Introduction: Most sewage treatment plants in China are located in temperate regions and experience relatively low temperatures during winter, especially in northern regions where sewage treatment operates for long periods of low temperature, low water temperature, high concentration of incoming pollutants, and weak sludge activity. This increases the difficulty of sewage treatment and is not conducive to its progress. Therefore, when entering winter operation, it is necessary to strengthen self operation management, cope with unfavorable factors of winter operation, ensure the efficient operation of sewage plants in winter, and thus achieve stable compliance and sufficient emission reduction. Based on past inflow conditions and winter operation experience, the following operating methods are summarized to strengthen and optimize the operation and management of sewage treatment plants, ensuring sufficient treatment of sewage and stable and compliant effluent quality.

1、 Strengthen the whole process management of sewage treatment plant operation

Starting from the details, ensure that each sewage treatment unit fully plays its due role. Malfunctions and problems that arise should be promptly identified, analyzed, and resolved. To avoid small problems and malfunctions that cannot be resolved and become major issues, which may affect the stable operation of the entire system. Special attention should be paid to the abnormal operation of grilles, sedimentation tanks, hydrolysis acidification tanks, sludge dewatering machines, etc., which increases the burden on the biochemical treatment system, causes abnormal operation of the biochemical system, and leads to unstable effluent. These situations need to be given sufficient attention and improved. Wastewater treatment plants should take into account the specific conditions of their biochemical systems, such as the operating rules of their own processes, the characteristics of sludge, and the degradation and changes of pollutants; Combining the daily and monthly changes in the quality and quantity of incoming water. By optimizing and adjusting the process appropriately, ensure sufficient treatment of sewage and stable compliance with effluent quality standards, while optimizing operating costs through energy conservation and consumption reduction.

2、 Adjust operating parameters

In winter, the inflow concentration of sewage treatment plants is generally high, the water temperature is low, the activity of activated sludge is weak, and the reaction speed is slow. Sewage treatment plants need to adjust their production and operation parameters based on their own processes and inflow characteristics.

The specific reference is as follows:

a、 Plants that mainly use domestic sewage can control a slightly lower F/M ratio, while plants that mainly use industrial wastewater should control a lower F/M ratio, preferably between 0.03-0.08kgBOD5/kgMLSS · d.

b、 According to the characteristics of its own process, carry out appropriate aeration control. Under the premise of ensuring sufficient aeration in all cells, the DO value should be controlled at 2.0-3.5mg/L and should not be too high. If there is excessive aeration, it may cause problems such as weak activity, poor properties, and poor settling performance of the sludge system, and also increase operating costs.

c. Ensure the normal operation of the pretreatment unit and ensure that the sludge MLVSS/MLSS, SV30, and SVI in each cell of the biochemical tank are within the normal range.

d. Adjust parameters such as internal and external reflux rates, reflux ratio, etc. based on specific process operation conditions.

e. Properly increasing the MLSS of sludge concentration can maintain a stable total sludge metabolic capacity while reducing bacterial metabolic capacity.

3、 Ensure denitrification efficiency

In the process of biological denitrification, nitrogen-containing compounds undergo the following reactions under the action of microorganisms: ammonification reaction, nitrification reaction, denitrification reaction, and finally Z is separated from the sewage in the form of N2.

The suitable temperature for nitrification reaction is 20-30 ℃. Below 15 ℃, the nitrification rate decreases and completely stops at 5 ℃. The suitable temperature for denitrification reaction is 20-40 ℃. When it is below 15 ℃, the proliferation rate and metabolic rate of denitrifying bacteria decrease. The winter sewage temperature in Northeast China is around 10 ℃ or even lower, far from reaching the optimal temperature for nitrifying and denitrifying bacteria, which has a significant impact on nitrogen removal efficiency.

Nitrifying bacteria are more susceptible to low temperatures than denitrifying bacteria, leading to insufficient nitrification reactions. Improper control during low-temperature operation can easily result in unstable NH3-N. By appropriately increasing MLSS, the sludge age can be increased (preferably controlled at 15-25 days). Appropriately increasing aeration can maintain water temperature to a certain extent and improve dissolved oxygen (DO), which is a commonly used method to control the effectiveness of NH3-N treatment. The key to NH3-N treatment is nitrifying bacteria, and the stable operation of the treatment system should be maintained without severe impact, otherwise it is difficult for nitrifying bacteria to recover in winter.

4、 Control sludge expansion

During low-temperature operation in winter, sludge expansion is prone to occur due to reduced sludge activity and abnormal process operation.

At this time, sludge expansion has three significant characteristics: firstly, the occurrence rate is extremely high, with 60% of urban sewage treatment plants experiencing sludge expansion every year; The second is universality, which exists in various types of activated sludge processes, even in intermittent aeration tanks that are not prone to sludge expansion; The third is serious harm, which not only causes sludge loss and excessive suspended solids (SS) in effluent, but also greatly reduces treatment capacity.

