Preserved fruit sludge-based biochar and its preparation method and application

Abstract

The invention discloses a kind of candied fruit sludge-based biochar and its preparation method and application, belonging to the technical field of resource utilization of food wastewater sludge and treatment of high-concentration organic candied fruit wastewater. The preparation method comprises the following steps: crushing dehydrated candied fruit sludge, dispersing and immersing in an alkaline solution, drying after immersion, pyrolyzing in an inert atmosphere, and immediately transferring the product into deionized water after pyrolysis, washing to neutrality, and drying to obtain the candied fruit sludge-based biochar. The invention uses dehydrated excess sludge generated in the biochemical treatment of candied fruit wastewater as raw material, and prepares a biochar material through a series of preparation methods such as activation and pyrolysis. The biochar material can be used for removing high-concentration organic matter and adjusting low pH value in candied fruit wastewater.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of food wastewater sludge and treatment of high-concentration organic preserved fruit wastewater, and in particular to preserved fruit sludge-based biochar and a preparation method and application thereof. Background Art

[0002] Wastewater generated during preserved fruit processing primarily comes from multiple processes, including washing, salting, and sugaring. The salting process produces the highest salt content and high concentrations of COD, accounting for approximately 5% to 10% of total preserved fruit wastewater. The sugaring process also produces wastewater containing high levels of organic matter and a slightly acidic nature, accounting for 10% to 15% of the total preserved fruit wastewater. Therefore, preserved fruit wastewater is highly acidic and contains high concentrations of organic pollutants. If discharged directly into rivers or farmland without proper treatment, it can lead to environmental problems such as water pollution and soil salinization.

[0003] Currently, coagulation is the most commonly used method to remove organic matter from preserved fruit wastewater. This method is unaffected by salinity and has strong resistance to shock loads from water quality fluctuations. However, its ability to remove organic matter is limited, the reagent costs are high, and it produces chemical sludge, leading to secondary pollution. Electrochemical and membrane treatment methods offer strong treatment capabilities, but are relatively expensive and unsuitable for large-scale industrial production. Preserved fruit wastewater has a high BOD5 / COD ratio, low nitrogen and phosphorus concentrations, and good biodegradability, making it suitable for biological treatment. However, the high organic matter concentration and low pH inhibit microbial activity. Therefore, water conditioning is urgently needed to adjust the pH and reduce the organic load before biological treatment of preserved fruit wastewater.

[0004] Given the water quality characteristics of preserved fruit wastewater, the sludge produced during its treatment contains high levels of sugars and, compared to other municipal and industrial sludges, higher carbon and ash content. This makes it potentially suitable for the production of biochar with a large specific surface area and pore volume, resistance to acid and salt corrosion, and rich functional groups. Currently, there are few reports on the research and application of preserved fruit sludge-based biochar. Summary of the Invention

[0005] In response to the above problems, the present invention provides a preserved fruit sludge-based biochar and a preparation method thereof, and also provides its application in removing high-concentration organic matter in preserved fruit wastewater and adjusting the pH value. The present invention can achieve zero pollutant emissions and resource utilization of sludge produced by preserved fruit enterprises.

[0006] The purpose of the present invention is achieved by adopting the following technical solutions:

[0007] A first aspect of the present invention is to provide a method for preparing preserved fruit sludge-based biochar, the method comprising the following steps:

[0008] The dehydrated preserved fruit sludge is crushed and dispersed and immersed in an alkaline solution. After the immersion is completed, it is dried and pyrolyzed in an inert atmosphere. After the pyrolysis is completed, the product is immediately transferred to deionized water, washed to neutrality, and dried to obtain the preserved fruit sludge-based biochar.

[0009] In some preferred embodiments, the moisture content of the dehydrated preserved fruit sludge is 20-30%.

[0010] In some preferred embodiments, the alkaline solution is a potassium hydroxide solution with a concentration of 5-25 wt%.

[0011] In other preferred embodiments, the dispersed solid-liquid ratio of the dehydrated preserved fruit sludge to the alkaline solution is 0.9-1.1 g / 10 mL.

[0012] In other preferred embodiments, the immersion temperature is 55-65° C., and the immersion time is 2.8-3.2 h.

