Deammonification for digester supernatant pretreated with thermal hydrolysis: overcoming inhibition through process...

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Bioreactor Optimization

Background:

• Thermal hydrolysis process (THP) enhances anaerobic digestion (AD) performance, increasing biogas production and reducing sludge.
• THP-generated sludge filtrate (digestate) contains organic inhibitors that can impede deammonification, a crucial nitrogen removal process.
• Efficient nitrogen removal from THP-AD digestate is essential for sustainable wastewater management.

Purpose of the Study:

• To optimize deammonification processes for effective nitrogen removal from thermal hydrolysis process-anaerobic digestion (THP-AD) sludge filtrate.
• To investigate and overcome the inhibitory effects of organic compounds present in THP-AD digestate on deammonification.
• To compare the performance of deammonification reactors treating conventional digestate versus THP-AD digestate.

Main Methods:

• Two sequencing batch reactors (SBRs) were operated, one with conventional digestate and the other with THP-AD digestate.
• Process control was enhanced by increasing the dissolved oxygen (DO) set-point to 1 mg O2/L and extending aeration times for THP-AD digestate treatment.
• Selective retention of anoxic ammonium-oxidizing bacteria (AnAOB) was maintained using a vibrating screen.

Main Results:

• Successful deammonification of THP-AD digestate was achieved by implementing higher DO set-points and longer aeration, overcoming organic inhibition.
• The contribution of anoxic ammonium-oxidizing bacteria (AnAOB) to total nitrogen removal decreased from 97% (conventional) to 72% (THP-AD), but remained stable with selective retention.
• Similar total nitrogen removal rates (approx. 520 mg N/L/day) were achieved for both conventional and THP-AD digestate treatments at comparable loading rates.

Conclusions:

• Optimized process control, particularly elevated dissolved oxygen levels, enables efficient deammonification of challenging THP-AD digestate.
• While AnAOB contribution decreases, maintaining their stability through methods like vibrating screens is feasible.
• The study demonstrates the viability of effective nitrogen removal from THP-AD wastewater, comparable to conventional digestate treatment.