A method for promoting sludge methanogenesis while controlling resistance gene dissemination

Abstract

This invention discloses a method for promoting methanogenesis from sludge while controlling the spread of resistance genes, relating to the field of organic solid waste treatment. The method includes the following steps: concentrating excess sludge and microalgae to obtain concentrated sludge and microalgae respectively; mixing the concentrated sludge and microalgae in a specific ratio; and performing anaerobic co-digestion of the treated microalgae-sludge mixed substrate. Compared to the separate digestion of sludge, this method increases methane production by more than 50%, promoting the conversion of organic solid waste into biomass energy; simultaneously, utilizing the antioxidant properties of microalgae, it alleviates oxidative stress, slows the spread of resistance genes during sludge treatment, and reduces sludge treatment costs. This invention provides a microalgae-sludge co-digestion system that is simple to operate, requires no additional pretreatment, and has significant effects. As a widely applicable and highly efficient treatment method for methanogenesis and inhibiting the spread of resistance genes, it has high application potential and commercial prospects in practical applications.

Description

Technical Field

[0001] This invention belongs to the field of organic solid waste treatment and relates to a method for enhancing anaerobic digestion of sludge, specifically a method for promoting methanogenesis while controlling the spread of antibiotic resistance genes by using microalgae and residual sludge for anaerobic co-digestion. Background Technology

[0002] The rapid pace of urbanization has led to a widespread increase in wastewater treatment plants across cities and towns nationwide, resulting in the generation of large quantities of waste activated sludge during the treatment process. Some novel, recalcitrant organic pollutants, such as antibiotics, are insufficient for biodegradation in traditional activated sludge processes, inevitably placing selective pressure on sludge microorganisms. This accelerates the acquisition of antibiotic resistance by exposed microorganisms, leading to a rapid increase in antibiotic-resistant bacteria and their associated antibiotic resistance genes in the excess activated sludge. The widespread transmission of antibiotic resistance has become a global problem, making the exploration of methods to reduce resistance genes in excess activated sludge particularly urgent and crucial.

[0003] Anaerobic digestion is a crucial biotechnology for recovering organic energy from waste sludge worldwide. This technology, through the collaborative efforts of anaerobic microbial alliances, efficiently degrades the organic components in waste sludge, ultimately generating biogas (a mixture of methane, carbon dioxide, and a small amount of hydrogen). However, digesting waste sludge alone is often ineffective, with problems such as acidification, ammonia nitrogen inhibition, and poor cellulose degradation easily occurring within the system. Furthermore, without appropriate measures to control antibiotic-resistant bacteria and antibiotic resistance genes, resistance may continuously increase during anaerobic digestion, posing a serious threat to the ecological environment and human health. The spread of resistance genes mainly occurs in two ways: vertical gene transfer from parent to offspring and horizontal gene transfer mediated by mobile genetic elements. Notably, oxidative stress and increased cell membrane permeability are considered to promote both vertical and horizontal gene transfer. Therefore, mitigating oxidative stress in microorganisms and reducing cell membrane permeability during anaerobic digestion are beneficial for inhibiting the spread of resistance genes.

[0004] Microalgae serve as an effective substrate for biomass resource utilization with sludge, and co-digestion of microalgae and sludge can effectively improve biogas production efficiency. Furthermore, microalgae can produce various antioxidants (such as astaxanthin, fucoxanthin, and lutein), which can alleviate oxidative stress in cells and reduce the increase in cell membrane permeability. Co-digestion of microalgae and sludge not only enhances methanogenesis but also effectively mitigates resistance genes and their horizontal gene transfer in sludge, preventing their further spread. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing anaerobic digestion technologies and provide a method for promoting methanogenesis and reducing antibiotic resistance genes through anaerobic co-digestion of microalgae and sludge. This method achieves the reduction and resource utilization of excess sludge while controlling the spread of resistance genes in the environment.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for enhancing the methanogenic performance of anaerobic digestion of sludge while slowing the spread of resistance genes by co-digesting microalgae and residual sludge includes the following steps:

[0008] S1. Concentrate the microalgae to obtain concentrated microalgae;

[0009] S2. Allow the remaining sludge to settle naturally to remove the water and obtain concentrated sludge;

[0010] S3. Mix the concentrated microalgae obtained in step S1 with the concentrated sludge obtained in step S2 in a balanced ratio, and adjust the pH.

[0011] S4. The mixed microalgae-sludge co-digestion substrate is subjected to anaerobic digestion to enhance methanogenesis performance while reducing antibiotic resistance genes.

[0012] In a further improvement to the above method, the microalgae in step S1 are Chlorella, Haematococcus pluvialis, or other microalgae widely used in wastewater treatment.

[0013] The above method can be further improved by harvesting the microalgae in step S1 through coagulation and flocculation, flotation, centrifugation and filtration, or a combination of multiple techniques.

[0014] In a further improvement to the above method, in step S3, the ratio of the volatile suspended solids (VSS) content of the mixed microalgae to the VSS content of the sludge is controlled to be 1:2.

[0015] In a further improvement to the above method, in step S3, a 2-5M sodium hydroxide solution or a 1-2M hydrochloric acid solution is used to control the initial pH of the mixture of sludge and microalgae to 6.8-7.2.

[0016] In a further improvement to the above method, in step S4, the anaerobic digestion temperature is controlled at 35–37°C.

