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1. pH value
2. Inlet water temperature
High water temperature affects oxygen flushing efficiency, and the difficulty in increasing dissolved oxygen is often due to this reason; if the temperature is too low (generally considered to be below 10°C, the effect is obvious), the flocculation effect will be significantly worse, the flocs will be small, and the interstitial water will be turbid.
3. Food-microbe ratio (F/M)
The food-microbe ratio (also called sludge load) is a ratio that reflects the relationship between the number of food and microorganisms. In operation management, it is necessary to understand: how much food can support how many microorganisms. Usually, the food-microbe ratio needs to be controlled at around 0.3, and experimental data is often used to substitute into the formula to determine the appropriate influent flow rate. The BOD value is calculated as 50% of the COD value, and the COD-BOD ratio suitable for the water quality of the treatment station is found in the comparison of daily laboratory data.
1) Relationship with sludge concentration: According to the principle that how much food can support how many microorganisms, the adjustment of sludge concentration should be adapted to the influent concentration. In the case of frequent changes in the influent water quality of the system, it is more reasonable to use the daily average concentration as a reference for adjusting the sludge concentration. In actual operation, the most direct way to adjust the sludge concentration is to control the discharge of residual sludge. If a sludge discharge curve suitable for the treatment station can be made based on the sludge discharge data, it will have a high reference value for future operation.
2) Relationship with dissolved oxygen: When the food-microorganism ratio is too low, the activated sludge is excessive, and the amount of oxygen consumed by the respiration of the excess sludge is greater than the oxygen required for the decomposition of organic matter, but the total oxygen demand remains unchanged, and the oxygen utilization rate is reduced, resulting in power waste. When the food-microorganism ratio is too high, the oxygen demand of the system increases, causing oxygen supply pressure. When it exceeds the oxygen supply capacity of the system, it causes system hypoxia, which will seriously cause system paralysis.
4. Dissolved oxygen
Dissolved oxygen monitoring during operation mainly relies on online monitoring instruments, portable dissolved oxygen meters and experimental measurements, three methods of monitoring. The instrument needs to frequently compare the experimental measurement results to ensure the accuracy of the instrument. When dissolved oxygen abnormalities occur, multi-point sampling methods should be adopted in the aeration tank to measure the dissolved oxygen concentration in different areas of the aeration tank to analyze the cause of the fault.
1) Relationship with raw water composition.
The impact of raw water on dissolved oxygen is mainly reflected in the fact that large water volume and high organic matter concentration will increase the oxygen consumption of the system. Therefore, after the aerator is fully opened during operation, the increase in water intake should be based on the dissolved oxygen situation. In addition, if there are more detergents in the raw water, there will be an isolation layer on the surface of the aeration tank that isolates the atmosphere, which will also reduce the oxygen flushing efficiency.
2) Relationship with sludge concentration.
The higher the sludge concentration, the greater the oxygen consumption. Therefore, it is necessary to control the appropriate sludge concentration during operation to avoid unnecessary excessive oxygen consumption. At the same time, it should be noted that when the sludge concentration is low, the aeration volume should be adjusted to avoid excessive oxygen flushing causing sludge decomposition.
3) Relationship with sedimentation ratio.
What should be avoided during operation is excessive aeration. Excessive aeration will cause tiny air bubbles in the sludge to attach to the sludge, causing the sludge to float, increase the sedimentation ratio, and a large amount of scum to appear on the surface of the sedimentation tank.
5. Activated sludge concentration (MLSS)
Activated sludge concentration refers to the content of mixed suspended solids at the outlet of the aeration tank, expressed in MLSS, which is an indicator of the number of microorganisms in the aeration tank.
1) Relationship with sludge age.
Sludge age is an operational means to achieve the sludge age index by excluding activated sludge. Therefore, controlling the sludge age will also result in a suitable sludge concentration range.
2) Relationship with temperature.
For normal activated sludge flora, the activity of microorganisms in it will double for every 10°C drop in temperature. Therefore, during operation, we only need to reduce the system sludge concentration when the temperature is high and increase the system sludge concentration when the temperature is low to achieve the purpose of stabilizing the treatment efficiency.
3) Relationship with sedimentation ratio.
The higher the concentration of activated sludge, the greater the final result of the sedimentation ratio, and vice versa. It should be noted during operation that the sedimentation ratio caused by high activated sludge concentration increases, and the observed sedimented sludge is compressed and dense; while the sedimentation ratio caused by increased non-activated sludge concentration is mostly poorly compacted and dark in color. The sedimentation ratio caused by low activated sludge concentration is too low, and the observed sedimented sludge is dark in color, poorly compressed, and the sedimented activated sludge is scarce.
6. Sedimentation ratio (SV30)
The activated sludge sedimentation ratio should be said to be the most referenced in all operation controls. By observing the sedimentation ratio, the approximate values of multiple control indicators can be inferred from the side, which has a positive guiding significance for the comprehensive judgment of operation failures and operation development direction.
Observation points of the sedimentation process:
1) Within the first 30 to 60 seconds of sedimentation, the sludge undergoes rapid flocculation and rapid sedimentation. If this stage consumes too much time, it is often a signal that the sludge system is about to fail. If the slow sedimentation is due to the high viscosity of the sludge and the inclusion of small bubbles, it may be due to the high sludge concentration, sludge aging, and high influent load.
2) As the sedimentation process deepens, the sludge flocs will continue to adsorb and combine to form larger and larger flocs, and the color will deepen. If the sludge color does not deepen during the sedimentation process, it may be that the sludge concentration is too low and the influent load is too high. If there is sedimentation sludge in the middle and clarified liquid above and below, it means that moderate sludge expansion has occurred.
3) The last stage of the sedimentation process is the compression stage. At this time, the sludge is basically at the bottom, and it is continuously compacted with the increase of sedimentation time, and the color continues to deepen, but it still maintains larger flocs. If it is found that the compaction is fine and the flocs are small, the sedimentation effect is not good, and the influent load may be too large or the sludge concentration is too low. If the flocs are too coarse and the edges of the flocs are light in color during the compaction stage, and the upper clear liquid is mixed with fine flocs, it means that the sludge is aged.
7. Sludge Volume Index (SVI)
Sludge volume index SVI = SV30/MLSS, SVI is 50-150 is a normal value, and it can be as high as 200 for industrial wastewater. When the activated sludge volume index exceeds 200, it can be determined that the activated sludge structure is loose, the sedimentation performance is poor, and there are signs of sludge expansion. When the SVI is lower than 50, it can be determined that the sludge is aged and the sludge age needs to be shortened.
8. Sludge age
Sludge age can be understood as the time required for activated sludge to double in size. In actual operation, the sludge age can be simply estimated based on the sludge volume and sludge discharge flow rate in the aeration tank. The range of sludge age from 7 to 15 days is only a reference value. In actual operation, a reasonable sludge age needs to be set according to the influent load on site.
Sludge age calculation formula:
(t) = VX1/24X2Q
Where: V—aeration tank volume m;
X1—aeration tank mixed suspended solids (MLSS) concentration (mg/L);
X2—return activated sludge mixed suspended solids (MLSS) concentration (mg/L);
Q—residual activated sludge discharge (m3/h)
Method for determining sludge age during operation:
Under the premise that "how much food can feed how many microorganisms", it is necessary to calculate a reasonable sludge concentration (MLSS) based on the average pollutant load over a period of time using the food-microorganism ratio formula, and then calculate a reasonable sludge age, and make corresponding adjustments to the system based on this.
