CN114132913A - Method for improving phosphorus bioavailability and solidifying heavy metal in town sludge by carrying clam shell pyrolysis and application - Google Patents

Method for improving phosphorus bioavailability and solidifying heavy metal in town sludge by carrying clam shell pyrolysis and application Download PDF

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CN114132913A
CN114132913A CN202111167197.4A CN202111167197A CN114132913A CN 114132913 A CN114132913 A CN 114132913A CN 202111167197 A CN202111167197 A CN 202111167197A CN 114132913 A CN114132913 A CN 114132913A
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sludge
phosphorus
pyrolytic carbon
temperature
pyrolysis
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曾薇
任紫嫣
彭晓静
彭永臻
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Beijing University of Technology
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    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
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    • B01J20/3078—Thermal treatment, e.g. calcining or pyrolizing
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    • C02F11/008—Sludge treatment by fixation or solidification
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    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/10—Treatment of sludge; Devices therefor by pyrolysis
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    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05F—ORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C, e.g. FERTILISERS FROM WASTE OR REFUSE
    • C05F1/00—Fertilisers made from animal corpses, or parts thereof
    • C05F1/005—Fertilisers made from animal corpses, or parts thereof from meat-wastes or from other wastes of animal origin, e.g. skins, hair, hoofs, feathers, blood
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05F—ORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C, e.g. FERTILISERS FROM WASTE OR REFUSE
    • C05F7/00—Fertilisers from waste water, sewage sludge, sea slime, ooze or similar masses
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
    • C05G3/00—Mixtures of one or more fertilisers with additives not having a specially fertilising activity
    • C05G3/40—Mixtures of one or more fertilisers with additives not having a specially fertilising activity for affecting fertiliser dosage or release rate; for affecting solubility
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2220/00—Aspects relating to sorbent materials
    • B01J2220/40—Aspects relating to the composition of sorbent or filter aid materials
    • B01J2220/48—Sorbents characterised by the starting material used for their preparation
    • B01J2220/4875—Sorbents characterised by the starting material used for their preparation the starting material being a waste, residue or of undefined composition
    • B01J2220/4881—Residues from shells, e.g. eggshells, mollusk shells
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
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    • B01J2220/40—Aspects relating to the composition of sorbent or filter aid materials
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    • B01J2220/4875—Sorbents characterised by the starting material used for their preparation the starting material being a waste, residue or of undefined composition
    • B01J2220/4887—Residues, wastes, e.g. garbage, municipal or industrial sludges, compost, animal manure; fly-ashes
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/105—Phosphorus compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
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    • C02F2101/20—Heavy metals or heavy metal compounds
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
    • Y02A40/10—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in agriculture
    • Y02A40/20—Fertilizers of biological origin, e.g. guano or fertilizers made from animal corpses
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    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
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Abstract

A method for improving phosphorus bioavailability and solidifying heavy metal in town sludge by carrying clam shell pyrolysis and an application thereof belong to the field of solid waste management and renewable resource utilization. The invention takes clam shells as an additional sludge modification material to be pyrolyzed with sludge to prepare a sludge product with higher phosphorus recycling value. The mixed clam shell powder can be pyrolyzed to realize the high-efficiency conversion of non-apatite phosphorus to apatite phosphorus, and the biological effectiveness of phosphorus in the pyrolytic carbon is obviously improved. The loss risk of phosphorus in the pyrolytic carbon and the leaching amount of heavy metals are analyzed, and the pyrolytic carbon added with the clam shell powder is changed to the direction beneficial to practical application. The heavy metal forms are changed from F1 and F2 with stronger activity to stable F4, which is also the reason for the sharp reduction of leaching rate. Three groups of planting experiments further verify that the phosphorus in the pyrolytic carbon has fertilizer efficiency. This successful co-pyrolysis process provides a new strategy for mitigating the growing scarcity of phosphorite resources and waste management.

Description

Method for improving phosphorus bioavailability and solidifying heavy metal in town sludge by carrying clam shell pyrolysis and application
Technical Field
The invention relates to a method for improving the bioavailability of phosphorus in town sludge and solidifying heavy metal by carrying clam shell pyrolysis, belongs to the field of solid waste management and renewable resource utilization, and is used for treating the town sludge and strengthening the recycling of the phosphorus.
