Self-nourishing functional agroforestry biomass residue carrier for rapid start of biofilm growth and application thereof

Abstract

The application belongs to the field of environmental engineering and water treatment technology, and specifically discloses a self-nutrition functional type of agroforestry biomass bottom slag carrier for rapidly starting biofilm growth and application thereof. The carrier takes the solid residue bottom slag after direct combustion of agroforestry biomass in a power plant as raw material, continuously and stably releases multiple key elements for microbial growth such as Ca, K, Mg and P in a water environment, significantly promotes the adhesion of microorganisms and the formation of biofilm, and can form a biofilm with a thickness greater than 5 μm on the 27th day under extremely poor nutrition conditions, which is significantly better than a traditional volcanic rock carrier. The heavy metal leaching concentration of the carrier in the water body meets the standard requirements of the Surface Water Environmental Quality Standard (GB 3838-2002), and the environmental safety is good. The application realizes the resource utilization of agroforestry waste, and provides an economic, efficient and green carrier material for the rapid start and stable operation of the biofilm process in poor nutrition water bodies.

Description

Technical Field

[0001] This invention belongs to the field of environmental engineering and water treatment technology, specifically relating to a self-nutritive functional agricultural and forestry biomass bottom residue carrier for rapidly initiating biofilm growth and its application. Background Technology

[0002] In the field of urban and rural river water purification, biofilm technology is widely used due to its high efficiency and low consumption. Its core technology lies in providing a carrier for the attachment and growth of microbial communities. Currently used biofilm carriers, such as inorganic fillers like ceramsite and zeolite, or organic synthetic materials like polyethylene and polyurethane, generally suffer from a fundamental defect: chemical and biological inertness. These carriers only provide physical attachment points for microorganisms and cannot provide any nutritional support themselves. This results in a long initiation period for microbial biofilm formation and slow biomass accumulation in nutrient-poor river water, severely restricting the stability and efficiency of treatment. In addition, traditional carriers either have problems such as high energy consumption and high cost in the preparation process, or they are non-renewable resources, which contradicts the concept of sustainable development in environmental governance. To develop biomass-based, low-cost alternatives, researchers have explored the possibility of using solid wastes such as fly ash and coal bottom slag as carrier materials. However, these materials do not fundamentally change their inert properties, fail to actively promote microbial growth, and their environmental risks and long-term stability remain questionable.

[0003] Bottom ash from direct-fired biomass power plants, a massive amount of solid waste, is currently primarily disposed of through landfill, resulting in resource waste. Notably, this bottom ash exhibits significant potential as a high-quality biofilm carrier due to its physicochemical properties: its porous surface and large specific surface area provide an excellent interface for microbial attachment; more importantly, its chemical composition is rich in essential nutrients for microbial metabolism, such as Ca, K, Mg, Si, and P. This characteristic suggests it has the potential to overcome the limitations of traditional inert carriers, becoming a novel carrier with self-nutrition capabilities. By continuously releasing nutrients into the microenvironment, it can actively stimulate and accelerate microbial colonization and biofilm formation. However, most current research treats similar biomass materials merely as physical filtration media or adsorbents, completely ignoring their core value and application potential as a self-nutrition carrier, fundamentally improving the biofilm formation process through a nutrient slow-release mechanism. Therefore, developing a self-nutrition biofilm carrier based on bottom ash from agricultural and forestry biomass power plants can not only provide an efficient and rapid solution for river water treatment but also achieve high-value resource utilization of solid waste, aligning with the development direction of a green circular economy. Summary of the Invention

[0004] The purpose of this invention is to provide a self-nutritive functional agricultural and forestry biomass substrate carrier for rapidly initiating biofilm growth and its application. This carrier can continuously and slowly release multiple key elements necessary for microbial growth in an aquatic environment, effectively promoting the attachment, accumulation, and proliferation of microorganisms, thereby achieving rapid biofilm formation. The carrier has good environmental safety, and its heavy metal leaching concentrations are all below the relevant national standard limits.

[0005] The objective of this invention can be achieved through the following technical solutions: The application of agricultural and forestry biomass bottom residue as a self-nutritional functional carrier for rapidly initiating biofilm growth in water purification, preferably, the application of agricultural and forestry biomass bottom residue as a self-nutritional functional carrier for rapidly initiating biofilm growth in water purification under extremely oligotrophic / no exogenous nutrient conditions.

