Adaptive Microbial Dynamics in Hydrochar-Enhanced Chain Elongation under Loading Rate Regulation Explored through...

Area of Science:

• Environmental Science
• Biotechnology
• Chemical Engineering

Background:

• Resource recovery from sewage sludge is crucial for sustainability.
• Chain elongation (CE) efficiency declines under high-rate conditions.
• Optimizing CE requires strategies to maintain performance at reduced sludge retention times (SRTs).

Purpose of the Study:

• To develop a hydrochar-assisted anaerobic fermentation strategy.
• To enhance CE performance and medium-chain fatty acid (MCFA) production.
• To investigate the mechanisms behind hydrochar's effects under reduced SRTs.

Main Methods:

• Hydrochar-assisted anaerobic fermentation experiments.
• Analysis of medium-chain fatty acid yields and selectivity.
• Mechanistic analyses including redox potential and humic acid effects.
• Dynamic time-series, path, and microbial analyses (identifying key species like *Clostridium_sensu_stricto_12*).

Main Results:

• Hydrochar significantly improved CE performance toward MCFAs.
• Comparable yields (14.0 g COD/L) were achieved at 7.5 days SRT with hydrochar versus 15 days without.
• Hydrochar promoted a reduced redox environment, stimulating acidogenesis and electron donor resynthesis.
• Humic acids enhanced caproate yield and selectivity.
• Microbial analysis revealed correlations between *Clostridium_sensu_stricto_12* and even-chain fatty acid accumulation.

Conclusions:

• Hydrochar effectively enhances CE performance and fermentation capacity under reduced SRTs.
• The study provides a robust framework for understanding adaptive responses in anaerobic systems.
• Hydrochar offers a promising strategy for efficient resource recovery from sewage sludge.