A method for the vermicomposting of excess sludge

Abstract

The application discloses an earthworm biological treatment method of residual sludge and relates to the technical field of sludge treatment, and comprises the following steps: mixing dry sludge and residual sludge at a mass ratio of 1:1-4, adjusting humidity and air permeability by using the dry sludge, and stacking the sludge into earthworm breeding materials with a height of 7cm-13cm; the water content of the earthworm breeding materials is 55%-65%; inoculating earthworms into the earthworm breeding materials, culturing, and obtaining earthworm compost. The method can improve the activity and growth and reproduction rate of the earthworms, shorten the treatment period of the residual sludge, reduce the treatment cost of the residual sludge, improve the productivity of the earthworms and the quality of the residual sludge compost, and the like.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment technology, specifically to a method for the biological treatment of excess sludge using earthworms. Background Technology

[0002] With the rapid advancement of urbanization, my country's urban wastewater treatment industry has developed rapidly, and the disposal of excess sludge has become a hot issue of concern. Excess activated sludge refers to the activated sludge discharged from the secondary sedimentation tank or sedimentation zone of an activated sludge system. Excess sludge is generated during the biochemical treatment process, where microorganisms in the activated sludge continuously consume organic matter in the wastewater. Excess sludge is a complex heterogeneous body composed of microorganisms, organic debris, inorganic particles, colloids, etc. Besides containing some harmful substances and nutrients such as nitrogen, phosphorus, and potassium, it also contains a large amount of easily perishable organic matter. Improper disposal can cause secondary environmental pollution and a significant waste of resources.

[0003] Currently, the main methods for disposing of residual sludge include incineration, landfill, and land application. Incineration can completely achieve the goals of harmlessness and volume reduction, but this method has high treatment costs and poor economic benefits. Landfill has low treatment costs and is easy to operate, but it occupies a large amount of land and is prone to secondary pollution. Land application uses residual sludge as fertilizer and soil conditioner, which is more economical, but because residual sludge contains easily decomposable organic matter, the degradation rate is slow when large amounts of residual sludge are applied, which can easily cause secondary pollution to the soil and surrounding environment.

[0004] Earthworms are widely found in nutrient-rich soils. Their unique physiological functions allow them to work synergistically with microorganisms in the environment to biodegrade organic matter, while simultaneously proliferating rapidly. Currently, the main technologies for treating waste sludge using earthworms include: vermicomposting, vermicomposting biofilters, and vermicomposting reactors for waste sludge treatment.

[0005] Vermicomposting technology introduces earthworms into the composting of organic waste, which solves the problem of heavy metal residue and increases soil fertility. However, its disadvantages include a long organic matter treatment cycle under natural conditions, easy generation of odors, susceptibility to weather conditions, high land occupation, and high treatment costs.

[0006] The earthworm biofilter system technology involves adding residual sludge with a water content of over 99.5% into the earthworm biofilter. Part of the residual sludge is consumed by earthworms, and the other part is decomposed by microorganisms. The residual sludge can also be recycled. However, the disadvantages are that the earthworms have low survival and reproduction rates, low treatment efficiency, and the filter is prone to clogging.

[0007] The worm retort for waste sludge treatment involves the controlled addition of waste sludge with high water content into the worm reactor, using other organic matter as a substrate, and then placing the waste sludge on top for treatment. However, its disadvantages include a long treatment cycle, a small amount of waste sludge treated, and high cost.

[0008] The above analysis shows that currently, the main method of using earthworms to treat waste sludge is to directly use the sludge as feed. However, the high water content of this feed hinders earthworm processing, resulting in a long composting cycle. Furthermore, earthworms may escape from the feed during the breeding process, affecting the treatment efficiency. Inappropriate feed thickness leads to a poor water-to-air ratio, slowing earthworm growth and further reducing sludge treatment efficiency. Significant environmental changes result in low earthworm activity, small sludge volume, and high treatment costs. Summary of the Invention

[0009] To address the problems of low sludge treatment efficiency, low earthworm survival rate, and low reproduction rate in existing technologies for treating sludge using earthworms, this invention provides a method for biological treatment of residual sludge using earthworms.

[0010] To achieve the above objectives, the specific technical solution of the present invention is as follows.

[0011] A method for the biological treatment of residual sludge by earthworms includes the following steps:

[0012] The dried sludge is mixed with the remaining sludge in a mass ratio of 1:1 to 4. The dried sludge is used to adjust the humidity and air permeability, and then piled into earthworm breeding material with a height of 7cm to 13cm.

[0013] The moisture content of the earthworm breeding feed is 55%–65%;

[0014] Earthworms are inoculated onto earthworm breeding material and cultured to obtain earthworm compost.