Background
Phosphorus is an essential mineral element for all living body compositions (such as genetic material DNA and RNA) and metabolic activities (material transfer, energy transfer and the like), and plays a unique and key role in social sustainable development. However, phosphorus is a unidirectional circulating substance, and according to statistics, with the exhaustion of available phosphorus ore, the extreme value of phosphorus yield is expected to be reached in the 21 st century, and then the shortage of phosphorus is increased sharply, and phosphorus is lost in various stages of the production and application system of phosphorus. In order to alleviate the risk of a shortage of phosphorus supply that will occur in the future, it is important to recover phosphorus from the waste as a substitute for phosphate ore. As the sludge is used as a main byproduct of an urban sewage treatment plant, with the vigorous popularization of a biological enhanced phosphorus removal technology and a flocculation precipitation process, about 90 percent of phosphorus in the wastewater is transferred and concentrated in the sludge finally. Therefore, the phosphorus-rich sludge can be used as a potential phosphorus resource utilization raw material. However, the original phosphorus in the sludge is low in bioavailability and contains a large number of harmful components including heavy metals, organic pollutants and pathogenic microorganisms, limiting the possibility of direct reuse. Undoubtedly, the transformation of the material morphology in the sludge and the reduction of the unfavorable parameters are key factors in resource recovery.
In recent years, pyrolysis in heat treatment is gradually regarded as the best approach for resource treatment of phosphorus in sludge, and pyrolysis can achieve high-efficiency sanitation in a short time while stabilizing organic carbon and nitrogen, as compared with incineration, hydrothermal carbonization, and gasification. It is to be noted that incineration and pyrolysis are both dry processes. Most of phosphorus is enriched in incineration ash after incineration, and extracting phosphorus from incineration ash or considering it as fertilizer has been the focus of attention. However, researches show that phosphorus enriched in the incineration ash has extremely low bioavailability and strong activity of heavy metals, and is not suitable for direct recycling. Acid leaching, electrodialysis, hydrothermal treatment and the like are the most extensive methods for recovering phosphorus in incineration ash, but dangerous trace elements (such as cadmium, chromium and the like) in the incineration ash can be precipitated simultaneously, so that the phosphorus recovery process faces more challenges. In view of these, although methods of reducing the content of toxic elements by complexing with chelating agents, adsorption, addition of chlorinating agents or deep eutectic solvents based on natural products have been developed, the above-mentioned various operations are still hindered in actual operation due to high energy costs and the need for appropriate sludge incineration ash components. In addition, the pyrolysis technology is considered as a good organic waste management strategy, and the pyrolysis is widely found in recent years to reduce the volume of waste, eliminate pathogenic microorganisms, fix heavy metals to a certain extent and generate biological energy with high added value and charcoal-rich biochar. Most of the existing researches focus on the preparation of the adsorbent by mixing and pyrolyzing sludge and biomass (such as rice husks, sawdust and the like), but because the adsorption needs to be carried out in solution, phosphorus in the sludge needs to be released first, and the problem of phosphorus extraction is also involved. It has also been studied to add inorganic salts containing calcium, aluminum, chlorine, sulfate, and phosphate directly into the sludge, such as CaO and Ca3(PO4)2、MgCl2And MgO and the like are pyrolyzed, but the operation cost is increased undoubtedly, and the large-scale popularization and application are difficult.
The invention is technically different from the prior art and mainly comprises the following two aspects:
(1) the main materials are different: the main material used in the invention is waste of aquaculture industry, has large yield and safe components, and proposes to add clam shell powder as a sludge modification substance into pyrolysis for the first time. The use of the main material not only further improves the bioavailability of phosphorus in the sludge, efficiently and reasonably solves the problem of subsequent treatment of the sludge, but also eliminates adverse environmental effects caused by the large discarding and accumulation of clam shells.
(2) Safety considerations for use of clam shell-sludge pyrolytic carbon as a slow-release phosphate fertilizer: in previous studies, when examining the agricultural value of biochar, the morphology of heavy metals in sludge mixture after pyrolysis was not analyzed. According to the invention, the BCR extraction technology of heavy metals is used as a chemical means for safety inspection of sludge pyrolysis regenerated phosphate fertilizer for the first time, and the content change of the heavy metals in the sludge pyrolysis product after the clam shells are added is researched to belong to different forms (F1: acid exchangeable state, F2: reduced state, F3: oxidation state, F4: residue state) and the practical feasibility of applying the heavy metals as the phosphate fertilizer.
