A method for modifying biogenic carbon and humic acid-iron step-by-step anchoring and application thereof

Abstract

This invention belongs to the field of solid waste resource utilization technology, specifically relating to a biochar from sludge residue, a stepwise anchoring modification method for humic acid and iron, and their applications. Raw biochar from sludge residue is added to a humic acid suspension, the pH is adjusted to 3.5-4.5, and the mixture is kept at a constant temperature of 25-30℃ and shaken for 8-12 hours. After filtration and drying, pre-coated biochar is obtained. The pre-coated biochar is then added to Fe... 2+ In a salt solution, the pH is adjusted to 6.0-6.5, and the mixture is kept at a constant temperature of 35-40℃ and shaken for 6-10 hours. It is then washed until neutral and dried at 80℃. This invention breaks through the traditional one-step blending method in its preparation process. Based on the principles of intermolecular forces and coordination chemistry, a stepwise process of "humic acid pre-coating - iron ion directional anchoring" is designed. The resulting modified biochar from sludge residue, when applied to the co-digestion of sludge and kitchen waste, simultaneously increases the production of lapis lazuli, the enrichment of VFA, and the removal rate of grease, overcoming the limitations of single-function enhancement.

Description

Technical Field

[0001] This invention belongs to the field of solid waste co-treatment and functional material modification technology, specifically involving a biochar from sludge residue, a stepwise anchoring modification method for humic acid and iron, and its application. Background Technology

[0002] Co-digestion of sludge and food waste is an important approach to achieving solid waste reduction and resource recovery. However, its industrial application has long been limited by three major technical bottlenecks: difficulty in stable phosphorus fixation, low enrichment efficiency of volatile fatty acids (VFAs), and poor recyclability of functional materials. To address these issues, researchers have attempted to enhance the co-digestion process through biochar modification technology. Among these, the composite modification of humic acid and iron salts has become a research hotspot due to its combined electron transfer and phosphorus fixation functions. However, existing technologies have consistently failed to break free from the mindset of "one-step co-modification," resulting in the following fundamental contradictions that persist and cannot be resolved through conventional methods:

[0003] 1. Insufficient stability of the binding between humic acid and biochar. Humic acid molecules contain a large number of polar functional groups such as carboxyl groups (-COOH) and hydroxyl groups (-OH). Under neutral or alkaline conditions, they easily ionize into negatively charged anions, which electrostatically repel the negatively charged surface of biochar (which is usually negatively charged after pyrolysis). This results in the two only being able to bind through physical adsorption (binding energy <20kJ / mol). Under the stirring and hydraulic scouring of co-digestion, the humic acid shedding rate is as high as 30%~50%, which cannot continuously provide an electron transport carrier for acid-producing bacteria (loss of quinone function) and cannot stably adsorb oils (inhibition rebound). In existing technologies, even by increasing the amount of humic acid (more than 20% of the biochar mass), the shedding rate can only be slightly reduced (still >20%), and the excessive humic acid will block the pores of the biochar, thus reducing the VFA adsorption capacity.

[0004] 2.Fe 2+ Its effective loading and sustained-release performance are poor. Fe 2+ It is a key raw material for the formation of lapis lazuli (Fe3(PO4)2·8H2O), but its chemical properties are highly reactive, presenting two major problems in one-step blending systems: ① It readily reacts with water to form ferrous hydroxide precipitate (precipitation rate >60% at pH>6.0), making it unable to effectively complex with humic acid; ② Even with a small amount of complexation, the weak binding force (mainly physical adsorption) leads to rapid release (release rate >80% within 7 days), while the co-digestion cycle typically lasts 25-30 days, and the later stages are affected by Fe... 2+ Insufficient phosphorus fixation led to a sharp drop in phosphorus fixation rate (from 50% in the early stage to 20% in the later stage). Researchers had previously attempted to use Fe... 3+ Fe replacement 2+ (Higher stability), but Fe 3+ It cannot directly participate in the synthesis of lapis lazuli; it requires microbial reduction within the system, which is far less efficient than directly using Fe.2+ .

[0005] 3. Lack of Matching Between Modification Processes and Co-digestion Requirements. Co-digestion of sludge and food waste can achieve the synergistic treatment of dual solid wastes, with core benefits including: ① Complementary carbon-to-nitrogen ratios, overcoming the bottleneck of single digestion of high-carbon food waste and high-nitrogen sludge, improving digestion stability and efficiency; ② Increased solid waste reduction rate by more than 30%, reducing dual treatment costs and environmental pressure; ③ Enhanced resource output such as VFA and biogas, simultaneously achieving phosphorus fixation and carbon source recovery, improving comprehensive resource utilization benefits. However, the core requirement of the co-digestion system for modified biochar is "continuous supply of Fe". 2+ "Highly efficient electron transfer + stable adsorption capacity," but one-step blending modification cannot achieve this synergy: increasing the reaction temperature (>40℃) to accelerate the combination of humic acid and biochar will lead to Fe... 2+ The oxidation rate increases by 2-3 times; lowering the pH (<5.0) inhibits Fe. 2+ Precipitation inhibits the ionization of humic acid, reducing its binding efficiency with biochar by 40%. This "conditional conflict" is an inherent defect that cannot be overcome by a one-step method. Those skilled in the art have long been limited by the understanding of "simplified process through single-step reaction" and have never realized that this contradiction needs to be resolved through step-by-step control. To date, no literature or patent has proposed a "step-by-step anchoring" solution, proving that this technical bottleneck is not obviously difficult to solve. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a stepwise anchoring modification method for biochar from sludge and humic acid-iron, and its application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for stepwise humic acid-iron anchoring modification of biochar from biogas residue, comprising humic acid pre-coating and iron ion directional anchoring; humic acid pre-coating: adding raw biogas residue biochar to a humic acid suspension, adjusting the pH to 3.5-4.5, constant temperature shaking at 25-30℃ for 8-12 hours, filtering and drying to obtain pre-coated biochar; iron ion directional anchoring: adding Fe... 2+ In a salt solution, adjust the pH to 6.0-6.5, maintain a constant temperature of 35-40℃ and shake for 6-10 hours, wash until neutral, and dry at 80℃ to obtain humic acid-iron stepwise anchored modified biochar.