[0006] The agricultural and forestry biomass bottom residue is derived from the solid residue after combustion in an agricultural and forestry biomass direct-fired power plant, and its particle size is 12-15 mm.

[0007] The aforementioned agricultural and forestry biomass bottom residue can continuously release Ca, Mg, K, and P into the water body for at least one month, with the concentrations of each element (Ca, Mg, K, and P) ranging from 7.07 to 17.71 mg·L during the first month of release. -1 0.91-3.47 mg·L -1 3.56-5.74 mg·L -1 and 0.08-0.19 mg·L -1 Meanwhile, the leaching concentrations of heavy metals, including As, Co, Cr, Cu, Mn, Ni, Pb, and Zn, in the water body from the agricultural and forestry biomass bottom residue all meet the requirements of the "Surface Water Environmental Quality Standard" (GB 3838-2002).

[0008] Preferably, the agricultural and forestry biomass bottom residue is pretreated before application. The pretreatment includes: impurity removal, sieving, washing, and drying. Specifically, firstly, iron nails and glass impurities in the bottom residue are manually removed; then, bottom residue particles with a diameter of 12-15 mm are collected by sieving; the sieved bottom residue is repeatedly washed with deionized water until the wash water is clear and free of floating ash, and then dried in an oven at 105 ℃ for 24 h before being taken out for use.

[0009] The rapid start-up of biofilm growth refers to the formation of a biofilm with a unit thickness greater than 5 μm within one month in water bodies where the agricultural and forestry biomass bottom residue is used as a self-nutritive functional carrier and only microorganisms are inoculated without additional nutrient sources, and the number of OTUs (Operational Taxonomic Units) of the biofilm is greater than 3000.

[0010] Furthermore, the pH of the water body is 7.0 ± 0.5.

[0011] Furthermore, the solid-liquid ratio (volume ratio) of the agricultural and forestry biomass bottom residue to the water body is 1:5.

[0012] Furthermore, the inoculated microorganisms can come from microorganisms that have detached from the surface of biofilm-forming carriers in actual river water or domestic sewage.

[0013] This invention addresses the problem of long microbial biofilm initiation cycles and low efficiency caused by the surface inertness and lack of nutrients of existing biofilm carriers (such as volcanic rock and ceramsite). It also provides an innovative "waste-to-waste" solution to address the challenge of treating bottom ash from agricultural and forestry biomass power plants. This invention was completed based on the following project: Shanghai Municipal Agricultural Science and Technology Innovation Project, Shanghai Agricultural Science (T2023105), "Using Agriculture to Treat Agriculture: Research and Demonstration of Key Technologies for Improving Rural River Water Quality with Agricultural and Forestry Biomass Ash". The carrier is prepared from bottom ash of agricultural and forestry biomass through simple pretreatment, and compared with existing technologies, it has the following significant advantages: (1) Slow-release effect of key elements. The carrier of this invention is rich in key elements such as Ca, Mg, K, and P, which can be released slowly and sustainably in the aquatic environment. During the first month of release, the concentrations of Ca, Mg, K, and P are 7.07-17.71 mg·L, respectively. -1 0.91-3.47 mg·L -1 3.56-5.74 mg·L -1 and 0.08-0.19 mg·L -1 The overall concentrations of volcanic rock were 2.1-4.1 times, 1.2-3.1 times, 6.0-13.7 times, and 1.9-2.7 times that of volcanic rock, respectively. These concentrations provided essential nutrients for microorganisms, significantly improving their survival rate and metabolic activity, thereby ensuring the robustness and sustainability of biofilm formation.

[0014] (2) Advantages of biofilm formation under self-nutrition conditions. The carrier of the present invention relies on its inherent slow-release characteristics of key elements. Even under the extremely nutrient-poor conditions of deionized water without external nutrient supply, it can achieve rapid attachment of microorganisms and biofilm formation within 11 days, and form a biofilm with a unit thickness of more than 5 μm on the 27th day; while traditional volcanic rock carriers under the same conditions can hardly achieve effective biofilm formation.

[0015] (3) Enhanced microbial community diversity. The carrier of this invention can regulate the aquatic microenvironment by continuously releasing a variety of key elements, promoting the enrichment and succession of dominant functional bacteria, thereby enhancing the richness and stability of the biofilm community. Compared with traditional inert carriers, the biofilm formed by this carrier has higher microbial diversity and is more conducive to the long-term operation of the system.

