Deciphering correlation between chromaticity and activity of anammox sludge

Area of Science:

• Environmental microbiology
• Biotechnology
• Biogeochemistry

Background:

• Anaerobic ammonium-oxidizing bacteria (AnAOB) exhibit a red color, often used for rough activity estimation.
• A quantitative link between AnAOB sludge color and its activity remains unestablished.
• Understanding this relationship is crucial for optimizing wastewater treatment processes.

Purpose of the Study:

• To establish a quantitative correlation between the chromaticity of AnAOB sludge and its anammox activity.
• To identify the molecular basis for the color and its relationship with AnAOB performance.
• To explore the potential of sludge chromaticity as an intuitive indicator for anammox process monitoring.

Main Methods:

• Digitalization of AnAOB sludge chromaticity using the CIE L*a*b* color space.
• Measurement of specific anammox activity under various nitrogen loading rates.
• Spectroscopic analysis to identify the origin of the visible spectra (cytochrome c).
• Correlation analysis between chromaticity, cytochrome c content, redox state, gene abundance, and enzyme activity.

Main Results:

• A significant positive correlation (r=0.940) was found between sludge chroma and specific anammox activity.
• The red color originates from cytochrome c, with its reduced form directly linking chromaticity to anammox activity.
• Cytochrome c content and redox ratio were determined as key factors influencing sludge color.
• Heme c, a component of cytochrome c, was the most significant factor explaining anammox community variation, positively correlating with dominant AnAOB abundance.

Conclusions:

• Anammox sludge chromaticity can be quantitatively linked to anammox activity via reduced cytochrome c content.
• Sludge color serves as a reliable indicator for both AnAOB quantity and activity.
• Chromaticity offers a potential alternative, intuitive method for monitoring and optimizing anammox processes in wastewater treatment.