[0008] Preferably, the method further includes: preparation of raw biogas residue biochar: after washing, drying and crushing, the biogas residue is subjected to hydrothermal reaction at 160~220℃ for 2~4 hours under a nitrogen atmosphere, and then ground and sieved to 100~200 mesh to obtain raw biogas residue biochar; stepwise modification: the raw biogas residue biochar first undergoes a humic acid pre-coating reaction, and then obtains pre-coated biochar through solid-liquid separation; the pre-coated biochar then undergoes an iron ion directional anchoring reaction to finally obtain modified biogas residue biochar.

[0009] Preferably, the concentration of the humic acid suspension is 5-15 g / L, and the solid-liquid ratio is 1:15-1:25; the Fe... 2+ The salt solution concentration is 0.5~2 mol / L, and the solid-liquid ratio is 1:10~1:20; the solid-liquid ratio is in g / mL.

[0010] Preferably, the humic acid is an industrial-grade product with a palm humic acid content of ≥70%, and the suspension is prepared into a uniform colloid by ultrasonic dispersion.

[0011] Preferably, Fe 2+ The salt is a mixture of ferrous sulfate and ferrous chloride.

[0012] A biochar made from biogas residue modified using the humic acid-iron stepwise anchoring modification method described above.

[0013] The application of modified biochar prepared by the above method in the co-digestion of sludge and kitchen waste includes the construction of the co-digestion system and process control. Construction of the co-digestion system: sludge and kitchen waste were mixed substrates at a dry weight ratio of 1:1 to 3:1, with modified biochar as the inoculum at a dosage of 2% to 8%. The volume ratio of inoculum to mixed substrate was 1:1 to 1:2 (dry weight), with a total solids content of 6% to 10% and an initial pH of 6.5 to 7.2. Process control: anaerobic environment at 35 to 37℃, with the oxidation-reduction potential (ORP) controlled at -220 to -160 mV, digestion lasting 25 to 30 days. Intermittent stirring was used for the first 12 days, followed by static reaction after 12 days, simultaneously achieving the formation of lapis lazuli and the enrichment of volatile fatty acids (VFA).

[0014] Preferably, the process is controlled by intermittent stirring at 120~180 r / min, with each stirring session lasting 30~40 min and an interval of 1~2 h.

[0015] Preferably, co-digestion also includes: product separation and resource recovery and recycling.

[0016] Preferably, recycling includes:

[0017] Biochar feedstock recycling: Hydrothermal biochar is mixed with fresh biogas residue at a mass ratio of 1:9 to 3:7 and returned to the original biogas residue biochar preparation process; and / or,

[0018] Co-digestion auxiliary circulation: Hydrothermal char and stepwise anchored modified biochar are mixed at a mass ratio of 1:3 to 1:5 and added together to the co-digestion system.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. A stepwise anchoring modification method using humic acid-iron is employed. In the pre-coating stage, humic acid tightly binds to biochar via hydrogen bonds and π-π stacking. Unlike traditional physical adsorption, the bond between humic acid and biochar is stable, and the humic acid is not easily detached under the stirring and hydraulic scouring during co-digestion. In the anchoring stage, Fe... 2+ It forms coordination bonds with the carboxyl / quinone groups of humic acid, without free precipitation, unlike traditional mixed physical loading, to achieve Fe 2+ Slow-release.

[0021] 2. Compared with traditional one-step blending modification, the modified biochar prepared by this invention improves the production of lapis lazuli, the enrichment of VFA and the removal rate of oil through a synergistic mechanism of "adsorption-complexation-reduction", thus breaking through the limitations of single-function enhancement.

[0022] 3. The quinone group of humic acid acts as an electron shuttle, accelerating the electron transfer in the metabolism of acid-producing bacteria and increasing the VFA generation rate; the porous structure of modified biochar adsorbs VFA, reducing the free concentration in the liquid phase and decreasing the probability of degradation by methanogenic bacteria; humic acid and biochar synergistically adsorb oils, preventing oils from encapsulating microorganisms and ensuring a stable acid-producing environment.

[0023] 4. In co-digestion applications, under a strong reducing environment (ORP = -220~-160mV), the endogenous Fe in the sludge is activated. 3+ Reduced to Fe 2+ A dual iron source system of "external + internal" was constructed, with relatively abundant iron source, combined with PO4 adsorption on the surface of biochar. 3- , forming "Fe 2+ -PO4 3- "High-concentration micro-regions promote the crystallization of vivianite (Fe3(PO4)2·8H2O), with a phosphorus fixation rate of ≥60%."

[0024] 5. Coordinated Fe 2+ The slow release, combined with the synergistic effect of humic acid electron transport, results in electron transport efficiency far exceeding that of traditional methods.

[0025] In summary, this invention breaks through the traditional mindset of one-step blending in preparation method. Based on the principles of intermolecular forces and coordination chemistry, it designs a stepwise process of "humic acid pre-coating - iron ion directional anchoring". The modified biochar obtained is applied to the co-digestion of sludge and kitchen waste, which simultaneously increases the amount of blue iron ore generated, VFA enrichment and oil removal rate, thus overcoming the limitations of single-function enhancement. Attached Figure Description

[0026] Figure 1 Flowchart of the entire process of humic acid-iron stepwise anchoring modification and enhanced co-digestion-hydrothermal carbon cycle.

[0027] Figure 2Figure 1 shows a comparison of SEM characterization of stepwise modified biochar and traditional biochar. Figure 2 shows the stepwise modified biochar of the biogas residue in this application, and Figure 3 shows the original biogas residue biochar. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0029] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0030] A method for stepwise anchoring modification of humic acid and iron in biochar from biogas residue and its application, combined with Figure 1 Understanding, detailed technical solution introduction:

[0031] (a) Humic acid-iron stepwise anchoring modification

[0032] (1) Preparation of biochar from raw biogas residue:

[0033] The biogas residue used in this invention is derived from the solid residue after anaerobic digestion of organic solid waste. The organic solids mainly include sludge, kitchen waste, straw, and livestock manure. After being washed and desalinated, the recovered biogas residue is dried at 105℃ for 12-24 hours and then crushed through a 40-mesh sieve. It is then pyrolyzed in a tubular furnace under a nitrogen atmosphere (0.8-1.2 L / min, preferably 1.0 L / min) at a rate of 10℃ / min to 160-220℃ for 2-4 hours. After cooling, it is ground through a 100-200 mesh sieve to obtain raw biogas residue biochar with a specific surface area of ​​220-320 m². 2 / g.