[0013] In other preferred embodiments, the pyrolysis temperature is 300-700° C., the heating rate is 9-11° C. / min / / , and the pyrolysis time is 1-3 h.

[0014] The second aspect of the present invention is to provide a jelly sludge-based biochar, which is prepared by the above-mentioned preparation method.

[0015] The third aspect of the present invention is to provide a specific application of the preserved fruit sludge-based biochar, which is specifically used to reduce the organic matter content in preserved fruit wastewater and / or increase the pH value of preserved fruit wastewater.

[0016] A fourth aspect of the present invention is to provide a method for treating preserved fruit wastewater, the method comprising the following steps:

[0017] Adding the preserved fruit sludge-based biochar into preserved fruit wastewater for adsorption; or,

[0018] Aerating the preserved fruit wastewater and passing it through a filter layer containing the preserved fruit sludge-based biochar; or

[0019] The preserved fruit wastewater is firstly adsorbed by the preserved fruit sludge-based biochar, and then passes through a filter material layer including the preserved fruit sludge-based biochar after aeration.

[0020] The fifth aspect of the present invention is to provide a treatment device for preserved fruit wastewater, the treatment device including an upflow filter tank, the upflow filter tank including a water distribution area, a water filtration area and a water outlet area in sequence according to the water flow direction, the water distribution area is respectively connected to the water inlet device and the aeration device pipe, a perforated plate is provided at the connection between the water distribution area and the water filtration area, the water filtration area includes a supporting layer and a packing layer in sequence according to the water flow direction, and the packing layer includes the preserved fruit sludge-based biochar.

[0021] In some preferred embodiments, the supporting layer is a pebble layer.

[0022] The beneficial effects of the present invention are:

[0023] (1) Compared with municipal and industrial sludge, fruit sludge has a higher content of organic matter such as sugars, proteins and aliphatic compounds, and has a relatively large potential for preparing sludge carbon. In addition, the sludge contains metal impurities, which can be directly converted into adsorption sites during the pyrolysis process. The present invention uses the residual sludge generated in the biochemical treatment of fruit wastewater as raw material and prepares a biochar material through a series of preparation methods such as alkaline activation and pyrolysis. The performance is better than that of commercial activated carbon and can be applied to the treatment of organic matter and / or low pH values ​​in high-concentration organic wastewater, thereby achieving carbon sequestration and carbon reduction, waste treatment with waste, and resource utilization of solid waste.

[0024] (2) The present invention uses candied fruit sludge-based biochar as filler to construct an upward flow filter and use it as a candied fruit wastewater treatment device. The synergistic effect of the sludge biochar can effectively reduce the organic matter concentration of candied fruit wastewater and adjust the pH value at the same time. The highest organic matter removal rate for candied fruit wastewater is 80.9%, and the effluent pH value is 7.76, which can ensure that the candied fruit wastewater meets the discharge standards. The present invention has important practical significance for promoting the healthy and benign development of enterprises, improving the resource utilization rate of sludge, reducing carbon emissions, and improving environmental benefits, economic benefits and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention is further described with reference to the accompanying drawings. However, the embodiments in the accompanying drawings do not constitute any limitation to the present invention. A person skilled in the art can obtain other drawings based on the following drawings without creative effort.

[0026] Figure 1 is a scanning electron micrograph of the preserved fruit sludge-based biochar described in Example 17;

[0027] Figure 2 is a Fourier transform infrared spectrum of the preserved fruit sludge-based biochar described in Example 17;

[0028] Figure 3 is the X-ray energy spectrum of the preserved fruit sludge-based biochar described in Example 17;

[0029] Figure 4 is a schematic diagram of the structural composition of the filter treatment device described in Example 17;

[0030] Figure 5 This is the appearance of the preserved fruit sludge-based biochar before (left) and after (right) biofilm formation;

[0031] Figure 6This is a diagram of the biofilm status during the operation of the fiber filler filter, showing the aging and shedding of the biofilm;

[0032] Figure 7 This is a diagram of the biofilm status during the operation of the activated carbon filler filter, and the loss of activated carbon filler can be seen.

