During the operation of wastewater treatment systems, pH is one of the most frequently monitored parameters. However, there are many cases where pH remains within an appropriate range but the effluent Ammonium tends to increase, the nitrification process becomes inefficient, or the microbial system becomes unstable. In such cases, the cause does not always stem from the pH but may be related to an often-overlooked indicator: alkalinity. Not only does it help maintain pH stability, but alkalinity also directly affects Ammonia removal efficiency and the activity of the microbial system. Therefore, properly understanding the role of alkalinity and knowing how to adjust it appropriately will help businesses maintain a stable operating system, limit incidents, and optimize costs during wastewater treatment.
Alkalinity is an indicator that reflects the capacity to neutralize acids and maintain pH stability in water. In wastewater treatment, alkalinity is typically expressed in units of mg/L CaCO₃ and is considered the buffering capacity of water against fluctuations caused by chemical and biological reactions. This is one of the crucial conditions that helps the microbial system, especially nitrifying bacteria, maintain stable activity and ensure Ammonia treatment efficiency in the system.
Although both are related to the acidity and alkalinity of water, alkalinity and pH have completely different meanings. pH reflects the level of acidity or alkalinity of the water at the time of measurement, whereas alkalinity indicates the capacity to maintain pH stability when the system is affected by biological reactions or fluctuations in the influent wastewater. This also means that a system with an appropriate pH does not necessarily have enough alkalinity to maintain a stable biological treatment process.
In reality, many systems still maintain pH within an appropriate range even though alkalinity has dropped below the required level. In such cases, the nitrification process may begin to decline even if the operator has not noticed any abnormal signs when only monitoring pH. This makes it easy for businesses to misjudge the operational status and makes it difficult to determine the cause when Ammonia treatment efficiency drops. This situation is commonly encountered in food processing, seafood, or livestock manufacturing plants, where the Ammonia load changes according to production output. Therefore, monitoring both pH and alkalinity simultaneously will provide a more accurate assessment of the biological treatment system's operating conditions.
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The pH scale (alkalinity/acidity)
Note: In the nitrification process, to oxidize 1 mg of Ammonia-N, the system consumes approximately 7.14 mg of alkalinity (converted as CaCO₃). Therefore, if alkalinity is not maintained at an appropriate level, pH will tend to gradually decrease, affecting the activity of nitrifying bacteria and Ammonia treatment efficiency.
In wastewater treatment systems, numerous chemical and biological reactions take place continuously, which can cause pH to change over time. Alkalinity acts as a "buffer system," helping to limit sudden fluctuations in pH and maintaining a stable environment for the entire treatment process.
Alkalinity is one of the critical conditions that helps the nitrification process take place stably. When the buffering capacity of water declines, pH will gradually drop during the treatment process, reducing the activity of nitrifying bacteria and causing Ammonia treatment efficiency to fall short of expectations. If this condition is prolonged, effluent Ammonia can increase and affect the quality of the treated water as well as the ability to meet discharge standards.
These impacts are analyzed in detail in the article "How Does High Ammonia Affect the Environment and the Wastewater Treatment System?". Therefore, in biological treatment systems requiring Ammonia removal, maintaining stable alkalinity should be monitored simultaneously with pH, DO, and influent/effluent Ammonia concentrations.
Alkalinity contributes to maintaining a favorable environment for the microbial system to grow. When the water's buffering capacity is stable, microorganisms will adapt better to fluctuations in wastewater load while mitigating the risk of being inhibited or losing activity after shock loads.
For food processing, seafood, or livestock manufacturing plants, the influent Ammonia load often changes with production output. If alkalinity is maintained appropriately, the system will adapt better to these fluctuations, reducing the risk of operational incidents and limiting adjustment costs during operation.
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The role of alkalinity in wastewater treatment
When operational results show that alkalinity no longer meets the requirements of the biological treatment process, businesses need to consider adding an appropriate alkali source. Chemical selection depends not only on cost but must also take into account wastewater characteristics, treatment technology, and the operational goals of each system.
