Preparation method of sludge biochar material and application thereof in wastewater treatment

Abstract

The application discloses a preparation method of sludge biochar material and application of the sludge biochar material in wastewater treatment, and particularly relates to the following steps: mixing residual sludge and fly ash, uniformly mixing, adding sodium silicate and sodium bicarbonate into the mixture to obtain a mixed material; adding water into the mixed material to obtain a mixed slurry; kneading the mixed slurry into spherical particles; performing dehydration treatment on the spherical particles; performing anaerobic carbonization treatment on the dehydrated spherical particles; loading manganese elements on the product after the anaerobic carbonization treatment by using a chemical precipitation method to obtain the required sludge biochar material. Compared with a traditional substrate, the removal performance of the sludge biochar material for water quality (COD, TN and TP) is greatly improved; meanwhile, the sludge biochar material modified by loading Mn elements can realize the valence state circulation of Fe 2+ / Fe 3+ and Mn 2+ / Mn 4+ , and can significantly reduce the relative abundance of methanogens in the artificial wetland, thereby reducing the CH4 emission amount of the artificial wetland system.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of sludge biochar material, and also relates to the application of the sludge biochar material prepared by the method in wastewater treatment. BACKGROUND

[0002] Compared with traditional sewage treatment technology, constructed wetland (CW) has become a mature sewage treatment technology due to its simple construction, convenient maintenance, low operation cost and simple operation. However, from the perspective of carbon emission, CW has no advantage compared with traditional water treatment process. Methane, as the main type of greenhouse gas emission in CW, contributes more than 60% to the greenhouse effect. Therefore, limiting CH4 emission in CW is the key to reducing carbon emission. SUMMARY

[0003] The present application relates to a preparation method of sludge biochar material, and also relates to the application of the sludge biochar material prepared by the method in wastewater treatment.

[0004] The preparation method of the sludge biochar material comprises the following steps:

[0005] (1) mixing residual sludge and fly ash, adding sodium silicate and sodium bicarbonate into the mixture after uniform mixing to obtain a mixture;

[0006] (2) adding water into the mixture to obtain a mixed sludge;

[0007] (3) kneading the mixed sludge into spherical particles, and performing dehydration treatment on the spherical particles, and then performing anaerobic carbonization treatment on the dehydrated particles;

[0008] (4) loading manganese element on the product after anaerobic carbonization treatment by chemical precipitation method to obtain the required sludge biochar material.

[0009] In step (1), the mass ratio of residual sludge to fly ash is 1:1-1:1.5; the addition amount of sodium silicate is 10%-15% of the mass of the mixture; and the addition amount of sodium bicarbonate is 5%-10% of the mass of the mixture. Sodium silicate acts as an adhesive in the system, and appropriate addition can improve the compression resistance of the sludge biochar material; and sodium bicarbonate can make the obtained sludge biochar material have good porosity.

[0010] In step (2), the water content of the mixed sludge is 20%-40%.

[0011] The dehydration treatment in step (3) is drying or natural air drying, the drying temperature is 105-110 DEG C, the drying time is 30-60 min, the natural air drying temperature is 20-25 DEG C, and the air drying time is 10-12 h.

[0012] The anaerobic carbonization temperature in step (3) is 1080 DEG C-1100 DEG C, and the anaerobic carbonization time is 25-30 min. Without air input, the oxidation of iron and aluminum in the activated sludge can be effectively prevented, so that the iron and aluminum can be kept as ferrous and aluminum salts. At the same time, a large amount of volatile gas is generated in the high-temperature pyrolysis of the internal organic matter of the sludge during the carbonization process, thereby effectively improving the pore structure of the sludge biochar, and obtaining sludge biochar with high porosity and large specific surface area.

[0013] In step (3), the product after anaerobic carbonization treatment is screened, and the particles that meet the conditions of a specific surface area greater than 5000 cm 2 / g, a porosity greater than 40%, and a particle size range of 5 mm-8 mm are selected for subsequent modification treatment.

[0014] In step (4), the chemical precipitation method specifically comprises the following steps: first, a mixed solution containing sludge biochar and manganese salt is prepared; then, the mixed solution is mixed with a potassium permanganate solution, and after the reaction, a preservative film is wrapped outside the reaction container containing the reaction solution, and the reaction is allowed to stand and age (the purpose is to ensure complete reaction and a high loading rate of Mn elements on the sludge biochar); finally, the supernatant is poured off, the solid product is collected, and vacuum drying treatment is performed.

[0015] The manganese salt is manganese sulfate monohydrate, and the mass ratio of the sludge biochar to the manganese sulfate monohydrate is 1:0.1-1:0.2.