Disclosure of Invention
The invention aims to provide a method for preparing pyrolytic carbon with high safety and phosphorus bioavailability by co-pyrolyzing clam shell powder and sludge. The environmental effect of the phosphate fertilizer application is examined through chemical and biological experiments. Wherein the chemical experiment is the analysis of the form change and the availability of phosphorus, and the biological experiment is the determination of the germination of mung bean seeds and the growth of seedlings. The method not only enables the phosphorus resource in the sludge to be better recycled, but also fully solves the problem of excess sludge from the perspective of environmental safety, and has higher application prospect.
Technical scheme of the invention
A method for preparing pyrolytic carbon by carrying out co-pyrolysis on clam shells and sludge is characterized by comprising the following steps: crushing cleaned and naturally air-dried clam shells by using a ball mill, sieving by using a 200-mesh sieve, putting the sieved powder into a muffle furnace, preheating for 30min, and keeping the temperature in the furnace to 800 ℃ for 60 min; after the heating program is finished, cooling the temperature to the room temperature, and taking out the product;
respectively mixing clam shell powder and sludge according to mass ratioWeighing 10% -30%, fully mixing the two, putting the mixture into a quartz boat, putting the quartz boat into one side of a tube furnace, and pushing the loaded quartz boat into a combustion chamber immediately after the temperature reaches the pyrolysis set temperature; before the pyrolysis starts, with N2Blowing off for 30min to exhaust air in the furnace; every time when the furnace is operated, the temperature in the furnace reaches a set value at a constant heating rate of 10 ℃/min, timing is started, the time is kept for 60min, and N is continuously introduced in the process2So as to prevent air from entering and maintain the nitrogen atmosphere in the tube furnace; after the program is finished, at N2Blowing to reduce the temperature in the furnace to room temperature to obtain the composite pyrolytic carbon; wherein the pyrolysis set temperature is selected to be 500-800 ℃, and the sludge-based pyrolytic carbon is prepared.
The method comprises the following steps of adding sludge-based pyrolytic carbon prepared by clam shell powder and sludge according to the mass ratio of 20% and the pyrolysis set temperature of 800 ℃ into a seedling tray using fine sand as a culture medium, wherein the mass ratio of the sludge-based pyrolytic carbon to the fine sand with the particle size of 0.5-1mm is 2%, paving a layer of cloth on the seedling tray to keep moisture, placing mung bean seeds in the seedling tray, carrying out germination of the seeds and growth of seedlings at the temperature of 28 ℃, carrying out dark cultivation before the mung beans germinate, and carrying out sunlight irradiation after the mung beans germinate.
Further, the preparation method of the clam shell powder modified sludge pyrolytic carbon is characterized by comprising the following steps:
(1) preparation of clam shell powder: washing Concha Meretricis Seu Cyclinae shell with tap water, removing meat residue, cleaning, standing in ventilation place for 2 days, naturally air drying, pulverizing with ball mill, and sieving with 200 mesh sieve. Placing the sieved powder in a muffle furnace, preheating for 30min, and keeping the temperature in the furnace at 800 ℃ for 60 min. After the heating procedure was completed and the temperature was cooled to room temperature, it was taken out and stored in a dry glass ware.
(2) Co-pyrolyzing the clam shell powder and sludge: accurately weighing dry sludge and clam shell powder according to a certain mass ratio, fully mixing the dry sludge and the clam shell powder, putting the mixture into a quartz boat, putting the quartz boat into one side of a tube furnace, and immediately pushing the quartz boat into a combustion chamber after the temperature reaches a set value. Before the pyrolysis starts, with N2Blowing off for 30min to exhaust the air in the furnace. Every time the furnace is operated, the temperature in the furnace reaches the set value at a constant heating rate of 10 ℃/minValue, from which timing was started, for 60min, during which N was continuously passed2. After the program is finished, at N2And (5) reducing the temperature in the furnace to room temperature under the blowing, thus obtaining the composite pyrolytic carbon. Wherein the pyrolysis temperature is selected to be 500 ℃, 600 ℃, 700 ℃ and 800 ℃, and the mixing mass ratio of the clam shell powder to the sludge is 10%, 20% and 30%.
