How to deal with a nitrification system crash

How to deal with a nitrification system crash

In the sewage treatment process, the collapse of the nitrification system is a serious problem, which may cause the effluent water quality to be substandard, affecting the environmental quality and the subsequent treatment effect. The manifestations of the collapse of the nitrification system usually include poor water quality, abnormal pH value, excessive nutrient salt content, excessive sludge production, and abnormal odor. So, when the nitrification system collapses, how should we deal with it?

Cause investigation

◆Sludge age is too short:

◇The generation cycle of nitrifying bacteria is long. If the sludge retention time (SRT) is too short, nitrifying bacteria cannot effectively gather in the system, resulting in weakened nitrification. ◇Poor sludge return or excessive sludge discharge will also reduce the sludge age and affect the nitrification effect.

◆Excessive load:

◇The organic load or ammonia nitrogen load is too high, and nitrifying bacteria are at a disadvantage in the competition with heterotrophic bacteria and cannot fully carry out nitrification. ◇Insufficient sludge volume at the initial start-up of the system or short system retention time will also lead to excessive load.

◆Unsuitable external environment:

◇Insufficient dissolved oxygen (DO): Nitrification requires sufficient oxygen. When DO is lower than 2.0 mg/L, nitrification will be inhibited. ◇Abnormal pH value: Nitrifying bacteria are sensitive to pH value, and the optimal range is 8-9. Exceeding this range will affect their biological activity. ◇Unsuitable temperature: Nitrifying bacteria can carry out normal physiological metabolic activities within the range of 5-35℃. When the temperature is lower than 5℃ or higher than 40℃, their activity will be inhibited.

◆Equipment failure or improper operation:

◇Aeration equipment failure leads to insufficient DO. ◇Abnormal return system affects sludge return and mixed liquor distribution. ◇Failure of the control system causes process parameters to deviate from the normal range.

Emergency response measures

◆Stop or reduce water inflow: reduce system load and provide nitrifying bacteria with a chance to recover.

◆Increase aeration volume: increase dissolved oxygen level and support the activity of nitrifying bacteria.

◆Adjust reflow ratio: appropriately increase internal reflow ratio to improve nitrification efficiency.

◆Maintain appropriate pH value: adjust pH value within the range suitable for nitrifying bacteria growth by adding acid and alkali substances.

◆Stop sludge discharge: avoid further loss of nitrifying bacteria.

Solution

◆Adjust sludge age:

◇Prolong sludge retention time, avoid excessive sludge discharge, and ensure that nitrifying bacteria can effectively gather in the system. ◇Optimize sludge return system to ensure smooth sludge return.

◆Reduce load:

◇Reduce influent load, reduce organic matter and ammonia nitrogen concentration. ◇Increase system retention time and improve treatment efficiency. ◇Activated sludge can be added during initial startup to quickly increase sludge concentration.

◆Optimize external environment:

◇Increase dissolved oxygen level to ensure DO is between 2.0-3.0mg/L. ◇ Adjust the pH value to the optimal range for nitrifying bacteria (8-9). ◇ Control the water temperature within the appropriate range (5-35℃) to avoid the impact of extreme temperature on nitrifying bacteria.

◆ Strengthen equipment maintenance and management:

◇ Regularly check key equipment such as aeration equipment and reflux system to ensure their normal operation. ◇ Strengthen control system maintenance to ensure stable process parameters. ◇ Improve the skill level of operators, strengthen training and management.

◆ Add nitrifying bacteria culture solution:

◇ After confirming that the system is stable, nitrifying bacteria culture solution can be added to accelerate the recovery of the nitrification system. ◇ Select appropriate nitrifying bacteria culture solution and add it according to the actual situation of the system.

◆ Strengthen water quality monitoring and early warning:

◇ Regularly monitor the effluent water quality to detect and deal with abnormal conditions in a timely manner. ◇ Establish an early warning mechanism to monitor and warn key indicators in real time.

Gradual recovery and reconstruction

◆ Supplement carbon source: If the C/N ratio is insufficient, an external carbon source can be added to support the denitrification process.

◆Add nitrifying bacteria: After confirming that the system is stable, nitrifying bacteria culture solution or activated sludge can be added to accelerate the recovery of the nitrification system.

◆Adjust the influent quality: For wastewater with high organic content, its concentration can be reduced by pretreatment.

◆Strengthen microbial community management: Enhance the tolerance of microbial communities by adding appropriate growth factors.

◆Optimize process control: Adjust process parameters such as sludge age and sludge load according to actual conditions.

Precautions

◆Gradual: In the process of restoring the nitrification system, the influent load and aeration volume should be increased step by step to avoid excessive impact on the system.

◆Avoid overtreatment: Do not blindly add chemical agents or change process parameters to avoid unnecessary interference with the system.

◆Flexible response: The actual situation and wastewater characteristics of each sewage treatment plant are different. Therefore, when dealing with the collapse of the nitrification system, it is necessary to respond flexibly based on the actual situation on site.