River sludge resource recycling treatment method based on MICP technology

Abstract

The application provides a river sludge resource recycling method. First, the river sludge is pumped out by using physical equipment, then the organic matter of the river sludge is decomposed by using solid fermentation of microorganisms combined with bentonite, and heavy metals are degraded, so that the effect of eliminating odor and harmless treatment is achieved. Then, a vacuum dewatering device is arranged in the fermentation box, so that the sludge is gradually dewatered in the fermentation process, and the water content is reduced to below 10%, finally, a cementing liquid containing calcium ions is sprayed on the sludge, and urease-producing microorganisms are induced to generate calcium carbonate precipitation (MICP), so that the sludge forms a certain strength of the raw soil, which can be used on the roadbed. In this process, the bentonite can play the roles of adsorbing bacterial flora, enhancing the MICP effect, fixing heavy metals and assisting fermentation. The method is low in cost, green and environmentally friendly, solves the problem that the sludge is difficult to be applied for a long time, has certain economic value, and is a disposal method worthy of promotion.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of microorganisms and relates to a treatment method for sludge resource recycling in river dredging. BACKGROUND

[0002] With the increasing of urban sewage discharge in China year by year, the sludge as a byproduct of sewage treatment is also increasing year by year. In 2021, the sludge production in China was about 12.32 million tons. The sludge contains a large amount of organic matter, heavy metals, microorganisms and other pollutants, so it is particularly important to harmlessly treat and reasonably utilize the sludge. The traditional sludge treatment process mainly includes concentration, dewatering, digestion (anaerobic digestion and aerobic digestion), composting and drying processes. However, the traditional sludge treatment method is generally used for incineration, sanitary landfill, composting, drying and granulation and sea dumping after treatment, and most of these treatment methods have complex process, high cost and poor environmental protection. Therefore, how to maximize the utilization of sludge in combination with social, economic and environmental benefits is a new direction for the development of sludge treatment and disposal technology in the future.

[0003] Microbial induced calcium carbonate precipitation (MICP) is a new technology that not only saves energy, is environmentally friendly, safe and economical, but also has a simple mechanism and is easy to operate, and is widely used in various engineering environments. Microbial solidification mainly generates carbonate and ammonium ions by urease-producing microorganisms hydrolyzing urea, and then obtains the final product calcium carbonate by introducing calcium source externally, so that it can be precipitated and cemented in the soil to glue the soil particles. SUMMARY

[0004] The present application provides a treatment method for river sludge resource recycling, which can reduce the organic matter and heavy metals of the treated sludge and has certain strength, and can be widely used in various engineering. The method is realized by the following steps:

[0005] Firstly, the sludge is extracted into a fermentation tank by river dredging mechanical equipment, then 5%-10% of soybean protein, 2%-5% of red bran, 3%-5% of bentonite and 10%-15% of microbial liquid are added, the mixture is stirred uniformly, the temperature is controlled at 30℃, and the fermentation is carried out for more than 24 hours. Then a vacuum dewatering device is arranged in the fermentation tank, so that the sludge is gradually dewatered during the fermentation process, and the water content is reduced to below 10%. Finally, it is used as roadbed backfill soil, and the calcium carbonate induced by Bacillus subtilis in the backfill soil is solidified by spraying or injecting cementing liquid.

[0006] The present application is through microbial fermentation activity, so that the microorganisms decompose the organic matter in the sludge in metabolism and remove the odor of the sludge. At the same time, the microorganisms can degrade Cd, Cr and Zn and other heavy metals, and the bentonite can adsorb, fix and remove Zn, Cu and Pb and other heavy metals.

[0007] Bentonite plays a certain auxiliary role in microbial fermentation process, because microbial fermentation process is also called anaerobic digestion process, when pH is too low, anaerobic digestion is mainly acidification process, at this time, the produced volatile fatty acids gradually accumulate, thus causing a certain inhibition to methanation process. Bentonite can form condensed compounds such as calcium silicate and aluminum silicate in microbial fermentation activity, these compounds can compress the double electric layer on the surface of bentonite, reduce the Zeta potential of bentonite, improve the flocculation ability of bentonite and the adsorption of hydrogen ions, thus playing a role of buffering pH.

[0008] In the process of microbial induced generation of calcium carbonate, bentonite also plays a certain auxiliary role in the process, the bentonite incorporated can form a nano-honeycomb pore structure after water absorption, and the specific surface area is significantly increased. In the process of injecting bacteria solution, the honeycomb pore structure enables the microorganisms to have sufficient aggregation points, in the process of injecting cementing fluid, bentonite has a strong adsorption of cations, can fully adsorb Ca2+ in the cementing fluid, and bentonite will be attached to the surface of sand particles due to the matrix suction, so that the inter-soil calcium carbonate precipitation is significantly increased.

