A method for resource utilization of sludge and preparation of soil conditioner

Abstract

The invention discloses a method for resource utilization of sludge and preparation of a soil conditioner, comprising the following steps: nitrogen is charged into a hydrothermal reactor to exhaust air, sludge is sent into the reactor for hydrothermal carbonization reaction, after the reaction is finished, solid-liquid separation is performed on the obtained hydrothermal product to obtain hydrothermal charcoal; the hydrothermal charcoal and eggshell are mixed, placed in an incinerator, air is introduced, and incineration is performed to obtain incineration ash, deionized water is added into the incineration ash, and then concentrated sulfuric acid is added to adjust pH, and phosphorus is leached by stirring, concentrated sulfuric acid is intermittently added during the leaching process to keep pH stable, and after the leaching is finished, acid leaching solution and acid leaching residue are respectively obtained by centrifugal filtration; straw and eggshell are immersed in a magnesium chloride solution, modified by magnesium chloride, and then subjected to high-temperature pyrolysis to obtain pyrolytic charcoal; the pyrolytic charcoal adsorbs phosphorus in the acid leaching solution, and the obtained phosphorus-rich biochar can be directly used as a soil conditioner.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge disposal and resource utilization, and specifically relates to a method for sludge resource utilization and preparing a soil conditioner. Background Art

[0002] Ways to dispose of and recycle sludge include landfill, incineration, pyrolysis, gasification, etc. Incineration is a preferred method for treating sludge. However, the hazardous compounds contained in sludge will cause a high level of flue gas pollutants during ordinary incineration. In addition, during the recovery of phosphorus from sludge incineration ash, more impurity ions and heavy metals will increase the purification steps and make phosphorus recovery more difficult. Therefore, improving the degree of clean sludge treatment and achieving efficient recovery and utilization of phosphorus in sludge are issues that need to be addressed urgently.

[0003] Phosphorus recovery from sludge incineration ash is usually done by thermochemical and wet chemical methods, but the thermochemical method is energy-intensive, complex to operate, and costly; the wet chemical method must be differentiated according to the characteristics of the ash, and the influence of heavy metals must be considered, and the phosphorus product is often of low purity. During the hydrothermal carbonization of sludge, the form of heavy metals will change to a more stable oxidizable state and residual state, and the heavy metals in the hydrothermal carbon are more stable.

[0004] Biochar has a highly enriched carbon skeleton and a loose porous surface structure, which can enhance the soil's ability to retain water and fertilizer. When applied to the soil, it provides a living space for microorganisms and promotes microbial reproduction. In addition, biochar also has strong adsorption capacity and high cation exchange capacity, and a small part of the mobile compounds. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a method for resource utilization of sludge and preparation of soil conditioner. The sludge is treated by hydrothermal carbonization coupled incineration to achieve the purpose of degrading organic matter, removing most of the polluting elements such as N and S, enriching phosphorus in sludge ash and stabilizing heavy metals; and agricultural waste modified pyrolytic carbon is used as an adsorbent to adsorb phosphorus in the acid leaching solution of sludge incineration ash, and the obtained phosphorus-rich biochar is used as a soil conditioner; the residue of the acid leaching solution is used as a cement mortar additive. On the one hand, it solves the problem of high flue gas pollutants during sludge incineration, and on the other hand, it can simply and efficiently utilize the phosphorus in the sludge incineration ash, and can achieve multiple utilizations of the sludge incineration ash.

[0006] In order to achieve the above objectives, the following technical solutions are proposed:

[0007] (1) Hydrothermal carbonization treatment: The sludge is fed into a hydrothermal reactor for hydrothermal carbonization reaction. The solid-liquid ratio is preferably 1: (10-20). Before the hydrothermal carbonization reaction, N2 needs to be filled into the reactor to exhaust the air. The stirring speed of the hydrothermal reactor is preferably 250-350 r / min. The hydrothermal carbonization reaction is carried out at a set temperature. The temperature is preferably 210°C-280°C. The hydrothermal reaction time is preferably 2-4h. After the reaction, the hydrothermal product obtained is subjected to solid-liquid separation.

