What measures should be prepared for wastewater ponds affected by low temperatures?

The decrease of temperature often brings severe challenges to wastewater treatment plants, especially to the growth of activated sludge and the effect of nitrogen and phosphorus removal.

Within a certain temperature range, when the water temperature decreases by 10℃, the microbial activity decreases by twice. When the water temperature is lower than 4℃, the microbial activity almost stops, and the wastewater treatment effect decreases or even disappears completely.

Therefore, in order to balance the adverse effects brought by low temperature, it is necessary to control the operating parameters in advance when the water temperature has not changed significa.

What are the effects of low temperature on sewage plant?

1. Low temperature will weaken nitrification and denitrification

The ambient temperature of nitrifying bacteria is between 4-45℃, the optimum temperature of nitrifying bacteria is 35℃, and the optimum temperature of nitrifying bacteria is 35-42℃.

Below the optimum temperature, the activity of nitrifying bacteria decreased with the decrease of temperature. When the temperature decreased by 10℃, the maximum specific proliferation rate and activity of nitrifying bacteria decreased by at least half. When the temperature decreased by 12℃, the reaction rate decreased by 50%, and the nitrification stopped at 5℃.

The optimum temperature for denitrification is between 15-20℃. Below this temperature, the metabolic capacity of denitrifying bacteria decreases to a low level, and the denitrification reaction is inhibited significantly. When the temperature is below 5℃, the denitrification almost stops.

2. Low temperature will indirectly affect biological phosphorus removal

Phosphorus-accumulating bacteria are cold-resistant bacteria. Usually, the effect of temperature reduction on phosphorus-accumulating bacteria in normal operation should be little, but the effect will be significantly decreased in the actual operation process.

The effect of low temperature on biological phosphorus removal is mainly in three aspects: the decrease of temperature affects the metabolism and physiological activity of microorganisms, and the decrease of microbial proliferation rate, thus affecting the effect of phosphorus release and absorption of phosphorus accumulating bacteria, resulting in the decrease of phosphorus removal function of the system.

3. Low temperatures may cause sludge to swell

When the temperature is low, the normal growth of active bacteria in sewage is inhibited and the reproduction is slow. Microfilaria, which is suitable for low temperature growth, will multiply and grow in large numbers at suitable temperature.

These bacteria will be linked to each other in the growth process, polymerization into groups, so as to form larger particles, produce a large amount of surplus sludge, if not removed in time, will cause sewage treatment plant sludge bulking.

4. Low temperature reduces sludge settling performance

When the temperature decreased, the activity of microbial community in activated sludge decreased, the amount of extracellular polymer secreted on the cell surface decreased, the interaction between microorganisms decreased, and it was difficult to combine to form clumpy polymer.

This will lead to fine particles of activated sludge, which is difficult to form large particles of floccule, thus reducing the sedimentation performance of sludge particles, reducing the effect of mud water separation, resulting in small suspended particles often appear in the water, affecting the effluent effect.

5. Low temperature reduces sludge activity

Low temperature will seriously affect the metabolism of microorganisms, resulting in the decrease of sludge activity. It is mainly reflected in the following three aspects:

Under the condition of low temperature, the activity of microbial surface protein in activated sludge decreases, and the fluidity of protoplasmic membrane on the surface decreases, which is not conducive to the transportation of nutrients by microorganisms.

The lower temperature also inhibits the enzyme activity in the microorganism, hinders the utilization of nutrients by the microorganism, and prevents the normal nutrient absorption of the microorganism, thus inhibiting the growth of the microorganism, and reducing the number of microbial flora in the activated sludge, and greatly reducing the activity.

In the process of nitrogen and phosphorus removal, the activity of nitrifying bacteria, phosphorus-accumulating bacteria and other microorganisms will also be affected by temperature, the growth rate is reduced, resulting in the aging of sludge, thus the loss of these active microorganisms.

6. Low temperatures affect the solubility of nutrients required by microorganisms

Low temperature usually reduces the solubility of organic matter in water, but the solubility of different organic matter in water is different, and the trend of its solubility is not the same with the temperature change.

Low water temperature changes the solubility of nutrients required for the growth of various microorganisms in activated sludge, which may change the proportion of different nutrient components, and may deviate from the optimal proportion required for microbial growth, which is not conducive to the metabolic process of microorganisms.

Lower water temperature reduces the overall content of nutrients needed for microbial growth in water. Compared with higher water temperature, more nutrients may be added to ensure the normal growth of microorganisms in activated sludge, which increases the operating cost of sewage treatment plant.

A large amount of organic matter that should be used as energy source cannot be dissolved in water and used by microorganisms, which may also lead to a large amount of sludge and affect the concentration of activated sludge.

Process adjustment measures under low temperature

1. Human intervention as early as possible to improve the adaptability of microorganisms to low temperature

Generally speaking, microorganisms will gradually adapt to the temperature of the surrounding environment during the process of growth and metabolism, but this adaptation process usually takes a long time.

At present, the seasonal transition is not obvious in most cities, and the ambient temperature often decreases suddenly when autumn and winter come. In this case, microbes find it difficult to adapt easily in the short term and need to be replaced by more adaptable microbes.

Therefore, the sewage plant should summarize the rule of temperature change in previous years and make corresponding plans in advance accordingly. When the temperature begins to drop in autumn, the replacement of activated sludge should be carried out slowly to steadily improve the adaptability of microorganisms to low temperature weather.

2. Pay attention to the nutrient component content of sewage, adjust the proportion of organic components

The activity of microorganisms in activated sludge is greatly affected by ambient temperature, and the normal growth of microorganisms will be greatly inhibited at low temperature. In order to maintain the growth, proliferation and metabolism of microorganisms at low temperature, it is necessary for sewage treatment plants to pay close attention to the content of nutrient components in sewage and adjust the proportion of organic components appropriately according to the actual situation.

3. Ensure stable discharge of sludge, controlthe age of sludge

In autumn and winter, the activity of microorganisms in activated sludge is low, so most of them choose to increase the concentration of sludge to maintain the activity.

The water treatment plant should adopt some moderate measures to control the sludge sludge age on the premise of ensuring the stable discharge of sludge, which requires a long process adjustment process.