[0015] The dried sludge in this invention not only reduces the content of mixed sludge, ensuring the earthworms' moisture requirements for growth, but its granular structure also increases the porosity of the earthworm feed, improving aeration and allowing earthworms to breathe smoothly during feeding and excretion. Furthermore, the organic matter in the dried sludge is concentrated, and it may contain more microorganisms and enzymes. By mixing dried sludge and regular sludge in a specific ratio, this invention achieves nutrient complementarity, providing earthworms with a more comprehensive and balanced nutritional environment.

[0016] In another preferred embodiment, the dried sludge refers to sludge with a moisture content of 45% to 55% obtained by drying earthworm compost.

[0017] In another preferred embodiment, the inoculation amount of earthworms is 0.01 worms / cm². 2 ~0.02 strips / cm 2 .

[0018] In another preferred embodiment, the cultivation process further includes:

[0019] When the height of the earthworm substrate is less than 7cm, add more earthworm substrate to keep the height between 7cm and 13cm.

[0020] In another preferred embodiment, the residual sludge is residual sludge with a water content of 75% to 85% obtained during the wastewater treatment process.

[0021] In another preferred embodiment, the cultivation conditions are: temperature of 25℃~30℃ and light duration of 6h / d~12h / d.

[0022] In another preferred embodiment, the soil is turned over every 3 to 4 days during the cultivation process.

[0023] In another preferred embodiment, the pH value of the earthworm breeding material is 6.0 to 7.5.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention mixes dried sludge and residual sludge in a specific ratio and controls the height of earthworm breeding material. This not only provides earthworms with sufficient water and nutrients, but also provides sufficient oxygen for earthworm growth, thereby improving earthworm activity and growth and reproduction rate, shortening the residual sludge treatment cycle, reducing residual sludge treatment cost, and improving earthworm productivity and residual sludge composting quality.

[0026] (2) In this invention, the dried sludge and organic waste in the residual sludge serve as food for earthworms. Earthworms can decompose a mixture of sludge equivalent to their own weight every day. This is mainly because earthworms have unique physiological functions that allow them to work synergistically with microorganisms in the environment to biodegrade the organic matter in the mixed sludge, converting nutrients such as carbon, nitrogen, phosphorus, and potassium in the mixed sludge into forms that are more easily absorbed by plants. At the same time, earthworms can also have a certain biotransformation effect on heavy metals in the mixed sludge.

[0027] (3) This invention utilizes a new earthworm farming technology to treat sludge, solving the problems of high treatment costs and low resource utilization rates associated with traditional incineration and landfill methods for treating residual sludge. Simultaneously, it utilizes the easily decomposable organic matter in the sludge to raise earthworms, achieving resource utilization of waste. This not only raises earthworms for sale as high-protein animal feed but also converts the residual sludge and earthworm excrement into compost, which is then sold as nutrient soil as green fertilizer. Attached Figure Description

[0028] Figure 1 The graph shows the content of available potassium, ammonium nitrogen, and available phosphorus in earthworm compost obtained under different cultivation days in the embodiments of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0031] Earthworms have a wide range of diets, using organic waste in waste sludge as food. They can decompose a volume of waste sludge equivalent to their own weight daily. Earthworms' unique physiological functions allow them to work synergistically with microorganisms in the environment, biodegrading organic matter in waste sludge and converting nutrients such as carbon, nitrogen, phosphorus, and potassium into forms more easily absorbed by plants. Earthworms also have a certain biotransformation effect on heavy metals in waste sludge. Utilizing new earthworm farming technology to treat waste sludge has led to the development of low-carbon and environmentally friendly technologies for waste sludge treatment and resource utilization, solving the problems of high treatment costs and low resource utilization rates associated with traditional incineration and landfill methods. Furthermore, by using the easily decomposable organic matter in waste sludge to raise earthworms, waste resource utilization is achieved. Earthworms are raised and sold as high-protein animal feed, while waste sludge and earthworm castings are converted into compost and sold as green fertilizer.

[0032] Traditional earthworm farming uses household waste as a substrate, adding drying agents or pressing to dehydrate it to adjust the substrate's moisture content and aeration to meet earthworm growth requirements. This invention recycles residual sludge, using the dried sludge (from the previous batch of earthworm farming, i.e., earthworm compost) as a conditioner for the next batch of residual sludge to regulate its moisture and aeration. Simultaneously, it replenishes the microorganisms and enzymes in the new batch of earthworm compost. This eliminates the need for additional conditioners and replenishes the microorganisms and enzymes in the dried sludge to the new batch of raw materials, accelerating earthworm growth and reproduction, thus creating a continuous cycle. Furthermore, this invention experimentally investigated the optimal raw material ratio for earthworm growth and reproduction, explored the environmental conditions affecting optimal earthworm growth, and determined the optimal height for single-layer treatment of mixed sludge. The aim is to improve earthworm activity and growth rate, shorten the sludge treatment cycle, reduce sludge treatment costs, and simultaneously improve earthworm productivity and sludge compost quality.