[0017] In a further improvement to the above method, in step S4, anaerobic digestion is completed in a shaker at 140–180 rpm.

[0018] In a further improvement to the above method, step S4 controls the anaerobic digestion reaction time to 20-35 days.

[0019] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0020] (1) This method realizes the resource utilization of microalgae and residual sludge, and converts organic solid waste into biomass energy. At the same time, the co-digestion of microalgae and residual sludge has a synergistic effect, which can effectively improve the performance of methanogenesis compared with the digestion of sludge alone, and the methane production is increased by more than 50%.

[0021] (2) This method effectively alleviates the oxidative stress response and increased cell membrane permeability of functional microorganisms during anaerobic digestion, thereby slowing down the spread of antibiotic resistance genes.

[0022] (3) This method has the advantages of simple equipment, convenient operation, low processing cost, no need for additional pretreatment and significant effect in reducing resistance genes. Attached Figure Description

[0023] Figure 1 The changes in methanogen production during the separate digestion of sludge and microalgae and the co-digestion of microalgae and sludge;

[0024] Figure 2 The abundance changes of representative ARGs before and after separate digestion of sludge and microalgae and co-digestion of microalgae and sludge;

[0025] Figure 3 The abundance changes of mobile genetic elements during the separate digestion of sludge and microalgae and the co-digestion of microalgae and sludge.

[0026] Figure 4 The changes in intracellular reactive oxygen species during the separate digestion of sludge and microalgae and the co-digestion of microalgae and sludge;

[0027] Figure 5 Figure 1 shows the cumulative methane production and abundance changes of ARGs in the reactor operated according to the method of the present invention under experimental conditions; Figure 2a: Changes in methane production during sludge and microalgae digestion alone and co-digestion of microalgae and sludge; Figure 3b: Abundance changes of representative ARGs before and after sludge and microalgae digestion alone and co-digestion of microalgae and sludge. Detailed Implementation

[0028] 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. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description should be included within the scope of protection of the present invention.

[0029] The following examples illustrate how this method can enhance methane production while inhibiting the spread of resistance genes.

[0030] This invention provides a method for enhancing methanogenesis through anaerobic digestion of excess sludge while controlling the spread of antibiotic resistance genes, comprising the following steps:

[0031] (1) First, the microalgae were centrifuged and concentrated microalgae with VSS of 9.4±0.5g / L and COD of 1.7±0.3g / L were obtained.

[0032] (2) Obtain residual sludge with VSS of 12.5±1.5g / L and COD of 3.3±1.2g / L.

[0033] (3) The obtained concentrated microalgae and the remaining sludge were mixed at a ratio of 1:2 (VSS), and then the pH of the mixture was adjusted to 7.0±0.1 using 1M hydrochloric acid solution.

[0034] (4) The mixed microalgae-sludge co-digestion substrate was anaerobically digested for 32 days in a shaker at 37°C and 180 rpm.

[0035] The methane yield in the microalgae:sludge (VSS) 1:2 reactor was 100.23 mL / g VS, a 52.72% increase compared to sludge digestion alone (69.14 mL / g VS). Furthermore, the spread of resistance genes was effectively suppressed: the relative abundance of some typical resistance genes showed varying degrees of reduction compared to digestion alone. For example, the common resistance gene rpoB2 was significantly downregulated (log2 fold change -0.4). The relative abundance of mobile genetic elements (insertion sequence elements, integrons, and plasmids) mediating horizontal transfer of resistance genes was significantly reduced, exceeding 20%. In addition, reactive oxygen species (ROS) generation levels were reduced by 19.29% during microalgae and sludge co-digestion.

Claims

1. A method for promoting methanogenesis in sludge while controlling the spread of resistance genes, characterized in that, include: Microalgae are concentrated to obtain concentrated microalgae; After settling the remaining sludge and removing the water, concentrated sludge is obtained. The concentrated microalgae and concentrated sludge are mixed in a controlled ratio, and the ratio of volatile suspended solids of microalgae to sludge in the co-digestion substrate is controlled to be 1:

2. The initial pH is adjusted to 6.8~7.2, and anaerobic co-digestion is carried out in a shaker at 35~37℃. By utilizing the synergistic effect of microalgae and sludge, methane production is increased while the spread of antibiotic resistance genes is slowed down.

2. The method as described in claim 1, characterized in that, The residual sludge is the residual sludge from the sewage treatment plant, and the residual sludge settles naturally at room temperature for 4 h - 36 h.

3. The method as described in claim 1, characterized in that, The microalgae mentioned are Chlorella, Haematococcus pluvialis, or other microalgae widely used in wastewater treatment.

4. The method as described in claim 1, characterized in that, The concentrated microalgae are harvested at room temperature through coagulation and flocculation, flotation, centrifugation and filtration, or a combination of multiple techniques.

5. The method as described in claim 1, characterized in that, The anaerobic environment treatment process includes: introducing an inert gas into the reaction vessel to purge oxygen, wherein the inert gas includes at least one of nitrogen, argon, helium, and neon.

6. The method as described in claim 1, characterized in that, The shaking table has a speed of 140~180 rpm and a temperature of 35~37 ℃.

7. The method as described in claim 1, characterized in that, The anaerobic co-digestion time was 20-35 days, and the temperature was 35-37℃.

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