Method for promoting polycyclic aromatic hydrocarbon degradation in sludge compost

Abstract

The application discloses a method for promoting polycyclic aromatic hydrocarbon degradation in sludge composting. Natural vermiculite powder is used in the composting process to degrade polycyclic aromatic hydrocarbons in compost fertilizer by using the catalytic performance. The advantages are as follows: waste mushroom residue is used as a bulking agent and a source of inoculant, and powdered natural vermiculite is used as a catalyst, so that the humification of sludge-waste mushroom residue compost and the reduction of room temperature gas emission are promoted, and the degradation efficiency of polycyclic aromatic hydrocarbons in the sludge composting process is greatly improved.

Description

Technical fields:

[0001] This invention relates to the field of organic solid waste resource utilization technology, specifically a method for using powdered natural vermiculite as a composting catalyst to promote the degradation of polycyclic aromatic hydrocarbons in sludge-waste mushroom residue co-composting. Background technology:

[0002] With the rapid urbanization and increasing emphasis on environmental protection in my country, the volume of urban wastewater treatment is constantly increasing, and sludge, as a byproduct of wastewater treatment, is also increasing dramatically. According to my country's "2022 Statistical Yearbook of Urban and Rural Construction," in 2021, a total of 4,602 wastewater treatment plants were built and put into operation in cities and counties nationwide, with a daily wastewater treatment capacity of 248 million cubic meters and an annual production of over 70 million tons of sludge with a moisture content of approximately 80%. Sludge has a complex composition, containing not only large amounts of organic matter and nitrogen, phosphorus, and potassium, but also pathogenic microorganisms, heavy metals, and toxic and harmful organic pollutants. How to safely, economically, and rationally treat, dispose of, and utilize the large quantities of sludge has always been an important issue of great concern to countries around the world in the field of biological solid waste resource utilization.

[0003] Driven by my country's ecological civilization construction and green, circular, and low-carbon development strategies, the sludge treatment and disposal industry in my country is experiencing rapid and diversified development. Municipal sludge treatment and disposal technologies mainly include sanitary landfill, incineration for power generation, anaerobic digestion, aerobic composting, pyrolysis carbonization, and building material utilization, among others. Currently, incineration (power generation), anaerobic digestion, and aerobic composting are the main development directions for sludge treatment and disposal technologies, accounting for 65.41%, 15.55%, and 9.61% respectively. Among these, aerobic sludge composting, as an environmentally friendly, simple, and resource-utilizing treatment technology, is one of the mainstream treatment and disposal methods for achieving sludge resource utilization both domestically and internationally, and has received widespread attention.

[0004] Aerobic composting is a complex biochemical process driven by microorganisms. Many technological parameters influence aerobic composting, among which composting temperature, aeration and oxygen supply, moisture content, C / N ratio, pH, and conditioners are key. Due to the high moisture content, fine particle size, and low C / N ratio of sludge, aerobic composting typically requires the addition of bulking agents (such as granular expanded vermiculite) and conditioners (such as straw, rice straw, and sawdust).

[0005] Polycyclic aromatic hydrocarbons (PHAs) are persistent toxic and harmful organic compounds found in sewage sludge. Traditional sewage sludge composting faces challenges such as low PHA degradation capacity, high emissions of ammonia nitrogen and greenhouse gases, and relatively weak heavy metal passivation ability. To address these challenges, biological and non-biological additives or catalysts are employed, such as inoculating with ultra-high temperature microorganisms or with bacteria (enzymes) that effectively degrade cellulose and lignin. 、 Adding biochar, metal oxides, and mineral materials has become a hot topic of research in recent years.

[0006] Vermiculite is a 2:1 layered magnesium aluminum hydrate silicate secondary metamorphic mineral, usually formed from biotite through hydrothermal alteration or weathering. Due to the isomorphic substitution of Si(IV) by Al(III), it generates a permanent diffuse negative charge. When heated and dehydrated, it expands, exhibiting a flexed shape resembling a leech, hence the name vermiculite. my country is a major producer of vermiculite. When heated to 300℃, vermiculite can expand 20 times its original size and bend, becoming expanded vermiculite. Expanded vermiculite is characterized by good air permeability, strong water absorption, loosening of soil, and minimal sensitivity to temperature changes, acting as a buffer against environmental changes. Its high adsorption capacity allows for the slow release of nutrients from the growth medium, reducing leaching and promoting nutrient utilization by plants. Therefore, expanded vermiculite is widely used in both soil-based and hydroponics techniques for crops.

