1. The dissolved oxygen in the effluent of carbon oxidation filter and nitrification filter should be controlled at 3.0 ~ 4.0mg/l.
2. The increase of filtration rate is disadvantageous to carbon oxidation, and some non dissolved organic matters are discharged for degradation, 6m / h is recommended.
3. However, in a certain volume load range, the increase of filtration rate will not reduce the removal rate of BAF, but also increase the nitrification and denitrification efficiency. The main reasons are as follows: 1. High filtration rate enhances the mass transfer efficiency in the filter, which makes more opportunities for contact between air, sewage and organisms; 2. Under high filtration rate, the biofilm renews rapidly and enhances the biological activity. 3、 At low speed, the filter material is easy to block, which shortens the backwashing cycle, while frequent backwashing is unfavorable to the nitrifying bacteria with slow propagation speed.
4. When the filter is mainly used for carbon oxidation, when the required BOD5 is 10-20mg / L, the recommended volume load is 3.5-5.0kg BOD5 / (m · d), when the required BOD5 is 5-10mg / L, the recommended volume load is 2.5-3.2kg BOD5 / (m · d).
5. When the filter is mainly used for carbon oxidation and nitrification, the volume load of BOD5 is recommended to be ≤ 3.0kgbod5 / (m · d). The study shows that when the volume load of BOD5 is greater than this value, the removal of ammonia nitrogen is inhibited, and when the volume load of BOD5 is ≥ 4.0kgbod5 / (m · d), the removal of ammonia nitrogen is obviously inhibited.
6. The effluent CODcr is 60 mg / L, and the influent load should be 4.0-5.0 kgcodcr / (m · d). When CODcr ≤ 50 mg / L, the influent load should be controlled below 3.0 kgcodcr / (m · d).
7. When there are nitrification and denitrification requirements in the filter, the volume load of nitrification and denitrification needs to be calculated. It is recommended that the volume load be less than 2.0kg NH3-N / (m · d) and 5.0kg NO3-N / (m · d) respectively, and 0.3-0.8kg NH3-N / (m · d) and 0.8-4.0kg NO3-N / (m · d) are recommended.
8. When denitrification is needed and the carbon source is insufficient, the denitrification tank can be placed in front of the nitrification tank, and part of the effluent from the nitrification tank can be returned to the denitrification tank to form pre denitrification. It has the following advantages: A. use the organic matter in the sewage as the carbon source to reduce the external carbon source. b. Organic matter is removed in the denitrification tank to ensure the nitrification capacity in the carbon oxidation / nitrification tank. c. The aeration capacity of the system is relatively small. d. Less sludge. For the domestic sewage with sufficient BOD5 and nitrogen removal, the advantages of pre denitrification process are obvious considering the operation cost.
9. The post denitrification process is more suitable for the following places: A. wastewater with significantly lower BOD5 content (high proportion of industrial wastewater). b. When it is used in the renovation and upgrading of the sewage plant, the nitrification index is not considered before. The BOD5 of the effluent is low, but the ammonia nitrogen is high.
10. In order to avoid the influence of carbon removal on nitrification, the post denitrification should be carried out in the pre-treatment stage to remove a part of BOD5. The design filtration rate of C / N tank is 6-10m / h, and the nitrification load should meet the following requirements: inlet BOD5 ≥ 60mg / L, about 0.3KG NH3-N / (m · d), when BOD5 = 20-50mg / L, about 0.6kg NH3-N / (m · d), when BOD5 ≤ 20mg / L, about 1.0kg NH3-N / (m · d), if methanol is used as the external carbon source, then DN is added The amount is 3.3kgch4o/kgno3-n.
11. The recommended denitrification load is 0.4-0.5 kgno3-n / (m · d), filtration rate ≥ 10 m / h, and the best influent BOD5 / NO3-N ≥ 6. Generally, the removal rate of BOD5 in DN tank is ≤ 60%, and the removal rate of CODCr is ≤ 70%. The remaining CODcr will enter the nitrification reactor. In order to ensure the nitrification capacity of N tank (greater than 0.5kgnh3-n / (m · d)), the load of CODCr is ≤ 2.0kgcodcr / (m · d).
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