A method for promoting co-fermentation of carbon source by seaweed sludge with microbial pretreatment

Abstract

The present application provides a method for promoting carbon source production by seaweed sludge co-fermentation through microbial pretreatment. The method comprises: adding microbial inoculum with protein degradation ability to the sludge; adding free nitrous acid and rhamnolipid to the sludge obtained in step one, and carrying out pretreatment in an anaerobic environment; mixing the pretreated sludge with seaweed, and carrying out seaweed sludge co-fermentation to obtain the supernatant of the fermentation mixture. The method for preparing seaweed sludge co-fermentation through microbial pretreatment can be widely applied to sludge treatment and recycling, and can improve the treatment efficiency of sludge and reduce the cost of sludge treatment. The seaweed sludge fermentation liquid prepared by the present application can be used as an additional carbon source for sewage treatment, which can provide sufficient nutrients for microorganisms, effectively promote the denitrification and polyphosphorus metabolism in the sewage treatment process, and thus improve the effect of denitrification and phosphorus removal in sewage treatment.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology, and specifically relates to a method for promoting the co-fermentation of seaweed sludge to produce carbon sources using microbial pretreatment. Background Technology

[0002] With the rapid advancement of urbanization, the total amount of wastewater is increasing, accompanied by a continuous rise in sludge production. As a byproduct of urban wastewater treatment, sludge is a typical organic waste, and its treatment and disposal face severe challenges and are costly, accounting for up to 60% of the total cost of wastewater treatment plants.

[0003] Microorganisms play a crucial role in wastewater treatment, participating in wastewater purification in the form of aggregates. However, microorganisms consume carbon sources, such as methanol and sodium acetate, during their metabolism, and the procurement of these carbon sources constitutes a significant expense for wastewater treatment plants. Simultaneously, microorganisms proliferate rapidly during wastewater treatment, and when their numbers become excessive, some microbial aggregates (i.e., sludge) need to be discharged to maintain the system's normal operation. If sludge is directly dumped without treatment, it will emit a foul odor due to the putrefaction of the microorganisms within it, and its total amount is considerable due to the addition of coagulants and other inorganic substances during wastewater treatment.

[0004] Currently, research on resource recycling mainly focuses on converting sludge into carbon sources through anaerobic fermentation. Under specific temperature and pH conditions, anaerobic microorganisms in the sludge can dissolve some substances and convert them into carbon sources. However, this process is inefficient; for example, only about one-tenth of one ton of sludge can be converted into usable carbon sources, which is insufficient to meet the carbon source requirements of wastewater treatment plants. Furthermore, the treatment and disposal of large quantities of sludge remains a pressing issue.

[0005] Therefore, seeking more efficient methods to improve the conversion of sludge into carbon sources and realize the resource utilization of sludge is of great significance for reducing wastewater treatment costs and reducing environmental pollution.

[0006] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] In order to solve one or more of the above-mentioned problems in the prior art, the present invention aims to provide a method for promoting the co-fermentation of seaweed sludge to produce carbon sources using microbial pretreatment and seaweed sludge fermentation broth.

[0008] The method of the present invention for promoting carbon source production by co-fermentation of seaweed sludge using microbial pretreatment may include the following steps: Step 1: Adding a microbial agent with protein degradation ability to the sludge; Step 2: Adding free nitrite and rhamnolipid to the sludge obtained in Step 1 and pretreating it in an anaerobic environment; Step 3: Mixing the pretreated sludge with seaweed and co-fermenting the seaweed sludge to obtain a supernatant of the fermentation mixture, wherein the supernatant is the seaweed sludge fermentation broth.

[0009] According to embodiments of the present invention, the microbial agent can be composed of a variety of microbial strains, wherein the microbial strains may include Vibrio diabolicus, Pseudomonas guguanensis, Thermobacillus, and Bacillus stequilensis.

[0010] According to an embodiment of the present invention, the concentration of Vibrio diabolicus in the microbial agent can be 30% to 95%.

