Directed evolution to produce sludge communities with improved oxygen uptake abilities

Area of Science:

• Environmental Microbiology
• Biotechnology
• Wastewater Treatment Engineering

Background:

• Activated sludge processes are crucial for wastewater treatment.
• Dissolved oxygen (DO) levels significantly impact microbial community structure and function.
• Hemoglobins (Hbs) are proteins that can facilitate oxygen transport within cells.

Purpose of the Study:

• To investigate the effect of low dissolved oxygen (DO) on activated sludge microbial communities.
• To determine if low DO conditions select for specific bacterial species, such as those encoding hemoglobins.
• To assess the impact of these changes on the efficiency of aerobic wastewater treatment.

Main Methods:

• Cultivation of two activated sludge cultures for 370 days in synthetic wastewater.
• Operation of one culture at high DO and the other at low DO (0.25 mg O2/L).
• Monitoring changes in bacterial species abundance, heme b levels, and specific oxygen uptake rates.

Main Results:

• Low DO culture showed a continuous increase in species encoding truncated hemoglobins (Hbs).
• Heme b levels, associated with Vitreoscilla hemoglobin, were significantly higher in the low DO culture.
• Specific oxygen uptake rates increased by 28% in the low DO culture, compared to 3% in the high DO culture.

Conclusions:

• Low DO conditions promote the selection of Hb-expressing bacteria in activated sludge.
• These selected bacteria exhibit enhanced oxygen utilization and ATP production, particularly under low aeration.
• Imposing low DO can be a strategy to develop more efficient aerobic wastewater treatment bacterial communities.