Impact of high temperature in summer on sewage treatment and solutions

High temperatures in summer not only affect the physiology of microorganisms and the oxygenation performance of equipment, but also affect the various reaction processes and the mental state of personnel in the sewage treatment process. Therefore, in operation management, attention should be paid to these characteristics and targeted solutions should be made.

1. Effect of high temperature on microbial activity

Water temperature is a very important parameter because of its effect on chemical reactions, reaction rates, aquatic organisms, and suitability for permanent use. The amount of oxygen dissolved in hot water is less than that in cold water, and the biochemical reaction rate increases with increasing temperature. Combined with the reduction of oxygen in surface water, summer months often cause severe depletion of dissolved oxygen in rivers. This effect is exacerbated when a large amount of hot water is discharged into natural receiving water bodies. 

The optimal temperature range for bacterial activity is 25-35℃. Many sewage treatments now use measures such as covering and deodorizing, which leads to heat accumulation. When the temperature rises to 50℃, aerobic digestion and nitrification stop. Therefore, cooling measures should be taken, such as water spraying, etc.

2. Effect of high temperature on dissolved oxygen in aeration tank

Due to the high temperature in summer, oxygen is not easily dissolved in water. Therefore, the dissolved oxygen transferred to water by the same mass of air is low, which often causes insufficient oxygen supply.

When the dissolved oxygen in the aeration tank is 2mg/L, the dissolved oxygen at the center of the floc with a diameter of 500ram is only 0.1mg/L, indicating that except for the microorganisms on the surface of the floc that reach a higher dissolved oxygen, most of the microorganisms inside are in anoxic state. Therefore, when the sludge concentration in the aeration tank is high, such as 4g/L, the dissolved oxygen concentration should be controlled at 3~4mg/L.

3. Management of the secondary sedimentation tank under high temperature

Due to the slowdown of stratification sedimentation under high temperature, the secondary sedimentation tank is prone to mud turning, which leads to an increase in effluent SS. 

Under high temperature, the metabolic capacity of microorganisms is accelerated, and anaerobic or denitrification may occur in the secondary sedimentation tank, often producing gas and causing sludge floating. Some algae will also use nutrients in the water to form algae on the surface of the secondary sedimentation tank, affecting the appearance. For this reason, it is necessary to ensure sufficient oxygen supply during summer operation, and add flocculants such as PAC when necessary to improve the sedimentation performance of sludge.

4. Management of structures, pipelines, and equipment under high temperatures

High temperatures and thunderstorms in summer often cause equipment failures, thus affecting the normal operation of the process. In order to ensure that the sewage treatment plant spends the summer smoothly, measures should be taken for some key equipment, pipelines, and structures according to their characteristics in summer to prevent problems before they occur.

High temperatures in summer have a greater impact on key process equipment, especially blowers. In summer, due to cooling problems, the lubricating oil temperature may be too high and the alarm may be shut down, and the air volume may be automatically reduced for safety reasons (such as anti-surge). Therefore, in the summer, ventilation must be ensured in the blower room and pump room to ensure the normal operation of the cooling fan of the rotating equipment and to ensure that the cooling air duct is unobstructed. If necessary, axial flow fans should be installed in time for equipment with heat dissipation problems to take forced ventilation measures to prevent equipment overheating. With the upgrading and transformation of equipment, sewage treatment plants in some areas have eliminated backward production capacity equipment such as Roots blowers, and new air suspension and magnetic suspension fans have become the first choice for upgrading or building new sewage treatment plants. These devices are expensive and have more stringent operating conditions. In order to ensure that these devices operate at the right temperature in summer, it is particularly important to install air conditioning in the blower room and insulation materials in the indoor pipelines!