How to quickly determine the dosage of flocculant during sewage treatment?

Wastewater treatment is a crucial step in maintaining public health and human well-being. In the wastewater treatment process, coagulants are essential substances that effectively aggregate suspended solids, colloidal particles, and other impurities in water into larger flocs, making them easier to separate and remove. The selection of coagulant dosage is a critical factor that determines treatment efficiency, cost-effectiveness, and water quality. Therefore, this paper delves into the importance of rapidly determining the optimal coagulant dosage in wastewater treatment and analyzes its advantages and challenges. Only by mastering the correct calculation methods can we better address the issues in wastewater treatment and effectively tackle pollution problems.

Coagulants are used in various wastewater treatment projects, but what is the appropriate dosage for coagulant addition? Generally, the selection of coagulant dosage should follow several principles, including coagulation efficiency, cost-effectiveness, and operability. Conventionally, we first obtain raw water samples and confirm the coagulant dosage through laboratory-scale experiments. This paper shares the process of determining the optimal coagulant dosage based on small-scale experiments.

First, coagulation experiments are conducted to confirm the coagulant dosage and suitable coagulation conditions (pH value, temperature, etc.). Further adjustments are made in the actual operating equipment. Only by doing so can we scientifically determine the optimal dosage.

Experiment Process:

Step 1: Take a set of beakers, usually three to five, with a volume of about 600ml and fill them with 500ml of raw water. Each beaker is equipped with a magnetic stirring device, with an adjustable speed range of 25-600r/min.

Step 2: To simulate rapid mixing of raw water and coagulant, initially set the stirring speed in the range of 100-160r/min and wait until the stirring state stabilizes. Then add different doses of coagulant to each beaker.

Step 3: Rapid mixing and coagulation should last for at least 30s, typically 1-3 minutes. Afterward, adjust the stirring speed to 20-40r/min to simulate slow mixing, and maintain this state for 15-20 minutes to ensure sufficient contact between the coagulant and suspended particles.

Step 4: Stop stirring to allow settling of coagulated materials under gravity. Carefully observe this process until all coagulated materials have settled to the bottom of the beaker.

Step 5: Starting from the observation time, measure the height between the clear water layer and the sediment layer at regular intervals. Typically, measurements are taken every 2 minutes. In cases of rapid settling, intervals can be shortened.

Step 6: Comparative analysis phase. Based on the time it takes for the clear water layer to reach a height of 100mm, the coagulation effect can be categorized into four levels.

1. If the time required for the clear water layer to reach 100mm is less than 2 minutes, the coagulation effect is optimal, suitable for upstream solid-contact clarifiers with high flow rates.
2. If the time is between 2 and 4 minutes, the coagulation effect is considered good and suitable for upstream solid-contact clarifiers with moderate flow rates.
3. If the time is between 4 and 7 minutes, the coagulation effect is moderate and satisfactory for upstream solid-contact clarifiers with moderate flow rates.
4. If the time exceeds 7 minutes, the coagulation effect is poor, and unless a low upstream flow rate is selected, the settling effect will be unsatisfactory.

Therefore, rapid determination of coagulant dosage is of great significance for improving treatment efficiency, reducing treatment costs, enhancing water quality, shortening treatment cycles, and adapting to changes in the physicochemical characteristics of wastewater. This ensures the efficiency, sustainability, and environmental friendliness of wastewater treatment.