[0009] In terms of fixing heavy metals, bentonite also has a significant effect: the cations in bentonite and heavy metal ions have mutual exchange effect. And the surface of bentonite particles can also form a hydrated oxide covering layer, the surface is negatively charged, which is conducive to complexing and adsorbing heavy metal ions. Secondly, the bentonite particles are fine, have a relatively developed specific surface area, and have a certain physical adsorption of heavy metal ions, and the main adsorption form should be ion exchange adsorption and surface complexation adsorption.

[0010] Compared with the prior art, the method has the following advantages: (1) using microbial fermentation technology to decompose organic matter in sludge and degrade heavy metals is a harmless treatment. (2) using bentonite to assist microbial fermentation plays a role of buffering pH, improves the fermentation effect, and maximizes the utilization of bentonite resources. (3) using bentonite to adsorb heavy metals can make heavy metals more easily degraded during fermentation, and can stabilize the incompletely degraded heavy metals, preventing secondary pollution caused by water migration carrying heavy metals. (4) the sludge after microbial fermentation alone does not have strength, and has a narrow application range. The sludge after fermentation is solidified by MICP technology, so as to have a certain strength, so that the application range is more extensive, and can be applied in roadbed backfilling and other engineering. (5) using bentonite to assist the MICP process can significantly increase the inter-soil calcium carbonate precipitation, thus improving the strength. DETAILED DESCRIPTION

[0011] The method is further illustrated in combination with examples.

[0012] Example 1: A certain river through mechanical dredging to obtain sludge amount 8 tons, it is pumped to fermentation tank, then add sludge quality of 5%-10% of soybean protein, 2%-5% of red bran, 3%-5% of bentonite and 10%-15% of microbial bacteria liquid, the mixture is stirred uniformly, then control the temperature at 30℃, fermentation for 24 hours or more, then set up vacuum dewatering equipment in the fermentation tank, make the sludge gradually dewatering in the fermentation process, make the water content reduced to below 10%. Finally, it is used as roadbed backfill soil, adopt cementing liquid spraying or injection and other ways to induce bacillus subtilis to generate calcium carbonate solidification in the backfill soil. Take the solidified soil sample, after detection, it contains organic matter 28%, pH value 7.3, internal friction angle 28°, cohesion 24.75kPa, CBR value 8, meet the requirements of roadbed filling.

Claims

1. A method for resource reuse and treatment of river sludge based on MICP technology, comprising the following steps: Step 1: Use river dredging machinery to pump the sludge into the fermentation tank; Step 2: Add 5%-10% soybean protein, 2%-5% red rice bran, 3%-5% bentonite, and 10%-15% microbial inoculum based on the weight of the sludge. The concentration of the bacterial culture was measured using spectrophotometry (OD600), and the OD600 was controlled between 1.0 and 1.

5. Step 3: After mixing the mixture from Step 2 at 100-150 rpm until homogeneous, maintain the temperature at 30℃ and ferment for at least 24 hours. Step 4: Then, a vacuum dewatering device is set up in the fermentation box to gradually dewater the sludge during the fermentation process, reducing the moisture content to below 10%. Step 5: Use the fermented mixture as roadbed backfill soil, and finally use cementing liquid spraying or injection to induce the formation of calcium carbonate by microorganisms in the backfill soil.

2. The method for resource reuse and treatment of river sludge according to claim 1, characterized in that, The bentonite mentioned in step 2 plays a certain auxiliary role in the microbial fermentation process. This is mainly reflected in the fact that when the pH is too low during the microbial fermentation process, anaerobic digestion is mainly an acidification process. At this time, the volatile fatty acids produced gradually accumulate, which inhibits the methanation process. Bentonite can form calcium silicate and aluminum silicate coagulating compounds during microbial fermentation. These compounds can compress the electric double layer on the surface of bentonite, reduce the zeta potential of bentonite, improve the flocculation capacity of bentonite and the adsorption of hydrogen ions, thereby playing a role in buffering the pH.

3. The method for resource reuse and treatment of river sludge according to claim 1, characterized in that, The bentonite mentioned in step 2 plays an auxiliary role in the MIP reaction; this is mainly reflected in the following aspects: after absorbing water, bentonite can form a nanoscale honeycomb pore structure, which significantly increases its specific surface area; during the bacterial injection process, the honeycomb pore structure provides sufficient aggregation points for microorganisms; during the cementing liquid injection process, bentonite has extremely strong cation adsorption properties, which can fully adsorb Ca2+ in the cementing liquid; and bentonite will adhere to the surface of sand particles due to matrix suction, which significantly increases the precipitation of calcium carbonate between soil particles.

4. The method for resource reuse and treatment of river sludge according to claim 1, characterized in that, The bentonite described in step 2 has a significant effect on the adsorption of heavy metals. This is mainly reflected in the following aspects: the cations in bentonite and heavy metal ions have mutual exchange interactions; and a hydrated oxide coating layer can be formed on the surface of bentonite particles, which is negatively charged and conducive to the complexation and adsorption of heavy metal ions; secondly, the bentonite particles are relatively fine and have a relatively developed specific surface area, which can physically adsorb heavy metal ions. The main adsorption forms should be ion exchange adsorption and surface complexation adsorption.