[0011] According to embodiments of the present invention, the *Vibrio frenulum*, *Pseudomonas aeruginosa*, *Bacillus thermophilus*, and *Bacillus tekirae* can be compounded in a ratio of 3:3:3:1, 5:2.5:2:0.5, 7:1.5:1:0.5, 19:0.4:0.4:2, or 6:2:1.5:0.5 to form the microbial agent.

[0012] According to an embodiment of the present invention, the concentration of the microbial agent is 10. 5 cfu / mL ~10 8 cfu / mL.

[0013] According to an embodiment of the present invention, the volume ratio of the microbial agent to the sludge can be 1:500 to 1:2000.

[0014] According to an embodiment of the present invention, the water content of the seaweed is 85% to 99%, and in step three, the ratio of the VSS content of the pretreated sludge to the VSS content of the seaweed can be in the range of 0.5 to 3.0.

[0015] According to an embodiment of the present invention, the concentration of free nitrite added to the sludge obtained in step one can be 0.3 mg / L to 1.2 mg / L, and the dosage of rhamnolipid added to the sludge can be 0.02 g / gTSS to 0.1 g / gTSS.

[0016] According to an embodiment of the present invention, in step two, the temperature at which the sludge is pretreated can be maintained at approximately 25°C.

[0017] According to an embodiment of the present invention, in step two, an anaerobic environment is obtained by introducing nitrogen gas, wherein the nitrogen gas blowing time can be 3 min to 10 min, and the sludge pretreatment time can be 36 h to 48 h.

[0018] According to an embodiment of the present invention, in step three, the pH value of the fermenter can be controlled to be approximately 7.5, and the co-fermentation time can be 10 to 20 days.

[0019] According to an embodiment of the present invention, the seaweed sludge fermentation broth includes volatile fatty acids, and the volatile fatty acids include acetic acid and / or propionic acid.

[0020] According to an embodiment of the present invention, the method may further include using a centrifuge to separate the fermentation mixture produced by co-fermentation of seaweed sludge, wherein the centrifugation speed of the centrifuge may be 4000 r / min and the centrifugation time may be 8 min to 10 min.

[0021] According to an embodiment of the present invention, the sludge in step one above can be obtained by the following method: take the sludge from the primary sedimentation tank of an urban sewage treatment plant as fermentation bottom mud, let it settle for 20h~24h, and then drain the liquid above to obtain the sludge in step one.

[0022] The present invention also provides a seaweed sludge fermentation liquid, which is prepared by using microbial pretreatment to promote the co-fermentation of seaweed sludge to produce carbon sources.

[0023] The present invention also provides an application of seaweed sludge fermentation liquid in wastewater treatment. The seaweed sludge fermentation liquid is prepared by the above-mentioned method of promoting co-fermentation of seaweed sludge to produce carbon source through microbial pretreatment. The seaweed sludge fermentation liquid can be added to wastewater as an external carbon source for wastewater treatment.

[0024] Beneficial effects: The method of using microbial pretreatment to promote the co-fermentation of seaweed sludge to produce carbon sources, as described in this invention, can be widely applied to the treatment and recycling of sludge, improving the biodegradability of sludge and thus increasing the carbon source conversion efficiency of sludge.

[0025] The seaweed sludge fermentation liquid prepared by this invention can be used as an external carbon source for wastewater treatment, improving the nitrogen and phosphorus removal effect of wastewater, while also improving sludge settling performance, reducing treatment costs and enhancing system stability. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings.

[0027] Figure 1 The graph shows the change of ammonia nitrogen concentration with fermentation time during the anaerobic fermentation process of Example A group and Comparative Examples F1 and G group. Figure 2 The graph shows the change of humic acid concentration with fermentation time during the anaerobic fermentation process of Example A group and Comparative Examples F1 and G group. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. It should be noted that, unless otherwise specified, the implementation methods and features in the implementation methods of the present invention can be combined, separated, interchanged, and / or rearranged. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Furthermore, when exemplary embodiments can be implemented differently, the specific process sequence can be performed in a different order than that described. For example, two consecutively described processes can be performed substantially simultaneously or in the reverse order of their description.

