Method for promoting sludge compost humification and PPCPs degradation by using laccase and biochar

Abstract

The invention discloses a method for promoting sludge compost humification and PPCPs degradation by using laccase and biochar, and the method comprises the following specific steps: crushing a conditioner rich in lignocellulose to 3-5mm, fully mixing the crushed conditioner and dewatered sludge according to a mass ratio of 1: 5 to obtain a compost material, adjusting the moisture content of the compost material to 65-75wt%, uniformly mixing the compost material with the biochar to obtain a mixture, and drying the mixture to obtain the product. The initial C / N element molar ratio is adjusted to be (7.5-8): 1; and S2, uniformly mixing charcoal and a laccase solution with the compost material obtained in the step S1 to obtain a mixed material, and composting the mixed material to obtain a compost product. According to the method, the biochar and the laccase are used as compost additives, and the degradation rate of microorganisms on PPCPs is increased and the content of the PPCPs in compost is reduced by utilizing the oxidability of the laccase on organic pollutants and the promotion effect of the biochar on enzyme activity expression.

Description

Technical Field

[0001] The invention belongs to the technical field of resource treatment and disposal of organic solid waste, and specifically relates to a method for promoting sludge compost humification and PPCPs degradation by utilizing laccase in combination with biochar. Background Art

[0002] Aerobic composting technology is an efficient means to achieve the harmlessness and resource utilization of dewatered sludge. It converts sewage sludge into mature and stable compost products through a biodegradation process involving microorganisms. During the composting process, macromolecular compounds such as lignocellulose, protein and fat are decomposed and converted into humus, and its content becomes an important indicator for evaluating the quality of compost. However, due to the abundance and insufficient activity of endogenous microorganisms, the humification degree of compost products is low, which reduces the agricultural value of compost.

[0003] Pharmaceuticals and personal care products (PPCPs) are an emerging pollutant, including various antibiotics, synthetic musks, analgesics, antihypertensive drugs, contraceptives, hypnotics, diet pills, hair sprays, hair dyes and fungicides, etc., which are a new type of pollutants that have attracted widespread attention in recent years. PPCPs are easily bioaccumulated through the food chain and have strong ecological risks such as disrupting endocrine, increasing bacterial resistance and "three-hazard" effects. Urban domestic sewage treatment plants are the main gathering places for PPCPs. However, due to the target positioning of traditional sewage treatment plants, their ability to remove PPCPs is limited, making the accumulation rate of PPCPs in sewage sludge as high as more than 60%. At present, 169 PPCPs have been found in sludge, of which 22 PPCPs such as triclosan (TCS), carbamazepine (CBZ), galaxolide (HHCB) and ibuprofen (IBU) have reached the mg / kg level, posing potential ecological and environmental risks.

[0004] Although PPCPs can be degraded by microbial decomposition-related enzymes through aerobic composting of sludge, the effect is not ideal: TCS, CBZ, HHCB and IBU are listed as PPCPs that are difficult to degrade in sludge composting, among which TCS still has a residue of up to 40%-65% in the compost product, and CBZ is even not degraded. Subsequent land use will inevitably lead to the undegraded PPCPs in the sludge entering the soil, further enriching in plants through the food chain and causing potential human exposure risks. Therefore, how to improve humification while promoting the degradation of PPCPs is of great significance for optimizing the sewage sludge composting treatment process, improving the quality of compost products and promoting environmentally friendly resource recycling.

[0005] Laccase is a copper-containing polyphenol oxidase. It can not only depolymerize lignocellulose, but also directly mediate the degradation process of organic pollutants, and the only product is water. Therefore, laccase is often used as an environmentally friendly additive to enhance the removal of organic pollutants in wastewater and activated sludge systems. However, laccase is a water-soluble protease and is easily decomposed or inactivated by microorganisms under the high-temperature and high-pH conditions of composting. Therefore, laccase can be added timely at the initial stage and at the end of the high-temperature stage of composting. At the same time, biochar has the characteristics of high carbon content, large specific surface area, developed porous structure, rich surface functional groups and the presence of inorganic compounds, and it has been widely used in the fields of improving composting and optimizing composting technology. Therefore, the combination of laccase and biochar can be considered, and the buffering and sheltering effects of biochar can be used to avoid or delay the inactivation of laccase in composting to maintain the stability of its degradation ability.

