Livestock and poultry breeding wastewater treatment method aiming at returning to field

Abstract

The invention provides a livestock and poultry breeding wastewater treatment method aiming at returning to the field, a short sludge age SBR + oxalic acid assisted Fenton technology is adopted, and the short sludge age SBR + oxalic acid assisted Fenton technology comprises the following steps: (1) an aerobic unit adopts a sequencing batch activated sludge process (SBR), the sludge age of an aerobic biological treatment process is controlled to be 3 days, and nitrifying bacteria growing slowly are removed from a system; and (2) an oxalic acid-assisted Fenton oxidation method is adopted to carry out advanced treatment on the effluent of the short-sludge-age SBR reactor, so that the initial pH range of the reaction can be widened, and tetracycline antibiotics in the effluent can be effectively removed. According to the method disclosed by the invention, antibiotics can be effectively removed while the livestock and poultry breeding wastewater is kept to be returned to the field and the fertilizer efficiency is utilized, and the treated wastewater can be directly used as irrigation water of a farmland.

Description

Technical Field

[0001] The invention relates to the field of sewage treatment, and in particular to a method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland. Background Art

[0002] Antimicrobial drugs cannot be fully utilized in animals and will enter the water and soil environment as livestock and poultry manure is returned to the fields, posing a threat to ecological and environmental safety. Especially in environmentally sensitive areas such as drinking water sources, they may pose potential risks to the safety of drinking water quality.

[0003] After proper treatment, livestock and poultry wastewater can be returned to the fields as fertilizer, which can not only make full use of the rich nitrogen and phosphorus in the wastewater and reduce the use of fertilizers in agricultural activities, but also effectively solve the problems of high wastewater treatment costs and low emission rates that meet standards. The current anaerobic livestock and poultry wastewater treatment model (sewage → biogas tank → storage tank → return to the field) has a poor removal effect on new antibiotic pollutants. When livestock and poultry wastewater is returned to the fields as fertilizer, the new antibiotic pollutants remaining in it will pollute the farmland and pollute groundwater or surface water through leaching or surface runoff. In addition, the current livestock and poultry wastewater return model also requires that the wastewater be appropriately diluted with nearby river water when it is returned to the fields, otherwise the concentration of pollutants (COD) is too high, which can easily cause crop root rot and seedling burn. Using river water to dilute sewage when returning to the fields will inevitably increase the total amount of irrigation water, resulting in the inability of the manure and sewage disposal land matched according to the principle of "matching planting and breeding" to absorb all sewage, and there is a high risk of environmental pollution.

[0004] Aerobic biological treatment processes can not only effectively degrade new antibiotic pollutants, but also further reduce the COD of wastewater, thereby reducing the amount of dilution water used when returning livestock and poultry wastewater to the fields, or even eliminating the need for dilution water. However, in the process of using aerobic biological treatment processes to degrade antibiotics and COD, ammonia nitrogen nitrification is often accompanied. The concentration of ammonia nitrogen in livestock and poultry wastewater is high, and ammonia nitrogen nitrification consumes a large amount of alkalinity. If the alkalinity is not recovered through pre-denitrification denitrification, the alkalinity must be supplemented artificially, otherwise the aerobic biochemical system cannot operate normally, but the cost of supplementing alkalinity is very high, which is difficult for livestock and poultry breeding companies to bear. On the contrary, if the alkalinity is recovered through pre-denitrification denitrification, a large amount of nitrogen will inevitably be lost, and the value of the treated water returned to the fields as fertilizer will be greatly reduced.

[0005] In addition, the nitrate nitrogen generated by the nitrification of ammonia nitrogen is negatively charged, while soil colloids have the same charge. The two repel each other, which easily causes the loss of nitrate nitrogen and reduces the fertilizer efficiency of nitrogen fertilizer. Therefore, inhibiting the nitrification of ammonia nitrogen can increase the utilization value of wastewater. Therefore, how to retain ammonia nitrogen while ensuring the efficient removal of new pollutants such as COD and antibiotics is the key to the livestock and poultry breeding wastewater treatment method with the goal of returning to the field.

[0006] Under short sludge age conditions (SRT≤4d), operating an aerobic biological treatment system can remove nitrifying bacteria with long generation times from the system, thereby completely inhibiting the nitrification of ammonia nitrogen. However, short sludge age operating conditions may have a negative impact on the removal of COD and antibiotic pollutants. The Fenton oxidation method is used as a deep treatment technology for livestock and poultry wastewater to remove residual COD and antibiotic pollutants. However, the conventional Fenton oxidation process has a narrow pH range (2.5-3.5), resulting in high wastewater treatment costs. The use of oxalic acid-assisted Fenton technology is expected to broaden the pH range of the reaction, thereby effectively reducing the cost of wastewater treatment. Therefore, the use of "short sludge age SBR + oxalic acid-assisted Fenton" technology for livestock and poultry wastewater treatment with the goal of returning to the field has certain application value. Summary of the invention

[0007] The purpose of the present invention is to provide a method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland.