[0034] (2) Humic acid pre-coating:

[0035] Preparation of humic acid suspension: Weigh humic acid (purity greater than 70%), add deionized water to prepare a 5~15 g / L suspension, solid-liquid ratio 1:15~1:25 (g / mL), ultrasonically disperse at 300W for 10~15 min to form a uniform colloid and avoid agglomeration.

[0036] Coating reaction: Add raw biochar at a solid-liquid ratio of 1:15~1 / 25, adjust the pH to 3.5~4.5 with dilute hydrochloric acid (this pH is precisely selected to inhibit carboxyl ionization while ensuring hydroxyl activity); shake at 25~35℃ and 120~150 rpm for 8~15 h. After filtration, dry at 80℃ for 6~8 h to obtain pre-coated biochar with a humic acid loading of 12~18 mg / g and a specific surface area of ​​210~300 m². 2 / g. Among them, the pH of the humic acid pre-coating is controlled at 3.5~4.5. Under this pH condition, the humic acid is tightly bound to the hydroxyl groups on the surface of biochar through hydrogen bonds, so that the humic acid shedding rate is less than 5%.

[0037] (3) Iron ion directional anchoring:

[0038] Fe 2+ Mixed salt solution: Prepare a 0.5~2.0 mol / L ferrous sulfate-ferrous chloride mixed solution at a molar ratio of 1:1-1 / 2, and aerate with nitrogen for 5~15 min to remove oxygen, avoiding Fe... 2+ Pre-oxidation.

[0039] Complexation reaction: Add pre-coated biochar at a solid-liquid ratio of 1:10~1:20 (g / mL), and adjust the pH to 6.0~6.5 with sodium hydroxide (weakly acidic conditions promote -COO) - (To generate and enhance coordination), the mixture is kept at 35-40℃ and 120-150 r / min for 6-10 h (under nitrogen protection throughout, flow rate 0.3-0.8 L / min). After the reaction, the mixture is washed with deionized water until the filtrate is neutral, dried at 80℃ for 10-14 h, and the modified biochar is anchored stepwise.

[0040] (II) Co-digestion and application and hydrothermal carbon recovery

[0041] 1. Construction and parameter control of the co-digestion system

[0042] Substrate pretreatment: Kitchen waste is crushed (particle size ≤ 5mm) to remove inert impurities (bones, plastics, etc.), and sludge is filtered by plate and frame filter press (moisture content reduced to 80%~85%). Sludge and kitchen waste are mixed at a dry weight ratio of 1:1~3:1, and the carbon-nitrogen ratio (C / N) is adjusted to 20~30:1 (by adding a small amount of straw powder or urea for fine adjustment).

[0043] Functional carrier addition: Stepwise anchored modified biochar is added to the mixed substrate at a dosage of 2% to 8% of the dry weight of the mixed substrate (low dosage is suitable for small-scale systems, while high dosage enhances the treatment of high-oil food waste); at the same time, anaerobic inoculum (taken from the anaerobic digester of a municipal wastewater treatment plant) is added, with the volume ratio of inoculum to mixed substrate being 1:1 to 1:2, and the total solids content is adjusted to 6% to 10% to avoid excessive viscosity affecting mass transfer.

[0044] Environmental control: The initial pH was adjusted to 6.5-7.2 with 0.1 mol / L hydrochloric acid or sodium hydroxide; the reaction apparatus was purged with nitrogen for 30 min to remove oxygen, then sealed to maintain a mesophilic anaerobic environment at 35-37℃. For the first 12 days, intermittent stirring (120-180 r / min, 30-40 min each time, 1-2 h interval) was used to promote sufficient contact between the modified biochar and the substrate; after 12 days, the reaction was allowed to stand to reduce VFA volatilization loss. Throughout the process, the ORP was adjusted to -220 to -160 mV via online monitoring (a small amount of sodium sulfite was added if necessary to maintain a reducing environment). The digestion cycle was 25-30 days, simultaneously achieving lapis lazuli formation (phosphorus fixation ≥65%) and VFA enrichment (concentration ≥9500 mg / L).

[0045] The underlying principles are explained, including the VFA enrichment mechanism and the formation mechanism of lapis lazuli.

[0046] (1) VFA enrichment mechanism

[0047] ① The quinone group of humic acid acts as an electron shuttle, accelerating the metabolic electron transfer of acid-producing bacteria (such as Clostridium) and increasing the VFA production rate (30% higher than the unmodified group).

[0048] ② The porous structure of modified biochar adsorbs VFA, reducing the free concentration in the liquid phase and decreasing the probability of degradation by methanogenic bacteria (such as Methanobacterium);

[0049] ③ Humic acid and biochar work together to adsorb oils, preventing oils from encapsulating microorganisms and ensuring a stable acid-producing environment (oil removal rate ≥60%).

[0050] (2) Formation mechanism of blue iron ore

[0051] ④ The carboxyl and hydroxyl groups of humic acid and Fe 2+ Formation of stable complexes to achieve Fe 2+ Slow-release (release period extended to more than 15 days);

[0052] ⑤ Under a strong reducing environment (ORP=-220~-160mV), humic acid mediates the reduction of Fe in sludge. 3+ (Residual iron from phosphorus removal) is reduced to Fe. 2+ Replenish endogenous iron sources;

[0053] ⑥ PO4 adsorption on biochar surface 3- , forming "Fe 2+ -PO4 3- "High-concentration micro-regions promote the crystallization of vivianite (Fe3(PO4)2·8H2O), with a phosphorus fixation rate of ≥60%."

[0054] 2. Product separation and resource recovery

[0055] After digestion, the liquid and solid phases are separated by plate and frame filtration (pressure 0.2~0.3MPa) or centrifugation (3000~4000r / min, 15min): the liquid phase is subjected to vacuum distillation (temperature 80~90℃, vacuum degree 0.08MPa) to recover VFA (mainly acetic acid and propionic acid, purity ≥90%); the solid residue (containing undegraded organic matter, blue iron crystals, and modified biochar) is collected for later use.

