Potential of endogenous PHA as electron donor for denitrification

Area of Science:

• Environmental Microbiology
• Biotechnology
• Wastewater Treatment

Background:

• Polyhydroxyalkanoates (PHA) are valuable bioplastics often produced from wastewater.
• Integrating nitrogen removal into PHA production processes remains a challenge.

Purpose of the Study:

• To determine optimal conditions for specific endogenous denitrifying activity (SEDA) using PHA as a carbon source.
• To evaluate the potential of PHA-accumulating biomass for nitrogen removal.

Main Methods:

• Experiments were conducted using biomass from sequencing batch reactors capable of storing PHA.
• Specific conditions tested included sludge concentration, COD_PHA/N ratio, and nitrate-nitrogen concentration.
• SEDA was measured, and PHA composition (hydroxybutyrate vs. hydroxyvalerate) was analyzed.

Main Results:

• Optimal SEDA was achieved at 0.5-2 g VSS/L sludge concentration, COD_PHA/N > 5.4, and 40-60 mg NO₃^--N/L.
• SEDA values ranged from 0.26-0.39 g N₂-N/(g VSS_act d).
• No preference for hydroxybutyrate over hydroxyvalerate was observed, and PHA content >5% wt/wt was necessary for maximum SEDA. Nitrous oxide (N₂O) production was not detected.

Conclusions:

• PHA-accumulating microbial cultures show significant potential for nitrogen removal in wastewater treatment.
• Optimized conditions facilitate efficient SEDA, making PHA a viable carbon source for denitrification.
• The process is effective and does not produce harmful N₂O emissions.