[0008] (2) Incineration treatment: The hydrothermal carbon obtained by hydrothermal carbonization is incinerated, and the incinerated hydrothermal carbon is mixed with eggshells, and the mixing ratio of eggshells is preferably 6wt%-12wt%. The mixture is placed in an incinerator, air is introduced, and the temperature of the incinerator is set, preferably 800℃-900℃, and the incineration time is preferably 1-2h. The hydrothermal carbon mixed with eggshells is incinerated, and the bioavailability of phosphorus in the obtained incineration ash is higher, and the stable state of heavy metals is greatly increased. Most of the eggshells are composed of CaCO3, which will be converted into CaO during the incineration process. CaO will promote the conversion of phosphorus in the sludge from non-apatite inorganic phosphorus to apatite inorganic phosphorus, and apatite inorganic phosphorus has better bioavailability, so the bioavailability of phosphorus in the incineration ash is improved. During the hydrothermal process of the sludge, the form of heavy metals will change to a more stable oxidizable state and residual state. The heavy metals in the hydrothermal carbon are more stable, and the addition of CaO during the incineration process will further promote the conversion of heavy metals to a stable state. Both hydrothermal coupled incineration and CaO addition have positive effects on reducing the ecological risks of sewage sludge ash.

[0009] (3) Phosphorus leaching: The ash from the hydrothermal charcoal incineration of the sludge is leached with H2SO4. The incineration ash is added to deionized water, and then concentrated H2SO4 is added to adjust the pH, which is preferably 1-2. Thereafter, concentrated H2SO4 is added intermittently to keep the pH stable. The leaching time is preferably 6-12 hours, and stirring is continued at a speed of 150-250 r / min. After the leaching is completed, the acid leaching solution and the acid leaching residue are obtained by centrifugation and filtration, and the centrifugal speed is preferably 8000 r / min-12000 r / min, and the time is preferably 8-15 min.

[0010] (4) Treatment of acid leaching residue: Acid leaching residue can be used as a cement mortar additive. The high phosphorus content is considered to be a disadvantage for the use of sludge ash as a cement mortar additive. However, the phosphorus content in acid leaching residue is low and has little effect on the mechanical strength. Therefore, the residue has better mechanical strength.

[0011] (5) Preparation of modified pyrolytic carbon: Straw and eggshell are immersed in a magnesium chloride solution, modified by magnesium chloride, and then subjected to high-temperature pyrolysis. The resulting pyrolytic carbon has good adsorption properties.

[0012] (6) Adsorption of phosphorus in acid leaching solution by pyrolytic carbon: Modified pyrolytic carbon is used to adsorb phosphorus in acid leaching solution. Since most heavy metals in the ash exist in a stable state after hydrothermal carbonization and co-burning of eggshells, less heavy metals and some impurity ions are leached during acid leaching. The obtained phosphorus-rich biochar can be directly used as a soil conditioner.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] 1) Use hydrothermal carbonization coupled with incineration to treat sludge to prepare phosphorus-rich and heavy metal-stabilized sludge ash, improve the bioavailability of phosphorus in sludge, and reduce the leaching of heavy metals in sludge ash.

[0015] 2) Taking advantage of the good adsorption properties of straw and eggshell modified pyrolysis biochar, phosphorus in the sludge incineration ash leaching liquid was recovered and utilized to prepare soil conditioner, and the leached residue was used as a cement mortar additive, realizing the combination and multiple utilization of solid waste, the reduction and harmless treatment of sludge, and the resource utilization of waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0017] The technical methods in the embodiments of the present invention are described clearly and completely below.