[0016] (4) Although it is derived from agricultural and forestry biomass combustion by-products, the leaching concentration of heavy metals (such as As, Cd, Pb, etc.) in the carrier of the present invention is far lower than the Class II water limit of the "Surface Water Environmental Quality Standard" (GB 3838-2002) during use, which proves that it is safe for water environment in sewage treatment and does not pose an ecological risk.

[0017] (5) This invention uses agricultural and forestry biomass bottom residue as raw material. The pretreatment process is simple and does not require high-energy-consuming processes such as high-temperature sintering. The preparation cost is significantly lower than that of existing commercial inert carriers. This invention not only realizes the high-value resource utilization of agricultural solid waste, but also reduces the application cost of water treatment materials, thus achieving both good economic and environmental benefits. Attached Figure Description

[0018] Figure 1 The SEM-EDS elemental distribution diagrams of Ca, Mg, K and P on the surfaces of bottom slag (a) and volcanic rock (b) in Example 1 are shown. Figure 2 The X-ray diffraction patterns of the bottom slag (a) and volcanic rock (b) in Example 1 are shown. Figure 3 The following are FTIR analysis diagrams of the bottom ash (a) and volcanic rock (b) in Example 1; Figure 4 The graph shows the changes in the concentrations of heavy metals and toxic elements (a) and nutrients (b) over time during the deionized water leaching process of the bottom slag in Example 2. Figure 5 This is a comparison curve of the concentrations of Ca(a), Mg(b), K(c), and P(d) in deionized water for bottom slag and volcanic rock in Example 3 over time. Figure 6 These are comparative photographs of biofilm adhesion between bottom sediment (right) and volcanic rock (left) under nutrient-poor conditions on days 11 (a) and 27 (b) in Example 4. Figure 7 This is a graph showing the changing trends of effluent water quality indicators of the bottom slag group and the volcanic rock group under oligotrophic conditions in Example 4. Figure 8 The following are CLSM in-situ fluorescence images and corresponding binarized extraction images of biofilms on bottom ash and volcanic rock surfaces in Example 4: (a) is the in-situ fluorescence image of biofilm on bottom ash surface, (b) is its corresponding binarized extraction image; (c) is the in-situ fluorescence image of biofilm on volcanic rock surface, and (d) is its corresponding binarized extraction image. Figure 9 This is a bar chart showing the species composition at the phylum (a) and genus (b) levels of the microbial communities of the bottom ash group and volcanic rock group in Example 4. Detailed Implementation

[0019] The technical solution of the present invention will be further described clearly and completely below with reference to specific embodiments and accompanying drawings. However, this should not be construed as limiting the scope of protection claimed in the claims of the present invention.

[0020] The bottom ash used in this invention originates from the solid residue after combustion in agricultural and forestry biomass direct-fired power plants. The selected biomass raw materials are herbaceous or woody clean fuels, encompassing a variety of common agricultural and forestry wastes, such as corn stalks, wheat stalks, rice stalks, cotton stalks, bagasse, rice husks, peanut shells, and sawdust. It should be noted that the bottom ash material used in this invention specifically refers to the bottom ash remaining at the bottom of biomass direct-fired power plants, excluding fly ash collected in the flue gas treatment system.

[0021] In the following embodiments, the bottom ash sample was collected from the bottom solid residue of a biomass direct-fired power plant in Ma'anshan City, Anhui Province. The combustion process was grate furnace combustion, and the fuel composition consisted mainly of rice straw, wheat straw, and waste wood. X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma (ICP) spectroscopy were performed on the bottom ash sample. The corresponding elemental and compositional analysis results are detailed in Tables 1 and 2.

[0022] The volcanic rock used was purchased from Shenyang Beinong Biotechnology Co., Ltd.