[0030] Furthermore, the terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting. As used herein, unless the context clearly indicates otherwise, the singular forms “a” and “the” are intended to include the plural forms as well. Additionally, when the terms “comprising” and / or “including” and variations thereof are used herein, it indicates the presence of the stated features, integrals, steps, operations, parts, components, and / or groups thereof, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, parts, components, and / or groups thereof. It should also be noted that, as used herein, the terms “substantially,” “about,” and other similar terms are used as approximate terms rather than as terms of degree, thus explaining the inherent biases in measurements, calculated values, and / or provided values ​​that would be recognized by one of ordinary skill in the art.

[0031] In the field of wastewater treatment, carbon source is a key factor affecting treatment efficiency, and anaerobic fermentation of sludge has attracted much attention as a potential carbon source production pathway. Currently, improving the carbon source conversion efficiency of sludge and reducing sludge discharge have become core tasks in overcoming the challenges of sludge treatment. Although anaerobic fermentation of sludge can produce a certain amount of carbon source, there are still issues such as the need to improve its efficiency.

[0032] Meanwhile, coastal areas are rich in seaweed, which is abundant in easily biodegradable components such as carbohydrates, making it a potential low-cost fermentation substrate. Therefore, seaweed and sludge can be treated simultaneously to synergistically degrade organic matter, achieving resource utilization through "waste treatment of waste."

[0033] Therefore, this invention proposes a method for promoting the co-fermentation of seaweed sludge to produce carbon sources using microbial pretreatment.

[0034] According to an embodiment of the present invention, a method for promoting carbon source production through co-fermentation of seaweed sludge using microbial pretreatment includes: adding a microbial agent capable of degrading proteins to the sludge; adding free nitrite (FNA) and rhamnolipid (RL) to the sludge obtained in step one, and pretreating the sludge in an anaerobic environment; mixing the pretreated sludge with seaweed and co-fermenting the seaweed sludge to obtain a supernatant of the fermentation mixture, which is the seaweed sludge fermentation broth. This seaweed sludge fermentation broth contains a large amount of volatile fatty acids and can be added to wastewater for wastewater treatment as an external carbon source.

[0035] In this invention, the method of promoting carbon source production through co-fermentation of seaweed sludge using microbial pretreatment involves adding a protease produced by a microbial agent capable of degrading proteins. This protease catalyzes the hydrolysis of proteins in the sludge, causing the microbial membrane proteins to denature and rupture, releasing the organic matter encapsulated within the cells. This, in turn, promotes the dissolution of proteins, polysaccharides, and other substances during the anaerobic digestion of the sludge, and enhances the activity of hydrolytic acidifying bacteria in the subsequent anaerobic fermentation process. On the other hand, the combined pretreatment of the sludge using surfactants such as free nitrite (FNA) and rhamnolipids (RL) effectively promotes the hydrolysis and acid production efficiency of the sludge, inhibits the activity of methanogenic bacteria, and converts more macromolecules into soluble small molecules, facilitating their subsequent utilization as a carbon source. Simultaneously, this combined pretreatment method can shorten the fermentation time by approximately one-third, improve the biodegradability of the sludge, and increase the yield of volatile fatty acids (VFAs).

[0036] This invention achieves efficient co-fermentation of sludge and seaweed by adding microbial agents for sludge pretreatment, thereby achieving the goals of resource utilization and volume reduction, reducing environmental pollution, and producing fermentation liquid with high utilization value of volatile fatty acids, which can supplement carbon sources for wastewater treatment, thus having significant economic and environmental benefits. According to an embodiment of the present invention, the sludge is taken from the secondary sedimentation tank or primary sedimentation tank of a sewage treatment plant, and the initial water content can be in the range of about 70% to 85% (by mass). Preferably, the initial water content of the sludge is about 80%.