[0033] Figure numerals: 1-filter tank; 2-water distribution area; 3-water filtration area; 4-water outlet area; 5-peristaltic pump; 6-aeration pump; 7-orifice plate; 8-water tank; 9-gas flow meter; 31-support layer; 32-packing layer. DETAILED DESCRIPTION

[0034] The present invention is further described with reference to the following examples.

[0035] The embodiment of the present invention relates to a kind of jelly sludge-based biochar, and the preparation method of the jelly sludge-based biochar comprises the following steps:

[0036] (1) The dehydrated preserved fruit sludge was put into a grinder and pulverized for 30 seconds. The pulverized preserved fruit sludge was added to a 5-20 wt% potassium hydroxide solution at a solid-liquid ratio of 1 g / 10 mL for activation. The mixture was immersed and activated on a constant temperature magnetic stirrer at 650 rpm and 60° C. for 3 hours. After activation, the mixture was taken out and centrifuged and dried.

[0037] (2) Place the activated sludge obtained in step (1) in a square quartz boat and push it into the furnace of a tube furnace. Introduce nitrogen (at a flow rate of about 300 mL / m / / ). After exhausting all the air, turn on the tube furnace switch, set the heating rate to 10°C / m / / , heat it to 300-700°C, and keep it warm for 1-3 hours. After the program is completed, turn off the tube furnace and nitrogen.

[0038] (3) taking out the pyrolysis product and immediately placing it in deionized water, washing it repeatedly until the pH value of the supernatant is 7, and drying it in an oven at 105° C. to constant weight to obtain the preserved fruit sludge-based biochar;

[0039] The preserved fruit sludge described in the embodiment of the present invention was taken from a preserved fruit factory in Jiexi City, and its basic properties are shown in Table 1.

[0040] Table 1 Main physical and chemical properties of preserved fruit sludge described in Example

[0041]

[0042] Examples 1-16

[0043] The present invention designs a three-factor four-level orthogonal experiment based on pyrolysis temperature, pyrolysis time and KOH concentration to determine the optimal preparation conditions. The level factor table of the orthogonal experiment is shown in Table 2.

[0044] Table 2 Factor levels of orthogonal experiment

[0045]

[0046] The COD removal rate was used as an evaluation index. The COD removal rate was determined by adding 2.5 g of preserved fruit sludge-based biochar to 100 mL of simulated wastewater with a COD concentration of 15,000 mg / L, placing the mixture in a water bath shaker at 28°C and 150 rpm for 8 h. The results are shown in Table 3.

[0047] Table 3 Orthogonal test results

[0048]

[0049]

[0050] According to the experimental results in Table 3, the COD removal rate of the preserved fruit sludge-based biochar obtained under different preparation conditions was 12.18%-23.73%, and the unit adsorption capacity was 73.07 mg / g-142.40 mg / g.

[0051] The results of Table 3 were analyzed visually, and the analysis results are shown in Table 4;

[0052] Table 4 Results of intuitive analysis of orthogonal experiment

[0053]

[0054] Within the scope of the orthogonal test, it can be determined that the optimal preparation conditions of the preserved fruit sludge-based biochar are a pyrolysis temperature of 500°C, a pyrolysis time of 2.5 h, and a KOH concentration of 20 wt%.

[0055] Example 17

[0056] A method for preparing biochar based on preserved fruit sludge for treating preserved fruit wastewater comprises the following steps:

[0057] (1) The dehydrated preserved fruit sludge was crushed in a grinder for 30 seconds, and the crushed preserved fruit sludge was added to a 20 wt% KOH solution at a solid-liquid ratio of 1 g / 10 mL for activation. The mixture was immersed in a constant temperature magnetic stirrer at 650 rpm and 60° C. for 3 hours. After activation, the mixture was taken out and centrifuged and dried;

[0058] (2) The activated sludge obtained in step (1) was placed in a square quartz boat and pushed into the furnace of a tube furnace. Nitrogen (flow rate of about 300 mL / m / / ) was introduced. After the air was exhausted, the tube furnace switch was turned on, and the temperature was raised to 500°C at a heating rate of 10°C / m / / and kept at this temperature for pyrolysis for 2.5 h. After the program was completed, the tube furnace and nitrogen were turned off;

[0059] (3) taking out the pyrolysis product and immediately placing it in deionized water, washing it repeatedly until the pH value of the supernatant is 7, and drying it in an oven at 105° C. to constant weight to obtain the preserved fruit sludge-based biochar;

[0060] The specific surface area and average pore diameter of the carbon mesopores are 25.26-25.28 m 2 / g, 170.23-170.25 angstroms, which are approximately 4 times and 2.9 times that of commercial activated carbon.