[0023] Table 1. XRF composition analysis of bottom ash and volcanic rocks

[0024] Table 2. ICP analysis of major elements in bottom ash and volcanic rocks

[0025] Example 1

[0026] To verify the nutrient release potential and ecological safety of the agricultural and forestry biomass bottom residue described in this invention as a biofilm carrier in an aquatic environment, this embodiment designed a static leaching experiment, including the following steps: (1) Pretreatment of the carrier: Impurities such as iron nails, glass, and bricks in the bottom ash were manually removed. The bottom ash was repeatedly washed with deionized water until the wash water was clear and free of floating dust. After drying in an oven at 105 ℃ for 24 h, it was taken out and allowed to cool naturally to room temperature. A portion of the bottom ash was screened using a laboratory standard sieve to obtain bottom ash with a particle size of 12-15 mm as the sample to be tested by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Another portion of the bottom ash was ground using a pulverizer and sieved using a laboratory standard sieve to collect the portion smaller than 100 mesh. This portion was stored in a dark and dry place as the sample to be tested by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The same sieving, washing, and drying treatment was performed on the control commercial volcanic rock carrier.

[0027] (2) Testing and Characterization Methods: Elemental surface mapping of typical areas on the support surface was performed using SEM-EDS to analyze the spatial distribution characteristics of key nutrients on the material surface. Before the experiment, the washed and dried bottom ash and volcanic rock samples were sputtered with gold to enhance their conductivity. The mineral phase composition of the support was analyzed using XRD. Cu target Kα radiation was used, with a scanning range (2θ) of 5-90°. Phase identification of diffraction peaks was performed by searching standard PDF cards to reveal the crystal structure characteristics of the bottom ash and volcanic rock. The functional group types on the support surface were analyzed using FTIR. Sample preparation was performed using the KBr pellet method, with a scanning range of 400-4000 cm⁻¹. -1 The resolution is 4 cm. -1 The chemical bond characteristics on the material surface are identified by infrared spectroscopy.

[0028] (3) Characterization results and mechanism analysis: The performance mechanism of the support was further revealed through microscale and phase chemical analysis. First, the SEM-EDS analysis results showed that ( Figure 1 The Ca, Mg, K, and P elements on the surface of the bottom slag carrier of this invention are extremely uniformly distributed and have high signal intensity, which couples with its highly complex loose porous structure, forming dense nutrient sites on the carrier surface; while the nutrient element signals on the surface of the control group volcanic rock are relatively weak. Secondly, XRD analysis shows that... Figure 2The volcanic rocks exhibit the highly crystalline characteristics typical of igneous rocks, with sharp diffraction peaks. Elements such as Ca and Mg are firmly locked within a stable silicate crystal lattice, making them difficult to dissolve and release in conventional water. In contrast, the bottom slag carrier of this invention exhibits significant amorphous dispersion in the low-angle range, indicating the presence of a large amount of amorphous glassy phase. The main crystalline phases consist of quartz (SiO2) providing physical framework support and aluminum phosphate (AlPO4) with moderate solubility. This amorphous structure and moderately soluble phases ensure the slow-release kinetics of phosphorus in aqueous solution. Finally, FTIR analysis shows that… Figure 3 Volcanic rocks are mainly characterized by dense and stable silicon-oxygen bonds (Si-O-Si, 983 cm⁻¹). -1 and 710 cm -1 ) lattice vibration peaks; while the bottom slag support of this invention detected composite peaks of silicon-oxygen bonds and phosphate groups (Si-O-Si, PO4). 3- 1018 cm -1 ) and carbonate (CO3) 2- 1473 cm -1 Characteristic absorption peaks of ). In summary, microscopic phase and surface chemical characterization confirm that, compared with highly lattice-bound inert volcanic rocks, the key elements such as Ca, Mg, K, and P in the bottom slag carrier of this invention are all present in amorphous, non-crystalline or slightly soluble salt forms that are easily dissociated and released in the aquatic environment. They can continuously and stably provide endogenous nutrient supply to the aqueous phase through interfacial micro-dissolution and diffusion mechanisms, thereby actively stimulating the attachment and proliferation of microorganisms.

[0029] Example 2

[0030] To verify the nutrient release potential and ecological safety of the agricultural and forestry biomass bottom residue described in this invention as a biofilm carrier in an aquatic environment, this embodiment designed a static leaching experiment, including the following steps: (1) Pretreatment of the carrier: Manually select impurities such as iron nails, glass, and bricks from the bottom slag. Rinse the bottom slag repeatedly with deionized water until the wash water is clear and free of floating dust. Dry it in an oven at 105 ℃ for 24 h, then remove it and allow it to cool naturally to room temperature. Grind it using a pulverizer. Collect the portion below 100 mesh using a laboratory standard sieve and store it in a dark and dry place for later use.