The phosphorus in the sludge is known as the second big phosphorus source which is second only to natural phosphorite. According to statistics, the sludge yield in China in 2019 is over 6000 million tons (calculated by the water content of 80%), the annual sludge yield in 2025 is estimated to be over 9000 million tons, wherein the mass fraction of phosphorus contained in the residual sludge accounts for about 1% -9% according to different treatment processes. Therefore, the recovery of phosphorus from these materials is both an urgent and long-term research. The invention prepares pyrolytic carbon by co-pyrolysis and applies the pyrolytic carbon to the growth and development of crops, and the result shows that the addition of 20 percent of clam shell powder can increase the plant-available Apatite phosphor (Apatite phosphor) in the sludge to 50.19mg/g (16.76 mg/g when the 500 ℃ sludge is pyrolyzed alone) at the temperature of 500 ℃, the content of water-soluble phosphor and the leaching amount of heavy metal are obviously reduced, wherein most heavy metal is converted into stable F4 component (being confined in mineral crystal lattice and difficult to be biologically utilized and having little migration) by F1, F2 and F3 components with biological effectiveness.
Innovation point of the invention
(1) According to the invention, the clam shell powder and the sludge are mixed for co-pyrolysis for the first time, and the pyrolytic carbon has high bioavailability and low environmental toxicity. The recycling of phosphorus in the pyrolysis sludge becomes possible under the condition that other additional treatment is not carried out on the pyrolysis sludge, the operation steps are reduced, and the operation cost is saved.
(2) The invention takes the BCR extraction method of heavy metal as a chemical verification means of the environmental safety of pyrolytic carbon in agriculture. The application of the pyrolytic carbon is reliably guaranteed through the distribution condition of the components of the heavy metal, and the application has practical application value.
(3) The invention directly uses the pyrolysis products of the two wastes for planting experimental study for the first time. The main component of the clam shell powder is CaCO3And a small amount of chitin, which is an environmentally friendly substance, whichThe sludge is modified by adding the modifier, so that the modification is changed to a direction beneficial to sustainable development, and theoretical support is provided for reasonable application of the modified sludge.
Drawings
FIG. 1 shows the effect of clam shell powder dosage on the contents of inorganic phosphorus and organic phosphorus in pyrolytic carbon at different temperatures, wherein (a)500 ℃; (b)800 deg.C
FIG. 2 shows the influence of clam shell powder dosage on the contents of non-apatite phosphorus and apatite phosphorus in pyrolytic carbon and the pH change condition at different temperatures
FIG. 3 shows the influence of the amount of clam shell powder added on the content of water-soluble phosphorus in pyrolytic carbon at different temperatures;
FIG. 4 shows XRD characterization results of pyrolytic carbon at different temperatures and with different amounts of clam shell powder
FIG. 5 shows the influence of clam shell powder dosage on the distribution of heavy metal components in pyrolytic carbon at different temperatures
Detailed Description
Example 1: accurately weighing clam shell powder and dry sludge according to the mass ratio of 10%, 20% and 30%, wherein the total mass of the mixture is 5 g. The two are mechanically mixed and then put into a quartz boat, the quartz boat is put into one side of a horizontal heating tube furnace in a laboratory, and the loaded quartz boat is pushed into a combustion chamber immediately after the temperature reaches a set value. Before the pyrolysis starts, with N2Blowing off for 30min to exhaust the air in the furnace. Every time when the furnace is operated, the temperature in the furnace reaches a set value at a constant heating rate of 10 ℃/min, timing is started, the time is kept for 60min, and N is continuously introduced in the process2. After the program is finished, at N2And (5) reducing the temperature in the furnace to room temperature under the blowing, thus obtaining the composite pyrolytic carbon. The pyrolysis temperature is 500 ℃, 600 ℃, 700 ℃ and 800 ℃, SS represents original sludge, S500 represents pyrolysis carbon obtained by singly pyrolyzing the sludge at 500 ℃, and S800-20 percent represents pyrolysis carbon obtained by adding 20 percent of clam shell powder and pyrolyzing at 800 ℃.
And (3) determining the content of organic phosphorus and inorganic phosphorus in the pyrolytic carbon:
(1) a0.2 g sample of the solid was taken, calcined at 450 ℃ for 3 hours, then 20ml of 3.5M HCl was added, shaken at room temperature for 16 hours, and then measured with a spectrophotometer to obtain the total phosphorus content.
