Method for preparing phosphorus adsorbent by anaerobic digestion and activation of sludge-based biochar

Abstract

The invention relates to a method for preparing a phosphorus adsorbent by anaerobic digestion activated sludge-based biochar. Raw material sludge (RSBC) pretreated by NaOH + Mg (OH) 2 and anaerobic digestion sludge (ADBC) are used as raw materials to synthesize two biochar, and the biochar is used for removing phosphate in an aqueous solution; aDBC has a higher pH value, a stronger aromatic condensation reaction and lower biotoxicity, and the content of Mg in ADBC-600 exceeds 2.84% (RSBC is 0.55%). A laboratory adsorption experiment shows that the maximum adsorption capacity of ADBC-600 on phosphate is 23.2 mg / g, and is 1.3 times that of RSBC-600. According to the method, the dynamic removal process of the ADBC-600 is well fitted through the quasi-secondary dynamic model, and the Langmuir model has good correlation on balance removal data of the ADBC-600. The chemical precipitation method may be the main mechanism of ADBC adsorption of phosphate. The method has very important application in phosphorus adsorption.

Description

Technical Field

[0001] The present invention belongs to the technical fields of adsorption materials and environmental protection, and particularly relates to a phosphorus adsorbent prepared from anaerobic digestion activated sludge-based biochar, a preparation method thereof, and an application thereof. Background Art

[0002] The activated sludge process has been widely used in municipal and industrial wastewater treatment plants (WWTPs) for more than 100 years due to its high efficiency in removing organic pollutants. However, a large amount of waste activated sludge (WAS) is inevitably generated during the biological wastewater treatment process, becoming a severe environmental problem faced by the sewage industry. Due to land shortages, severe secondary pollution, and increasingly strict environmental regulations, most commonly used waste disposal methods (such as landfills and incineration) are not suitable. Therefore, appropriate strategies are needed to achieve the recycling and waste-to-energy conversion of WAS. At this critical moment, anaerobic digestion is recommended as an effective WAS treatment technology, through which sludge reduction and the recovery of renewable resources (such as volatile fatty acids (VFAs) and biogas) can be achieved simultaneously. The potential application of anaerobic digestion as a viable and sustainable sludge management solution has been widely recognized. This study proposed a new strategy for producing beneficial products of anaerobic digestion sludge-based biochar by pyrolysis treatment of sludge. Biochar was prepared by pyrolyzing raw sludge and anaerobic digestion sludge, and the physicochemical properties of the prepared biochar were characterized. At the same time, the anaerobic digestion sludge-based biochar was used as an adsorbent to adsorb phosphate. Subsequently, the effect of applying phosphate-adsorbing biochar on plant growth was evaluated through pot experiments. The specific objectives of this study were: (1) to investigate whether anaerobic digestion sludge can be considered a potentially promising raw material for biochar production, (2) to determine the adsorption characteristics of phosphate on biochar produced from anaerobic digestion sludge, and (3) to evaluate the effectiveness of phosphate-adsorbing biochar as a plant growth fertilizer. Summary of the Invention

[0003] Technical Problem to be Solved: In view of the research field of phosphorus adsorption mentioned above, especially the problems currently faced by anaerobic digestion activated sludge-based biochar, the present invention provides a phosphorus adsorbent, a preparation method thereof, and an application thereof.

[0004] Technical solution: 1. A method for preparing a phosphorus adsorbent from anaerobic digested activated sludge-based biochar, which is characterized in that biochar is synthesized from NaOH + Mg(OH)2 pre-anaerobic digested sludge (ADBC) as raw material and is used to remove phosphate in aqueous solution. The preparation steps are as follows: (1) Add a mixture of NaOH and Mg(OH)2 to anaerobic digested sludge (ADBC) to adjust the pH value to 10.0; (2) First, centrifuge at a speed of 5000 revolutions per minute for 5 minutes, collect the solid residue, and dry it in an oven at 80°C for 3 days; (3) Place a certain amount of the dried sample in a porcelain boat and pyrolyze it in a horizontal muffle furnace under N2 atmosphere; (4) After pyrolysis, sieve the prepared biochar through a 2 mm sieve, weigh and package it, and then conduct characterization; Preferably, in step (1), a mixture of NaOH and Mg(OH)2 is added to anaerobic digested sludge (ADBC) to adjust the pH value to 10.0.

[0005] Preferably, in step (2) above, centrifuge at a speed of 5000 revolutions per minute for 5 minutes.

[0006] Preferably, in step (3) above, at the required temperatures of 400, 500, and 600°C, the pyrolysis rate is 10°C min - 1, and the residence time is 2 h.