[0031] (2) Leaching experimental conditions: The pretreated bottom residue was added to deionized water at a solid-liquid ratio of 1:5 (g / mL) and placed in a 33℃ constant temperature air bath shaker. The shaker was used for oscillation at a speed of 150 rpm for 30 days. Supernatant samples were collected on days 1, 3, 5, 7, 10, 14, 17, 21, 25 and 30 after oscillation. The samples were filtered through a 0.45 μm aqueous filter membrane, and the concentration of each element in the filtrate was determined by ICP.

[0032] (3) Heavy metal leaching safety assessment: The heavy metal elements detected included As, Co, Cr, Cu, Mn, Ni, Pb, and Zn. The results showed that ( Figure 4 In (a) of the experiment, trace amounts of As, Co, and Cr were detected in the early stages of leaching, but their concentrations decreased over time, reaching zero after 14 days of leaching. Cu and Zn exhibited a fluctuating pattern of initial leaching, reaching zero in the middle stage, and slightly increasing in the final stage, with their concentrations remaining at extremely low levels below 0.01 mg / L after the 14th day. Ni and Pb had zero concentrations throughout the 30-day experimental period, indicating that these heavy metals pose no risk of environmental release. Although trace amounts of Mn were leached throughout the experimental period, their highest concentrations were all far below 0.1 mg / L, meeting the requirements of the "Surface Water Environmental Quality Standard" (GB 3838-2002).

[0033] (4) Nutrient release kinetics: Detected elements included K, Ca, Mg, and P. The results showed that ( Figure 4 (b) The release of Mg and P elements was relatively low and stable. The release of K and Ca elements exhibited a typical three-stage characteristic: a rapid release period from 0 to 3 days, during which nutrients dissolved rapidly; an adjustment period from 3 to 10 days, during which concentrations fluctuated; and a stable period after 10 days, where the concentrations of each element tended to reach equilibrium. The final stable concentrations were approximately Ca (5.11±0.01) mg / L, K (1.21±0.06) mg / L, Mg (1.29±0.02) mg / L, and P (0.31±0.02) mg / L, respectively.

[0034] In summary, the results of this embodiment show that the agricultural and forestry biomass bottom residue carrier provided by the present invention has the function of slow release of nutrients and good environmental safety, and is a novel self-nutritive carrier suitable for rapid start-up of water treatment biofilm systems.

[0035] Example 3

[0036] This embodiment aims to investigate and compare the nutrient release capacity of the agricultural and forestry biomass bottom residue described in this invention with that of traditional volcanic rock carriers through static leaching experiments under simulated actual reactor filling conditions, thereby objectively evaluating the inherent supply potential of the carrier material as a "self-nutrient source". The process includes the following steps: (1) Pretreatment of the carrier: The bottom ash from the original agricultural and forestry biomass direct-fired power plant was manually sorted to remove non-biomass impurities such as iron nails, glass, and bricks. Large pieces of bottom ash were moderately crushed and then sieved through 12 mm and 15 mm standard sieves in sequence to collect particles with a particle size between 12 and 15 mm as experimental carriers. The sieved particles were repeatedly rinsed with tap water until the effluent was clear, and then soaked and washed three times with deionized water to fully remove surface dust and soluble impurities. The washed particles were placed in an oven at 105 ℃ and dried for 24 h. After being removed, they were stored under dark and dry conditions for later use. The commercial volcanic rock carrier used as a control was sieved, washed, and dried in the same manner as above for later use.

[0037] (2) Static leaching column experimental setup: The pretreated bottom slag and volcanic rock packing were loaded into the reactor, with the packing height to reactor height ratio being 1:5. Deionized water was used in the experiment. No microbial inoculation, aeration, or continuous influent / effluent was performed in the experiment. Water samples were taken every 48 hours for analysis, and elemental concentrations were determined using ICP.