(2) 0.2g of solid sample is taken, 20ml of 1M HCl is added, the mixture is shaken for 16h at room temperature, and the supernatant is taken and measured by a spectrophotometer, so that the inorganic phosphorus content is obtained. The solid residue was calcined at 450 ℃ for 3h, then 20ml of 1M HCl was added, the mixture was shaken for 16h, and the supernatant was taken and measured with a spectrophotometer, resulting in the organophosphorus content.
The results in figure 1 show that the addition of clam shell powder can promote the further decomposition of organic phosphorus into inorganic phosphorus at different temperatures. At a relatively low temperature (500 ℃), the total phosphorus content in the pyrolytic carbon is in a descending trend along with the addition of the clam shell powder, and the total phosphorus hardly changes along with the change of the addition amount at a temperature of 800 ℃. This is because clam shell powder has low volatility, and when the temperature is low, the addition of clam shell powder suppresses the volatilization of sludge, the weight loss of pyrolytic carbon decreases, the yield increases more, and the total phosphorus content decreases accordingly. However, when the pyrolysis temperature is sufficiently high, the inhibition of the clam shell powder is reduced.
Example 2: accurately weighing clam shell powder and dry sludge according to the mass ratio of 10%, 20% and 30%, wherein the total mass of the mixture is 5 g. The two are mechanically mixed and then put into a quartz boat, the quartz boat is put into one side of a horizontal heating tube furnace in a laboratory, and the loaded quartz boat is pushed into a combustion chamber immediately after the temperature reaches a set value. Before the pyrolysis starts, with N2Blowing off for 30min to exhaust the air in the furnace. Every time when the furnace is operated, the temperature in the furnace reaches a set value at a constant heating rate of 10 ℃/min, timing is started, the time is kept for 60min, and N is continuously introduced in the process2. After the program is finished, at N2And (5) reducing the temperature in the furnace to room temperature under the blowing, thus obtaining the composite pyrolytic carbon. The pyrolysis temperature is 500 ℃, 600 ℃, 700 ℃ and 800 ℃, SS represents original sludge, S500 represents pyrolysis carbon obtained by singly pyrolyzing the sludge at 500 ℃, and S800-20 percent represents pyrolysis carbon obtained by adding 20 percent of clam shell powder and pyrolyzing at 800 ℃.
And (3) measuring the content of apatite phosphorus and non-apatite phosphorus in the pyrolytic carbon:
(1) 0.2g of the solid sample was added with 20ml of 1M NaOH and shaken at room temperature for 16 hours, and 10ml of the supernatant was added with 4ml of 3.5M HCl and further shaken for 16 hours, followed by measurement with a spectrophotometer, whereby the non-apatite phosphorus content was obtained.
(2) 20ml of 1M HCl was added to the solid residue in (1), and the mixture was shaken at room temperature for 16 hours and measured with a spectrophotometer to obtain the apatite phosphorus content.
As shown in figure 2, the pH of the pyrolytic carbon is higher than that of the product which is not added at the same temperature after the clam shell powder is added, and OH is well known in an alkaline environment-Will be in contact with PO4 3-Compete for adsorption sites on oxides or hydroxides of Fe, Al, etc., resulting in free PO4 3-The content of non-apatite phosphor is reduced and the content of apatite is increased by adding the clam shell powder from the angle of pH change. XRD characterization results in FIG. 3 further show that phosphorus in the pyrolytic carbon is mainly Ca10(PO4)6(OH)2、CaHPO4、Ca3(PO4)2In an iso-chemical state, wherein Ca10(PO4)6(OH)2Has biocompatibility with soil, and can promote plant growth.