[0006] Therefore, it is of great significance to use the combination of laccase and biochar and set different addition times as additives to promote the humification process of sludge composting and enhance the degradation of PPCPs. Summary of the Invention

[0007] The technical problem solved by the present invention is to provide a method for promoting the humification of sludge composting and the degradation of PPCPs by using the combination of laccase and biochar. This method uses laccase and combines it with biochar to achieve an increase in the humus content and effective degradation of PPCPs in sludge compost products by setting reasonable addition methods and addition times.

[0008] The present invention adopts the following technical solutions to solve the above technical problems. A method for promoting the humification of sludge composting and the degradation of PPCPs by using the combination of laccase and biochar, characterized in that the specific steps are as follows:

[0009] Step S1, crush the conditioner rich in lignocellulose to 3-5 mm, and fully mix the crushed conditioner and dewatered sludge according to a mass ratio of 1:5 to obtain compost materials, wherein the moisture content of the compost materials is adjusted to 65wt% - 75wt%, and the initial C / N elemental molar ratio is adjusted to 7.5 - 8:1;

[0010] Step S2: Mix the biochar and laccase solution evenly with the compost material obtained in Step S1 to obtain a mixed material, and then perform composting on the mixed material to obtain a compost product. The specific process of composting is as follows: The entire composting process lasts for 24 days. The composting process is carried out in a constant temperature incubator and is divided into 4 stages: The first stage is the heating period. On the first day of composting, set the temperature of the incubator to 40 °C. The second stage is the high-temperature period. From the 2nd to the 8th day, adjust the temperature of the incubator to 50 °C. The third stage is the cooling period. Starting from the 9th day, reduce the temperature by 2 °C every day until the temperature drops to 24 °C and then stop cooling. The fourth stage is the maturity period. Starting from the 20th day, maintain the temperature at 24 °C without change. Turn the pile once every afternoon at 4 o'clock during the heating period and the high-temperature period, and control the turning time at 10 - 20 min each time. Stop turning the pile after entering the cooling period. The concentration of the laccase solution is 40 - 60 mg / mL, and the mass ratio of biochar, laccase solution to compost material is 8 - 12:0.8 - 1.2:100. Add 40wt% - 60wt% of the laccase solution at the initial stage of composting and the remaining laccase solution at the end of the high-temperature period of composting respectively.

[0011] Further, in Step S1, the conditioner rich in lignocellulose is sawdust, the moisture content of the compost material is adjusted to 70wt%, and the initial C / N elemental molar ratio is adjusted to 7.8:1.

[0012] Further, in Step S2, the mass ratio of biochar, laccase solution to compost material is 10:1:100.

[0013] Further, in Step S2, add 50wt% of the laccase solution at the initial stage of composting and the remaining 50wt% of the laccase solution at the end of the high-temperature period of composting respectively, and the concentration of the laccase solution is 50 mg / mL.

[0014] Further, the composting in Step S2 is used to promote the humification of sludge compost and the degradation of PPCPs, where PPCPs are one or more of ibuprofen (IBU), galaxolide (HHCB), triclosan (TCS), and carbamazepine (CBZ).

[0015] The present invention has the following advantages and beneficial effects compared with the prior art:

[0016] 1. The present invention uses biochar and laccase as compost additives. Laccase can effectively degrade carbon-containing organic matters such as lignin, improve the degree of compost maturity. The microporous structure of biochar can provide a shelter for laccase, which is beneficial to improving its enzyme activity, and effectively improves the quality and utilization efficiency of the compost product;

[0017] 2. The present invention uses biochar and laccase as compost additives. By utilizing the oxidizing property of laccase towards organic pollutants and the promoting effect of biochar on the expression of enzyme activity, the degradation rate of PPCPs by microorganisms is increased, and the content of PPCPs in the compost is reduced. Description of the Drawings

[0018] Figure 1 It is a graph showing the change in water content during the composting process.

[0019] Figure 2 It is a graph showing the change in laccase activity during the composting process.

[0020] Figure 3 It is a graph showing the change in organic carbon content during the composting process.

[0021] Figure 4 It is a graph showing the change in humus during the composting process.

[0022] Figure 5 It is a graph showing the change in nitrate nitrogen content during the composting process.