[0061] The treatment performance of the preserved fruit sludge-based biochar on preserved fruit wastewater was evaluated using simulated preserved fruit wastewater:

[0062] 1. Static adsorption treatment

[0063] A solution with an initial COD concentration of 8000 mg / L, a pH value of 4, a salinity of 2%, and a sodium metabisulfite concentration of 2.5 g / L was used as simulated wastewater. 15 g / L of the preserved fruit sludge-based biochar was added to the simulated wastewater solution. A shake flask test was carried out at 150 rpm and 28°C for 8 hours. The COD removal rate was 27.12%-28.91%, and the effluent pH was 7.0.

[0064] The saturated adsorption fruit sludge-based biochar was dried at 105°C to constant weight, placed in a tube furnace, and pyrolyzed at 800°C for 10 min / / under N2 protection for three regenerations. After washing and drying with deionized water, a shake flask test was carried out in a constant temperature water bath shaker maintained at 28°C and 150 rpm for 8 hours. Its adsorption and organic matter removal performance can be restored to 90% of the initial value, indicating that the sludge-based biochar of the present invention has good regeneration performance.

[0065] 2. Biochar filter treatment

[0066] Set up the filter treatment device, see the attached Figure 4The treatment device includes an upflow filter 1, which is a rectangular parallelepiped made of organic glass material, 10.5 cm long, 8 cm wide and 70 cm high. The filter 1 includes a water distribution area 2, a water filtration area 3 and a water outlet area 4 in the direction of water flow. The water distribution area 2 is connected to the water inlet device and the aeration device pipeline respectively. The water inlet device includes a peristaltic pump 5, and the aeration device includes an aeration pump 6. A perforated plate 7 is provided at the connection between the water distribution area 2 and the water filtration area 3. The water filtration area 3 includes a supporting layer 31 and a filler layer 32 in the direction of water flow. The supporting layer is a pebble layer with a layer height of 5 cm, and the filler layer is preserved fruit sludge-based biochar with a layer height of 20 cm. During operation, the wastewater in the water tank 8 is pumped into the bottom of the filter tank 1 through the peristaltic pump 5, and the wastewater enters the filtration area 3 evenly through the water distribution area 2 and the orifice plate 7, and contacts the supporting layer 31 and the filler layer 32 in turn, and is finally discharged through the outlet area 4. The bottom of the filter tank 1 is connected to the aeration pump 6, and the dissolved oxygen content in the filter tank 1 is adjusted by the gas flow meter 9. Increasing the gas volume will significantly enhance the biochemical action of microorganisms on the filler surface, and synergize the adsorption and physical interception effects of the biochar to purify the wastewater.

[0067] A solution with an initial COD concentration of 8000 mg / L and a pH value of 4 was used as simulated wastewater. The water quality composition of the simulated wastewater is shown in Tables 5-6. A peristaltic pump was used for continuous upflow water inflow with an inlet flow rate of 20 L / d. The dissolved oxygen concentration was controlled to be 1 mg / L, the hydraulic retention time (HRT) was 120 m / / , and the biofilm was formed naturally. After 45 days of operation, the maximum COD removal rate was 66.9%, the pH value was stabilized at 3.61-3.96, and the biofilm was stably formed. The appearance of the fruit sludge-based biochar before (left) and after (right) biofilm formation is shown in FIG. Figure 5 .

[0068] Table 5 Water quality composition of the simulated wastewater

[0069]

[0070] Table 6 Water quality composition of the trace element solution

[0071]

[0072] 3. Static adsorption-biochar filter combined treatment

[0073] A solution with an initial COD concentration of 8000 mg / L, a pH value of 4, a salinity of 1%, and a sodium metabisulfite concentration of 2.5 g / L was used to simulate wastewater. 15 g / L of the preserved fruit sludge-based biochar was added. After 8 hours, the effluent entered the filter treatment device through a peristaltic pump, with continuous water inflow and outflow. After the filter treatment device was operated for 48 hours under the conditions of a dissolved oxygen concentration of 2.0 mg / L, a hydraulic retention time (HRT) of 120 m / / , and a temperature of 25°C, the maximum COD removal rate was 80.9% and the pH value was 7.76.