[0037] According to embodiments of the present invention, the microbial agent is composed of a variety of microbial strains. These microbial strains may include Vibrio diabolicus, Pseudomonas guguanensis, Thermobacillus, and Bacillus tequilensis.

[0038] According to a preferred embodiment of the present invention, the microbial concentration of Vibrio diabolicus in the mixed microbial agent can be 30% to 95%. As the main microbial species forming the microbial agent of the present invention, when Vibrio diabolicus is in the concentration range of 30% to 95%, the protein degradation ability of the microbial agent can be maximized.

[0039] According to a preferred embodiment of the present invention, *Vibrio frenulum*, *Pseudomonas aeruginosa*, *Bacillus thermophilus*, and *Bacillus tekirae* can be compounded in a ratio of 3:3:3:1, 5:2.5:2:0.5, 7:1.5:1:0.5, 19:0.4:0.4:2, or 6:2:1.5:0.5 to form a microbial inoculum.

[0040] The compounded microbial agent can efficiently degrade organic matter such as cellulose, polysaccharides, and proteins in seaweed and sludge. According to a preferred embodiment of the present invention, the concentration of the microbial agent in the sludge can be 10. 5 cfu / mL ~10 8 cfu / mL. Furthermore, after determining the concentration of the microbial agent in the sludge, it can be added at different volume ratios of microbial agent to sludge. According to a preferred embodiment of the present invention, the volume ratio of the added microbial agent to sludge can be 1:500 to 1:2000. Additionally, in the present invention, the hydrolysis time of the added microbial agent can be 4 hours.

[0041] Furthermore, the concentration of free nitrite in the sludge can be in the range of 0.3 mg / L to 1.2 mg / L, and the dosage of rhamnolipin in the sludge is in the range of 0.02 g / g TSS to 0.1 g / g TSS. Preferably, the dosage of free nitrite is 0.67 mg / L, and the dosage of rhamnolipin is 0.04 g / g TSS.

[0042] According to an embodiment of the present invention, in the step of pretreating sludge, an anaerobic environment can be obtained by introducing nitrogen gas into the reactor, wherein the nitrogen gas blowing time can be 3 min to 10 min, and the sludge pretreatment time can be 36 h to 48 h. The temperature for sludge pretreatment can be maintained at approximately 25°C.

[0043] According to embodiments of the present invention, the seaweed mixed with the sludge can be fresh seaweed, and the water content of the seaweed can be in the range of 85% to 99%, and the ratio of the VSS (volatile suspended solids) content of the sludge to the VSS content of the seaweed can be in the range of 0.5 to 3.0. For example, the VSS content of the sludge can range from 5.2 g / L to 24.6 g / L, and the VSS content of the seaweed can range from 1.7 g / L to 10.4 g / L. According to an embodiment of the present invention, the co-fermentation of seaweed sludge can be carried out in a fermenter (e.g., an anaerobic fermentation reactor), and potassium bicarbonate at a concentration of 200 mg / L can be added using a potassium bicarbonate buffer solution to control the pH value of the fermenter to approximately 7.5. The co-fermentation time can be 10 to 20 days.

[0044] After the sludge and seaweed are mixed, they can be shaken evenly in a water bath shaker at a speed of 130 r / min to 150 r / min, with the water bath temperature maintained at 25℃. In other words, the anaerobic fermentation reaction can be carried out simultaneously with the sludge and seaweed mixture in the water bath shaker.

[0045] According to an embodiment of the present invention, after the co-fermentation of seaweed sludge is completed, a centrifuge can be used to separate the fermentation mixture produced by the co-fermentation of seaweed sludge. The centrifugation speed of the centrifuge can be 4000 r / min, and the centrifugation time can be 8 min to 10 min. The supernatant separated then is the seaweed sludge fermentation liquid rich in VFAs.

[0046] Before centrifugal dewatering, the sludge from the bottom of the anaerobic acid-producing tank and sedimentation tank is collected in a sludge storage tank, and then centrifuged for dewatering. After obtaining the supernatant, the remaining sludge cake is transported off-site. According to an embodiment of the present invention, the dewatered sludge cake has a moisture content of 40-60%. Compared with the initial sludge, approximately 20-40% of the sludge is converted into a carbon source and dissolved in the supernatant, resulting in significant sludge reduction and carbon source production effects.