[0056] 3. Hydrothermal carbon recovery and recycling

[0057] Hydrothermal carbonization treatment: Solid residue and deionized water are added to a hydrothermal reactor at a solid-liquid ratio of 1:5~1:10 (g / mL). After sealing, the temperature is increased to 180~220℃ at a rate of 5~10℃ / min, maintaining an autogenous pressure of 1.0~2.0MPa, and the reaction is carried out for 2~4 hours (temperature and time synergistically regulate the pore structure of hydrothermal carbon: low temperature and long time are conducive to the retention of functional groups, while high temperature and short time increase the specific surface area). After the reaction, the mixture is naturally cooled to room temperature, the solid phase is separated by filtration, and the filtrate is washed with deionized water until the pH reaches 6.5~7.5. The filtrate is then vacuum dried at 80℃ for 10~12 hours, ground through a 100~200 mesh sieve to obtain hydrothermal carbon (specific surface area 250~400m²). 2 / g, with surface hydroxyl and carboxyl content of 1.2~1.8mmol / g).

[0058] Loop path:

[0059] ① Biochar raw material recycling: Hydrothermal carbon and fresh biogas residue are mixed at a mass ratio of 1:9~3:7 and returned to step (1) (1) original biogas residue biochar preparation process (high carbon content of hydrothermal carbon can increase biochar yield by 5%~10%).

[0060] ② Co-digestion auxiliary circulation: Hydrothermal char and stepwise anchored modified biochar are mixed at a mass ratio of 1:3 to 1:5 and added together to the co-digestion system (utilizing the high adsorption capacity of hydrothermal char to assist in the removal of oils and increase VFA enrichment by 5% to 8%).

[0061] Example 1: This is the baseline group, and the parameters used are defined as standard parameters.

[0062] Stepwise anchoring modification: Anaerobic fermentation biogas residue from a municipal wastewater treatment plant was repeatedly washed three times with deionized water until the conductivity of the filtrate was <500μS / cm. It was then dried at 105℃ for 12 hours and crushed by a universal pulverizer before passing through a 40-mesh sieve. The pretreated biogas residue was placed in a tubular furnace, and nitrogen gas was introduced (flow rate 1.0L / min). The temperature was increased to 600℃ at a rate of 10℃ / min and pyrolyzed at a constant temperature for 3 hours. After natural cooling, it was ground through a 150-mesh sieve to obtain the original biogas residue biochar. Prepare a 10 g / L humic acid suspension (70% humic acid content), ultrasonically disperse it at 300 W for 15 min to form a uniform colloid, add the original biochar residue to the suspension at a solid-liquid ratio of 1:20 (g / mL), adjust the pH of the system to 4.0 with 0.1 mol / L hydrochloric acid, place it in a constant temperature water bath shaker, shake at 28℃ and 120 r / min for 10 h, filter, and dry at 80℃ for 8 h to obtain humic acid pre-coated biochar (humic acid loading 15 mg / g). Prepare a 1.0 mol / L mixed salt solution of ferrous sulfate and ferrous chloride in a 1:1 molar ratio. Aerate the solution with nitrogen gas for 10 min to remove dissolved oxygen. Add pre-coated biochar at a solid-liquid ratio of 1:15 (g / mL). Adjust the pH to 6.2 with 0.1 mol / L sodium hydroxide. Place the solution in a 38℃ constant temperature water bath shaker and shake at 140 r / min for 8 h, maintaining nitrogen protection throughout (flow rate 0.5 L / min). After the reaction, wash with deionized water until the pH of the filtrate is 6.5~7.5. Dry at 80℃ for 12 h to obtain stepwise anchored modified biochar.

[0063] Anaerobic co-digestion process: Food waste is manually sorted to remove inert impurities such as bones and plastics, then crushed to a particle size ≤5mm using a high-speed crusher. After drying at 105℃, the moisture content is measured to be 78% and the volatile solids (VS) content is 82%. Wastewater from municipal wastewater treatment plants is filtered through a plate and frame filter press to a moisture content of 82%, with a VS content of 65% and a total phosphorus content of 18mg / g. Sludge and food waste are mixed at a dry weight ratio of 2:1, with a small amount of straw powder added to adjust the carbon-to-nitrogen ratio (C / N) to 25:1, controlling the total solids content of the mixed substrate to 8%. 2kg of the above mixed substrate is added to a 5L anaerobic digester, followed by stepwise anchored modified biochar (5% of the dry weight of the mixed substrate), and then anaerobic inoculum (taken from the anaerobic digester of a municipal wastewater treatment plant, with a VS content of 70%). The volume ratio of inoculum to mixed substrate is controlled at 1:1.5, and deionized water is used to replenish the digester to 80% of its effective volume. The initial pH of the system was adjusted to 7.0 using 0.1 mol / L hydrochloric acid or sodium hydroxide. Nitrogen gas was introduced into the fermenter for 30 minutes to completely remove oxygen. After sealing, the fermenter was placed in a constant temperature water bath to maintain the reaction temperature at 37°C. For the first 12 days, an intermittent stirring mode was used, with a stirring rate of 150 r / min, stirring for 40 minutes each time with an interval of 1.5 hours. After 12 days, stirring was stopped and the system was allowed to stand. The redox potential of the system was monitored in real time using an online ORP monitor. When the ORP was higher than -190 mV, sodium sulfite solution was added in small amounts several times to maintain the ORP stable at around -190 mV. The digestion cycle lasted for 28 days. During this period, VFA concentration and pH value were measured at regular intervals every day. After digestion, the amount of lapis lazuli and the oil removal rate were measured.

[0064] Results: Modified biochar Fe 2+ Loading amount 112 mg / g (coordinated state ratio 91%), blue iron ore formation 26.8 mg / g, VFA concentration 10600 mg / L, oil removal rate 70%.

[0065] Example 2: Fe in this example 2+ The salt ratio was adjusted, with an increased proportion of ferrous sulfate.

[0066] Stepwise anchoring modification: The preparation of original biochar from sludge and the pre-coating steps with humic acid are the same as in Example 1; a 1.0 mol / L mixed salt solution of ferrous sulfate and ferrous chloride in a molar ratio of 2:1 is prepared, and the remaining iron ion anchoring conditions (nitrogen aeration for 10 min, solid-liquid ratio of 1:15, pH 6.2, 38℃, shaking at 140 r / min for 8 h, and nitrogen flow rate of 0.5 L / min) are consistent with those in Example 1.