[0023] Figure 6 It is a graph showing the change in PPCPs content during the composting process. Detailed Embodiment

[0024] The above content of the present invention will be further described in detail through the following examples. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. All technologies implemented based on the above content of the present invention belong to the scope of the present invention.

[0025] In the examples and comparative examples: The dewatered sludge comes from Xiaoshangzhuang Wastewater Treatment Plant in Xinxiang City, Henan Province, and its initial moisture content is approximately 80%. Laccase is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with an enzyme activity ≥ 0.5 U / mg, and is configured into a laccase solution with a concentration of 50 mg / mL; Biochar is prepared from common bamboo as the raw material, purchased from Pingdingshan Lvyuan Activated Carbon Co., Ltd., and sawdust is taken from a local furniture factory in Xinxiang City, with a particle size of 1 - 2 cm.

[0026]

[0027] Example 1

[0028] Step S1: Crush the sawdust with a crusher to 3 - 5 mm, and fully mix the sawdust and dewatered sludge according to a mass ratio of 1:5 to obtain compost materials, where the moisture content of the compost materials is adjusted to 70 wt%, and the C / N elemental molar ratio is adjusted to 7.8:1;

[0029] Step S2: Mix 10 g of biochar and 10 mL of laccase solution (concentration 50 mg / mL) evenly with 100 g of the compost material obtained in Step S1 at the initial stage of composting (day 0) to obtain a mixed material, and then carry out composting on the mixed material; at the end stage of the high-temperature period of composting (day 8), mix 10 mL of laccase solution (concentration 50 mg / mL) evenly with the above-mentioned compost material to obtain a mixed material, and then continue to carry out composting on the mixed material to obtain a compost product; the specific process of composting is as follows: The entire composting process lasts for 24 days, and the composting process is carried out in a constant-temperature incubator, which is divided into 4 stages: The first stage is the heating-up period. On the first day of composting, set the temperature of the incubator to 40 °C; the second stage is the high-temperature period, from the 2nd to the 8th day, adjust the temperature of the incubator to 50 °C; the third stage is the cooling-down period. Starting from the 9th day, lower the temperature by 2 °C every day and stop cooling when it reaches 24 °C; the fourth stage is the ripening period. Starting from the 20th day, maintain the temperature at 24 °C and do not change it anymore. The ventilation volume during the composting process is controlled at 0.5 L / min; turn the pile once every afternoon at 4 o'clock during the heating-up period and the high-temperature period, and control the turning time at 10 - 20 min each time; stop turning the pile after entering the cooling-down period.

[0030] Comparative Example 1

[0031] Step S1: Crush the sawdust to 3 - 5 mm with a crusher, and fully mix the sawdust and dewatered sludge in a mass ratio of 1:5 to obtain a compost material, where the moisture content of the compost material is adjusted to 70 wt%, and the C / N element molar ratio is adjusted to 7.8:1;

[0032] Step S2: Mix deionized water and the compost material obtained in Step S1 evenly in a mass ratio of 1:50 to obtain a mixed material, and then carry out composting on the mixed material to obtain a compost product; the specific process of composting is as follows: The entire composting process lasts for 24 days, and the composting process is carried out in a constant-temperature incubator, which is divided into 4 stages: The first stage is the heating-up period. On the first day of composting, set the temperature of the incubator to 40 °C; the second stage is the high-temperature period, from the 2nd to the 8th day, adjust the temperature of the incubator to 50 °C; the third stage is the cooling-down period. Starting from the 9th day, lower the temperature by 2 °C every day and stop cooling when it reaches 24 °C; the fourth stage is the ripening period. Starting from the 20th day, maintain the temperature at 24 °C and do not change it anymore. The ventilation volume during the composting process is controlled at 0.5 L / min; turn the pile once every afternoon at 4 o'clock during the heating-up period and the high-temperature period, and control the turning time at 10 - 20 min each time; stop turning the pile after entering the cooling-down period.