[0047] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in this industry.

[0048] I. Experimental Procedure The seaweed used in this invention is taken from the seaside of Maidong Park in Qingdao City and used directly after being harvested. The sludge comes from the sludge of a sewage treatment plant in Qingdao City and is added to the fermentation tank after being allowed to settle.

[0049] The inventors completed the following seven sets of experiments. Among them, the implementation examples and comparative examples in the first to sixth sets of experiments all included the following implementation steps: Step 1: Add a microbial agent with protein-degrading ability to the sludge with a moisture content of about 80%; Step 2: After hydrolysis, free nitrite and rhamnolipid are added. The dosage of free nitrite is 0.67 mg / L, and the dosage of rhamnolipid is 0.04 g / gTSS. Then, the sludge is anaerobically stirred in a completely sealed fermenter for 36 hours, and the temperature is maintained at 25℃. Step 3: Mix the pretreated sludge with fresh seaweed, add KHCO3 at a concentration of 200 mg / L, adjust the pH to approximately 7.5, and carry out anaerobic co-fermentation for 20 days.

[0050] In addition, in the following first to sixth groups of experiments, the volume ratio of microbial inoculant to sludge, the concentration of inoculant in sludge, the VSS ratio of sludge to seaweed, the proportion of Vibrio moniliforme in microbial inoculant, and different microbial species were varied.

[0051] II. Experimental Design and Variable Combination In the experiments below, the inventors have selectively listed only a portion of the experimental data in each table as examples. For instance, in Table 1, the volume ratio of the microbial agent to the sludge is listed as a variable for experimental groups A1-A4, while the concentration of the microbial agent, the VSS ratio of the sludge to the algae, the proportion of Vibrio globulus, and other bacterial compositions are listed only as examples with values ​​close to the middle of the corresponding ranges.

[0052] However, in fact, the inventors also selected various concentrations of bacterial agents (i.e., 10... 5 cfu / mL ~10 8 Other values ​​within the range of cfu / mL), VSS ratios of various sludge to algae (i.e., other values ​​within the range of 0.5 to 3.0), different proportions of Vibrio globulus (other values ​​within the range of 30% to 95%), and other bacterial compositions with different ratios (other proportional relationships of Pseudomonas aeruginosa, Bacillus thermophilus, and Bacillus tekirae) were used as fixed quantities, and only the volume ratio of the inoculum to the sludge was used as a variable in the experiment. The results of these experimental data are similar to the results of the experimental data listed in Table 1. Therefore, since the experimental data and results in Table 1 (such as...) Figure 1 and Figure 2The figures (shown) clearly illustrate the effect of changes in the volume ratio of microbial agent to sludge on the experimental results. Therefore, only these values ​​are listed as examples in Table 1. However, those skilled in the art should understand that other experimental results within the above range also conform to the experimental results of the data in Table 1, that is, the description of the experimental results in Table 1 also applies to other data within the above range.

[0053] The situations in Tables 2 to 4 are similar to those in Table 1, so their detailed descriptions are omitted. Furthermore, in the multivariate co-variable experiment in Table 5, experimental data from some endpoint values ​​within the aforementioned range are listed as examples to further verify the rationality of the selected numerical range.

[0054] Table 6 shows comparative examples of the above experimental embodiments. In each experimental group of the comparative examples, at least one data point is outside the scope of the present application. Similar to Tables 1 to 5, Table 6 also shows only some experimental data. That is, it only shows some cases where the data is outside the scope of the present application as examples of comparative examples. However, those skilled in the art should understand that other experimental results outside the scope of the present application also conform to the experimental results of the data in Table 6.

