Nitritation, the biological conversion of ammonia to nitrite, is critical in sustainable wastewater treatment processes. However, knowledge gaps and challenges still exist for achieving stable nitritation in low-ammonia, low-temperature mainstream municipal wastewater. To help bridge the gap between the technical concept and practical engineering applications, researchers from the Beijing University of Technology present a convenient and implementable solution based on the “Fresh Start” concept to show how to move promising sustainability-related nitritation technology out of the lab and into real-world use.
The traditional nitrification-denitrification process employed in wastewater treatment plants (WWTPs) is energy-intensive and requires an excess carbon source, leading to high operational costs and substantial greenhouse gas emissions. In contrast, integrating nitritation with the anammox process, which utilizes nitrite as an electron acceptor, offers a low-carbon and economically viable alternative.
How can sewage treatment be made more sustainable with rapid nitritation? An innovative nitritation strategy has been successfully demonstrated in a pilot-scale bioreactor treating real mainstream municipal wastewater, paving the way for sustainable sewage management and contributing to the achievement of the 2030 Sustainable Development Goals.
Liang Zhang
Quick start-up of nitritation
Nevertheless, effectively suppressing nitrite-oxidizing bacteria and promoting ammonia-oxidizing bacteria under real-world conditions has proven elusive. The study, published in Nature Sustainability, describes a strategy for swiftly initiating and maintaining high nitrite accumulation ratios even under low temperatures and varying seasonal conditions. The first phase involves a high organic loading rate to decrease ammonia-oxidizing and nitrite-oxidizing bacteria levels. In the second phase, the organic loading rate sharply decreases to enhance ammonia-oxidizing bacteria and promote their bioactivity while containing nitrite-oxidizing bacteria.
From the lab to real-world use
The strategy was successfully demonstrated in a pilot-scale (6.5 m³) bioreactor treating real mainstream municipal wastewater. Nitritation was initiated within seven days and maintained a high nitrite accumulation ratio of approximately 98.1% for over 450 days, even at temperatures as low as 5.9°C. The average effluent ammonium and nitrite levels were kept at 8.3 mg N L-1 and 13.8 mg N L-1, respectively, making it ideal for further nitrogen removal through the anammox process.
One of the key findings of the study is the strategy’s resilience to low temperatures. The pilot-scale reactor demonstrated stable nitritation performance even under seasonally varying temperatures ranging from 5.9°C to 29.8°C. This is achieved by controlling the residual ammonium concentration, which enhances the bioactivity of AOBs and minimizes the opportunity for NOBs to re-proliferate. The study highlights the importance of moving from laboratory experiments to pilot-scale and full-scale processes under real-world conditions.
Implications, future research, and recommendations
As noted in the accompanying editorial in Nature Sustainability, “One of the first steps towards exploring the real-world potential of lab-scale technologies is to test how well they operate under real-world conditions”. The success of this loading rate switch strategy in a pilot-scale reactor treating real municipal wastewater underscores its potential for widespread implementation in WWTPs. In a related News & Views article, reviewers provided an in-depth introduction to the “Fresh Start” concept-based nitritation strategy. They commented on the significance of the results—highly evaluating the significance of the results, emphasizing its potential to further mitigate greenhouse gas emissions, particularly nitrous oxide, through integration with anammox in a single-stage bioreactor.
With further research and optimization, this technology promises to revolutionize nitrogen removal processes worldwide, contributing to a greener and more sustainable future. The study also raises important questions for future research, including how to couple with subsequent anammox processes and quantify greenhouse gas emissions of the present pilot-scale system, which appears necessary to determine the overall carbon footprint. Nonetheless, the development of this loading rate switch strategy represents a significant step forward in the field of sustainable wastewater treatment.
To tackle urgent wastewater management challenges and uphold global justice, decisive actions by governments and industries are crucial. Prioritized recommendations include investing in sustainable technologies, offering policy incentives for low-carbon approaches, fostering international cooperation, setting ambitious greenhouse gas reduction targets, and introducing robust monitoring systems. Comprehensive, forward-looking wastewater management plans considering population, urbanization, and climate change are paramount for a sustainable future.
Conclusion
The loading rate switch strategy presents a viable and environmentally friendly approach to nitrogen removal. By enabling ultra-stable nitritation, this strategy paves the way for more efficient and cost-effective sewage management, which is crucial for achieving the 2030 Sustainable Development Goals. This work opens new avenues for sustainable sewage management, offering a replicable and sustainable control strategy for full-scale municipal wastewater nitritation.
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Journal reference
Wang, Z., Zhang, L., Zeng, W., Li, J., Zhang, Q., Li, X., & Peng, Y. (2024). A loading rate switch strategy for stable nitritation in mainstream municipal wastewater. Nature Sustainability, 7(3), 305-314. https://doi.org/10.1038/s41893-024-01276-z