Once sludge swelling occurs, it is difficult to control or takes a considerable amount of time to recover. The appropriate sludge load should be controlled to cope with sludge expansion, and should not be too low. Workers with anaerobic selection zones can use biological selection function to inhibit the production of filamentous bacteria and avoid sludge expansion. Process operators should promptly understand the characteristics of sludge, and when the SVI exceeds 150, sufficient attention should be paid. If necessary, chemical agents can be added for control. Artificially synthesized high molecular weight cationic polymers have a good effect on controlling sludge expansion and have little impact on sludge production, but the cost is high. In some cases, adding inorganic flocculants (such as lime or ferric chloride) can also be effective, but it can greatly increase sludge production and pose certain difficulties for subsequent sludge treatment. In addition, adding soil and fiber materials is also suitable for the treatment of some industrial wastewater (such as papermaking wastewater), but this is only a short-term behavior.

Chlorine and hydrogen peroxide have been successfully applied in inhibiting the growth of filamentous bacteria. Due to its relatively low cost and easy on-site operation, chlorine is widely used, with over 50% of sewage treatment plants utilizing chlorine to control sludge expansion caused by filamentous bacteria. The purpose of adding chlorine is to kill filamentous bacteria attached to the surface of floc microorganisms, but there is no significant difference in the sensitivity of these two types of bacteria to chlorine. Therefore, the amount of chlorine added should be controlled to just kill filamentous bacteria without harming floc microorganisms. Excessive amounts are also not conducive to improving sludge performance.

5、 Reasonably adjust the dosage of medication

During the operation of sewage treatment plants with efficient sedimentation tanks or chemical treatment units, the first consideration should be to strengthen the treatment of pollutants by the biochemical system, and then adopt chemical treatment to ensure quality control. Avoid overly relying on chemical treatment to maintain water stability. Chemical treatment will generate a large amount of chemical sludge, and if not treated properly, it will lead to a vicious cycle in the system. The dosing process and system must be standardized, and a dedicated person is responsible for dosing management; The dosage of medication at different times of the day must be combined with the water conditions of the secondary sedimentation tank, the experimental data of the beaker, and the online data of the effluent; Reasonably adjust to avoid wasting medication.

6、 Strictly control the inflow indicators

The inflow in winter is relatively small, and the proportion of industrial wastewater has increased. Therefore, it is necessary to strengthen the control of the inflow source. Once abnormal water inflow online data is detected, operators should immediately conduct on-site verification. Once the abnormal situation of high inflow pollutants is determined, emergency measures should be taken, evidence should be left, and timely communication with the competent department should be made. If necessary, a written report should be made.

7、 Strengthen the collection, organization, statistics, and analysis of production data

Special attention should be paid to strengthening the statistical analysis of data and guiding the adjustment and regulation of production operations based on the conclusions of data analysis. Each branch and sewage treatment plant should strengthen their laboratory analysis work to ensure timely, accurate, and reliable laboratory data; At the same time, ensure the effectiveness and reliability of production related data. The reliability of data is a prerequisite for conducting data analysis. If the premise is incorrect, it will inevitably lead to errors in the results.

8、 Strengthen the management of sludge dewatering system

The poor activity of sludge in winter poses difficulties for the operation and management of sludge dewatering systems, and the moisture content of dewatered sludge is difficult to control. We should strengthen the operation and management of sludge concentration and dewatering systems, and arrange the operation of dewatering machines reasonably according to production needs; Ensure that the biochemical system maintains appropriate MLSS. Be careful not to avoid a vicious cycle of residual sludge (or chemical sludge) in the treatment system caused by abnormal operation of the dewatering machine, which can lead to an increase in concentration entering the biochemical system and have adverse effects on activated sludge. At the same time, active exploration can be conducted on the dosage of coagulants, and small-scale trials can be carried out to explore the rules. Tap water should be used as much as possible for drug preparation to reduce the dosage of PAM. Due to the low water temperature during winter dispensing, which seriously affects the dissolution of polyacrylamide, it is recommended to install heating devices at the dispensing tank, water distribution pipe, and water tank to increase the water temperature.

9、 Pay attention to inspection safety

During low temperatures in winter, outdoor facilities are prone to frost heave, icing, and other conditions. Therefore, it is necessary to strengthen the inspection work of each processing unit in the factory, including process inspection and equipment inspection, to promptly detect and handle any abnormal situations during operation. Special attention should be paid to the inspection of water inflow, outflow, and biochemical tanks; Promptly detect abnormal situations and handle them promptly.

10、 Strengthen equipment and instrument maintenance

After snowfall and freezing in winter, maintenance and upkeep of equipment and facilities will shift from outdoor work to indoor work. Key equipment maintenance and repair work should be done in advance, especially for the aeration and sludge discharge systems, to ensure that key equipment does not malfunction in winter. If these equipment malfunction in winter, the losses and difficulty of maintenance will increase exponentially.

During operation, it is also necessary to ensure the normal operation of online instrument facilities (influent COD, NH3-N, and DO, PH in process control), to ensure accurate and effective data acquisition and upload, in order to fully utilize the monitoring role of online instruments and timely detect and adjust any abnormal situations that occur.

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