I. The impact of high temperature on wastewater treatment
1、The effect of high temperature on microbial activity
Water temperature is a very important parameter because of its effect on chemical reactions, reaction rates, aquatic life, and suitability for Yonex uses. The amount of oxygen dissolved in hot water is less than in cold water, and as the temperature rises, the rate of biochemical reactions increases. Together with the reduction of oxygen in surface water, summer months often cause serious depletion of dissolved oxygen in rivers. This effect is exacerbated when there is a large amount of hot water discharged into the natural receiving water body.
The optimal temperature range of bacterial activity 25-35 ℃, now many sewage treatment are used to cover the deodorization measures, resulting in the accumulation of heat, when the temperature rises to 50 ℃, aerobic digestion and nitrification stop, so, to do a good job of cooling measures, such as water spraying, cooling fans, etc.
2、The effect of high temperature on dissolved oxygen in the aeration tank
Due to the high summer temperatures, oxygen is not easily dissolved in water, therefore, the same quality of air transferred to the water dissolved oxygen is low, often resulting in insufficient oxygen supply.
It is reported that when the dissolved oxygen in the aeration tank is 2mg/L, the dissolved oxygen at the center of the floc with a diameter of 500μm is only 0.1mg/L, indicating that in addition to the microorganisms on the surface of the floc reaching a high dissolved oxygen, most of the microorganisms inside are in anoxic condition. For this reason, 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.
Second, the management of high-temperature wastewater treatment
1、The management of the secondary sedimentation tank
Due to the high temperature, the sedimentation rate is reduced and the secondary sedimentation tank is prone to mud flip, which leads to the increase of SS in the effluent.
Under high temperature conditions, the metabolic capacity of microorganisms is accelerated and anaerobic or denitrification may occur in the secondary sedimentation tank, often generating gas and producing sludge upwelling. Some algae will also use the nutrients in the water to generate 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 to add flocculants such as PAC to improve the sludge sedimentation performance if necessary.
2、Structures, pipelines, equipment management
Summer heat, thunderstorms often trigger equipment failure, thus affecting the normal operation of the process. To ensure that the wastewater treatment plant smoothly through the summer, some key equipment, pipelines, structures to take measures for their characteristics in the summer, to prevent problems before they occur.
High summer temperatures have a significant impact on critical process equipment, especially blowers. In summer, cooling problems may cause high lubricating oil temperatures and alarm shutdowns, and also automatically reduce airflow for safety reasons (such as anti-surge). Therefore, in the summer blower room and pump room to ensure ventilation, to ensure the normal operation of the rotating equipment cooling fan, to ensure that the cooling air duct smooth. If necessary, add axial fans to the equipment with heat dissipation problems in a timely manner to take forced ventilation measures to prevent equipment overheating. With the upgrading of equipment, some areas of the sewage plant has eliminated the Roots fan and other backward capacity equipment, the new air suspension, magnetic suspension fan has become the first choice for upgrading or new sewage plant. These devices are expensive and more demanding conditions of use, in order to protect the temperature of these devices in the summer operation, the blower room with air conditioning, indoor piping with insulation is particularly important!
Wastewater treatment plants use some UP, VC, FRPP and other plastic pipelines due to anti-corrosion considerations. However, there is a problem of UV protection for such pipelines . Some of the plastic pipes in the open are more heat deformation, and the use of these materials in the southern high-temperature areas should take these factors into account. Microporous aeration systems often also use plastic piping for the distribution of air. If the aeration basin is deep (e.g., greater than 8 meters), the piping will collapse when the blower is activated, and underwater maintenance of these piping lines is very problematic.
In the summer, the lubricant level of the equipment will rise, and some of the oil should be drained in time; as the oil viscosity decreases, the oil leakage phenomenon of the equipment in the summer intensifies. For the site control cabinet, automatic control cabinet and other integrated electrical systems, before the arrival of summer should be sure to do a good job of the internal exhaust fan, timely repair of faulty exhaust fan to ensure the normal operation of the control system.
The power distribution room is the power source of the whole plant, and because transformers and other equipment dissipate large amounts of heat, there is a high risk of power outages if they are not properly ventilated and cooled. Therefore, it is crucial to install sufficient industrial air conditioners in the distribution room before the summer.
Seasonality is a major pattern of sewage treatment plant accidents, in our country from May to September in most areas of the country high temperature season sewage treatment plant accidents occur at a higher rate, compared to October in our country to the next year in April when the temperature of the national region is lower, in this accident sewage plant accidents occur at a lower rate.
In terms of the level of accidents in China’s wastewater treatment plants, the incidence of general and major accidents is high, while the incidence of major accidents is relatively low, and the incidence of major accidents is higher than that of general accidents.
Summer as the high incidence of safety accidents, sewage plants in the daily management of the water plant in addition to ensuring flood control and stable standards, more safety should be given priority.
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