[0074] Example 18

[0075] The static adsorption method was used to evaluate the treatment performance of the cold fruit sludge-based biochar on actual cold fruit wastewater. The initial COD concentration of the cold fruit wastewater was 8800 mg / L, pH value was 3.95, salinity was 2%, and sodium metabisulfite concentration was 2.4 g / L. The cold fruit sludge-based biochar described in Example 17 was added to the wastewater, and a shake flask test was carried out at 150 rpm and 28°C for 8 hours. The COD removal rate was measured to be 26.21%-26.91%, and the effluent pH value was 6.5, which also indicated that the cold fruit sludge-based biochar was salt-tolerant.

[0076] Comparative Example 1

[0077] The same as the "filter tank treatment" described in Example 17 was used, except that the preserved fruit sludge-based biochar was replaced by fiber filler and commercial activated carbon filler for comparison.

[0078] The commercial activated carbon filler is 300 mesh powder from Tianjin Kemeiou Chemical Reagent Co., Ltd.; the fiber filler is a fiber bundle combined filler, and its specifications are shown in Table 7.

[0079] Table 7 Specifications of fiber bundle combined fillers

[0080]

[0081] Comparative Example 2

[0082] Biochar was prepared using municipal sludge as raw material. The preparation method was the same as that in Example 17, except that municipal sludge was used instead of the dehydrated preserved fruit sludge. The municipal sludge came from the dehydrated excess sludge of a sewage treatment plant and had a moisture content of 30%.

[0083] Comparative results show that under the same influent conditions and operating time, the maximum COD removal rate of the fiber-filled filter is 44.9%, and the effluent pH is 2.67-2.77; the maximum COD removal rate of the activated carbon-filled filter is 49.96%, and the effluent pH is 2.75-2.84; the maximum COD removal rate of the municipal sludge-based filter is 51.45%, and the effluent pH is 4.15-4.22. It can be seen that the three fillers are significantly less effective in removing organic matter than sludge carbon. At the same time, fiber fillers and commercial activated carbon fillers will cause a significant decrease in pH value. In addition, see the attached Figure 6-7 The biofilm in the fiber-filled filter frequently ages and falls off, the activated carbon-filled filter filler is easy to lose, and the fruit sludge-based biochar filler is the most stable.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for treating preserved fruit wastewater, characterized in that: The following steps are involved: Adding biochar based on preserved fruit sludge to preserved fruit wastewater for adsorption; or, Aerating the preserved fruit wastewater and passing it through a filter layer comprising preserved fruit sludge-based biochar; or First, the preserved fruit wastewater is adsorbed with preserved fruit sludge-based biochar, and then aerated and passed through a filter layer containing preserved fruit sludge-based biochar; The method for preparing the preserved fruit sludge-based biochar comprises the following steps: The dehydrated preserved fruit sludge is crushed and dispersed and immersed in an alkaline solution. After the immersion is completed, it is dried and pyrolyzed in an inert atmosphere. After the pyrolysis is completed, the product is immediately transferred to deionized water, washed to neutrality, and dried to obtain the preserved fruit sludge-based biochar.

2. The method for treating preserved fruit wastewater according to claim 1, wherein: The moisture content of the dehydrated preserved fruit sludge is 20-30%.

3. The method for treating preserved fruit wastewater according to claim 1, wherein: The alkaline solution is a potassium hydroxide solution with a concentration of 5-25wt%.

4. The method for treating preserved fruit wastewater according to claim 1, wherein: The dispersed solid-liquid ratio of the dehydrated preserved fruit sludge to the alkaline solution is 0.9-1.1 g / 10 mL.

5. The method for treating preserved fruit wastewater according to claim 1, wherein: The immersion temperature is 55-65° C., and the immersion time is 2.8-3.2 hours.

6. The method for treating preserved fruit wastewater according to claim 1, wherein: The pyrolysis temperature is 300-700° C., the heating rate is 9-11° C. / min, and the pyrolysis time is 1-3 hours.

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