[0016] In the mixed solution, the concentration of the sludge biochar is 200-2200 g / L, and the concentration of Mn 2+ is 29-30 g / L.

[0017] The mixed solution and the potassium permanganate solution are mixed in a volume ratio of 1-2:20, and the concentration of the potassium permanganate solution is 90-92 g / L.

[0018] Advantages: Compared with the prior art, the present application has the following significant advantages:

[0019] (1) The present application recycles residual sludge, and through anaerobic carbonization technology, a sludge biochar capable of storing carbon elements is prepared (the carbon element content of the sludge biochar material prepared in the present application is significantly higher than that of ordinary ceramsite materials, and the storage of carbon elements is achieved), and through chemical precipitation method modification, a sludge biochar material loaded with Mn elements is obtained, thereby realizing the resource utilization of waste;

[0020] (2) The sludge biochar material prepared by the application can be applied to a constructed wetland, and due to the iron element contained in the sludge biochar material and the modified Mn element, the Fe 2+ / Fe 3+ and Mn 2 + / Mn 4+ valence cycle is realized through the dissimilatory metal reduction process, the mutual valence state conversion can effectively promote the nitrification and denitrification reaction of the constructed wetland system, thereby improving the denitrification performance of the constructed wetland system; in addition, the existence of Fe 2+ and Mn 2+ can form a precipitate with inorganic carbonate and phosphorus elements in the constructed wetland system, thereby improving the phosphorus removal effect of the constructed wetland system.

[0021] (3) Meanwhile, when the sludge biochar material prepared by the application is applied to a constructed wetland, the relative abundance of methanogens can also be reduced, because on the one hand, the existence of Mn 4+ can inhibit the growth of methanogens, and on the other hand, under the action of an electric field, the relative abundance of electrogenerating bacteria can be greatly increased, further significantly reducing the relative abundance of methanogens (the system after power-on is more suitable for the growth of electrogenerating bacteria and is not conducive to the growth of methanogens), thereby effectively reducing the CH4 emission amount of the constructed wetland system. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a real object diagram of the sludge biochar before loading Mn element prepared in Example 1;

[0023] Figure 2 is a morphology diagram of ordinary ceramsite (a), sludge biochar before loading Mn element (b) and sludge biochar material (c) prepared in Example 1 under a scanning electron microscope;

[0024] Figure 3 is an XRD characterization diagram of ordinary ceramsite (a), sludge biochar before loading Mn element (b) and sludge biochar material (c) prepared in Example 1

[0025] Figure 4 is an FTIR diagram of ordinary ceramsite, sludge biochar before loading Mn element and sludge biochar material prepared in Example 1;

[0026] Figure 5 is a mapping diagram of ordinary ceramsite, sludge biochar before loading Mn element and sludge biochar material prepared in Example 1 under a scanning electron microscope;

[0027] Figure 6Figures (a) and (b) are a corresponding physical diagram and a schematic diagram of the constructed constructed wetland device to which the sludge biochar material prepared in Example 1 is applied;

[0028] Figure 7 Figures showing the abundance of each bacterial group in the constructed wetland systems of groups 1, 2, 3 and 4;

[0029] Figure 8 Figure showing the abundance of methanogens in the constructed wetland systems of groups 1, 2, 3 and 4. DETAILED DESCRIPTION

[0030] The source of the excess sludge in the embodiments of the present application is: the excess sludge is taken from the dewatered sludge of a sewage treatment plant in Xinzheng, Zhengzhou, which adopts an A2 / O treatment process, and has a daily sewage treatment capacity of 100,000 tons. The fly ash is purchased from a certain thermal power plant and is off-white. The excess sludge is pretreated: because the sludge has a high water content, the water is removed by natural air drying (drying in an oven at 105℃ for 10h). The treated sludge and waste activated carbon are ground in a sample preparation machine and pulverized to a powder. Finally, the sludge, waste activated carbon and fly ash are sieved with a 100-mesh standard sieve (stored in a sealed bag).

[0031] Example 1

[0032] The preparation method of the sludge biochar material of the present application comprises the following steps:

[0033] (1) 400g of excess sludge and 400g of fly ash are mixed, and 100g of sodium silicate and 50g of sodium bicarbonate are added to the mixture to obtain a mixed material;

[0034] (2) water is added to the mixed material to obtain a mixed slurry; the water content of the mixed slurry is 20%;

[0035] (3) the mixed slurry is kneaded into spherical particles, which are first subjected to a dewatering treatment, and then subjected to an anaerobic carbonization treatment after dewatering; a sludge biochar is obtained, which has a specific surface area of 25.518m 2 / g, a porosity of 51.05%, and a particle compressive strength of 100N;