[0018] like Figure 1 As shown, a method for recycling sludge and preparing a soil conditioner comprises the following steps:

[0019] Hydrothermal carbonization treatment: The sludge was subjected to hydrothermal reaction by mixing dry sludge with deionized water, and the solid-liquid ratio was set to 1:10. Before the hydrothermal carbonization reaction, N2 was filled into the reactor to exhaust the air. The stirring speed of the hydrothermal reactor was set to 300r / min. The hydrothermal carbonization reaction was carried out at the set temperature of 240℃ and the hydrothermal reaction time of 4h. After the reaction, the hydrothermal product was separated into solid and liquid.

[0020] Incineration treatment: The hydrothermal carbon obtained by hydrothermal carbonization was dried, crushed and mixed with eggshell powder at a mixing ratio of 10wt%. The mixture was placed in an incinerator, air was introduced, the incinerator temperature was set to 850℃, the incineration time was set to 1h, and the hydrothermal carbon mixed with eggshell was incinerated.

[0021] Phosphorus leaching: Sludge hydrothermal charcoal incineration ash is leached with H2SO4. The ash is added to deionized water, and then concentrated H2SO4 is added to adjust the pH to 2. After that, concentrated H2SO4 is added intermittently to keep the pH stable. The leaching time is set to 12 hours. Stir continuously, and the speed is set to 250r / min. After the reaction is completed, centrifuge at 8000r / min for 15 minutes, pass through a 0.45mm filter membrane, and obtain the acid leaching solution and acid leaching residue.

[0022] Preparation of modified pyrolytic carbon: The straw and eggshell are immersed in a magnesium chloride solution, stirred for 6 hours, and then placed in a drying oven for drying. The pyrolytic carbon is then subjected to high-temperature pyrolysis and rinsed with deionized water and dried for later use.

[0023] Adsorption of phosphorus in acid leaching solution by pyrolytic carbon: Phosphorus in acid leaching solution is adsorbed by modified pyrolytic carbon, and the obtained phosphorus-rich biochar can be directly used as a soil conditioner.

[0024] Treatment of acid leaching residue: The acid leaching residue can be used as cement mortar additive after filtering.

Claims

1. A method for recycling sludge and preparing a soil conditioner, characterized in that The steps include: 1) Nitrogen is filled into the reactor to expel air, and the sludge is sent into the reactor for hydrothermal carbonization reaction. After the reaction is completed, the obtained hydrothermal product is separated into solid and liquid to obtain hydrothermal charcoal; 2) mixing the hydrothermal charcoal obtained in step 1) with the eggshell, placing the mixture in an incinerator, introducing air, and incinerating the mixture to obtain incineration ash; 3) adding deionized water to the incineration ash of step 2), and then adding concentrated sulfuric acid, adjusting the pH, stirring to carry out phosphorus leaching, and intermittently adding concentrated sulfuric acid to keep the pH stable during the leaching process. After the leaching is completed, centrifugal filtration is performed to obtain an acid leaching solution and an acid leaching residue, and the acid leaching residue is used as a cement mortar additive; 4) Immersing straw and eggshell in magnesium chloride solution, modified by magnesium chloride, and then pyrolyzed at high temperature to obtain pyrolytic carbon; 5) using the pyrolytic carbon of step 4) to adsorb phosphorus in the acid leaching solution of step 3) to obtain phosphorus-rich biochar, which can be directly used as a soil conditioner; In step 2), the proportion of eggshell added to the hydrothermal charcoal is 6wt%-12wt%; The hydrothermal reaction temperature in step 1) is 210-280°C, the hydrothermal reaction time is 2-4h, and the stirring speed of the reactor is 250-350r / min; In step 3), concentrated sulfuric acid is added to adjust the pH to 1-2.

2. The method according to claim 1, characterized in that In step 1), the solid-liquid ratio of the sludge is 1:10-20.

3. The method according to claim 1, characterized in that In step 2), the incineration temperature is 800-900°C and the incineration time is 1-2h.

4. The method according to claim 1, characterized in that In step 3), the stirring speed is 150-250 r / min and the leaching time is 6-12 h.

5. The method according to claim 1, characterized in that In step 3), the centrifugal speed is 8000-12000 r / min and the time is 8-15 min.

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