after 2-4 days of biological drying, which also results in a slow heating rate. As can be seen, compared with conventional sludge biological drying methods, the present invention adds calcium oxide and magnesium chloride sequentially to the biological drying system. Under the combined action of calcium oxide and magnesium chloride, the temperature of the sludge is rapidly increased, which is conducive to the effective removal of water from the sludge.

[0082] Depend on Figure 3It can be seen that in Comparative Example 1, the final moisture content of bio-drying can reach 15.94% without the addition of calcium oxide and magnesium chloride; in Comparative Example 2, the final moisture content of bio-drying can reach 22.13% when magnesium chloride is added alone; in Comparative Example 3, the final moisture content of bio-drying can reach 25.27% when calcium oxide is added alone; in Comparative Example 4, when magnesium chloride is added first and then calcium oxide is added, the moisture content of bio-drying reaches over 15% after 11 days of bio-drying, and the final moisture content of bio-drying can reach 11.65% after 21 days of bio-drying. Completely different from these examples, in Example 1, when calcium oxide is added first and then magnesium chloride is added, the moisture content of bio-drying can be reduced to 10% after 8 days of bio-drying, and after 11 days of bio-drying, the moisture content of bio-drying can be maintained below 10%, with a final moisture content of 7.76%. Furthermore, in existing conventional sludge biological drying methods, the moisture content can only be reduced to 26.9% after 11 days of biological drying treatment. Comparison shows that, compared to conventional sludge biological drying methods, this invention adds calcium oxide and magnesium chloride sequentially to the biological drying system. The combined effect of calcium oxide and magnesium chloride can efficiently remove moisture from the sludge, thereby significantly reducing the sludge moisture content during the biological drying process.

[0083] Depend on Figure 4 It can be seen that in Comparative Example 1, without the addition of calcium oxide and magnesium chloride, the greenhouse gas potential caused by greenhouse gas emissions during the bio-drying process is 354.29 g / m³. 2 In Comparative Example 2, the greenhouse gas potential caused by the emission of greenhouse gases during the bio-drying process when magnesium chloride was added alone was 186.22 g / m³. 2 In Comparative Example 3, when calcium oxide was added alone, the greenhouse gas potential caused by greenhouse gas emissions during the bio-drying process was 340.14 g / m³. 2 In Comparative Example 4, magnesium chloride was added first, followed by calcium oxide. The greenhouse gas potential caused by emissions during the bio-drying process was 186.70 g / m³. 2 In stark contrast, in Example 1, calcium oxide was added first, followed by magnesium chloride, resulting in a greenhouse gas potential of 104.24 g / m³ caused by greenhouse gas emissions during the bio-drying process. 2Greenhouse gas emissions in biological systems are primarily a result of microbial activity. In greenhouse gas reduction operations, the order in which additives are added mainly reduces emissions from two directions. The first aspect relies on the inherent chemical properties of calcium oxide. Since greenhouse gas emissions begin at the initial stage of biological drying, adding calcium oxide first can reduce carbon dioxide emissions throughout the entire biological drying cycle. However, in Comparative Example 4, calcium oxide was added on the second day, making it difficult for calcium oxide to absorb the large amounts of carbon dioxide emitted during the warming and high-temperature stages. Therefore, its overall emission reduction effect is weaker than that of Example 1. The second aspect relies on the microbial community structure within 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 carbon dioxide emission reduction. Specifically, in Example 1, adding calcium oxide first promotes the growth and reproduction of thermophilic microorganisms, which is beneficial for improving the drying effect, while inhibiting the growth and reproduction of anaerobic microorganisms, which is beneficial for reducing the production of greenhouse gases such as methane. Comparison shows that, compared with conventional sludge biological drying methods, the addition of calcium oxide and magnesium chloride to the biological drying system in this invention, under the combined effect of calcium oxide and magnesium chloride, can significantly reduce greenhouse gas emissions during the biological drying process.