[0036] The specific process of the dewatering treatment is as follows: the drying temperature is set to 105℃, and the drying time is 60min; to ensure the integrity of the green balls in the preheating stage without cracking, and to reduce the content of free water;

[0037] The specific process of the anaerobic carbonization treatment is as follows: the prepared raw material ball is loaded into a ceramic boat, placed into a tube furnace, sealed, and the process starts to rise to the target temperature at 5 DEG C / min from room temperature according to the setting, and the nitrogen flow rate is kept at 50 mL / min; the preheating temperature is set to 400 DEG C, the preheating time is 30 min, the sintering temperature is selected to be 1100 DEG C, and the holding time is 30 min; after the roasting is completed, the high-temperature box furnace is automatically controlled to room temperature, and then the sintered ceramsite (sludge biochar) is taken out.

[0038] (4) The manganese element is loaded on the product after the anaerobic carbonization treatment by using the chemical precipitation method to obtain the required sludge biochar material, specifically as follows: 200 g of the sludge biochar dried to a constant weight is taken in a 2L beaker, 29.26 g of MnSO4·H2O is taken, then 1000 mL of ultrapure water is added, and the stirring is continuously carried out for 2 h; 18.22 g of KMnO4 is dissolved in 200 mL of ultrapure water to obtain a potassium permanganate solution, then the potassium permanganate solution after the dissolution is slowly added to the above-mentioned 2L beaker and continuously stirred until a brown precipitate is generated and the stirring is continuously carried out for 30 min, then the beaker containing the mixed solution is wrapped with a preservative film, and is placed and aged for 24 h; finally, the supernatant is poured off, the solid product is collected, the oven temperature is set to 105 DEG C, and the drying is carried out for 20 h to obtain the sludge biochar material of the application.

[0039] The sludge biochar material prepared in Example 1 is applied to the constructed wetland system:

[0040] Four groups of constructed wetland systems are provided, and the system structure schematic diagram is shown in Figure 6 The four groups of constructed wetland systems are all made of acrylic material, with an inner diameter of 15 cm and a height of 48 cm. According to the different filter materials filled, each device is divided into four regions from bottom to top, which are the bottom region, the anode region, the middle region and the cathode region. Specifically, the bottom region of the four groups of devices is filled with zeolite (particle size 8 cm-12 cm) as the water distribution layer, and the filling height is 10 cm; the anode region of the four groups of devices is filled with coconut activated carbon (particle size 3 cm-5 cm) and carbon felt-stainless steel mesh is placed in the middle as the anode electrode of CW-MFC, and the filling height is 5 cm; the cathode region of the four groups of devices is filled with the same filter material as the anode region, and the filling height is also 5 cm; in addition, the anode and cathode are respectively connected with the lead wire (copper wire, 1 mm) and the external power supply, and the lead wire connection submerged in the device is first coated with conductive glue, and then coated with epoxy resin after air drying, to avoid short circuit of the lead wire and water.

[0041] The middle matrix of the first, second and third groups of devices is ordinary ceramsite, sludge biochar before loading Mn element and sludge biochar material prepared in Example 1 respectively. The middle matrix of the fourth group of devices is the sludge biochar material prepared in Example 1, and the device is connected with an external circuit.

[0042] Four sets of devices were operated for 15 days to treat artificially prepared wastewater at hydraulic retention times (HRTs) of 12h, 24h, 48h, and 72h. The results showed that the sludge biochar before Mn loading and the sludge biochar material prepared in Example 1 significantly improved the purification capacity of the constructed wetland system for traditional water quality indicators such as COD, TN, and TP compared to ordinary ceramsite. The enhanced pollution reduction capacity of the sludge biochar material prepared in Example 1 for the constructed wetland system is related to its larger specific surface area and higher porosity. Furthermore, the sludge biochar material prepared in Example 1, rich in the metal elements Fe and Mn, can achieve the system in a reduced Fe state. 2+ / Mn 2+ and oxidized Fe 3+ / Mn 4+ The changes in valence states between electrons accelerate the electron transfer rate within the system, which helps to enhance the water purification effect of the system.

[0043] Table 1 shows the water treatment effects of the four constructed wetlands.

[0044]

[0045]

[0046] The CO2 and CH4 emissions from the four constructed wetlands were then monitored using the static gas chamber method. The application of the sludge biochar material prepared in Example 1 relatively increased the CO2 emission flux of the constructed wetlands, increasing it by 19.6%, but significantly reduced the CH4 emission flux, decreasing it by 32.7%. The carbon emissions of the four constructed wetlands were calculated using the global warming potential (GWP). In summary, the CO2-eq emission flux of the constructed wetland system using the sludge biochar material prepared in Example 1 was reduced by approximately 30.2% compared to ordinary expanded clay pellets, indicating that the sludge biochar material prepared in Example 1 can effectively suppress greenhouse gas emissions in the CW-MFC system.