[0033] The following is a detailed explanation of a method for the biological treatment of residual sludge using earthworms.

[0034] Example 1

[0035] A method for the biological treatment of residual sludge by earthworms includes the following steps:

[0036] S1. Mix the dried sludge with the sludge at a mass ratio of 1:1 to obtain mixed sludge; pile the mixed sludge to a thickness of 7cm to obtain earthworm breeding material; wherein, the pH value of the earthworm breeding material is 6.5 and the moisture content is 55%.

[0037] S2. Place earthworms at a rate of 0.02 worms / cm². 2 The inoculation was applied to the earthworm culture medium, and the soil was turned over every 3 days. The earthworms were cultured at 25℃ with a light exposure of 6 hours per day. During the culture process, earthworm culture medium was continuously added to ensure that the height of the earthworm culture medium was always maintained at 7cm, resulting in earthworms and earthworm compost.

[0038] Example 2

[0039] A method for the biological treatment of residual sludge by earthworms includes the following steps:

[0040] S1. Mix the dried sludge with the sludge at a mass ratio of 1:2 to obtain mixed sludge; pile the mixed sludge to a thickness of 8cm to obtain earthworm breeding material; wherein, the pH value of the earthworm breeding material is 6 and the moisture content is 60%.

[0041] S2. Place earthworms at a rate of 0.02 worms / cm². 2The inoculation was applied to the earthworm culture medium, and the soil was turned over every 3 days. The earthworms were cultured at 30℃ with a light exposure of 10 hours per day. During the culture process, earthworm culture medium was continuously added to ensure that the height of the earthworm culture medium was always maintained at 8cm, resulting in earthworms and earthworm compost.

[0042] Example 3

[0043] A method for the biological treatment of residual sludge by earthworms includes the following steps:

[0044] S1. Mix the dried sludge with the sludge at a mass ratio of 1:3 to obtain mixed sludge; pile the mixed sludge to a thickness of 11cm to obtain earthworm breeding material; wherein, the pH value of the earthworm breeding material is 7 and the moisture content is 65%.

[0045] S2. Place earthworms at a rate of 0.02 worms / cm². 2 The inoculation was applied to the earthworm culture medium, and the soil was turned over every 3 days. The earthworms were cultured at 30℃ with a light exposure of 12h / d. During the culture process, earthworm culture medium was continuously added to ensure that the height of the earthworm culture medium was always maintained at 11cm, resulting in earthworms and earthworm compost.

[0046] Example 4

[0047] A method for the biological treatment of residual sludge by earthworms includes the following steps:

[0048] S1. Mix dried sludge with sludge at a mass ratio of 1:4 to obtain mixed sludge; pile the mixed sludge into a 13cm thick layer to obtain earthworm breeding material; wherein, the pH value of the earthworm breeding material is 7.5 and the moisture content is 65%;

[0049] S2. Place earthworms at a rate of 0.02 worms / cm². 2 The inoculation was applied to the earthworm culture medium, and the soil was turned over every 3 days. The earthworms were cultured at 30℃ with a light exposure of 12h / d. During the culture process, earthworm culture medium was continuously added to ensure that the height of the earthworm culture medium was always maintained at 13cm, resulting in earthworms and earthworm compost.

[0050] To further illustrate the effects of the ratio of dried sludge to sludge and the thickness of the mixed sludge, we conducted the following experiments.

[0051] 1. Effect of the ratio of dried sludge to sludge usage

[0052] The effect of different raw material ratios on earthworm growth. The ratios of dried sludge to residual sludge were 1:1, 1:2, 1:3, 1:4, and 1:0, with a total mass of 3 kg for each sample. The earthworms were cultured for 45 days, and the survival rate and final mass of the earthworms were recorded. The results are shown in Table 1.

[0053] Table 1. Earthworm farming under different ratios of dried sludge to residual sludge

[0054]

[0055] The results in Table 1 show that the final weight and average weight gain of earthworms were highest when the mass ratio of dried sludge to residual sludge was 1:3. This indicates that a 1:3 mass ratio of dried sludge to residual sludge is most beneficial for earthworm growth. This is mainly because adding dried sludge in a specific ratio not only ensures the earthworms' water requirements for growth, but also, due to its granular structure, increases the porosity of the earthworm feed, improving aeration and allowing the earthworms to breathe smoothly during feeding and excretion. Furthermore, the organic matter in the dried sludge is concentrated, and it may also contain more microorganisms and enzymes.

[0056] 2. Thickness of mixed sludge

[0057] Based on optimized raw material ratios, raw materials were laid to varying heights for earthworm degradation treatment. Residual sludge was added only after the height decreased, ensuring the residual sludge height remained at the set value. The study investigated raw material laying heights of 7cm, 9cm, 11cm, and 13cm, using a ratio of 0.02 earthworms / cm. 2 The number of earthworms added and the sludge degradation and earthworm reproduction over two months were recorded. The results are shown in Table 2.