[0067] Anaerobic co-digestion process: The pretreatment parameters of kitchen waste and sludge, mixing ratio (dry weight ratio 2:1), C / N adjustment (25:1), and total solids content control (8%) were the same as in Example 1. 2 kg of mixed substrate was added to a 5L anaerobic digester, along with 5% (dry weight of mixed substrate) of modified biochar. The inoculum to mixed substrate volume ratio was 1:1.5. Deionized water was added to 80% of the effective volume, and the initial pH was adjusted to 7.0. After purging with nitrogen for 30 min, the digester was sealed and reacted in a constant temperature water bath at 37℃. For the first 12 days, the mixture was intermittently stirred (150 r / min, 40 min each time, 1.5 h interval). After 12 days, the mixture was allowed to stand. The ORP was maintained at -190 mV throughout the process. Digestion lasted 28 days. VFA concentration and pH were monitored daily at regular intervals. Target indicators were tested after the digestion was completed.

[0068] Result: Fe 2+ Loading amount 125mg / g (coordinated state accounts for 93%), vivianite 28.1mg / g, VFA 10300mg / L, oil removal rate 68%.

[0069] Example 3: This example is the high humic acid loading group.

[0070] Stepwise anchoring modification: The preparation of original biochar from sludge was the same as in Example 1; a 15 g / L humic acid suspension (70% humic acid content) was prepared, ultrasonically dispersed at 300 W for 15 min, and the original biochar was added at a solid-liquid ratio of 1:20. The pH was adjusted to 4.0, and the mixture was shaken at 28℃ and 120 r / min for 10 h. After filtration and drying, humic acid pre-coated biochar (humic acid loading 18 mg / g) was obtained; the iron ion anchoring steps (mixed salt ratio 1:1, concentration 1.0 mol / L, solid-liquid ratio 1:15, pH 6.2, etc.) were the same as in Example 1.

[0071] Anaerobic co-digestion process: Food waste was crushed to a particle size ≤5mm (moisture content 78%, VS 82%), and sludge was filtered to a moisture content of 82% (VS 65%, total phosphorus 18mg / g). The waste was mixed at a dry weight ratio of 2:1, and the C / N ratio was adjusted to 25:1 with a total solids content of 8%. 2kg of mixed substrate was added to a 5L fermenter, along with 5% modified biochar. The inoculum to mixed substrate volume ratio was 1:1.5. Deionized water was added to 80% of the volume, and the initial pH was adjusted to 7.0. Nitrogen gas was purged for 30 minutes to remove oxygen, and the mixture was sealed and reacted in a 37℃ constant temperature water bath. For the first 12 days, the mixture was intermittently stirred (150r / min, 40min / time, 1.5h interval). After 12 days, the mixture was allowed to stand, maintaining the ORP stable at -190mV. Digestion lasted for 28 days, with daily sampling and monitoring. The indicators were tested after the digestion was completed.

[0072] Results: Humic acid shedding rate was 4.2%, electron transport rate increased by 20%, VFA concentration was 11000 mg / L, vivianite concentration was 25.5 mg / g, and oil removal rate was 69%.

[0073] Example 4: This example is a high proportion of food waste group. The modified biochar is exactly the same as in Example 1, but the specific application has changed.

[0074] Stepwise anchoring modification: All modification steps (biochar preparation, humic acid pre-coating, iron ion anchoring) are completely consistent with those in Example 1.

[0075] Anaerobic co-digestion process: Food waste pretreatment was the same as in Example 1 (particle size ≤ 5mm, moisture content 78%, VS 82%), and sludge pretreatment was the same as in Example 1 (moisture content 82%, VS 65%, total phosphorus 18mg / g). Sludge and food waste were mixed at a dry weight ratio of 1:1, and a small amount of urea was added to adjust the C / N ratio to 30:1, controlling the total solids content of the mixed substrate to 6%. 2kg of the above mixed substrate was added to a 5L anaerobic digester, along with 5% (dry weight of the mixed substrate) of modified biochar. The inoculum to mixed substrate volume ratio was 1:1.5, and deionized water was added to... The effective volume was 80%, the initial pH was adjusted to 6.9, nitrogen gas was introduced for 30 minutes to remove oxygen, and then the container was sealed and placed in a 37℃ constant temperature water bath for reaction. For the first 12 days, an intermittent stirring mode was used, with the stirring rate increased to 170 r / min, each stirring for 40 minutes with an interval of 1.5 h, to enhance the mass transfer efficiency of the high oil substrate. After 12 days, stirring was stopped and the container was allowed to stand. Throughout the process, sodium sulfite was added to maintain the ORP at around -180 mV. The digestion cycle was 29 days. VFA concentration, pH value and oil content were measured daily at regular intervals. After digestion, the amount of lapis lazuli was measured.

[0076] Results: The oil removal rate was 75%, the VFA concentration was 11500 mg / L, the vivianite concentration was 24.3 mg / g, and the pH of the system remained stable at 6.8~7.1.

[0077] Example 5: Low modified biochar dosage group.

[0078] Stepwise anchoring modification: The modification process is completely consistent with that of Example 1.

[0079] Anaerobic co-digestion process: The pretreatment parameters of kitchen waste and sludge, mixing ratio (dry weight ratio 2:1), C / N adjustment (25:1), and total solids content control (8%) were the same as in Example 1; 2 kg of mixed substrate was added to a 5L anaerobic digester, and the amount of modified biochar added was reduced to 2% of the dry weight of the mixed substrate. The remaining operations (inoculum ratio 1:1.5, adding deionized water to 80% of the volume, adjusting the initial pH to 7.0, and purging with nitrogen for 30 min for oxygen removal) were the same as in Example 1; after sealing, the digester was placed in a 37℃ constant temperature water bath, and intermittently stirred for the first 12 days (150 r / min, 40 min / time, 1.5 h interval). After 12 days, the digester was allowed to stand, maintaining the ORP at -190 mV. The digestion was carried out for 28 days, and the system indicators were sampled and monitored daily. The target performance parameters were measured after the digestion was completed.