[0033] Comparative Example 2

[0034] Step S1: Crush the sawdust to 3 - 5 mm with a crusher, and fully mix the sawdust and dewatered sludge in a mass ratio of 1:5 to obtain a compost material, where the moisture content of the compost material is adjusted to 70 wt%, and the C / N element molar ratio is adjusted to 7.8:1;

[0035] Step S2: Mix 20 mL of laccase solution (concentration 50 mg / mL) with 100 g of the compost material obtained in Step S1 evenly at the initial stage of composting (day 0) to obtain a mixed material, and then carry out composting on the mixed material to obtain a compost product; the specific process of composting is as follows: The entire composting process lasts for 24 days and is carried out in a constant temperature incubator, which is divided into 4 stages: The first stage is the heating-up period. On the first day of composting, set the temperature of the incubator to 40 °C; the second stage is the high-temperature period. From the 2nd to the 8th day, adjust the temperature of the incubator to 50 °C; the third stage is the cooling-down period. Starting from the 9th day, lower the temperature by 2 °C every day and stop cooling when it reaches 24 °C; the fourth stage is the ripening period. Starting from the 20th day, maintain the temperature at 24 °C without change. The ventilation volume during the composting process is controlled at 0.5 L / min; turn the pile once at 4 pm every day during the heating-up period and the high-temperature period, and control the turning time at 10 - 20 min each time; stop turning the pile after entering the cooling-down period.

[0036] Comparative Example 3

[0037] Step S1: Crush sawdust with a crusher to 3 - 5 mm, and fully mix sawdust and dewatered sludge in a mass ratio of 1:5 to obtain a compost material, where the moisture content of the compost material is adjusted to 70 wt%, and the C / N elemental molar ratio is adjusted to 7.8:1;

[0038] Step S2: Mix 10 mL of laccase solution (concentration 50 mg / mL) with 100 g of the compost material obtained in Step S1 evenly at the initial stage of composting (day 0) to obtain a mixed material, and carry out composting on the mixed material; at the end of the high-temperature period of composting (the 8th day), mix 10 mL of laccase solution (concentration 50 mg / mL) with the above-mentioned compost material evenly to obtain a mixed material, and carry out composting on the obtained mixed material to obtain a compost product: The specific process of composting is as follows: The entire composting process lasts for 24 days and is carried out in a constant temperature incubator, which is divided into 4 stages: The first stage is the heating-up period. On the first day of composting, set the temperature of the incubator to 40 °C; the second stage is the high-temperature period. From the 2nd to the 8th day, adjust the temperature of the incubator to 50 °C; the third stage is the cooling-down period. Starting from the 9th day, lower the temperature by 2 °C every day and stop cooling when it reaches 24 °C; the fourth stage is the ripening period. Starting from the 20th day, maintain the temperature at 24 °C without change. The ventilation volume during the composting process is controlled at 0.5 L / min; turn the pile once at 4 pm every day during the heating-up period and the high-temperature period, and control the turning time at 10 - 20 min each time; stop turning the pile after entering the cooling-down period.

[0039] Measure the temperature at the center of the compost pile every day during the heating period and high-temperature period in Example 1 and Comparative Examples 1-3. Collect the compost products on the 0th, 4th, 8th, 12th, 18th, and 24th days of composting as samples to be tested, and measure the physical and chemical indexes such as moisture content, organic carbon content, and nitrate nitrogen. The results are as follows Figure 1 As shown, it can be seen from the figure that the additive significantly reduces the moisture content of the compost pile and effectively improves the activity of microorganisms in the compost pile. As follows Figure 3 As shown, adding biochar and laccase effectively reduces the organic carbon content in the compost and can significantly improve the quality and utilization efficiency of the compost products. As follows Figure 5 As shown, biochar and laccase as additives can also effectively increase the nitrate nitrogen content during the composting process and effectively improve the quality and utilization value of the compost products.

[0040] Collect the compost products on the 0th, 4th, 12th, and 24th days of composting respectively, and measure the laccase activity using a UV-2600i spectrophotometer with ABTS as the substrate. The results are as Figure 2 shown. It can be seen from the figure that the laccase activity shows an upward trend in the early stage of the high-temperature period. Due to the increase in temperature and pH, the laccase activity is inhibited, so the laccase activity shows an obvious downward trend in the later stage of the high-temperature period; after adding laccase during the cooling stage, the laccase activity in Example 1 increases significantly; due to the fractional addition of laccase and the protection of the microporous structure of biochar, it is more conducive to improving the laccase activity, making the effect of Example 1 better. The promotion effect of laccase enzyme activity from strong to weak is: Example 1 > Comparative Example 3 > Comparative Example 2 > Comparative Example 1.

