During the operation of wastewater treatment systems, Total Phosphorus (TP) is often one of the most difficult parameters to control. There are many cases where the treated water has met COD, BOD, Ammonia, or TSS requirements, but the analysis results still show Total Phosphorus exceeding the allowable limits. In such situations, many units choose to increase the dosage of PAC, aluminum alum, or iron salts with the expectation of improving treatment efficiency.
However, effluent Total Phosphorus exceeding standards does not always stem from a lack of chemicals. Phosphorus can exist in many different forms, such as dissolved, within microbial biomass, or attached to suspended solids. Therefore, the removal efficiency simultaneously depends on the influent load, the activity of the microbial system, the chemical precipitation process, flocculation ability, sludge separation efficiency, and the sludge wasting regime. If the exact form of Phosphorus present and the location of the problem within the system have not been correctly identified, increasing chemicals will not only fail to improve effluent water quality but also increase sludge generation, lower the pH, and significantly raise operating costs.
1. Signs That Effluent Total Phosphorus is Exceeding Standards
In actual operation, Total Phosphorus rarely increases suddenly. Most systems exhibit abnormal signs before this parameter exceeds standards. By regularly monitoring analysis results in combination with operating parameters, incidents can be detected very early.
Common signs include:
Each sign reflects a different set of causes. Therefore, correctly identifying the cause is always more important than making adjustments based on feeling.
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Signs to recognize Total Phosphorus exceeding standards
Effluent Total Phosphorus exceeding standards usually does not originate from a single cause. In many cases, it is the result of multiple factors interacting simultaneously during operation. Correctly isolating the cause will help in selecting the appropriate solution, limiting multiple adjustments that yield no improvement.
In systems applying biological phosphorus removal technology, treatment efficiency depends heavily on the operating conditions of the microorganisms. When the carbon source is unstable, the sludge age is inappropriate, or the anaerobic, anoxic, and aerobic zones are not maintained at their design conditions, the phosphorus uptake capacity will drop significantly. This group of causes usually does not make Total Phosphorus increase immediately but rather gradually over time. Therefore, if you only add more chemicals without re-evaluating the biological process, the treatment efficiency is usually unsustainable, and operating costs will continue to rise.
In many systems, the amount of PAC or aluminum alum has been significantly increased, but the Total Phosphorus analysis results remain almost unchanged. This does not mean the chemicals are ineffective; it usually stems from inappropriate reaction conditions. Phosphorus precipitation efficiency depends on many factors such as pH, chemical dosing location, mixing capability, and reaction time. If just one of these factors is not at its optimal condition, treatment efficiency can decrease significantly even if the chemical dosage is maintained at a high level. Therefore, a Jar Test should be performed before adjusting the chemical dosage in the actual system.
When the influent Phosphorus load suddenly increases, the treatment efficiency of the entire system will also be affected. The cause could be a change in production raw materials, the use of additional phosphorus-containing chemicals, or an unusually high volume of CIP or equipment cleaning water. If the equalization tank lacks the capacity to balance the load, the downstream treatment facilities will have to receive a larger amount of Phosphorus than designed, leading to a high effluent Total Phosphorus even if the system is still operating according to standard procedures.
After being absorbed or precipitated, most of the Phosphorus will reside in the sludge. Therefore, sludge separation efficiency has a direct impact on the effluent Total Phosphorus parameter. When sludge is hard to settle, the settling tank operates unstably, or the sludge wasting regime is unreasonable, Phosphorus can escape with the solids or be released back into the wastewater if the sludge is retained in the system for too long. This is a fairly common cause but is often confused with a lack of chemicals, leading to misdirected troubleshooting.
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Causes of increased phosphorus
When effluent Total Phosphorus exceeds standards, many systems often choose the quickest solution: increasing the amount of PAC or aluminum alum. However, without identifying the correct cause, this approach only increases chemical costs and generates more sludge, with negligible improvement in efficiency.
In reality, troubleshooting will be more effective if it starts with evaluating the entire system, from the influent Phosphorus load and biological facilities to the precipitation and sludge separation processes. Correctly identifying the cause right from the start will help select the appropriate solution and avoid having to make multiple adjustments without seeing improvement.
Before adjusting the system, it is necessary to check the influent Total Phosphorus concentration and compare it with operating data from previous days. If the influent TP increases abnormally, the cause is highly likely due to a change in production raw materials, CIP water, equipment cleaning water, or newly generated wastewater streams. Conversely, if the influent TP remains stable but the effluent TP gradually increases, the problem usually lies in the treatment efficiency of the system rather than the pollution load. In this case, focus on evaluating the treatment facilities instead of immediately adjusting the chemical dosage.
For systems applying biological phosphorus removal technology, it is necessary to re-evaluate the carbon source, sludge age, sludge return ratio, and operating conditions of the anaerobic, anoxic, and aerobic zones. When one of these factors is no longer suitable, the phosphorus uptake capacity of the microorganisms will decline even if COD or BOD parameters still meet requirements. If the cause is determined to be from the biological facility, restoring operating conditions should be prioritized before increasing chemicals. This solution helps stabilize the system in the long run while minimizing unnecessary operating costs.
For systems using PAC, aluminum alum, or iron salts, do not immediately increase the chemical dosage when analysis results exceed standards. First, check the pH, chemical dosing location, mixing capability, and reaction time of the reaction tank to ensure precipitation conditions are effective. After ruling out the above factors, perform a Jar Test to determine the optimal chemical dosage before applying it to the actual system. Adjusting based on test results will help enhance Phosphorus removal efficiency while limiting excess chemical usage and reducing the amount of physicochemical sludge generated.
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Ensure total phosphorus is stable and does not exceed standards before discharging into the environment
After being absorbed or precipitated, most of the Phosphorus will be retained in the sludge. Therefore, if the water after the settling tank still has a lot of fine flocs, small sludge particles, or poor settling sludge, you need to recheck the flocculation process, the settling tank's efficiency, and the sludge wasting regime. Additionally, do not change multiple parameters simultaneously in a single adjustment. If you increase chemicals, adjust pH, and change the sludge wasting regime all at once, it will be very difficult to determine which factor actually brought about the improvement. In actual operation, only one group of parameters should be adjusted at a time, followed by continuous monitoring of the analysis results before taking the next steps if necessary.
Effluent Total Phosphorus exceeding standards can stem from many different causes, ranging from fluctuations in the influent wastewater, biological treatment processes, and chemical precipitation to the sludge separation capacity of the system. Therefore, correctly identifying the cause is always more important than just increasing chemicals or adjusting operations based on feeling.
With experience in designing, upgrading, and operating numerous wastewater treatment systems for industrial and civil sectors, Dai Nam is ready to assist in surveying, evaluating causes, and proposing suitable solutions for each facility. Addressing the root cause correctly not only ensures that effluent Total Phosphorus meets standards but also contributes to enhancing operational efficiency and optimizing costs in the long term.