[0055] 1. Volume ratio gradient group (other parameters are fixed) Table 1 2. Inoculum concentration gradient group (other parameters fixed) Table 2 3. VSS (Volume Scaling) vs. Gradient Set (Other parameters fixed) Table 3 4. Gradient group of Vibrio virosa proportions (other parameters fixed) Table 4 5. Combined Implementation Examples (Multivariate Collaborative Validation) Table 5 6. Comparative group Table 6 7. Comparative example group (missing key steps or components; other parameters are set according to Example A1) Comparative Example G1: Step 1 was omitted (no microbial inoculant was added), and steps 2 and 3 were performed directly; Comparative Example G2: Free nitrite was missing in step two, but other operations remained unchanged; Comparative Example G3: No seaweed was added in step three; only sludge fermentation was carried out.

[0056] III. Effect Verification and Comparison Figure 1 and Figure 2 The changes in ammonia nitrogen and humic acid content with fermentation time are shown for the volume ratio gradient groups (A1-A4) and the comparative group G, respectively. The concentration levels of ammonia nitrogen and humic acid can characterize the degree of hydrolysis of sludge cells and have an important impact on the subsequent acid production process.

[0057] from Figure 1 and Figure 2 As can be seen, when the volume ratio of microbial agent to sludge changes, even with the same concentration of microbial agent, the accumulation effects of ammonia nitrogen and humic acid are different. Furthermore, the larger the volume ratio, the higher the initial density of the added microbial agent, which promotes sludge fermentation more quickly. Therefore, experimental group A1 in group A produced ammonia nitrogen the fastest and produced the most ammonia nitrogen, and this experimental group also showed the best humic acid accumulation effect. However, when the volume ratio is greater than 1:500 (e.g., when the volume ratio is 1:400 of the control group F1), the excessively high initial density of the added microbial agent may prevent some of the agent from being effectively applied, leading to a decrease in the accumulation of ammonia nitrogen and humic acid. When the volume ratio is less than 1:2000 (e.g., when the volume ratio is 1:2100 of the control group F2), the excessively low initial density of the added microbial agent leads to a competitive disadvantage for the microbial population, reduced metabolic activity, and consequently, delayed fermentation start-up and a significant reduction in the yield of ammonia nitrogen and humic acid. This indicates that a volume ratio in the range of 1:500 to 1:2000 has the best effect on promoting fermentation.

[0058] Therefore, under the same volume ratio, group A showed significantly better accumulation of ammonia nitrogen and humic acid compared to group G and comparative groups F1 and F2, with the highest ammonia nitrogen concentration reaching 27.8 mg / L and the humic acid concentration reaching 225.5 mg / L. Furthermore, the overall ammonia nitrogen increase rate was higher during the co-fermentation of seaweed and sludge, reaching its peak on the ninth day of fermentation. This indicates that the addition of necessary components FNA, RL, and microbial agents, along with the better overall effect of seaweed-sludge co-fermentation, resulted in higher ammonia nitrogen levels.

[0059] The changes in ammonia nitrogen and humic acid content in Group A, Comparative Example F (F1 and F2), and Comparative Example G are visually presented using line graphs to clearly compare the dynamic changes of key indicators under different conditions. Meanwhile, the fermentation effects of the inoculum concentration gradient groups (Group B), VSS ratio gradient groups (Group C), Vibrio globulin proportion gradient groups (Group D), the remaining comparative example groups, and the combined example group (Group E) are described in detail in text, demonstrating the influence of each variable on the fermentation process and products.