[0008] The present invention provides a livestock and poultry breeding wastewater treatment method with the goal of returning to farmland, adopting the "short sludge age SBR + oxalic acid assisted Fenton" technology, wherein the "short sludge age SBR + oxalic acid assisted Fenton" technology comprises the following steps:

[0009] (1) The aerobic unit adopts the sequencing batch activated sludge process (SBR), and the sludge age of the aerobic biological treatment process is controlled at 3 days to remove slow-growing nitrifying bacteria from the system;

[0010] (2) The effluent from the short sludge age SBR reactor was deeply treated by oxalic acid-assisted Fenton oxidation, which could broaden the initial pH range of the reaction and effectively remove the antibiotics.

[0011] Preferably, the sludge age of the wastewater aerobic biochemical treatment system is such that it operates under short sludge age conditions.

[0012] Preferably, the operating conditions of the short sludge age SBR are: operating time 1 to 22 days, chemical oxygen demand COD = 4600 to 4800 mg / L, hydraulic retention time HRT = 3 days, sludge age SRT = 3 days, dissolved oxygen concentration DO = 2.0 to 4.0 mg / L, and pH = 7.0 to 8.0.

[0013] Preferably, the operating conditions of the short sludge age SBR are: operating time 23 to 62 days, chemical oxygen demand COD = 4600 to 4800 mg / L, hydraulic retention time HRT = 3 days, sludge age SRT = 3 days, dissolved oxygen concentration DO = 2.0 to 4.0 mg / L, pH = 7.0 to 8.0, and artificial addition of tetracycline antibiotics.

[0014] Preferably, the operating conditions of the short sludge age SBR are: operating time 63 to 102 days, chemical oxygen demand COD = 4600 to 4800 mg / L, hydraulic retention time HRT = 6 days, sludge age SRT = 3 days, dissolved oxygen concentration DO = 2.0 to 4.0 mg / L, pH = 7.0 to 8.0, and artificial addition of tetracycline antibiotics.

[0015] Preferably, the operating conditions of the short sludge age SBR are: operating time 103-168 d, chemical oxygen demand COD = 4600-4800 mg / L, hydraulic retention time HRT = 6 d, sludge age SRT = 6 d, dissolved oxygen concentration DO = 2.0-4.0 mg / L, pH = 7.0-8.0, and artificial addition of tetracycline antibiotics.

[0016] Preferably, a complexing agent-assisted Fenton oxidation is used instead of traditional Fenton oxidation, and oxalic acid (OA) is selected as the complexing agent for iron.

[0017] Preferably, the oxalic acid-assisted Fenton oxidation conditions are: [Fe 2+ ]=0.75mM, [OA]:[Fe 2+ ]:[H2O2]=2:1:3, initial pH=3.0~8.0.

[0018] Preferably, the oxalic acid-assisted Fenton oxidation conditions are: [Fe 2+ ]=0.75mM, [Fe 2+ ]:[H2O2]=1:3、pH=6.0、[OA]:[Fe 2+ ]=0~2:1.

[0019] Preferably, the oxalic acid-assisted Fenton oxidation conditions are: [Fe 2+ ]=0.25~1.25mM, H2O2=2.25mM, [OA]:[Fe 2+ ]=2:1, pH=6.0.

[0020] Preferably, the oxalic acid-assisted Fenton oxidation conditions are: [Fe 2+ ]=1.25mM, H2O2=1.25~3.75mM, [OA]:[Fe 2+ ]=2:1, pH=6.0.

[0021] The advantages of the present invention are that the present invention controls the aerobic biological treatment system to operate under short sludge age conditions (SRT=3d), so that the slow-growing nitrifying bacteria are removed from the aerobic pool, and the effluent of the short sludge age SBR reactor is deeply treated by using the oxalic acid-assisted Fenton oxidation method, thereby degrading the concentration of COD and antibiotics in livestock and poultry wastewater and inhibiting the nitrification of ammonia nitrogen. At the same time, the initial pH range of the reaction is widened, achieving the purpose of both effectively removing antibiotics and retaining ammonia nitrogen. DETAILED DESCRIPTION

[0022] In order to better understand the present invention, the technology of the present invention is further explained below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to help those skilled in the art understand the present invention, rather than limiting the present invention.