[0084] The results above show that, compared with conventional sludge biological drying, this invention, by adding calcium oxide and magnesium chloride sequentially during the biological drying process, can efficiently remove moisture from the sludge and significantly reduce greenhouse gas emissions under the combined action of calcium oxide and magnesium chloride. Specifically: the first addition of calcium oxide can rationally adjust the structure and richness of the microbial community within the sludge, screening out alkali-loving and thermophilic microbial communities. Especially in the early stage of biological drying, due to its screening and stress effect on microorganisms, the activity of microorganisms is reduced, and greenhouse gas emissions are also reduced accordingly. Then, when the pile begins to heat up at 25 hours of biological drying, the introduction of magnesium chloride can lower the pH value of the pile, providing a suitable living environment for microorganisms and extending the heating and high-temperature periods of biological drying. In addition, the heating and high-temperature periods of biological drying are the times when the pile emits the most greenhouse gases. The first addition of calcium oxide reacts with the moisture in the sludge to form calcium hydroxide and releases a large amount of heat. Therefore, the carbon dioxide generated during the heating and high-temperature periods can be absorbed by calcium hydroxide to form calcium carbonate, thus achieving greenhouse gas emission reduction. Furthermore, magnesium chloride can promote oxidation on the surface of the dried material, achieving negative methane emissions during bio-drying. Therefore, this invention, for the first time, applies different introduction strategies of calcium oxide and magnesium chloride to sludge bio-drying. This not only simplifies the bio-drying process but also rapidly dewaters the sludge and reduces greenhouse gas emissions during bio-drying. It boasts advantages such as simple process, convenient operation, low cost, high drying efficiency, low pollutant emissions, and environmental friendliness. It effectively addresses greenhouse gas emission reduction during sludge bio-drying and facilitates rapid sludge reduction, demonstrating high practical value and promising application prospects.

[0085] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for reducing sludge moisture content and greenhouse gas emissions during bio-drying, characterized in that, Includes the following steps: S1. Sludge A, biomass A, biochar A, and calcium oxide are mixed to obtain mixture A; the amount of calcium oxide added is 1% to 4% of the dry weight of mixture A. S2. The mixture A obtained in step S1 is subjected to biological drying. During the biological drying process, magnesium chloride is added to the mixture A during the period of 25h to 50h to complete the biological drying treatment of the sludge. The amount of magnesium chloride added is 1% to 4% of the dry weight of the mixture A.

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

3. The method according to claim 1 or 2, characterized in that, Step S1 also includes adding acclimatized sludge; the amount of acclimatized sludge added is 20% to 25% of the weight of sludge A.

4. The method according to claim 3, characterized in that, The acclimated sludge is prepared by acclimating sludge B, biomass B, and biochar B, and includes the following steps: (1) Mix sludge B, biomass B, and biochar B to obtain mixture B; (2) The mixture B is subjected to acclimatization treatment to obtain acclimatized sludge.

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

6. The method according to claim 3, characterized in that, In step S1, the moisture content of the mixture A is 55%–60%; the biomass A is at least one of wheat straw, camellia oil cake, camellia oil shell, and reed; the amount of biomass A added is 35%–40% of the weight of sludge A; the wheat straw is in powder form with a particle size of 4 mm–5 mm; the camellia oil cake is in powder form with a particle size of 20 mesh–50 mesh; the biochar A is at least one of bamboo charcoal, straw biochar, peanut shell biochar, sludge biochar, and fecal biochar; the amount of biochar A added is 5% of the total dry weight of the acclimatized sludge, sludge A, and biomass A; the biochar A is in powder form with a particle size of 60 mesh–80 mesh.

7. The method according to claim 1 or 2, characterized in that, In step S2, the biological drying time is 6 to 21 days.

8. The method according to claim 7, characterized in that, In step S2, the biological drying process also includes the following treatments: aerating and turning the mixture A, aerating the mixture A on day 0, aerating 3 times, controlling the aeration rate at 0.4 L / min kg, and aerating for 30 min for each aeration treatment, and turning the mixture once on days 1, 3, 5, 8, 11, 15 and 21.

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