[0007] Expanded vermiculite, sintered at high temperatures, has large particles and is commonly used as a leavening agent, water-retaining agent, and slow-release nutrient agent in composting. However, expanded vermiculite has a small specific surface area and low catalytic performance. Natural vermiculite powder has a larger specific surface area, and the unsintered metal oxides within it exhibit better catalytic performance. Although vermiculite has been reported as a leavening agent, oxygen scavenger, or room-temperature gas release inhibitor in the composting of green waste, food waste, and livestock manure, there are few studies or reports on its use as a catalyst in the catalytic degradation of polycyclic aromatic hydrocarbons (PAHs) in sludge composting. Summary of the Invention:

[0008] The purpose of this invention is to provide a method for promoting the degradation of polycyclic aromatic hydrocarbons (PAHs) through sludge composting. This method significantly enhances the catalytic degradation performance of PAHs while promoting the sludge composting process. Specifically, this method involves adding natural vermiculite powder during the sludge composting process.

[0009] Furthermore, the particle size range of natural vermiculite powder is less than 1 mm, which is different from the large-particle expanded vermiculite with a particle size of 1 mm to 230 mm.

[0010] Furthermore, the natural vermiculite powder accounts for 1% to 20% of the weight of the compost raw materials; the preferred proportion range is 1-10%.

[0011] Furthermore, waste mushroom residue and sawdust are added during the composting process. The waste mushroom residue serves as both a bulking agent and an inoculant for sludge composting, while the sawdust acts as a C / N ratio regulator for sludge composting.

[0012] Furthermore, the proportions of waste mushroom residue and sawdust added to compost range from 1% to 30% and 1% to 10%, respectively.

[0013] Furthermore, the moisture content of the composting raw materials is 55%-70%.

[0014] Furthermore, the carbon-to-nitrogen ratio of the composting raw materials is 15-30.

[0015] The compost of this invention spontaneously undergoes stages of heating, high temperature, cooling, and maturation.

[0016] The method of this invention maintains the composting temperature above 55°C for 4-6 days to meet the requirements of compost products for killing pathogenic microorganisms and weed seeds, and turns the compost pile regularly. The entire composting process lasts for 20-50 days.

[0017] The method of this invention involves weighing sludge, waste mushroom residue, wood chips, and powdered natural vermiculite in a certain proportion, putting them into a mixer, stirring them thoroughly, and then loading them into a solid fermentation tank (vessel) to begin aerobic composting; and determining the polycyclic aromatic hydrocarbons and their content in the compost mixture.

[0018] This invention uses sludge as composting material, waste mushroom residue as a compost loosening agent and a source of composting microbial agents, sawdust as a C / N ratio regulator for composting raw materials, and powdered natural vermiculite as a catalyst for degrading polycyclic aromatic hydrocarbons.

[0019] Advantages of this invention:

[0020] (1) In the sludge composting process, adding natural vermiculite powder as a catalyst for the degradation of polycyclic aromatic hydrocarbons (PAHs) mainly utilizes natural vermiculite powder.

[0021] However, the porosity, large specific surface area, and catalytic properties of unsintered metal oxides contained in vermiculite powder mainly enhance the catalytic performance of polycyclic aromatic hydrocarbons (PAHs) during composting, promoting the catalytic degradation of PAHs in sludge compost. Secondly, apart from lacking the bulky and oxygen-repellent properties of expanded vermiculite, natural vermiculite powder retains the other functions of expanded vermiculite.

[0022] (2) Because powdered natural vermiculite is not heat-treated, it has better catalytic performance than expanded vermiculite, while also maintaining its particle size.

[0023] Other properties of granular expanded vermiculite in composting: Powdered natural vermiculite is cheaper than large-particle expanded vermiculite, saving costs. Furthermore, waste mushroom residue can replace granular expanded vermiculite as a leavening agent, ensuring aeration and oxygen supply in the compost. Waste mushroom residue contains a large number of cellulose-degrading bacteria and many decay-causing bacteria, which can be used as an inoculum agent for composting, eliminating the need for additional inoculation or external composting agents. Waste mushroom residue can also rapidly raise the compost temperature in the initial stage of sludge composting, shortening the composting time by 1 / 4.

[0024] (3) Powdered natural vermiculite is used in sludge composting, which saves time, reduces costs, and has a good effect on degrading stubborn polycyclic aromatic hydrocarbons. Attached Figure Description

[0025] Figure 1The physicochemical properties of sludge-mushroom residue-wood chip compost modified with different doses of natural vermiculite powder changed with composting time: (a) temperature change; (b) pH change; (c) electrical conductivity change; (d) moisture content change; (e) organic matter content change; (f) dissolved organic matter change.

[0026] The results showed that the physicochemical properties of sludge-mushroom residue-wood chips co-composted with different doses of natural vermiculite powder changed significantly, including temperature, pH, electrical conductivity, moisture content, organic matter content, and dissolved organic matter.

[0027] Figure 2 The degradation of 16 polycyclic aromatic hydrocarbons (PAHs) and total PAHs before and after the addition of natural vermiculite powder to sludge composting; (a) degradation efficiency of 16 PAHs; (b) degradation rate of low molecular weight and high molecular weight PAHs and total PAHs;

[0028] The results showed that different doses of natural vermiculite powder significantly promoted the catalytic degradation of various polycyclic aromatic hydrocarbons (PAHs), low molecular weight and high molecular weight PAHs, and total PAHs in sludge compost, especially the catalytic degradation effect on low molecular weight PAHs.