[0023] Example 1

[0024] (1) Short sludge age SBR

[0025] Aerobic biological treatment experiments were conducted in four SBR reactors with an effective volume of 4L. The SBR reactors were made of plexiglass and had a microporous aeration plate at the bottom. During the experiment, the pH value of the SBR reactor was controlled at 7.0-8.0, the dissolved oxygen (DO) was controlled at 2.0-4.0 mg / L, and the temperature was room temperature (when the temperature was low in winter, the laboratory temperature was controlled at around 25°C by air conditioning). An operation cycle of the SBR reactor was 24h, aeration for 22h, and static sedimentation for about 2h. The time for sampling, water change, sludge discharge and drug addition was very short and negligible. The inoculated sludge of the SBR reactor was taken from a newly built aeration tank in a pig farm and stored in a cold storage before use.

[0026] The aerobic biological treatment experiment was divided into four stages: I (1-22d), II (23-62d), III (63-102d), and IV (103-168d). From the 1st to the 62nd day, SRT = HRT = 3d. From the 63rd day, HRT was extended from the original 3d to 6d. From the 103rd day, SRT was extended to 6d. From the 23rd day, four tetracycline antibiotics, oxytetracycline (OTC), chlortetracycline (CTC), tetracycline (TCN), and doxycycline (DC), were artificially added to the influent of each SBR reactor. The addition amount was 100μg / L each. The results showed that when the short sludge age SBR method was used to treat pig farm wastewater, the nitrification of ammonia nitrogen was almost completely inhibited under the condition of SRT = 3d, and the COD removal rate was about 10% lower than that of the conventional sludge age. Under the condition of SRT = HRT = 3d, the removal rate of tetracycline antibiotics was about 75%. When SRT remained unchanged, the HRT was extended to 6 days, and the removal rate of tetracycline antibiotics increased to about 82%, indicating that reducing the load is conducive to the removal of tetracycline antibiotics. When HRT = SRT = 6 days, the removal rate of tetracycline antibiotics further increased to 85%, indicating that the extension of sludge age is conducive to the removal of tetracycline antibiotics. In addition, regardless of the working conditions, although the removal rates of the four tetracycline antibiotics are not much different, the removal rate of OTC is always the highest, and the removal rate of CTC is the lowest.

[0027] (2) Oxalic acid-assisted Fenton oxidation method

[0028] The conditions for oxalate-assisted Fenton oxidation are: [Fe 2+ ]=0.75mM, [OA]:[Fe 2+ ]:[H2O2]=2:1:3. By optimizing the initial pH value, it was found that the smaller the initial pH value, the higher the removal rate of tetracycline antibiotics. When the initial pH was 3.0 and 4.0, the total removal rate of four tetracycline antibiotics was as high as 96%. When the initial pH values ​​were 5.0 and 6.0, the total removal rates of tetracycline antibiotics were approximately 86% and 72%, respectively. When the initial pH values ​​were increased to 7.0 and 8.0, the total removal rates of tetracycline antibiotics were only approximately 51% and 26%, respectively. When the initial pH value was close to neutral, the effect of oxalic acid-assisted Fenton oxidation on the degradation of tetracycline antibiotics was much higher than that of conventional Fenton oxidation, indicating that the addition of oxalic acid in the Fenton oxidation system broadened the suitable pH range.

[0029] Therefore, by comprehensively considering factors such as the removal effect of tetracycline antibiotics, acid and alkali consumption, and total dissolved solids generation, it is advisable to control the initial pH value of the oxalate-assisted Fenton oxidation reaction to around 6.0.

[0030] Example 2

[0031] (1) Short mud age SBR is the same as in Example 1

[0032] (2) Oxalic acid-assisted Fenton oxidation method

[0033] The conditions for oxalate-assisted Fenton oxidation are: [Fe 2+ ]=0.75mM, [Fe 2+ ]:[H2O2]=1:3, pH=6.0. OA and Fe 2+ When the molar ratio of OA and Fe increased from 0 to 2, the removal rate of tetracycline antibiotics increased significantly; 2+ When the molar ratio of OA to Fe 2+ When the molar ratio of OA is ≥2, the dosage of OA continues to increase, the steric hindrance effect of the complex increases, making the degradation efficiency of oxalic acid-assisted Fenton oxidation lower.

[0034] Therefore, in the oxalate-assisted Fenton oxidation system, OA and Fe 2+ The suitable molar ratio is 2:1.

[0035] Example 3

[0036] (1) Short mud age SBR is the same as in Example 1

[0037] (2) Oxalic acid-assisted Fenton oxidation method

[0038] The conditions for oxalate-assisted Fenton oxidation were: H2O2 = 2.25 mM, [OA]: [Fe 2+ ]=2:1,pH=6.0. 2+ The dosage of Fe was gradually increased from 0.25mM to 1.25mM, and the removal rate of tetracycline antibiotics increased from 61% to 72%. 2+ The removal rate of tetracycline antibiotics remained almost unchanged.