NaHCO₃ is often preferred in biological treatment systems that need to maintain a stable nitrification process or when alkalinity is declining but pH has not yet fluctuated significantly. This is a commonly used alkali source due to its ability to add alkalinity gradually, minimizing sudden pH spikes and creating favorable conditions for the microbial system to operate stably. Although the cost is typically higher than some other chemicals, NaHCO₃ remains the choice for many businesses when long-term biological treatment efficiency needs to be sustained.
NaOH is often used when there is a need to quickly adjust the pH of acidic wastewater. However, the main purpose of this chemical is to raise pH rather than supplement alkalinity for the nitrification process. Therefore, NaOH is more suitable for cases requiring quick fixes for pH fluctuations than for maintaining alkalinity over a long period. Nevertheless, if the goal is long-term alkalinity maintenance, businesses should consider combining it with other appropriate alkalinity supplements.
When using NaOH, businesses also need to dose the chemical slowly and control the dosage properly to limit sudden pH increases that can affect the activity of the microbial system.
Lime (Ca(OH)₂) is often chosen for large-flow wastewater treatment systems due to its low cost and good alkalinity supplementation capacity. However, if used improperly, lime can generate scale, causing buildup in pipes or equipment; hence, its dosage and feeding method must be well-controlled. The preparation and dosing of lime must also be appropriately designed to minimize sedimentation within the system. Additionally, the lime dissolving and dosing system needs periodic cleaning to limit scaling and clogging of pipelines during operation.
Na₂CO₃ (Soda ash) is also an alkalinity supplement source used in some wastewater treatment systems. This chemical helps efficiently increase alkalinity and limits excessive pH fluctuations, though the dosage still needs to be calculated to match the characteristics of each wastewater source. In practice, Soda ash is often selected when businesses need to strike a balance between alkalinity supplementation efficiency and operating costs, particularly for systems with a medium level of fluctuation in pollution loads.
Chemical selection should not be based solely on cost but must consider adjustment goals, wastewater characteristics, and treatment technology. For biological treatment systems requiring nitrification maintenance, NaHCO₃ is usually the appropriate choice. Meanwhile, NaOH is suitable for rapid pH adjustment, and lime or Na₂CO₃ can be considered for large-scale systems to optimize operating costs. Businesses should assess the current status of their systems before deciding on the appropriate chemical type.
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Consider chemical options carefully before use
Supplementing chemicals helps improve alkalinity, but it does not always resolve the root cause of an issue. Businesses should simultaneously evaluate parameters such as pH, DO, Ammonia, and the operating status of the microbial system to determine the correct cause before making adjustments.
In addition to choosing the right chemical, businesses should also monitor alkalinity periodically, especially for systems with large Ammonia load fluctuations or batch operations. Supplementing alkalinity at the right time will help maintain a stable nitrification process and limit treatment costs when the system encounters issues.
For biological Ammonia treatment systems, businesses should establish a plan for periodic alkalinity monitoring instead of only checking when the system encounters an issue. Early detection of a declining alkalinity trend will make adjustments more proactive, limiting impacts on microbial activity and reducing operating costs.
Furthermore, chemicals should not be added in large quantities over a short period, as sudden changes in pH and alkalinity can affect the activity of the microbial system. Following adjustments, businesses should continue to track the fluctuation trends of pH, alkalinity, DO, and Ammonia over the next few days to evaluate effectiveness, rather than relying solely on a single analysis result right after the chemical addition.
Alkalinity is not only an indicator of the water's buffering capacity but also directly affects Ammonia treatment efficiency and the stability of the microbial system in wastewater treatment systems. Maintaining alkalinity at an appropriate level, choosing the right chemical type, and monitoring it simultaneously with parameters like pH, DO, and Ammonia will ensure an efficient nitrification process, limit incidents, and optimize long-term operating costs.
Along with timely chemical addition, businesses need to periodically monitor alkalinity and related parameters to make timely adjustments when operating conditions change. If your system is experiencing increasing effluent Ammonia, fluctuating pH, or an unstable nitrification process, Dai Nam's engineering team is ready to survey the current status, evaluate the causes, and consult on appropriate solutions for each wastewater treatment system.
