The relationship between dissolved oxygen and water quality indicators

Definition of Dissolved Oxygen Dissolved oxygen is the content of free oxygen in water, expressed in DO, and the unit is mg/L. It is theoretically understood that when the dissolved oxygen value monitored at each point of the aeration tank is slightly greater than 0, it can be considered that the oxygenation just meets the requirements of the microorganisms in the activated sludge for dissolved oxygen. As far as the whole aeration tank is concerned, the distribution of dissolved oxygen and the demand for dissolved oxygen in each aeration tank area are different, so in order to stabilize the demand for dissolved oxygen in the process of decomposing organic matter or self-metabolism of activated sludge, theoretically Above all, it is necessary to control the dissolved oxygen in the effluent of the aeration tank within the range of 1~3mg/L. However, in actual operation, it is found that controlling the dissolved oxygen in the range of 1~3mg/L, the only result can only be a waste of electric energy and cause the effluent to contain fine suspended particles, which is unnecessary. Therefore, it is only necessary to control the dissolved oxygen at about 1.0mg/L, which is reasonable and energy-saving. Dissolved oxygen monitoring Because dissolved oxygen is easily affected by factors such as oxygen in the air, temperature, humidity, etc., online detection instruments or portable dissolved oxygen detectors are commonly used for on-site monitoring. When testing, the entire aeration tank should be divided into several areas, and the dissolved oxygen monitoring value of the entire area should be statistically analyzed to find out the dissolved oxygen distribution of the system at different stages and time points, and to grasp the overall follow-up system and Activated sludge failure analysis is very beneficial. If such detection conditions are not available, the final result of the degradation process of organic matter by the activated sludge system can be judged by monitoring the dissolved oxygen at the outlet of the aeration tank. Under normal circumstances, the oxygenation effect in winter is significantly better than that 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 in summer the saturation of dissolved oxygen is low. : The relationship between dissolved oxygen and raw water components The key point of the relationship between dissolved oxygen and raw water components is the relationship between the content of organic matter in raw water and dissolved oxygen. Specifically, the more organic matter in raw water, the more dissolved oxygen that microorganisms need to consume to metabolize and decompose these organic matter. The more, the less the opposite. Therefore, when controlling aeration, attention should be paid to matching the amount of water with the content of organic matter in the wastewater. When the water inflow is 1.5 times the normal amount, if the aeration volume is not adjusted, the dissolved oxygen in the effluent of the aeration tank will be too low, sometimes even lower than 0.5mg/L, which is not conducive to the high-efficiency treatment effect of activated sludge. If the influent flow rate does not increase, but the concentration of organic matter in the wastewater is too high, the demand for dissolved oxygen will also increase, and then the dissolved oxygen in the effluent of the aeration tank will be too low. The existence of some special components in raw water will also affect the oxygenation effect. For example, the presence of detergent in the water makes the liquid surface of the aeration tank have an isolation layer that isolates the atmosphere, which in turn affects the improvement of the aeration effect. The relationship between dissolved oxygen and activated sludge concentration The relationship between dissolved oxygen and activated sludge concentration is relatively close. It is usually seen that the demand for dissolved oxygen with high activated sludge concentration is significantly higher than that with low activated sludge concentration. need. Therefore, in order to achieve the removal of pollutants and achieve the discharge concentration, the concentration of activated sludge should be reduced as much as possible, which is very beneficial to reduce aeration and reduce power consumption. At the same time, in the case of low activated sludge concentration, care should be taken not to over-aerate, so as to avoid excessive dissolved oxygen and excessive oxidation of the only activated sludge, which is not good for the effluent of the secondary sedimentation tank. Usually, it can be seen that there are more unsettled particles mixed in the effluent of the secondary sedimentation tank, which is the reason why the oxidized activated sludge is disintegrated and decomposed in the effluent. Similarly, the high activated sludge concentration has a high demand for dissolved oxygen, and the activated sludge concentration cannot be increased without control, so that the oxygen supply cannot keep up and the phenomenon of hypoxia will occur. The treatment of natural activated sludge The effect is also suppressed. The relationship between dissolved oxygen and the sedimentation ratio of activated sludge The relationship between dissolved oxygen and the sedimentation ratio of activated sludge can be understood as the influence of dissolved oxygen on the sedimentation of activated sludge. The following two situations will mainly occur: 1: Excessive aeration will easily cause tiny air bubbles to attach to the bacteria micelles of the activated sludge, causing the activated sludge to float to the liquid surface and generate scum. :2: The compressibility of activated sludge deteriorates. Especially when the activated sludge is expanded by filamentous bacteria, it is more likely to cause the fine air bubbles of aeration to attach to the bacterial micelles, which in turn leads to a large amount of scum on the liquid surface.