[0080] Results: The concentrations of lapis lazuli (18.5 mg / g), VFA (9200 mg / L), and grease removal rate were 60%, which were 50%, 41%, and 43% higher than those of the control group (lapis lazuli (12.3 mg / g), VFA (6500 mg / L), and grease removal rate (42%), respectively.

[0081] Example 6: Hydrothermal char recycling path ①: Biochar raw material.

[0082] Stepwise anchoring modification and first co-digestion: The modification process and the first anaerobic co-digestion process are completely consistent with those in Example 1. After digestion, the solid residue is collected.

[0083] Hydrothermal char preparation and recycling modification: The collected solid residue and deionized water were added to a hydrothermal reactor at a solid-liquid ratio of 1:8 (g / mL). After sealing, the temperature was increased to 200℃ at 5℃ / min, and the autogenous pressure was maintained at 1.5MPa for 3 hours. After natural cooling to room temperature, the mixture was filtered and washed with deionized water until the pH of the filtrate was 6.5~7.5. The filtrate was then vacuum dried at 80℃ for 12 hours and ground through a 150-mesh sieve to obtain hydrothermal char. The hydrothermal char was mixed with fresh biogas residue at a mass ratio of 2:8, and the biochar preparation (pyrolysis at 600℃ for 3 hours), humic acid pre-coating, and iron ion anchoring steps of Example 1 were repeated to obtain recycled modified biochar.

[0084] Cyclic anaerobic co-digestion process: Anaerobic digestion was carried out according to the co-digestion parameters of Example 1 (substrate dry weight ratio 2:1, C / N 25:1, total solids content 8%, modified biochar addition 5%, inoculum ratio 1:1.5), with the reaction temperature controlled at 37°C. For the first 12 days, the mixture was intermittently stirred (150 r / min, 40 min / time, 1.5 h interval). After 12 days, the mixture was allowed to stand, maintaining an ORP of -190 mV, and digestion was carried out for 28 days. The above steps were repeated 3 times, and the co-digestion process and results of the third cycle were recorded.

[0085] Results (Cycle 3): Modified biochar Fe 2+ With a loading of 98 mg / g (88% in coordinated state), 23.2 mg / g of lapis lazuli, 9800 mg / L of VFA, a grease removal rate of 66%, a performance retention rate of 86%, and a biochar raw material cost that is 18% lower than that of the non-recycled group.

[0086] Example 7: Hydrothermal carbonization low-temperature group.

[0087] Stepwise anchoring modification and co-digestion: The modification process and anaerobic co-digestion process are the same as in Example 1. After digestion, the solid residue is collected.

[0088] Hydrothermal char preparation and auxiliary circulation co-digestion: Solid residue and deionized water were added to a hydrothermal reactor at a solid-liquid ratio of 1:8 (g / mL). After sealing, the temperature was increased to 180°C at 5°C / min, and the autogenous pressure was maintained at 1.0 MPa. The reaction was carried out at a low temperature for 4 hours. After cooling, the mixture was filtered and washed until neutral, and then vacuum dried at 80°C for 12 hours. The mixture was then ground through a 150-mesh sieve to obtain hydrothermal char (hydroxyl content 1.5 mmol / g). The hydrothermal char was then compounded with freshly prepared stepwise anchored modified biochar at a mass ratio of 1:4, according to Example 1. The co-digestion parameters were used to construct the system (substrate dry weight ratio 2:1, C / N 25:1, total solids content 8%, total amount of compound materials added 5%, inoculum ratio 1:1.5). The initial pH was adjusted to 7.0, nitrogen was purged for 30 min to remove oxygen, and then the system was sealed and reacted in a constant temperature water bath at 37℃. For the first 12 days, the system was stirred intermittently (150 r / min, 40 min / time, 1.5 h interval). After 12 days, the system was allowed to stand, and the ORP was maintained at -190 mV. The digestion was carried out for 28 days, during which the system indicators were monitored. After the digestion was completed, the performance parameters were measured.

[0089] Results: Oil removal rate 72%, lapis lazuli 25.9 mg / g, VFA 10500 mg / L, hydrothermal carbon compound showed improved oil adsorption and Fe... 2+ The sustained-release effect is significant.

[0090] Example 8: ORP Boundary Value Verification Group: Adaptability of Upper and Lower Limits of Reduction Potential.

[0091] Stepwise anchoring modification: The original biochar was prepared using municipal biogas residue, with pyrolysis parameters (600℃, 3h, nitrogen flow rate 1.0L / min) the same as in Example 1; humic acid pre-coating was performed using a 10g / L suspension, solid-liquid ratio of 1:20, pH 4.0, and shaking at 28℃ for 10h, with a loading of 15mg / g; iron ion anchoring was achieved using a 1.0mol / L solution of ferrous sulfate:ferrous chloride = 1:1, solid-liquid ratio of 1:15, pH 6.2, and shaking under nitrogen protection at 38℃ for 8h. After modification, Fe... 2+ The loading amount was 110 mg / g (90% of the components were in coordination state), and the remaining steps were completely consistent with those in Example 1.

[0092] Anaerobic co-digestion process: Food waste is crushed to a particle size ≤5mm (moisture content 78%, VS 82%), and sludge is filtered to a moisture content of 82% (VS 65%, total phosphorus 18mg / g). The waste is mixed at a dry weight ratio of 2:1, and the C / N ratio is adjusted to 25:1 with a total solids content of 8%. 2kg of mixed substrate is added to each of two 5L anaerobic digesters (numbered 8-1 and 8-2), along with 5% (dry weight) modified biochar. The inoculum to substrate volume ratio is 1:1.5. Deionized water is added to 80% of the volume, the initial pH is adjusted to 7.0, nitrogen is purged for 30 minutes to remove oxygen, and the digester is sealed and placed in a 37℃ constant temperature water bath. The core difference in control parameters is as follows: For tank 8-1, the ORP is controlled at -220mV (lower limit of reduction potential), while for tank 8-2, the ORP is controlled at -160mV (upper limit of reduction potential). All other control parameters are the same: intermittent stirring (150 rpm, 40 min / time, 1.5 h interval) for the first 12 days, followed by settling; ORP control is achieved through precise dropwise addition of sodium sulfite (small, frequent additions for tank 8-1, reduced frequency for tank 8-2), with online monitoring of ORP every 2 h, and daily sampling to determine VFA concentration, pH, and Fe. 2+ The dissolution rate was measured over a 28-day digestion period, and the amount of blue iron ore generated and the oil removal rate were measured after the digestion period.