Example 3: accurately weighing clam shell powder and dry sludge according to the mass ratio of 10%, 20% and 30%, wherein the total mass of the mixture is 5 g. The two are mechanically mixed and then put into a quartz boat, the quartz boat is put into one side of a horizontal heating tube furnace in a laboratory, and the loaded quartz boat is pushed into a combustion chamber immediately after the temperature reaches a set value. Before the pyrolysis starts, with N2Blowing off for 30min to exhaust the air in the furnace. Every time when the furnace is operated, the temperature in the furnace reaches a set value at a constant heating rate of 10 ℃/min, timing is started, the time is kept for 60min, and N is continuously introduced in the process2. After the program is finished, at N2And (5) reducing the temperature in the furnace to room temperature under the blowing, thus obtaining the composite pyrolytic carbon. The pyrolysis temperature is 500 ℃, 600 ℃, 700 ℃ and 800 ℃, SS represents original sludge, S500 represents pyrolysis carbon obtained by singly pyrolyzing the sludge at 500 ℃, and S800-20 percent represents pyrolysis carbon obtained by adding 20 percent of clam shell powder and pyrolyzing at 800 ℃.
Determination experiment of water-soluble phosphorus in pyrolytic carbon: to 0.1g of pyrolytic carbon, 100ml of distilled water was added, and the mixture was shaken at 180rpm for 24 hours and then measured. The results are shown in FIG. 4. The content of soluble phosphorus in the pyrolytic carbon added with the clam shell powder is obviously lower than that of the soluble phosphorus which is not added, the content of water-soluble phosphorus in the biochar is continuously reduced along with the increase of the added amount, and when the added amount is 30 percent, the concentration of the water-soluble phosphorus reaches the lowest 0.11mg/g (800 ℃). The conversion of soluble phosphorus and exchangeable phosphorus to slow-release phosphorus is promoted, the utilization efficiency of the phosphate fertilizer is improved, and the phenomenon that the unused phosphorus enters a water body through leaching and the like to cause environmental problems again is avoided.
Example 4: accurately weighing clam shell powder and dry sludge according to the mass ratio of 10%, 20% and 30%, wherein the total mass of the mixture is 5 g. The two are mechanically mixed and then put into a quartz boat, the quartz boat is put into one side of a horizontal heating tube furnace in a laboratory, and the loaded quartz boat is pushed into a combustion chamber immediately after the temperature reaches a set value. Before the pyrolysis starts, with N2Blowing off for 30min to exhaust the air in the furnace. Every time when the furnace is operated, the temperature in the furnace reaches a set value at a constant heating rate of 10 ℃/min, timing is started, the time is kept for 60min, and N is continuously introduced in the process2. After the program is finished, at N2And (5) reducing the temperature in the furnace to room temperature under the blowing, thus obtaining the composite pyrolytic carbon. The pyrolysis temperature is 500 ℃, 600 ℃, 700 ℃ and 800 ℃, SS represents original sludge, S500 represents pyrolysis carbon obtained by singly pyrolyzing the sludge at 500 ℃, and S800-20 percent represents pyrolysis carbon obtained by adding 20 percent of clam shell powder and pyrolyzing at 800 ℃.
Heavy metal form determination experiment in pyrolytic carbon: the results of measuring the different components of heavy metals in the pyrolytic carbon are shown in FIG. 5. Among the S800-20%, the stable components (F3+ F4) of Zn, Mn, Cr, Cu, Cd, Pb account for 92.49%, 91.16%, 98.95%, 89.44%, 85.72%, and 93.05%, respectively. The possible reasons why the clam shell powder can reduce the bioavailability and toxicity of heavy metals in the pyrolytic carbon are presumed to be that: (1) the pH value of the pyrolytic carbon is changed by a large amount of CaO existing after the clam shell powder is calcined, the surface of the pyrolytic carbon is provided with more negative charges in an alkaline environment, and the adsorption performance to heavy metals is enhanced; (2) the clam shell powder has some catalytic properties, which are beneficial to the immobilization of heavy metals.
Leaching experiment of heavy metal in pyrolytic carbon: the effective heavy metals in different solid samples are extracted by using acetic acid buffer solution (HJ/T300-2007) as a leaching agent, and the measurement results are shown in Table 1. Clearly observed that after the clam shell powder is added, the leaching amount of six heavy metals is lower than the single pyrolysis value at the same temperature, and the effect is more remarkable at high temperature. Cr, Cd and Pb were added to 20% clam shell powder at 800 ℃ and no leaching was detected. The reason is that the clam shell powder promotes various matrixes and heavy metals to form new minerals with high strength and chemical durability in the pyrolysis process, thereby reducing the leaching probability of the heavy metals from the pyrolytic carbon.
Table 1.