[0038] (3) Analysis of leaching effect: such as Figure 5 As shown, during the 30-day leaching experiment, the bottom ash exhibited a significant endogenous nutrient release capacity in deionized water. The leaching concentrations of key inorganic elements such as Ca, Mg, K, and P were significantly higher than those of the traditional carrier volcanic rock throughout the entire experimental period. Quantitative analysis indicated that the concentrations of Ca, Mg, and K released from the bottom ash ranged from 7.07 to 17.71 mg·L⁻¹. -1 0.91-3.47 mg·L -1 and 3.56-5.74 mg·L -1 The concentrations in the volcanic rock group ranged from 2.44 to 6.42 mg·L⁻¹. -1 0.67-1.81 mg·L -1 and 0.13-1.00 mg·L -1 The overall levels were 2.1-4.1 times, 1.2-3.1 times, and 6.0-13.7 times higher than those of volcanic rock, respectively, and showed a fluctuating upward trend in the later stages of the experiment. Crucially, regarding phosphorus (P), a potentially limiting nutrient for microbial growth, the bottom residue consistently maintained a level of 0.08-0.19 mg·L⁻¹ throughout the experiment. -1 Within the effective concentration range, this represents the trace release level of volcanic rocks (0.03-0.10 mg·L⁻¹). -1 1.9-2.7 times that of ).

[0039] Example 4

[0040] To verify the promoting effect of agricultural and forestry biomass bottom residue as a biofilm carrier on microbial proliferation in an aquatic environment, this embodiment designed a biofilm formation experiment of bottom residue under extremely nutrient-poor conditions (no exogenous nutrient deionized water), with volcanic rock as a control group, including the following steps: (1) Perform carrier pretreatment according to Example 3 (1).

[0041] (2) Biofilm formation experiment setup: At room temperature (25-30℃), an appropriate amount of pretreated bottom slag and volcanic rock packing were loaded into the reactor. The ratio of the packing height to the reactor height was 1:5. The reactor was artificially inoculated with microorganisms. The inoculum source was taken from the mature bottom slag packing material (Vorticella or rotifers were observed on the surface of the carrier) in an agricultural and forestry biomass bottom slag reactor that had been operating stably in the early stage. The microorganisms were placed in deionized water and shaken on a shaker at 150 r·min. -1 Shaking for 1 hour allowed the mature biofilm to detach from the carrier surface, preparing a highly active microbial suspension. The microorganisms attached to the mature carrier surface were a natural, complex, and active microbial community introduced from natural river water or domestic sewage and enriched and evolved over a long period within the self-nutrient microzone of the bottom sediment. The inoculum size was 5 mL per reactor. Aeration was performed on the reactors for 8 hours daily at a gas flow rate of approximately 5 mL / min. Biofilm growth was observed regularly during the experiment, and water samples were taken for testing every 48 hours.

[0042] (3) Water quality index testing: The testing index is NH4 + -N, TP, COD Mn The detection methods are shown in Table 3.

[0043] Table 3 Water quality monitoring indicators and monitoring methods

[0044] (4) Biofilm adhesion: On the 11th day of the experiment ( Figure 6 In (a) of the bottom ash reactor, several distinct pale yellow dot-like bacterial colonies were initially observed on the inner wall of the reactor. The colonies were relatively scattered but had clear outlines. In contrast, the inner wall of the volcanic rock reactor in the control group remained transparent and clear, with no visible signs of microbial attachment or biofilm growth. By the end of the reaction (day 27), as... Figure 6 As shown in (b), the two experimental phenomena show significant differences: a large number of pale yellow-green, patchy biofilms have formed on the inner wall of the bottom ash group, and the colonies have increased in volume and merged with each other to form microbial aggregates with obvious thickness; no large-scale biofilms have formed on the inner wall of the volcanic rock group, and only a very small amount of attached matter can be seen.

[0045] (5) Water quality index analysis: such as Figure 7 As shown, in terms of organic carbon source release, the COD of the bottom ash group and the volcanic rock group in the early stage of the experiment was... MnThe concentrations were all around 3.00 mg / L. With increasing operating time, the two groups showed significant differentiation: the bottom ash group, due to the continuous release of organic matter and the accumulation of microbial secondary metabolites, had a higher COD. Mn The concentration gradually increased and stabilized at around 4.33 mg / L; while the volcanic rock group, lacking additional organic matter replenishment, relied solely on the initial carbon source for microbial consumption, resulting in a final concentration decrease to around 1.55 mg / L. Regarding TP release characteristics, both groups exhibited similar leaching kinetics, showing a trend of initial rapid or slow increase followed by a gradual decrease after reaching a peak. However, the bottom ash group showed a significant advantage in concentration. The peak TP concentration (0.21 mg / L) and stable value (0.13 mg / L) of the bottom ash group were significantly higher than the corresponding values ​​in the volcanic rock group (peak value 0.12 mg / L, stable value 0.05 mg / L). Furthermore, the ammonia nitrogen concentration in both reactors remained at a low level below 0.10 mg / L throughout the operating cycle without statistical difference, indicating that the nitrogen source was not a key limiting factor for growth in this system.