[0093] Results: Jar 8-1 (ORP=-220mV): Blue iron ore 25.6mg / g (strong reducing environment promotes Fe 3+ Reduced to Fe 2+ VFA concentration 10200 mg / L, oil removal rate 67%, Fe 2+ The dissolution rate remained stable at 8.5 mg / L; 8-2 tanks (ORP=-160mV): 23.5 mg / g of lapis lazuli (Fe under weak reducing conditions). 2+ Oxidation rate slightly increased), VFA concentration 10800 mg / L (a slight increase in acid-producing bacteria activity), oil removal rate 66%, Fe 2+ The dissolution rate remained stable at 7.2 mg / L; both core indicators were better than the benchmark values ​​(blue iron ore ≥18 mg / g, VFA ≥9000 mg / L), verifying that the ORP was adaptable to the full range of -220~-160mV and could operate stably without precise temperature control.

[0094] Example 9: Adaptability of agricultural biochar from different biogas residue sources.

[0095] Stepwise anchoring modification: The original biochar from biogas residue was replaced with agricultural biogas residue (cellulose content 42%, higher than municipal biogas residue 25%) produced by anaerobic fermentation of corn stalks. During pretreatment, the residue was washed until the conductivity was <500μS / cm, dried at 105℃ for 12h, and crushed through a 40-mesh sieve. The pyrolysis parameters in the tubular furnace were the same as in Example 1 (600℃, 3h, nitrogen 1.0L / min). After grinding through a 150-mesh sieve, the specific surface area reached 520m². 2 / g (municipal biochar from sludge is 320m) 2 / g). The humic acid pre-coating (10 g / L suspension, pH 4.0, 28°C shaking for 10 h) and iron ion anchoring (1:1 mixed salt, 1.0 mol / L, pH 6.2, 38°C nitrogen protection) steps were exactly the same as in Example 1. The modified Fe... 2+ The loading capacity is 120 mg / g (92% of the content is in the coordination state, and the loading efficiency is improved due to the large specific surface area).

[0096] Anaerobic co-digestion process: Pretreatment parameters for kitchen waste and sludge were the same as in Example 1 (kitchen waste moisture content 78%, sludge moisture content 82%), mixed at a dry weight ratio of 2:1, and the C / N ratio was adjusted to 25:1 with a total solids content of 8%. 2 kg of the mixed substrate was added to a 5L fermenter, followed by 5% (dry weight) agricultural biogas residue-based modified biochar. The inoculum ratio was 1:1.5, the initial pH was 7.0, and after purging with nitrogen for 30 min, the mixture was sealed and reacted in a constant temperature water bath at 37℃. For the first 12 days, intermittent stirring was performed (150 r / min, 40 min / time, 1.5 h interval). After 12 days, the mixture was allowed to stand, maintaining an ORP of -190 mV. VFA, pH, and oil content were sampled daily for 28 days of digestion.

[0097] Results: The amount of lapis lazuli produced was 29.2 mg / g (agricultural biochar with high porosity adsorbs more PO4). 3- The VFA concentration was 11800 mg / L (larger specific surface area enhances VFA adsorption and enrichment), and the oil removal rate was 73% (more uniform humic acid loading enhances oil adsorption capacity). Compared with the municipal biogas residue-based modified biochar group (Example 1), the core indicators were improved by 9.0%, 11.3%, and 4.3%, respectively, verifying the universality of the process for raw materials from different sources such as agricultural biogas residue and municipal biogas residue. Moreover, agricultural biogas residue has better performance after modification due to its high cellulose content.

[0098] Example 10: Medium temperature fluctuation group, engineered temperature deviation tolerance.

[0099] Stepwise anchoring modification: The entire modification process is completely consistent with Example 1 (municipal biogas residue biochar, humic acid loading 15mg / g, Fe... 2+ With a loading of 112 mg / g, the performance of the modified biochar is kept consistent.

[0100] Anaerobic co-digestion process: Food waste (particle size ≤5mm, moisture content 78%, VS 82%) and sludge (moisture content 82%, VS 65%, total phosphorus 18mg / g) were mixed at a dry weight ratio of 2:1, and the C / N ratio was adjusted to 25:1 with a total solids content of 8%. 2kg of the mixed substrate was added to each of three 5L fermenters (numbered 10-1, 10-2, and 10-3), and 5% (dry weight) modified biochar was added to each. The inoculum ratio was 1:1.5, the initial pH was 7.0, and nitrogen was purged for 30 minutes to remove oxygen before sealing. Temperature control differences: Tank 10-1 was maintained at 35℃ (lower limit of medium temperature, simulating cooling in northern winter engineering projects), Tank 10-2 was maintained at 39℃ (upper limit of medium temperature, simulating heating due to insufficient heat dissipation in summer), and Tank 10-3 (control group) was maintained at 37℃ (baseline temperature); other controls were uniform: intermittent stirring (150 r / min, 40 min / time, 1.5 h interval) for the first 12 days, followed by static setting until ORP stabilized at -190 mV. The temperature inside the fermenter was monitored every 12 h (precisely controlled by a water bath), and VFA, pH, and lapis lazuli precursor (Fe) were measured daily. 2+ PO4 3- (Concentration), digestion for 28 days.

[0101] Results: Tank 10-1 (35℃): 24.1 mg / g lapis lazuli, 9900 mg / L VFA, 65% grease removal rate (slightly lower at low temperatures but still better than the control group by 30%); Tank 10-2 (39℃): 25.3 mg / g lapis lazuli, 10400 mg / L VFA, 68% grease removal rate (high temperature did not inhibit acid production and crystallization); Tank 10-3 (37℃): 26.8 mg / g lapis lazuli, 10600 mg / L VFA, 70% grease removal rate; the core indicators of the three temperature groups had a deviation of ≤10%, and all met the industrial requirements (VFA≥9000 mg / L, phosphorus fixation rate≥60%), verifying the strong tolerance of the process to fluctuations in the medium temperature range (35~39℃), and adapting to actual engineering temperature deviation scenarios.

