The effect of alternating influent carbon source composition on activated sludge bioflocculation

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Activated sludge processes

Background:

• Activated sludge processes are crucial for biological wastewater treatment.
• Bioflocculation is a key factor influencing the efficiency of activated sludge systems.
• Understanding the impact of influent characteristics on bioflocculation is essential for process optimization.

Purpose of the Study:

• To investigate the effect of alternating carbon sources (glucose and starch) on activated sludge bioflocculation.
• To determine if switching frequency (fast vs. slow) influences these effects.
• To identify the mechanisms behind changes in sludge characteristics.

Main Methods:

• Operation of four lab-scale activated sludge reactors under different influent carbon source alternation frequencies.
• Long-term monitoring of bioflocculation using macroscopic and microscopic analyses.
• Measurement of sludge hydrophobicity, floc size, settleability, and protein concentration.

Main Results:

• Sludge hydrophobicity remained high (>80%), indicating persistent good bioflocculation.
• Sludge settleability decreased significantly after a 60-day adaptation period across all reactors.
• Floc size initially decreased due to microcolony release, then increased with primary particle release, linked to surface protein concentration and EPS matrix deterioration.

Conclusions:

• Alternating glucose and starch negatively impacts activated sludge settleability, independent of the carbon source ratio or switching frequency.
• Changes in protein concentration at the floc surface, particularly hydrolytic enzymes for starch degradation, contribute to EPS matrix deterioration.
• Further research is needed to mitigate the observed decrease in sludge settleability in alternating carbon source environments.