1. PH value:
In the actual adjustment process, the pH value prefers to be alkaline rather than acidic, mainly because alkaline is more conducive to improving the coagulation and precipitation effect in the later stage.
The relationship between pH value and other indicators:
(1) The relationship between water quality and quantity: The fluctuation of pH in industrial wastewater is mainly caused by the use of acid-base drugs in production. It is necessary to gradually familiarize oneself with the drainage situation of the enterprise during operation, accumulate experience, and judge whether the water quality is acidic or alkaline through physical properties such as color.
(2) Relationship with sedimentation ratio: pH values below 5 or above 10 can cause impact on the system, resulting in slow sludge sedimentation, turbid supernatant, and even floating sludge flocs on the liquid surface.
(3) The relationship with sludge concentration (MLSS): The higher the sludge concentration, the stronger the tolerance to pH fluctuations. After being impacted, the sludge discharge should be increased to promote the renewal of activated sludge.
(4) Relationship with reflux ratio: Increasing the reflux ratio to dilute the pH of the influent is also one of the methods to reduce the impact of pH fluctuations on the system.
2. Inlet water temperature
High water temperature affects oxygenation efficiency, and the difficulty in increasing dissolved oxygen is often due to this reason; If the temperature is too low (generally believed to have a significant impact below 10 ℃), the flocculation effect will deteriorate significantly, with small flocs and turbid interstitial water.
3. Raw water composition
The impact of changes in raw water composition on activated sludge is as follows:
Changes in raw water composition/impact on activated sludge/cause analysis/abnormal fluctuations in pH value
Inhibition of growth, leading to death/unsuitable growth environment/high organic matter concentration/impact load, poor settling ability/rapid microbial growth, high activity
Organic matter concentration is too low/activated sludge is prone to aging/food supply is insufficient, activated sludge dies/suspended solids concentration is too high/insufficient removal in the physicochemical stage, and the effective components of activated sludge are low
Excessive mixing of solid particles leads to a false increase in activated sludge concentration/toxic substances in the influent/disintegration of activated sludge, activity inhibition/poisoning occurs, and cell synthesis is inhibited
Excessive surfactant
Too much foam in the tank body, low oxygen charging efficiency
The foam does not cover the surface of the pool, resulting in low oxygen transfer rate.
4. Food Micro Ratio (F/M)
Food micro ratio is a ratio that reflects the relationship between the quantity of food and microorganisms. In operation management, it is necessary to understand how much food can support how many microorganisms. Usually, it is necessary to control the food to micro ratio at around 0.3, and experimental data is often used to calculate the appropriate inflow rate using formulas. The BOD value is calculated based on 50% of the COD value, and the appropriate COD/BOD ratio for the water quality of the treatment station is found through daily laboratory data comparison.
The calculation method is:
NS=QLa/XV
Where Q - sewage flow rate (m3/d);
V - aeration tank volume (m3);
X - Concentration of Mixed Liquid Suspension (MLSS) (mg/L);
La - influent organic matter (BOD) concentration (mg/L).
(1) The relationship with sludge concentration: According to the principle of how much food can support how many microorganisms, the adjustment of sludge concentration should be adapted to the inflow concentration. In the case of frequent changes in the inflow water quality of the system, it is more reasonable to use the daily average concentration as a reference for adjusting sludge concentration. In practical operation, the most direct method to adjust sludge concentration is to control the remaining sludge discharge. If a sludge discharge curve suitable for the treatment station can be created based on the discharge data, it will have high reference value for future operation.
(2) Relationship with dissolved oxygen: When the food to micro ratio is too low, there is an excess of activated sludge, and the oxygen consumed by the respiration of the excess sludge is greater than the oxygen required to decompose organic matter, but the total oxygen demand remains unchanged, resulting in a decrease in oxygen utilization efficiency and waste of power. When the food to micro ratio is too high, the system's oxygen demand increases, causing oxygen supply pressure. When it exceeds the system's oxygen supply capacity, it can lead to system hypoxia, and in severe cases, it can cause system paralysis.
(3) Corresponding relationship with sedimentation ratio of activated sludge:
Food micro ratio performance
Corresponding settlement ratio performance
Food micro ratio is too low
1. The sedimentation process may result in excessive activated sludge and small flocs
2. Activated sludge has a darker color
3. The settlement process is relatively rapid
4. The supernatant contains small particles
5. The settled activated sludge has good compressibility
Food to micro ratio is too high
1. Rare activated sludge
2. Activated sludge has a fresh and light color
3. The flocculation settling speed is relatively slow
4. The supernatant is turbid
5. Poor compressibility during the settling stage of activated sludge
5. Dissolved oxygen
The dissolved oxygen monitoring during operation mainly relies on online monitoring instruments, portable dissolved oxygen meters, and experimental measurements. There are three methods of monitoring, and the instruments need to frequently compare experimental measurement results to ensure accuracy. When abnormal oxygen content occurs, multi-point sampling should be adopted in the aeration tank to analyze the cause of the malfunction by measuring the dissolved oxygen concentration in different areas of the aeration tank.
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(1) Relationship with the composition of raw water. The impact of raw water on dissolved oxygen is mainly reflected in the fact that a large amount of water 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 inflow should be determined according to the dissolved oxygen situation. In addition, if there are too many detergents in the raw water, there will be an isolation layer at the liquid level 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 rate should be adjusted to avoid excessive aeration and sludge decomposition.
(3) Relationship with settlement ratio. During operation, excessive aeration should be avoided. Excessive aeration can cause small air bubbles in the sludge to adhere to it, resulting in sludge floating, increased settling ratio, and the appearance of a large amount of floating debris on the surface of the sedimentation tank.
6. 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 reflecting the number of microorganisms in the aeration tank.
(1) Relationship with sludge age. Sludge age is a feasible method to achieve the sludge age index by eliminating activated sludge. Therefore, controlling the age of sludge also determines the appropriate range of sludge concentration.
(2) The relationship with temperature. For a normal activated sludge microbial community, the microbial activity doubles for every 10 ℃ decrease in temperature. Therefore, during operation, we only need to reduce the system sludge concentration when the temperature is high and increase it when the temperature is low to achieve stable treatment efficiency.
(3) Relationship with settlement ratio. The higher the concentration of activated sludge, the greater the final sedimentation ratio, and vice versa. During operation, it should be noted that the high concentration of activated sludge causes an increase in settling ratio, and the observed settling sludge is compressed and compacted; The increase in sedimentation ratio caused by non activated sludge concentration is mostly due to poor compaction and dull color. The sedimentation ratio caused by low activated sludge concentration is too low, and the observed sedimentation sludge has a dull color, poor compressibility, and sparse sedimentation of activated sludge.