[0007] Preferably, in step (4) above, it is a 2 mm sieve.

[0008] The phosphorus adsorbent prepared by the above preparation method.

[0009] The above phosphorus adsorbent, a method for preparing a phosphorus adsorbent from anaerobic digested activated sludge-based biochar.

[0010] The application of the above phosphorus adsorbent in catalytic phosphorus adsorption.

[0011] The application of the above phosphorus adsorbent in phosphorus adsorption, which is characterized in that the phosphate adsorption experiment is carried out in a 250 mL conical flask. 0.1 g of each biochar (RSBC or ADBC) is added to 100 mL of 50 mg / L P phosphate solution. The flask is placed in an air bath shaker with a rotation speed of 150 rpm and a constant temperature of 25±2°C. After stirring for 24 h, centrifuge at 5000 rpm for 5 min, filter with a 0.22 μm PFS filter membrane, and then conduct analysis. The filtered solid sample is dried at 60°C, ground, and sieved through a 2 mm sieve. The biochar adsorbed with phosphorus is respectively labeled as P-RSBC and P-ADBC for subsequent plant experiments.

[0012] Beneficial effects

[0013] (1) ADBC has a higher pH value, stronger aromatic condensation reaction and lower biotoxicity, and the Mg content in ADBC-600 exceeds 2.84%; (2) The maximum adsorption capacity of ADBC-600 for phosphate is 23.2 mg / g 432 (3) It is considered to be a phosphorus-rich fertilizer that can improve soil fertility and plant growth. These findings provide a clear closed-loop method for sludge management to achieve resource recovery and zero sludge discharge. Description of the Drawings

[0014] Figure 1 Phosphate adsorption of two biochars at different temperatures; Figure 2 Closed-loop integrated system of NaOH + Mg(OH)2 anaerobic digestion and pyrolysis in sewage treatment plants;

[0015] Embodiments To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the typical but non-limiting embodiments of the present invention are as follows: Example 1

[0016] A method for preparing a phosphorus adsorbent from anaerobic digestion activated sludge-based biochar, characterized in that biochar is synthesized from NaOH + Mg(OH)2 pre-anaerobic digested sludge (ADBC) as a raw material and used to remove phosphate in aqueous solution. The preparation steps are: (1) Add a mixture of NaOH and Mg(OH)2 to anaerobic digested sludge (ADBC) to adjust the pH value to 10.0; (2) First, centrifuge at a speed of 5000 revolutions per minute for 5 minutes, collect the solid residue, and dry it in an 80°C oven for 3 days; (3) Place a certain amount of the dried sample in a porcelain boat and pyrolyze it at 400°C in a horizontal muffle furnace under N2 atmosphere; (4) After pyrolysis, pass the prepared biochar through a 2 mm sieve, weigh it, package it, and then conduct characterization; Example 2

[0017] A method for preparing a phosphorus adsorbent from anaerobic digestion activated sludge-based biochar, characterized in that biochar is synthesized from NaOH + Mg(OH)2 pre-anaerobic digested sludge (ADBC) as a raw material and used to remove phosphate in aqueous solution. The preparation steps are: (1) Add a mixture of NaOH and Mg(OH)2 to anaerobic digested sludge (ADBC) to adjust the pH value to 10.0; (2) First, centrifuge at a speed of 5000 revolutions per minute for 5 minutes, collect the solid residue, and dry it in an 80°C oven for 3 days; (3) Place a certain amount of the dried sample in a porcelain boat and pyrolyze it at 500°C in a horizontal muffle furnace under N2 atmosphere; (4) After pyrolysis, pass the prepared biochar through a 2 mm sieve, weigh it, package it, and then conduct characterization; Example 3

[0018] A method for preparing a phosphorus adsorbent from anaerobic digestion activated sludge-based biochar, characterized in that biochar is synthesized from NaOH + Mg(OH)2 pre-anaerobic digestion sludge (ADBC) as a raw material and is used to remove phosphate in an aqueous solution. The preparation steps are as follows: (1) Add a mixture of NaOH and Mg(OH)2 to the anaerobic digestion sludge (ADBC) to adjust the pH value to 10.0; (2) First, centrifuge at a speed of 5000 revolutions per minute for 5 minutes, collect the solid residue, and dry it in an oven at 80 °C for 3 days; (3) Place a certain amount of the dried sample in a porcelain boat and pyrolyze it at 600 °C in a horizontal muffle furnace under a N2 atmosphere; (4) After pyrolysis, pass the prepared biochar through a 2 mm sieve, weigh it, package it, and then conduct characterization; Comparative Example 1