[0029] Figure 3 The degradation of low molecular weight and high molecular weight polycyclic aromatic hydrocarbons (PAHs) and total PAHs before and after the addition of expanded vermiculite to compost sludge. Detailed Implementation

[0030] The following examples are intended to further illustrate the present invention, but not to limit it.

[0031] The sludge used in this invention is sludge from a wastewater treatment plant, with a water content of approximately 80%.

[0032] Waste mushroom residue consists of cottonseed hulls, sawdust, rice bran, etc., and is a waste material generated during mushroom production.

[0033] Wood chips are waste materials from wood processing plants, with a length not exceeding 2cm.

[0034] Comparative Example 1: CK

[0035] Composting materials were prepared using a weight ratio of sludge: waste mushroom residue: sawdust = 7:5:2, with a moisture content of approximately 60%. No natural vermiculite powder was added. The compost pile reached a temperature of 62.6℃ within 2 days and was maintained above 55℃ for 5 days, with a total composting time of 35 days. The degradation rates of low molecular weight polycyclic aromatic hydrocarbons (PAHs), high molecular weight PAHs, and total PAHs were 64.7%, 41.6%, and 52.1%, respectively.

[0036] Comparative Example 2: TT1

[0037] Composting materials were prepared with a weight ratio of sludge: waste mushroom residue: sawdust = 7:5:2, with a moisture content of approximately 60%. 1% (by weight) of 20 mm expanded vermiculite was added to the mixture before composting. The compost pile temperature reached 62.2℃ within 2 days and was maintained above 55℃ for 5 days, with a total composting time of 35 days. The degradation rates of low molecular weight polycyclic aromatic hydrocarbons (PAHs), high molecular weight PAHs, and total PAHs were 69.3%, 42.8%, and 54.9%, respectively.

[0038] Example 1: T1

[0039] Composting materials were prepared using a weight ratio of sludge: waste mushroom residue: sawdust = 7:5:2, with a moisture content of approximately 60%. 1% natural vermiculite powder was added by weight of the mixed materials, followed by composting. Within 2 days, the compost pile temperature reached 61.8℃, and was maintained above 55℃ for 5 days, with a total composting time of 35 days. The degradation rates of low molecular weight polycyclic aromatic hydrocarbons (PAHs), high molecular weight PAHs, and total PAHs were 82.8%, 54.5%, and 73.2%, respectively.

[0040] Example 2: T2

[0041] Composting materials were prepared with a weight ratio of sludge: waste mushroom residue: sawdust = 7:5:2, with a moisture content of approximately 60%. 5% natural vermiculite powder was added by weight of the mixed materials, followed by composting. Within 2 days, the compost pile temperature reached 60.1℃, and was maintained above 55℃ for 5 days, with a total composting time of 35 days. The degradation rates of low molecular weight polycyclic aromatic hydrocarbons (PAHs), high molecular weight PAHs, and total PAHs were 76.4%, 50.0%, and 65.2%, respectively.

[0042] Example 3: T3

[0043] Composting materials were prepared with a weight ratio of sludge: waste mushroom residue: sawdust = 7:5:2, with a moisture content of approximately 60%. 10% natural vermiculite powder was added by weight of the mixed materials, followed by composting. The compost pile temperature rose to 58.5℃ within 2 days, was maintained above 55℃ for 5 days, and the composting period lasted 35 days. The degradation rates of low molecular weight polycyclic aromatic hydrocarbons (PAHs), high molecular weight PAHs, and total PAHs were 71.1%, 44.3%, and 55.4%, respectively.

Claims

1. A method for promoting the degradation of polycyclic aromatic hydrocarbons through sludge composting, characterized in that, Add natural vermiculite powder with a particle size of less than 1 mm during the sludge composting process; the natural vermiculite powder accounts for 1 to 10% of the weight of the composting raw materials.

2. The method according to claim 1, characterized in that, Waste mushroom residue and sawdust are added during the composting process. The waste mushroom residue serves as both a bulking agent and an inoculant for sludge composting, while the sawdust acts as a C / N ratio regulator for sludge composting.

3. The method according to claim 2, characterized in that, The proportions of waste mushroom residue and sawdust added to compost range from 1% to 30% and 1% to 10%, respectively.

4. The method according to claim 1, characterized in that, The moisture content of compost raw materials is 55% to 70%.

5. The method according to any one of claims 1-4, characterized in that, The carbon-to-nitrogen ratio of composting raw materials is 15–30.

6. The method according to claim 1, characterized in that, Composting spontaneously goes through stages of heating, high temperature, cooling, and maturation.

7. The method according to claim 1, characterized in that, The composting temperature should be maintained above 55℃ for 4 to 6 days, and the compost pile should be turned regularly. The entire composting process should last for 20 to 50 days.

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