Bioaugmentation as a solution to increase methane production from an ammonia-rich substrate

Area of Science:

• Environmental Microbiology
• Biotechnology
• Anaerobic Digestion

Background:

• High ammonia concentrations in anaerobic digestion (AD) inhibit microbial activity, leading to reduced biogas production and energy recovery in full-scale reactors.
• Many AD reactors operate in an ammonia-induced inhibited steady-state, resulting in substantial losses of potential biogas yield.
• Current methods to mitigate ammonia toxicity often disrupt reactor operation or require feedstock replacement, lacking efficient solutions.

Purpose of the Study:

• To evaluate bioaugmentation as a strategy to alleviate ammonia toxicity in mesophilic continuously stirred-tank reactors (CSTRs) operating under inhibited steady-state conditions.
• To assess the impact of introducing a specific hydrogenotrophic methanogen on methane production yield and microbial community dynamics.
• To determine if bioaugmentation can improve biogas production without operational interruptions or feedstock modification.

Main Methods:

• A mesophilic continuously stirred-tank reactor (CSTR) operating under inhibited steady-state conditions was bioaugmented with Methanoculleus bourgensis MS2(T) at high ammonia levels (5 g NH4(+)-N L(-1)).
• A control CSTR reactor without bioaugmentation was maintained under identical conditions for comparison.
• High-throughput 16S rRNA gene sequencing was employed to analyze shifts in microbial community composition, particularly the abundance of Methanoculleus species.

Main Results:

• Bioaugmentation resulted in a significant 31.3% increase in methane production yield in the treated CSTR reactor at steady-state.
• High-throughput 16S rRNA gene sequencing revealed a 5-fold increase in the relative abundance of Methanoculleus species following bioaugmentation.
• The bioaugmentation process was successfully implemented without interrupting the continuous operation of the reactor or altering the ammonia-rich feedstock.

Conclusions:

• Bioaugmentation with Methanoculleus bourgensis MS2(T) is an effective method for alleviating ammonia toxicity in AD systems.
• This approach significantly enhances methane production yield, offering a viable solution for optimizing biogas recovery from ammonia-rich substrates.
• The study demonstrates a novel, non-disruptive strategy for improving the efficiency of full-scale anaerobic digestion plants facing ammonia inhibition.