[0060] In the gradient inoculant concentration group experiment (B1-B4), as the inoculant concentration increased from 10... 5 Increase CFU / mL to 10 8 The cfu / mL concentration, ammonia nitrogen production, and humic acid release showed a trend of first increasing and then slightly decreasing, with the concentration at 10... 6 At a concentration of cfu / mL, ammonia nitrogen production and humic acid release reached their maximum. However, when the inoculum concentration was too low (F3 group, 10...), the ammonia nitrogen production and humic acid release reached their maximum. 4 When the concentration of the inoculum is too high (cfu / mL), the fermentation effect may be negatively affected due to the low microbial biomass and relatively insufficient nutrients, resulting in no further increase or even a slight decrease in ammonia nitrogen production and humic acid release. When the inoculum concentration is too high (F4 group, 10...), the fermentation effect is negatively affected. 9 The ammonia nitrogen content (cfu / mL) fluctuates abnormally due to intense competition among microorganisms, which interferes with the normal decomposition and utilization of nitrogenous organic matter and humic acid. Furthermore, the release of humic acid fails to decrease according to the normal trend. This result verifies that a microbial agent concentration of 10... 5 ~10 8 Within the range of cfu / mL, it is more effective in promoting ammonia nitrogen production and humic acid decomposition during the co-fermentation of seaweed sludge.

[0061] For the VSS ratio gradient groups (C1-C6), as the VSS ratio (sludge:algae) gradually increased from 0.5 to 3.0, the ammonia nitrogen production and humic acid release showed a trend of first increasing and then decreasing, reaching their maximum at a VSS ratio (sludge:algae) of 1.5. When the VSS ratio was too low (F5 group, 0.4), the relative content of algae was too high, leading to an imbalance of nutrients available to microorganisms and resulting in lower ammonia nitrogen production and humic acid release. When the VSS ratio was too high (F6 group, 3.5), the proportion of sludge to algae was too large, causing an imbalance of nutrients for microorganisms, resulting in ammonia nitrogen content changes deviating from the normal trend, and the decomposition and utilization of humic acid being interfered with, leading to abnormal changes in release. This result indicates that a VSS ratio within the range of 0.5–3.0 can optimize the co-fermentation of algae and sludge, increase ammonia nitrogen production and humic acid release, and improve fermentation efficiency.

[0062] In the gradient group experiment of Vibrio brevicornu proportion (D1-D4), as the proportion of Vibrio brevicornu increased from 30% to 95%, the ammonia nitrogen production and humic acid release showed a trend of first increasing and then decreasing. When the proportion of Vibrio brevicornu was too low (F7 group, 25%), its role in the microbial community was not significant, and it could not fully exert its promoting effect on fermentation, resulting in low ammonia nitrogen production and humic acid release. When the proportion of Vibrio brevicornu was too high (F8 group, 100%), due to the lack of synergy with other bacterial species, the microbial community structure was unbalanced, the decomposition of nitrogenous organic matter in the sludge was hindered, the ammonia nitrogen content rose slowly and was difficult to reach the normal peak, and the subsequent conversion and utilization were also limited; the decomposition and utilization of humic acid was also ineffective, and the decrease in humic acid release was far less than the normal level, and overall efficient fermentation could not be achieved. Comparative experimental groups F9, F10, F11 and F12 were set up to remove Pseudomonas guarnanense, Bacillus thermophilus, Bacillus tekirae, and Vibrio brevicornu, respectively. During the experiment, the ammonia nitrogen content fluctuated abnormally, with an unstable rate of increase in the early stages and a subsequent downward trend, failing to stabilize within a reasonable range. This indicates that the decomposition and transformation process of nitrogen-containing organic matter was disrupted. Humic acid release was also affected, with a significantly smaller decrease, and the fermentation effect was far inferior to the normal experimental group, fully demonstrating the severe negative impact of the absence of key microbial species on the co-fermentation of seaweed and sludge. This result verifies the importance of maintaining microbial community balance and promoting ammonia nitrogen production and humic acid decomposition during the co-fermentation of seaweed and sludge when the proportion of *Vibrio frenulum* is within the range of 30% to 95% and the microbial species are reasonably combined.

[0063] The combined example groups (E1, E2, E3, E4, E5) were tested within the specified range of multiple parameter combinations. Group E consistently yielded relatively high ammonia nitrogen production and humic acid release. Simultaneously, the settling performance of the treated sludge was significantly improved, and the fermentation products demonstrated good efficiency in practical wastewater treatment applications. The experiments in Group E fully demonstrate that when the parameters are combined according to the numerical ranges specified in this application, synergistic optimization of seaweed-sludge co-fermentation can be achieved, comprehensively improving the quality and performance of the fermentation products.