[0058] Table 2. Earthworm farming conditions with different thicknesses of mixed sludge.

[0059] sludge thickness Earthworm initial weight Earthworm final weight Number of earthworms Volume reduction 7cm 13.23g 18.37g 74 articles <![CDATA[2080cm 3 ]]> 9cm 12.98g 46.43g 232 items <![CDATA[3380cm 3 ]]> 11cm 13.42g 70.64g 373 items <![CDATA[4420cm 3 ]]> 13cm 13.01g 32.58g 172 articles <![CDATA[4730cm 3 ]]>

[0060] The results in Table 2 show that an 11cm sludge thickness resulted in the fastest earthworm reproduction rate and the largest decrease in sludge volume, indicating the best sludge treatment effect. Precise control of the sludge thickness not only provides sufficient oxygen for earthworm growth, increasing their growth and reproduction rate, but also provides ample nutrients, further accelerating their growth.

[0061] 3. Cultivation conditions

[0062] Dried sludge was mixed with sludge at a mass ratio of 1:3 to obtain mixed sludge; the mixed sludge was piled up to a thickness of 11 cm to obtain earthworm breeding material; earthworms were introduced at a rate of 0.02 worms / cm². 2 The inoculation was applied to the earthworm culture substrate, and the soil was turned over every 3 days. The earthworms were cultured according to the culture conditions of groups 1 to 3 in Table 3 to obtain the suitable conditions for earthworm culture. The results are shown in Table 3.

[0063] Table 3 Suitable Culture Conditions for Earthworm Farming

[0064]

[0065]

[0066] The results in Table 3 show that the optimal conditions for earthworm cultivation are a raw material moisture content of 55%–65%, a pH value of 6.0–7.5, a temperature of 25℃–30℃, a light duration of 6h / d–12h / d, and turning the soil every 3 days. The number of earthworms in the latter group was 2.8 times that of the former and 1.9 times that of the latter.

[0067] To further illustrate the treatment effect of the method of the present invention on sludge, we used the method in Example 3 to measure the contents of available potassium, ammonium nitrogen, and available phosphorus in earthworm compost obtained after different cultivation days. The results are as follows: Figure 1 As shown.

[0068] from Figure 1 It can be seen that with the increase of cultivation time, the content of available potassium in earthworm compost generally shows an upward trend, the content of ammonium nitrogen generally shows a relatively stable trend, and the content of available phosphorus increases slightly.

[0069] Using the method in Example 3, earthworm compost obtained after 2 months of cultivation was compared with traditional nutrient soil to conduct a morning glory planting experiment. The results of the comparison of the growth of the morning glories are shown in Table 4.

[0070] Table 4. Effects of different compost types on morning glory growth

[0071]

[0072] As can be seen from the results in Table 4, the earthworm compost obtained by the method of this invention has a high organic matter content and is more easily absorbed by plants, thus effectively shortening the germination time, silking time, flowering time, and fruiting time. It also promotes plant growth, increases plant height, and deepens leaf color. Therefore, it can be seen that the earthworm compost of this invention effectively promotes plant growth compared to traditional nutrient soil.

[0073] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims and their equivalents, this invention also intends to include these modifications and variations. The above-described embodiments are merely preferred embodiments for fully illustrating the invention, and their scope of protection is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on this invention are all within the scope of protection of this invention, which is defined by the claims.

Claims

1. A method for the earthworm biotreatment of excess sludge, characterized by, The method comprises the following steps: The dried sludge and the residual sludge are mixed in a mass ratio of 1:3, the dried sludge is used to adjust the humidity and air permeability, and the mixture is stacked into earthworm breeding material with a height of 11 cm; The moisture content of the earthworm breeding material is 55% to 65%; The earthworms are inoculated into the earthworm breeding material for culture to obtain earthworm compost; The dried sludge refers to sludge with a moisture content of 45% to 55% obtained by drying the earthworm compost; and the residual sludge refers to residual sludge with a moisture content of 75% to 85% obtained in the sewage treatment process; The inoculation amount of the earthworms is 0.02 worms / cm 2 ; The culture conditions are as follows: the temperature is 25 DEG C to 30 DEG C, and the light time is 6 h / d to 12 h / d; The pH value of the earthworm breeding material is 6.0 to 7.

5.

2. The method for earthworm biotreatment of excess sludge according to claim 1, characterized by, The culture process further comprises the following steps: When the height of the earthworm breeding material is lower than 7 cm, the earthworm breeding material is added to keep the height of the earthworm breeding material at 7 cm to 13 cm.

3. The method for earthworm biotreatment of excess sludge according to claim 1, characterized by, The soil is turned over every 3 to 4 days during the culture process.

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