[0039] Therefore, by comprehensively considering the removal effect of tetracycline antibiotics and the effect of iron on plant growth, the Fe 2+ It is more appropriate to control the dosage at 1.25mM.

[0040] Example 4

[0041] (1) Short mud age SBR is the same as in Example 1

[0042] (2) Oxalic acid-assisted Fenton oxidation method

[0043] The conditions for oxalate-assisted Fenton oxidation are: [Fe 2+]=1.25mM, [OA]:[Fe 2+ ]=2:1,pH=6.0. As the amount of H2O2 increased from 1.25mM to 3.75mM, the removal rate of tetracycline antibiotics increased from 64% to 87%. However, as the amount of H2O2 continued to increase, the removal rate of tetracycline antibiotics decreased slightly.

[0044] Therefore, it is advisable to control the amount of H2O2 added for the oxalic acid-assisted Fenton oxidation degradation of tetracycline antibiotics at 3.75 mM.

[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland, characterized in that: The method comprises the following steps: (1) The aerobic unit adopts the sequencing batch activated sludge process (SBR), and the sludge age of the aerobic biological treatment process is controlled at 3 days to remove slow-growing nitrifying bacteria from the system; (2) The effluent from the short sludge age SBR reactor was deeply treated by oxalic acid-assisted Fenton oxidation, which could broaden the initial pH range of the reaction and effectively remove tetracycline antibiotics.

2. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland as claimed in claim 1, characterized in that: The sludge age of the wastewater aerobic biochemical treatment system is to enable it to operate under short sludge age conditions.

3. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland as claimed in claim 2, characterized in that: Short sludge age SBR operating conditions: operating time 1 ~ 22 days, chemical oxygen demand COD = 4600 ~ 4800 mg / L, hydraulic retention time HRT = 3 days, sludge age SRT = 3 days, dissolved oxygen concentration DO = 2.0 ~ 4.0 mg / L, pH = 7.0 ~ 8.

0.

4. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland as claimed in claim 2, characterized in that: Short sludge age SBR operating conditions: operating time 23 ~ 62 days, chemical oxygen demand COD = 4600 ~ 4800 mg / L, hydraulic retention time HRT = 3 days, sludge age SRT = 3 days, dissolved oxygen concentration DO = 2.0 ~ 4.0 mg / L, pH = 7.0 ~ 8.0, artificial addition of tetracycline antibiotics.

5. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland as claimed in claim 2, characterized in that: Short sludge age SBR operating conditions: operating time 63 ~ 102d, chemical oxygen demand COD = 4600 ~ 4800mg / L, hydraulic retention time HRT = 6d, sludge age SRT = 3d, dissolved oxygen concentration DO = 2.0 ~ 4.0mg / L, pH = 7.0 ~ 8.0, and artificial addition of tetracycline antibiotics.

6. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland as claimed in claim 2, characterized in that: Short sludge age SBR operating conditions: operating time 103 ~ 168d, chemical oxygen demand COD = 4600 ~ 4800mg / L, hydraulic retention time HRT = 6d, sludge age SRT = 6d, dissolved oxygen concentration DO = 2.0 ~ 4.0mg / L, pH = 7.0 ~ 8.0, artificial addition of tetracycline antibiotics.

7. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland as claimed in claim 1, characterized in that: Complexing agent-assisted Fenton oxidation was used instead of traditional Fenton oxidation, and oxalic acid (OA) was selected as the complexing agent for iron.

8. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland as claimed in claim 7, characterized in that: Oxalate-assisted Fenton oxidation conditions: [Fe 2+ ]=0.75mM, [OA]:[Fe 2+ ]:[H2O2]=2:1:3, initial pH=3.0~8.

0.

9. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland as claimed in claim 7, characterized in that: Oxalate-assisted Fenton oxidation conditions: [Fe 2+ ]=0.75mM, [Fe 2+ ]:[H2O2]=1:3、pH=6.0、[OA]:[Fe 2+ ]=0~2:

1.

10. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland as claimed in claim 7, characterized in that: Oxalate-assisted Fenton oxidation conditions: [Fe 2+ ]=0.25~1.25mM, H2O2=2.25mM, [OA]:[Fe 2+ ]=2:1, pH=6.

0.

11. A method for treating livestock and poultry breeding wastewater with the goal of returning the wastewater to farmland as claimed in claim 7, characterized in that: Oxalate-assisted Fenton oxidation conditions: [Fe 2+ ]=1.25mM, H2O2=1.25~3.75mM, [OA]:[Fe 2+ ]=2:1, pH=6.0.