[0064] The method for promoting carbon source production through co-fermentation of seaweed and sludge using microbial pretreatment, as provided by this invention, significantly improves the acid production efficiency of the fermentation system by utilizing seaweed with high organic matter content and sludge for co-fermentation, enabling efficient recovery of biomass energy from seaweed. Furthermore, by directly applying the VFAs produced during fermentation to wastewater treatment plants, wastewater denitrification efficiency is improved, achieving the goal of simultaneous reduction and resource recovery of sludge and seaweed.

[0065] The method for promoting carbon source production through co-fermentation of seaweed sludge using microbial pretreatment according to the present invention improves fermentation efficiency by adding protease-producing microorganisms through microbial pretreatment. Simultaneously, the added FNA, a green antibacterial agent, may already be present in the wastewater, avoiding additional treatment costs and effectively shortening the fermentation time. Furthermore, the added RL significantly reduces the surface tension of the sludge hydrolysate and has advantages such as low toxicity and easy degradation in the environment. The combined action of FNA and RL enhances the activity of hydrolytic acidifying bacteria while inhibiting the activity of methanogenic bacteria, increasing the amount of available substrate for the hydrolysis fermentation process and thus increasing the accumulation of VFAs. The overall operation process is simple, cost-effective, and has good environmental and economic benefits.

[0066] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for promoting carbon source production through co-fermentation of seaweed sludge using microbial pretreatment, characterized in that, Includes the following steps: Step 1: Add microbial agents with the ability to degrade proteins to the sludge; Step 2: Add free nitrite and rhamnolipid to the sludge obtained in Step 1 and pretreat it in an anaerobic environment; Step 3: Mix the pretreated sludge with seaweed and co-ferment the seaweed and sludge to obtain the supernatant of the fermentation mixture. The supernatant is a seaweed sludge fermentation liquid. The microbial agent is composed of a variety of microbial strains, including Vibrio diabolicus, Pseudomonas guguanensis, Thermobacillus, and Bacillus tequilensis.

2. The method according to claim 1, characterized in that, The concentration of Vibrio diabolicus in the microbial agent is 30% to 95%.

3. The method according to claim 2, characterized in that, The *Vibrio globulus*, *Pseudomonas aeruginosa*, *Bacillus thermophilus*, and *Bacillus tegiratus* are mixed in a ratio of 3:3:3:1, 5:2.5:2:0.5, 7:1.5:1:0.5, 19:0.4:0.4:2, or 6:2:1.5:0.5 to form the microbial agent.

4. The method according to any one of claims 1-3, characterized in that, The concentration of the microbial agent in the sludge is 10. 5 cfu / mL ~10 8 cfu / mL.

5. The method according to any one of claims 1-3, characterized in that, The volume ratio of the microbial agent to the sludge is 1:500 to 1:2000.

6. The method according to claim 1, characterized in that, The seaweed has a water content of 85% to 99%, and in step three, the ratio of the VSS content of the pretreated sludge to the VSS content of the seaweed is in the range of 0.5 to 3.

0.

7. The method according to claim 1, characterized in that, The concentration of free nitrite added to the sludge obtained in step one is 0.3 mg / L to 1.2 mg / L, and the dosage of rhamnolipin added to the sludge is 0.02 g / gTSS to 0.1 g / gTSS.

8. A seaweed sludge fermentation liquid, characterized in that, The seaweed sludge fermentation broth is prepared by the method described in any one of claims 1 to 7, which utilizes microbial pretreatment to promote the co-fermentation of seaweed sludge to produce carbon sources.

9. An application of seaweed sludge fermentation liquid in wastewater treatment, characterized in that, The seaweed sludge fermentation liquid is prepared by the method described in any one of claims 1 to 7, which utilizes microbial pretreatment to promote the co-fermentation of seaweed sludge to produce carbon sources, and the seaweed sludge fermentation liquid can be added as an external carbon source to wastewater for wastewater treatment.

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