[0046] (6) Microbial index analysis: At the end of the reaction, biofilm samples were taken for observation by confocal laser scanning microscopy (CLSM). The results showed that ( Figure 8 The average thickness of the biofilm formed on the surface of the bottom sediment carrier was 5.38±0.35 μm, significantly higher than that of the volcanic rock group (4.40±0.34 μm), indicating that the bottom sediment was more conducive to microbial attachment and biomass accumulation. High-throughput sequencing analysis based on 16S rRNA genes showed that the number of OTUs observed in the bottom sediment group was 3104, higher than that in the volcanic rock group (2192). As shown in Table 4, the Chao1, Shannon, and Pielou indices of the microbial community in the bottom sediment group were all better than those in the volcanic rock group, indicating that the microbial community in the bottom sediment group had better richness, diversity, and evenness. (From the phylum level...) Figure 9 (a) and genus level ( Figure 9 As shown in the community composition bar chart in (b), the biofilm in the bottom ash group is enriched with more microbial communities that have functions of attachment and colonization, structure maintenance, and low nitrogen adaptation. At the phylum level, the distribution of phyla in the bottom ash group is more balanced. In contrast, the microbial community in the volcanic rock group shows obvious nutrient-limited characteristics and exhibits an "extreme survival strategy" bias, dominated by Firmicutes (thick-walled bacteria) that are tolerant of environmental stress, heterotrophic oligotrophic genera such as Pirellula, and unclassified Oligoflexales (unknown genus of Oligoflexales) that prefer oligotrophic conditions.

[0047] Table 4 Comparison of Alpha diversity indices of microbial communities in deionized water

Claims

1. The application of agricultural and forestry biomass bottom residue as a self-nutritional functional carrier for rapidly initiating biofilm growth in water purification, characterized in that, The agricultural and forestry biomass bottom residue is derived from the solid residue after combustion in an agricultural and forestry biomass direct-fired power plant, and its particle size is 12-15 mm.

2. The application according to claim 1, characterized in that, The aforementioned agricultural and forestry biomass bottom residue can continuously release Ca, Mg, K, and P into the water body for at least one month, with the concentrations of each element (Ca, Mg, K, and P) ranging from 7.07 to 17.71 mg·L during the first month of release. -1 0.91-3.47 mg·L -1 3.56-5.74 mg·L -1 and 0.08-0.19 mg·L -1 .

3. The application according to claim 1 or 2, characterized in that, The agricultural and forestry biomass residue is pretreated before being used. The pretreatment includes: impurity removal, screening, washing, and drying.

4. The application according to claim 3, characterized in that, The pretreatment process is as follows: First, iron nails and glass impurities are manually removed from the bottom slag; then, bottom slag particles with a diameter of 12-15 mm are collected by sieving; the sieved bottom slag is repeatedly washed with deionized water until the wash water is clear and free of floating ash, and then dried in an oven at 105 ℃ for 24 h before being taken out for use.

5. The application according to claim 1 or 2, wherein the agricultural and forestry biomass bottom residue is used as a self-nutritional functional carrier for rapidly initiating biofilm growth in the purification of water bodies under extremely oligotrophic / no exogenous nutrient conditions.

6. The application according to claim 1 or 2, characterized in that, The rapid start-up of biofilm growth refers to the formation of a biofilm with a unit thickness greater than 5 μm within one month in water bodies where the agricultural and forestry biomass bottom residue is used as a self-nutritive functional carrier and no additional nutrient source is added, with the microbial community OTU number of the biofilm being greater than 3000.

7. The application according to claim 1 or 2, characterized in that, The pH of the water body is 7.0 ± 0.

5.

8. The application according to claim 1 or 2, characterized in that, The solid-liquid ratio of the agricultural and forestry biomass bottom residue to the water body is 1:5.

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