Efficient nitrogen removal by microalgal-bacterial granular sludge-marimo coupling process

Area of Science:

• Environmental Biotechnology
• Wastewater Treatment
• Microbiology

Background:

• Conventional biological wastewater treatment often exhibits inadequate nitrogen removal, leading to global eutrophication of aquatic environments.
• There is a critical need for advanced processes to improve nitrogen management in wastewater.
• Microalgal-bacterial symbiotic systems offer potential for enhanced nutrient removal.

Purpose of the Study:

• To investigate the efficacy of a novel microalgal-bacterial granular sludge-marimo (MBGS-MA) coupling process for nitrogen removal.
• To elucidate the underlying microbial and genetic mechanisms driving nitrogen transformation within the MBGS-MA system.
• To assess the potential of this hybrid system for high-efficiency nitrogen removal from wastewater.

Main Methods:

• Development and operation of a coupled microalgal-bacterial granular sludge and marimo (MBGS-MA) system.
• Quantification of nitrogen removal efficiency and effluent nitrogen concentrations.
• Metagenomic analysis to identify shifts in microbial gene abundance related to nitrogen cycling pathways (nitrification, denitrification, assimilation, fixation).

Main Results:

• The MBGS-MA process achieved an 83.4% overall nitrogen removal efficiency, with an effluent nitrogen concentration of 4.0 mg/L.
• Microbial community analysis revealed a shift in microalgal-bacterial granular sludge towards nitrification and denitrification genes, and away from ammonia assimilation.
• Marimo demonstrated nitrogen fixation capabilities, with enriched nitrogen-fixing genes and increased assimilatory nitrate reduction genes due to symbiotic interactions between Proteobacteria and Cyanobacteria.

Conclusions:

• The integrated MBGS-MA process is highly effective for achieving significant nitrogen removal from wastewater.
• The study reveals distinct genetic mechanisms within the bacterial sludge and marimo components contributing to efficient nitrogen cycling.
• This innovative hybrid system presents a promising new approach for developing advanced wastewater treatment technologies focused on high-efficiency nitrogen removal.