The Role and Function of Sodium Acetate in Wastewater Treatment

With the acceleration of industrialization and urbanization, wastewater treatment has become an important part of environmental protection. In the biological and chemical processes of wastewater treatment, the supplementation and regulation of carbon sources is one of the key factors in improving treatment efficiency. Sodium acetate (CH₃COONa), as a rapid and stable organic carbon source, is widely used in wastewater treatment. This article will elaborate on its mechanism of action and practical applications from aspects such as denitrification and phosphorus removal, carbon source supplementation, and pH adjustment.

I. Chemical Properties of Sodium Acetate and Adaptability to Wastewater Treatment
Sodium acetate is a salt formed by the neutralization of acetic acid (a weak acid) and sodium hydroxide (a strong alkali). It is easily soluble in water and exhibits weak alkalinity (pH≈8.5) after hydrolysis. The acetate group (CH₃COO⁻) in its molecular structure can serve as an easily degradable organic carbon source, while the sodium ion (Na⁺) has no significant inhibitory effect on microbial activity. This characteristic makes it an ideal carbon source and regulator in wastewater treatment.

II. Core Roles of Sodium Acetate in Wastewater Treatment

1. Enhanced Biological Denitrification
Biological denitrification includes two stages: nitrification (ammonia nitrogen → nitrite → nitrate) and denitrification (nitrate → nitrogen gas). The denitrification process requires sufficient organic carbon sources as electron donors.
Mechanism of action: The acetate in sodium acetate can be rapidly utilized by denitrifying bacteria to reduce nitrate (NO₃⁻) to nitrogen gas (N₂).
Advantages: Compared with carbon sources such as methanol and glucose, sodium acetate has a faster denitrification rate (reducing reaction time by 30%), lower toxicity, and higher operational stability.

2. Promoting Biological Phosphorus Removal
Phosphorus removal depends on the metabolic activity of polyphosphate-accumulating organisms (PAOs):
Anaerobic stage: Polyphosphate-accumulating organisms decompose intracellular polyphosphate to release phosphorus, while simultaneously absorbing acetate to synthesize polyhydroxyalkanoates (PHA).
Aerobic stage: Polyphosphate-accumulating organisms decompose PHA and absorb excessive phosphorus, forming phosphorus-rich sludge that is discharged from the system.
Sodium acetate, as a high-quality carbon source, can significantly improve the metabolic activity of polyphosphate-accumulating organisms and enhance phosphorus removal efficiency (up to 90% or more).

3. pH Regulation and Buffering Action
The nitrification process consumes alkalinity (7.14g alkalinity is required to oxidize 1g of ammonia nitrogen), leading to a decrease in pH and inhibiting the activity of nitrifying bacteria.
The HCO₃⁻ and OH⁻ produced by the hydrolysis of sodium acetate can supplement alkalinity, maintaining the pH within the suitable range of 6.5~8.5 and ensuring the stability of the microbial community.

4. Supplementing Carbon Sources and Optimizing the C/N Ratio
For wastewater with a low carbon-nitrogen ratio (C/N < 4) (such as industrial wastewater and late-stage landfill leachate), adding sodium acetate can increase the C/N ratio to 5~6, avoiding the decrease in denitrification efficiency caused by insufficient carbon sources for denitrification.

III. Operational Points in Practical Applications

1. Dosage and Location
Dosage: Dynamically adjusted according to the influent C/N ratio, usually 50~200mg/L (calculated as acetate).
Dosage point: Prioritize the front end of the anoxic tank to ensure that the carbon source fully participates in denitrification.

2. Economy and Alternative Solutions
Although the cost of sodium acetate is higher than that of methanol, it does not require explosion-proof facilities and leaves no residue, resulting in lower overall maintenance costs.
It can be used in combination with other carbon sources (such as acetic acid and glucose) to balance effectiveness and cost.

3. Potential Problems and Countermeasures
Excessive addition: May lead to increased COD in the effluent or sludge expansion, requiring real-time control through online monitoring.
Sodium salt accumulation: Long-term use may increase the Na⁺ concentration in the system, requiring regular monitoring of the potential inhibition of microorganisms.
With its rapid carbon source supply capacity, pH regulation function, and environmentally friendly characteristics, sodium acetate has become an indispensable auxiliary agent in modern wastewater treatment processes. Reasonable application can significantly improve the efficiency of denitrification and phosphorus removal, helping to achieve the recycling of water resources and ecological protection.