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Most of the current biological treatment in sewage treatment uses a combination of anaerobic and aerobic treatment processes. Dissolved oxygen plays a pivotal role in the actual wastewater biological treatment operations. Inappropriate or excessive fluctuation of this indicator will quickly lead to The activated sludge system is impacted, which affects the treatment efficiency. Therefore, in the actual biochemical treatment process, the content of dissolved oxygen must be strictly controlled.
Overview of dissolved oxygen
Dissolved oxygen (DO) is the abbreviation of Dissolved Oxygen. It is a parameter that characterizes the concentration of oxygen in an aqueous solution and is the free oxygen dissolved in water.
The unit of dissolved oxygen is mg/L, expressed in milligrams of oxygen per liter of water. The amount of dissolved oxygen in the water is an indicator of the self-purification ability of the water body. High dissolved oxygen is conducive to the degradation of various pollutants in the water body, so that the water body can be purified faster; on the contrary, when the dissolved oxygen is low, the pollutants in the water body degrade slowly.
Factors affecting dissolved oxygen
The dissolved oxygen content in water is affected by two effects: one is the oxygen consumption that reduces DO, including oxygen consumption for aerobic organic matter degradation, and advanced metabolism oxygen consumption; the other is the reoxygenation that increases DO, mainly including Dissolution of oxygen in the air, aeration methods, etc. The mutual ebb and flow of these two effects makes the dissolved oxygen content in water show temporal and spatial changes.
Environmental factors affecting the content of dissolved oxygen in water include water temperature, oxygen partial pressure, salinity and other factors.
1. Water temperature
When the oxygen partial pressure and the salt content are constant, the saturated content of dissolved oxygen decreases as the water temperature increases. The saturation content of dissolved oxygen at low temperatures changes more significantly with temperature.
2. Salt content
When the water temperature and oxygen partial pressure are constant, the higher the salt content of the water, the lower the saturated content of dissolved oxygen in the water. The salt content of seawater is much higher than that of fresh water. Under the same conditions, dissolved oxygen is in the seawater. The saturation content is much lower than in fresh water. The salt content of natural fresh water has a very small change, so the salt content has little effect on the saturation content of dissolved oxygen, which can be calculated approximately based on the saturation content of pure water.
3. The partial pressure of oxygen
When the salt content of the water temperature is constant, the saturated salt content of dissolved oxygen in the water increases with the increase of the oxygen partial pressure on the liquid surface.
Monitoring of dissolved oxygen DO
Since dissolved oxygen is easily affected by factors such as oxygen in the air, temperature, humidity, etc., online detection equipment or portable dissolved oxygen meters are often used for on-site monitoring. During testing, the entire aeration tank should be divided into several areas, and the dissolved oxygen monitoring values of the entire area should be statistically analyzed to find out the distribution of dissolved oxygen at different stages and time points of the system. The overall understanding and analysis of activated sludge failure are very useful. If such detection conditions are not available, the dissolved oxygen at the outlet of the aeration tank can be monitored as the final result of the degradation process of organic matter by the activated sludge system. Under normal circumstances, the effect of oxygenation in winter is significantly better than in summer. The main reason is that the water temperature is low in winter and the saturation of dissolved oxygen is high. On the contrary, the saturation of dissolved oxygen is low in summer.
RK500-04 Dissolved Oxygen(DO) Sensor design based on the principle of fluorescence and high performance through oxygen membrane, with short response time, measurement accuracy, stable performance, etc. It can be widely used in chemical fertilizer, metallurgy, environmental protection water treatment engineering, pharmaceutical, biochemical, food, aquaculture and water such as continuous monitoring of dissolved oxygen in the solution.
How to install and use：
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