As a readily biodegradable organic carbon source, sodium formate is widely used in biological denitrification of wastewater. There is no unified fixed standard for its dosage, which needs to be dynamically adjusted according to water quality characteristics, treatment processes and discharge standards. Scientific control of dosage is crucial to balancing treatment efficiency and operation cost. Excessive dosage is likely to cause an increase in effluent COD and sludge bulking, while insufficient dosage fails to meet denitrification requirements and affects total nitrogen removal efficiency.
From the perspective of key application scenarios, sodium formate is mainly used for denitrification in anoxic zones, and its dosage needs to be calculated based on the carbon-nitrogen balance principle. In activated sludge treatment systems, the optimal nutrient ratio for microorganisms is BOD₅:N:P=100:5:1. When the carbon source in wastewater is insufficient (BOD₅/TKN < 4), sodium formate needs to be supplemented. Referring to the dosage logic of similar carbon sources, approximately 7g of sodium formate (converted to the corresponding carbon source product) is required to remove 1g of nitrate nitrogen, but this value needs to be corrected according to actual water quality.
Water quality characteristics are the core factor affecting dosage. For low-concentration organic wastewater, the dosage of sodium formate is usually controlled at 50-200mg/L, which can meet the metabolic needs of microorganisms; while for high-nitrogen industrial wastewater, the dosage needs to be increased to 300-800mg/L. It should be noted that sodium formate will inhibit microorganisms when its concentration exceeds 3000mg/L, and the inhibitory effect strengthens with increasing concentration. Therefore, fractional dosage is required in the treatment of high-concentration wastewater.
Differences in treatment processes directly determine dosage standards. In mainstream denitrification processes such as A²/O and SBR, sodium formate should be dosed into anoxic zones, where dissolved oxygen is controlled at ≤0.5mg/L and hydraulic retention time is 2-4 hours. The dosage needs to match the hydraulic load of the process. For example, when treating sodium hydrosulfite wastewater with an upflow anaerobic sludge blanket (UASB), the dosage should be adjusted in combination with sludge load (0.4-1.2kgCOD/kgMLSS·d), and nitrogen and phosphorus nutrients should be supplemented to maintain COD:N:P between 100:5:1 and 200:5:1.
The practical control of dosage must follow the principle of "theoretical calculation + small-scale test calibration". First, a preliminary estimate is made using carbon source dosage formulas based on influent total nitrogen, nitrite nitrogen and dissolved oxygen concentrations, and then the optimal dosage is determined through small-scale tests. During operation, sludge indicators such as SV30 and SVI should be monitored. Loose sludge structure may indicate carbon source dosage imbalance, which requires timely fine-tuning. In addition, sodium formate can be prepared by CO₂ conversion, and its application in wastewater treatment can realize carbon cycle. The dosage can be optimized in combination with low-carbon treatment goals.
In summary, the dosage of sodium formate must be based on water quality testing and process adaptation, with the core of maintaining microbial nutrient balance and avoiding inhibitory effects and resource waste. In practical applications, dynamic adjustment should be carried out in combination with small-scale test data and operation monitoring to balance denitrification efficiency, sludge performance and treatment cost, so as to achieve up-to-standard discharge and maximum benefits.
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