[0047] Table 2. GWP calculation results for four groups of constructed wetlands

[0048]

[0049]

[0050] pass Figure 2 Scanning electron microscopy (SEM) revealed that, compared to ordinary ceramsite materials, the sludge biochar material of this invention has higher porosity and a larger specific surface area. This not only provides favorable attachment sites and reproductive space for microorganisms but also delays the clogging of constructed wetlands (achieved by increasing the abundance of EPS-degrading bacteria), thereby extending the service life of constructed wetlands and improving their treatment efficiency.Figure 5 Mapping results show that the carbon content in sludge biochar material is as high as 28%, which is significantly higher than that of ordinary ceramsite material of 12%. Through Figure 4 Fourier infrared spectroscopy (FTIR) analysis shows that the carbon element in sludge biochar material exists in the form of C single element. Through Figure 3 X-ray diffraction (XRD) analysis shows that sludge biochar material has strong chemical stability and mechanical strength, and has the effect of sealing toxic and harmful substances in residual sludge.

[0051] Through Figures 7-8 It can be seen that in the first, second, third and fourth groups of devices, the relative abundance of electricity-producing bacteria is higher and higher, while the relative abundance of methanogens decreases significantly, thereby achieving the effect of effectively reducing the CH4 emission of constructed wetland system.

[0052] Compared with traditional substrates, the removal performance of sludge biochar material constructed by constructed wetland device on water quality (COD, TN, TP) has been greatly improved; at the same time, the sludge biochar material modified by loading Mn element can realize the valence cycle of Fe 2+ / Fe 3+ and Mn 2+ / Mn 4+ , on the one hand, and can significantly reduce the relative abundance of methanogens in constructed wetland, thereby reducing the CH4 emission of constructed wetland system.

Claims

1. A method for preparing sludge biochar material, characterized in that, Includes the following steps: (1) Mix the remaining sludge and fly ash, and after mixing, add sodium silicate and sodium bicarbonate to obtain a mixture; (2) Add water to the mixture to obtain a mixed mud; (3) The mixed mud is kneaded into spherical particles. The spherical particles are first dehydrated and then anaerobic carbonized. The temperature of anaerobic carbonization is 1080℃~1100℃ and the time of anaerobic carbonization is 25~30min. (4) Manganese element is loaded onto the product after anaerobic carbonization by chemical precipitation to obtain the desired sludge biochar material. The sludge biochar material prepared by the above method is applied to constructed wetlands as a substrate, and the constructed wetland device is connected to an external circuit.

2. The method for preparing sludge biochar material according to claim 1, characterized in that: In step (1), the mass ratio of residual sludge to fly ash is 1:1 to 1:1.5; the amount of sodium silicate added is 10% to 15% of the mass of the mixture; and the amount of sodium bicarbonate added is 5% to 10% of the mass of the mixture.

3. The method for preparing sludge biochar material according to claim 1, characterized in that: In step (2), the moisture content of the mixed mud is between 20% and 40%.

4. The method for preparing sludge biochar material according to claim 1, characterized in that: In step (3), the dehydration process is as follows: drying or natural air drying; the drying temperature is 105~110℃ and the drying time is 30~60min; the natural air drying temperature is 20~25℃ and the air drying time is 10~12h.

5. The method for preparing sludge biochar material according to claim 1, characterized in that: In step (3), the products after anaerobic carbonization are screened, and those that simultaneously meet the requirement of a specific surface area greater than 5000 cm² are selected. 2 Particles with a porosity greater than 40% and a particle size range of 5mm to 8mm were subjected to subsequent modification treatment.

6. The method for preparing sludge biochar material according to claim 1, characterized in that: In step (4), the chemical precipitation method is as follows: first, prepare a mixed solution containing sludge biochar and manganese salt; then mix the mixed solution with potassium permanganate solution, and after the reaction, wrap the reaction container containing the reaction solution with plastic wrap and let it stand for aging; finally, pour off the supernatant, collect the solid product, and vacuum dry it.

7. The method for preparing sludge biochar material according to claim 6, characterized in that: The manganese salt is manganese sulfate monohydrate; the mass ratio of sludge biochar to manganese sulfate monohydrate is 1:0.1~1:0.

2.

8. The method for preparing sludge biochar material according to claim 7, characterized in that: In the mixed liquor, the concentration of sludge biochar is 200~2200 g / L, and Mn 2+ The concentration is 29~30g / L.

9. The method for preparing sludge biochar material according to claim 6, characterized in that: The mixing volume of the mixed solution and the potassium permanganate solution is 1~2:20; the concentration of the potassium permanganate solution is 90~92g / L.

Images