Technical and operational feasibility of psychrophilic anaerobic digestion biotechnology for processing ammonia-rich waste

• Long-term anaerobic digestion (AD) process at high-ammonia (>5 gN/L) is limited.
• PADSBR technology was validated to treat N-rich waste with 8.2 ± 0.3 gNH3-N/L.
• Excess ammonia (8.2 gN/L) did not affect the digestion process with no inhibition.
• VFA, an indicator for process stability, did not accumulate in PADSBR.
• Biomass acclimation in PADSBR ensured a high-stabilization of the AD process.

Ammonia nitrogen plays a critical role in the performance and stability of anaerobic digestion (AD) of ammonia rich wastes like animal manure. Nevertheless, inhibition due to high ammonia remains an acute limitation in AD process. A successful long-term operation of AD process at high ammonia (>5 gN/L) is limited. This study focused on validating technical feasibility of psychrophilic AD in sequencing batch reactor (PADSBR) to treat swine manure spiked with NH4Cl up to 8.2 ± 0.3 gN/L, as a representative of N-rich waste. CODt, CODs, VS removals of 86 ± 3, 82 ± 2 and 73 ± 3% were attained at an OLR of 3 gCOD/L.d, respectively. High-ammonia had no effect on methane yields (0.23 ± 0.04 L CH4/gTCODfed) and comparable to that of control reactors, which fed with raw swine manure alone (5.5 gN/L). Longer solids/hydraulic retention times in PADSBRs enhanced biomass acclimation even at high-ammonia. Thus VFA, an indicator for process stability, did not accumulate in PADSBR. Further investigation is essential to establish the maximum concentrations of TKN and free ammonia that the PADSBR can sustain.