How Does Chitosan Affect Methane Production in Anaerobic Digestion?

Area of Science:

• Environmental Science
• Biotechnology
• Chemical Engineering

Background:

• Chitosan is increasingly used in sewage and sludge treatment.
• Its environmental impacts, especially on anaerobic digestion, require further investigation.
• Limited data exists on chitosan's effects at substantial concentrations in sludge.

Purpose of the Study:

• To investigate the impacts of chitosan on sewage sludge anaerobic digestion.
• To quantify the inhibition of methane production by chitosan.
• To elucidate the mechanisms behind chitosan's effects on anaerobic digestion.

Main Methods:

• Long-term and batch anaerobic digestion tests.
• Mass balance and organic metabolism analyses.
• Microbial community and key enzyme gene analyses.

Main Results:

• Chitosan at 8-32 g/kg total suspended solids (TSS) inhibited methane production by 7.2-30.3%.
• Chitosan hindered organic substrate transfer and reduced anaerobe metabolic activity by suppressing extracellular polymeric substances secretion.
• Chitosan is more persistent to degradation than indigenous sludge organics, and it severely inhibits CO2-dependent methanogenesis.

Conclusions:

• Chitosan significantly inhibits sludge anaerobic digestion and methane production at concentrations above 4 g/kg TSS.
• The inhibition mechanism involves reduced substrate bioavailability and suppressed microbial activity.
• Wastewater treatment strategies using chitosan must consider its potential negative impacts on anaerobic digestion efficiency.