[0041] Collect the compost products on the 0th, 4th, 8th, 12th, 18th, and 24th days of composting respectively, and extract and measure humus and humic acid using the method provided by the International Humic Substances Society (IHSS), and calculate the humification index. The results are as Figure 4 shown. It can be seen from the figure that the final humification index of the compost from high to low is: Example 1 > Comparative Example 3 > Comparative Example 2 > Comparative Example 1. It shows that the combination of laccase and biochar has a better effect.

[0042] Collect the compost products on the 0th, 4th, 12th, and 24th days of composting respectively, and measure the concentration of PPCPs by high performance liquid chromatography. The results are as Figure 6 shown. It can be seen from the figure that biochar and laccase as additives effectively improve the enzyme activity during the composting process and significantly degrade PPCPs. The final degradation promotion effect from strong to weak is: Example 1 > Comparative Example 3 > Comparative Example 2 > Comparative Example 1.

[0043] Comprehensively Figures 1 to 6 It can be seen that the best comprehensive improvement effect on composting is Example 1, followed by Comparative Example 3, Comparative Example 2, which is slightly stronger than Comparative Example 1 without adding laccase and biochar.

[0044] It can be seen from the above that the technical solution provided by the present invention can promote the humification of compost, increase the humic acid content and humification index in the compost product, and improve the yield and quality of the compost product.

[0045] The above embodiments have described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for promoting sludge composting humification and PPCPs degradation by using laccase combined with biochar, characterized in that The specific steps are: Step S1, crushing the lignocellulose-rich conditioning agent into 3-5 mm, and fully mixing the crushed conditioning agent and dehydrated sludge in a mass ratio of 1:5 to obtain a compost material, wherein the moisture content of the compost material is adjusted to 65wt%-75wt%, and the initial C / N element molar ratio is adjusted to 7.5-8:1; Step S2: Evenly mix the biochar and laccase solution with the compost material obtained in step S1 to obtain a mixed material, and then compost the mixed material to obtain a compost product, wherein the specific process of composting is: the entire composting process lasts for 24 days, and the composting process is carried out in a constant temperature incubator, which is divided into 4 stages: the first stage, the heating period, on the first day of composting, the incubator temperature is set to 40°C; the second stage, the high temperature period, from the 2nd to the 8th day, the incubator temperature is adjusted to 50°C; the third stage, the cooling period, starting from the 9th day, the temperature is reduced by 2°C every day to 24°C stop cooling when the temperature drops to 0.5°C; in the fourth stage, the maturity stage, the temperature is maintained at 24°C from the 20th day without changing; the compost is turned once every day at 4 pm during the warming and high temperature periods, and the time of each turning is controlled within 10-20 min; no turning is performed after entering the cooling period; the concentration of laccase solution is 40-60 mg / mL, the mass ratio of biochar, laccase solution and compost material is 8-12:0.8-1.2:100, and 40wt%-60wt% laccase solution is added at the initial stage of composting and the remaining laccase solution is added at the end of the high temperature period of composting.

2. The method for promoting sludge compost humification and PPCPs degradation by using laccase combined with biochar according to claim 1, characterized in that: In step S1, the lignocellulose-rich conditioning agent is sawdust, the moisture content of the compost material is adjusted to 70 wt %, and the initial C / N element molar ratio is adjusted to 7.8:

1.

3. The method of promoting sludge compost humification and PPCPs degradation by using laccase combined with biochar according to claim 1, characterized in that: In step S2, the mass ratio of biochar, laccase solution and compost material is 10:1:

100.

4. The method of promoting sludge compost humification and PPCPs degradation by using laccase combined with biochar according to claim 1, characterized in that: In step S2, 50 wt% of the laccase solution is added at the initial stage of composting and the remaining 50 wt% of the laccase solution is added at the end of the high-temperature composting stage. The concentration of the laccase solution is 50 mg / mL.

5. The method of promoting sludge compost humification and PPCPs degradation by using laccase combined with biochar according to claim 1, characterized in that: The composting in step S2 is used to promote humification of sludge compost and degradation of PPCPs, wherein the PPCPs are one or more of ibuprofen, galaxol, triclosan and carbamazepine.

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