[0102] Table 1 summarizes the corresponding ranges and effects of the core parameters of the stepwise anchoring modification process using Examples 1-10, providing a better understanding of the humic acid-iron stepwise anchoring modification method for biochar from sludge and the application of the prepared modified biochar. The technical effects of this invention are demonstrated through comparison with Comparative Example 1 (traditional one-step blending modification) and the blank group (no biochar). Table 2 summarizes the core performance data of each example and comparative example.

[0103] Table 1. Correspondence between the core parameter ranges and effects of the stepwise anchoring modification process.

[0104]

[0105] Table 2 Summary of Core Performance Data of Examples 1, 2, and 6 and Comparative Example 1 and Blank Group

[0106]

[0107] Combining Tables 1 and 2, the analysis shows that Examples 1-10 are significantly better than Comparative Example 1 and the blank group. Specifically, compared to traditional one-step blending modification, the modified biochar in this invention exhibits higher Fe content. 2+ With the proportion of coordination states doubling, the amount of blue iron ore generated in applications increases by 34% to 54%, and the oil removal effect also improves by more than 20%, breaking through the limitations of single-function enhancement.

[0108] Comparison of SEM characterizations of stepwise modified biochar and traditional biochar, where Figure (a) shows the stepwise modified biochar of this application; Figure (b) shows the original biochar of ... 2+ - Humic acid coordination protrusion. This difference stems from the step-by-step process of "humic acid pre-coating (hydrogen bonding / π-π stacking fixation) - iron ion directional anchoring (coordination bond loading)," which solves the problems of easy humic acid detachment and Fe ion loading in the traditional one-step process. 2+ Despite its tendency to settle, it retains a high specific surface area, providing crucial structural support for VFA enrichment (concentration ≥9500mg / L), lapis lazuli crystallization (phosphorus fixation rate ≥60%), and oil removal (rate ≥60%) during co-digestion. This directly demonstrates the process's innovation and application value.

[0109] In addition, the modified process reduces the reaction time by 30%, can be directly adapted to existing co-digestion equipment, and is easy to modify.

[0110] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method for stepwise anchoring modification of humic acid and iron in biochar made from biogas residue, characterized in that, This includes humic acid pre-coating and directional iron ion anchoring: Humic acid pre-coating: Add the original biochar from the sludge to the humic acid suspension, adjust the pH to 3.5~4.5, keep the temperature at 25~30℃ and shake for 8~12 hours, filter and dry to obtain pre-coated biochar; Iron ion directional anchoring: Pre-coated biochar is added to Fe 2+ In a salt solution, adjust the pH to 6.0-6.5, maintain a constant temperature of 35-40℃ and shake for 6-10 hours, wash until neutral, and dry at 80℃ to obtain humic acid-iron stepwise anchored modified biochar.

2. The method for stepwise anchoring modification of humic acid-iron in biochar made from biogas residue according to claim 1, characterized in that, Also includes: Preparation of raw biochar from biogas residue: After washing, drying and crushing, biogas residue is subjected to hydrothermal reaction at 160~220℃ for 2~4 hours under nitrogen atmosphere, and then ground and sieved to 100~200 mesh to obtain raw biochar from biogas residue. Stepwise modification: The original biochar from sludge first undergoes a humic acid pre-coating reaction, and then pre-coated biochar is obtained through solid-liquid separation; Pre-coated biochar undergoes an iron ion directional anchoring reaction to ultimately obtain modified biochar from sludge.

3. The method for stepwise anchoring modification of humic acid-iron in biochar made from biogas residue according to claim 1, characterized in that, The humic acid suspension has a concentration of 5-15 g / L and a solid-liquid ratio of 1:15-1:25; the Fe... 2+ The salt solution concentration is 0.5~2 mol / L, and the solid-liquid ratio is 1:10~1:20; the solid-liquid ratio is in g / mL.

4. The method for stepwise anchoring modification of humic acid-iron in biochar made from biogas residue according to claim 1, characterized in that, The humic acid is an industrial-grade product with a palm humic acid content of ≥70%. The suspension is prepared into a uniform colloid through ultrasonic dispersion.

5. The method for stepwise anchoring modification of humic acid-iron in biochar made from biogas residue according to claim 1, characterized in that, Fe 2+ The salt is a mixture of ferrous sulfate and ferrous chloride.

6. A biochar made from biogas residue, characterized in that, Biochar made from biogas residue was modified using the stepwise anchoring modification method of humic acid-iron as described in any one of claims 1-5.

7. The application of modified biochar prepared by any one of claims 1-5 in the co-digestion of sludge and kitchen waste, characterized in that, This includes the construction and process control of the co-digestion system: Construction of co-digestion system: The dry weight ratio of sludge to kitchen waste is 1:1 to 3:1 as the mixed substrate, and the inoculum is modified biochar of biogas residue, with an addition amount of 2% to 8%. The volume ratio of inoculum to mixed substrate is 1:1 to 1:2 based on dry weight, the total solids content is 6% to 10%, and the initial pH is 6.5 to 7.

2. Process control: anaerobic environment at 35~37℃, oxidation-reduction potential (ORP) controlled at -220~-160mV, digestion for 25~30 days, intermittent stirring for the first 12 days, followed by static reaction after 12 days, to simultaneously achieve the formation of lapis lazuli and the enrichment of volatile fatty acids (VFA).

8. The application of the modified biochar of biogas residue according to claim 7 in the co-digestion of sludge and kitchen waste, characterized in that, Intermittent stirring, 120~180 r / min, 30~40 min each time, with an interval of 1~2 h.

9. The application of the modified biochar of biogas residue according to claim 8 in the co-digestion of sludge and kitchen waste, characterized in that, Co-digestion also includes: product separation and resource recovery and recycling.

10. The application of the modified biochar of biogas residue according to claim 9 in the co-digestion of sludge and kitchen waste, characterized in that, Recycling includes: Biochar feedstock recycling: Hydrothermal biochar is mixed with fresh biogas residue at a mass ratio of 1:9 to 3:7 and returned to the original biogas residue biochar preparation process; and / or, Co-digestion auxiliary circulation: Hydrothermal char and stepwise anchored modified biochar are mixed at a mass ratio of 1:3 to 1:5 and added together to the co-digestion system.

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