1. Introduction
Enhanced biological nutrient removal (BNR) is a critical component of conventional activated sludge (CAS) systems, aiming to reduce nitrogen and phosphorus concentrations to meet increasingly stringent effluent discharge regulations. Traditional CAS systems often rely on continuous aeration and fixed operational parameters, which can limit nutrient removal efficiency, particularly under fluctuating influent conditions. The study investigates operational modifications, including intermittent aeration and sludge age optimization, to enhance nutrient removal without major infrastructure changes, providing practical guidance for retrofitting existing plants.
2. Materials and Methods
Pilot-scale reactors were designed to compare different operational conditions. Aeration modes included continuous and intermittent aeration cycles, while sludge retention times (SRT) ranged from 5 to 20 days. The carbon-to-nitrogen (C/N) ratios were adjusted from 4 to 10 to evaluate their effect on nutrient removal. Municipal secondary effluent was used as influent. Nitrogen and phosphorus concentrations were monitored daily. Microbial community composition was assessed using 16S rRNA sequencing, focusing on the enrichment of nitrifying and denitrifying bacteria under various operational strategies. Adaptive control strategies were implemented to evaluate effluent stability under influent variability.
3. Results
Intermittent aeration combined with optimized sludge age significantly improved nutrient removal efficiency. Ammonium removal consistently exceeded 95%, total nitrogen removal ranged from 80% to 90%, and total phosphorus concentrations dropped below 1 mg/L under optimal conditions. Microbial analysis revealed selective enrichment of nitrifying and denitrifying bacteria, which correlated with improved nutrient removal. Continuous monitoring and adaptive control maintained stable effluent quality even when influent concentrations varied. Comparative analysis demonstrated that intermittent aeration provided superior nitrogen and phosphorus removal compared to continuous aeration, while optimizing SRT further enhanced process performance.
4. Discussion
The results indicate that operational modifications in CAS systems can significantly enhance nutrient removal without requiring expensive infrastructure upgrades. Intermittent aeration creates alternating aerobic and anoxic conditions that favor simultaneous nitrification and denitrification. Optimized sludge age maintains a balanced microbial population, supporting stable biological activity. The study highlights the importance of understanding microbial community dynamics and applying adaptive control to respond to influent variability. These findings offer practical guidance for wastewater treatment facilities seeking to improve effluent quality cost-effectively while meeting stricter regulatory requirements.
5. Conclusion
Enhanced biological nutrient removal in conventional activated sludge systems can be achieved by combining intermittent aeration with optimized sludge age. This strategy improves nitrogen and phosphorus removal, promotes beneficial microbial community shifts, and ensures stable effluent quality under variable conditions. The comparative approach provides a feasible and cost-effective method for retrofitting existing CAS plants, demonstrating that operational modifications can achieve substantial environmental and regulatory benefits without major infrastructure investments.