[0019] A method for preparing a phosphorus adsorbent from anaerobic digestion activated sludge-based biochar, characterized in that biochar is synthesized from NaOH + Mg(OH)2 raw sludge (RSBC) as a raw material and is used to remove phosphate in an aqueous solution. The preparation steps are as follows: (1) Add a mixture of NaOH and Mg(OH)2 to the raw sludge (RSBC) to adjust the pH value to 10.0; (2) First, centrifuge at a speed of 5000 revolutions per minute for 5 minutes, collect the solid residue, and dry it in an oven at 80 °C for 3 days; (3) Place a certain amount of the dried sample in a porcelain boat and pyrolyze it at 600 °C in a horizontal muffle furnace under a N2 atmosphere; (4) After pyrolysis, pass the prepared biochar through a 2 mm sieve, weigh it, package it, and then conduct characterization; Table 1 Activity evaluation results of phosphorus adsorbents sample Example 1 Example 2 Example 3 Comparative Example 1 temperature 400 500 600 600 experimental substance ADBC ADBC ADBC RSBC Adsorption rate (%) 17.5 20 22.5 10 As can be seen from Table 1, biochar phosphorus adsorbents were prepared from ADBC in the examples, while the comparative example used RSBC as the raw material. It can be seen from the table that although the calcination temperature is the same, the biochar phosphorus adsorbent using ADBC as the raw material has a very high adsorption rate. For adsorbents with the same raw material, when the temperature is changed, 600 °C has a higher adsorption rate.

[0020] Figure 2 As shown. A closed-loop integrated system for NaOH + Mg(OH)2 anaerobic digestion and pyrolysis in a sewage treatment plant was established.

Claims

1. A method for preparing a phosphorus adsorbent from anaerobic digestion activated sludge-based biochar, characterized in that, Using pre - anaerobic digested sludge (ADBC) with NaOH + Mg(OH) 2 as raw materials, biochar was synthesized and used to remove phosphate in aqueous solution. The preparation steps were as follows: (1) Add a mixture of NaOH and Mg(OH)2 to anaerobic digested sludge (ADBC) to adjust the pH value to 10.0; (2) First, centrifuge at a speed of 5000 revolutions per minute for 5 minutes, collect the solid residue, and dry it in an oven at 80 °C for 3 days; (3) Place a certain amount of the dried sample in a porcelain boat and pyrolyze it in a horizontal muffle furnace under N2 atmosphere; (4) After pyrolysis, sieve the prepared biochar through a 2 - mm sieve, weigh it, package it, and then conduct characterization; According to the preparation method of the phosphorus adsorbent described in claim 1, a mixture of NaOH and Mg(OH)2 is added to the anaerobic digestion sludge (ADBC) in step (1), and the pH value is adjusted to 10.0 According to the preparation method of the phosphorus adsorbent described in claim 1, characterized in that, In step (2), centrifuge at a speed of 5000 revolutions per minute for 5 minutes According to the preparation method of the phosphorus catalyst described in claim 1, characterized in that, In step (3), at the required temperatures of 400, 500 and 600 °C, the pyrolysis rate is 10 °C min-1, and the residence time is 2 h According to the preparation method of the manganese carbonate catalyst described in claim 1, characterized in that in step (4) it is a 2 mm sieve A phosphorus adsorbent prepared from anaerobic digestion activated sludge-based biochar by the preparation method according to any one of claims 1-5.

2. According to the manganese carbonate catalyst described in claim 6, characterized in that, Using pre - anaerobic digested sludge (ADBC) with NaOH + Mg(OH) 2 as raw materials, biochar was synthesized and used to remove phosphate in aqueous solution.

3. The biochar catalyst described in claim 7 is used for removing phosphate in an aqueous solution.

4. Application of the phosphorus adsorbent prepared from anaerobic digestion activated sludge-based biochar according to claim 8, characterized in that, The phosphate adsorption experiment is carried out in a 250 mL conical flask. 0.1 g of each biochar (RSBC or ADBC) is added to 100 mL of a 50 mg / L P phosphate solution. The flask is placed in an air bath shaker at a speed of 150 rpm and a constant temperature of 25 ± 2 °C. After stirring for 24 h, centrifuge at 5000 rpm for 5 min, filter with a 0.22 μm PFS filter membrane and then analyze. The filtered solid sample is dried at 60 °C, ground and passed through a 2 mm sieve. The biochar adsorbed with phosphorus is respectively labeled as P-RSBC and P-ADBC for subsequent plant experiments.

Images