Carbon source and temperature effects on nitrogen removal performance in a novel adaptive activated sludge process

Area of Science:

• Environmental Engineering
• Wastewater Treatment
• Microbial Ecology

Background:

• Low temperatures and limited carbon availability challenge wastewater treatment, especially in resource-constrained rural areas.
• Adaptive Activated Sludge (AAS) systems offer potential for efficient nitrogen removal but require optimized carbon source strategies.
• Understanding microbial responses to different carbon sources under varying temperatures is crucial for process optimization.

Purpose of the Study:

• To investigate the impact of glucose, acetate, and a glucose-acetate mixture on nitrification and denitrification in AAS systems at 24°C and 12°C.
• To evaluate the efficiency of nitrogen removal and carbon consumption with different carbon sources under varying temperature conditions.
• To analyze microbial community shifts and gene expression patterns related to carbon metabolism and nitrogen removal.

Main Methods:

• Systematic investigation of AAS performance using glucose, acetate, and a glucose-acetate mixture at 24°C and 12°C.
• Measurement of ammonia-nitrogen and aerobic denitrification rates, total nitrogen (TN) removal efficiency, and chemical oxygen demand (COD) consumption.
• Microbial community analysis using 16S rRNA sequencing and gene expression analysis of key metabolic pathways (glyoxylate cycle, TCA cycle, PHA synthesis).

Main Results:

• Acetate as a sole carbon source yielded the highest nitrogen removal rates (5.47 mg/L·h nitrification, 4.50 mg/L·h denitrification) at 24°C.
• A glucose-acetate mixture demonstrated the lowest carbon consumption (14.33 g COD/g TN at 24°C, 12.56 g COD/g TN at 12°C).
• At 12°C, the mixed system enriched Flavobacterium, associated with heterotrophic nitrification, and upregulated polyhydroxyalkanoate (PHA) synthesis, indicating adaptation to carbon scarcity and enhanced denitrification.

Conclusions:

• A glucose-acetate mixture is an energy-efficient carbon source for AAS systems in cold environments, maintaining high treatment efficiency and reducing operational costs.
• Microbial community structure and metabolic pathways, including acetate metabolism and endogenous carbon storage (PHA), play critical roles in cold-temperature denitrification.
• Strategic selection of mixed carbon sources optimizes wastewater treatment performance and energy efficiency in cold climates.