Figure RE-GDA0003496062020000071
Example 5: accurately weighing clam shell powder and dry sludge according to the mass ratio of 10%, 20% and 30%, wherein the total mass of the mixture is 5 g. The two are mechanically mixed and then put into a quartz boat, the quartz boat is put into one side of a horizontal heating tube furnace in a laboratory, and the loaded quartz boat is pushed into a combustion chamber immediately after the temperature reaches a set value. Before the pyrolysis starts, with N2Blowing off for 30min to exhaust the air in the furnace. Every time when the furnace is operated, the temperature in the furnace reaches a set value at a constant heating rate of 10 ℃/min, timing is started, the time is kept for 60min, and N is continuously introduced in the process2. After the program is finished, at N2And (5) reducing the temperature in the furnace to room temperature under the blowing, thus obtaining the composite pyrolytic carbon. The pyrolysis temperature is 500 ℃, 600 ℃, 700 ℃ and 800 ℃, SS represents original sludge, S500 represents pyrolysis carbon obtained by singly pyrolyzing the sludge at 500 ℃, and S800-20 percent represents pyrolysis carbon obtained by adding 20 percent of clam shell powder and pyrolyzing at 800 ℃.
Verification experiment of bioavailability of phosphorus in pyrolytic carbon: mung bean planting experiments were performed under laboratory conditions. Three culture conditions were set: the fine sand alone, the fine sand and the pyrolytic carbon S800 are uniformly mixed according to 2 percent, and the fine sand and the pyrolytic carbon S800-20 percent are uniformly mixed according to 2 percent. A layer of cloth is laid on each seedling tray to keep moisture, 20 mung bean seeds are put into each seedling tray, and the seedling trays are placed in a constant temperature incubator at 28 ℃ and are carried out under the same conditions of illumination, humidity and temperature. The average plant height of seedlings in a pure fine sand culture medium is 16cm, and the average plant height in an S800 culture medium is 18.6 cm. The S content is about 21.9cm in 800-20%, and the root system of mung bean seedling in the culture medium is the best developed, and the leaves are larger and thicker than the other two.

Claims (2)

1. A method for preparing pyrolytic carbon by carrying out co-pyrolysis on clam shells and sludge is characterized by comprising the following steps: crushing cleaned and naturally air-dried clam shells by using a ball mill, sieving by using a 200-mesh sieve, putting the sieved powder into a muffle furnace, preheating for 30min, and keeping the temperature in the furnace to 800 ℃ for 60 min; after the heating program is finished, cooling the temperature to the room temperature, and taking out the product;
weighing clam shell powder and sludge according to the mass ratio of 10-30%, fully mixing the clam shell powder and the sludge, putting the mixture into a quartz boat, putting the quartz boat into one side of a tubular furnace, and pushing the quartz boat into a combustion chamber immediately after the temperature reaches a pyrolysis set temperature; before the pyrolysis starts, with N2Blowing off for 30min to exhaust air in the furnace; every time when the furnace is operated, the temperature in the furnace reaches a set value at a constant heating rate of 10 ℃/min, timing is started, the time is kept for 60min, and N is continuously introduced in the process2So as to prevent air from entering and maintain the nitrogen atmosphere in the tube furnace; after the program is finished, at N2Blowing to reduce the temperature in the furnace to room temperature to obtain the composite pyrolytic carbon; wherein the pyrolysis set temperature is selected to be 500-800 ℃, and the sludge-based pyrolytic carbon is prepared.
2. The use of the sludge-based pyrolytic carbon prepared according to the method of claim 1, wherein: the method comprises the following steps of adding sludge-based pyrolytic carbon prepared by clam shell powder and sludge according to the mass ratio of 20% and the pyrolysis set temperature of 800 ℃ into a seedling tray using fine sand as a culture medium, wherein the mass ratio of the sludge-based pyrolytic carbon to the fine sand with the particle size of 0.5-1mm is 2%, paving a layer of cloth on the seedling tray to keep moisture, placing mung bean seeds in the seedling tray, carrying out germination of the seeds and growth of seedlings at the temperature of 28 ℃, carrying out dark cultivation before the mung beans germinate, and carrying out sunlight irradiation after the mung beans germinate.
CN202111167197.4A 2021-10-03 2021-10-03 Method for improving phosphorus bioavailability and solidifying heavy metal in town sludge by carrying clam shell pyrolysis and application Pending CN114132913A (en)

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