Optimisation strategies for ammonia-tolerant syntrophic propionate-oxidising microorganisms: effects of additives, ammonium levels and temperature on biogas production

Biogas production is a promising technology for cleaner energy production. It converts biodegradable waste in anaerobic reactors into two products: biogas and digestate. However, industrial biogas processes often face challenges, particularly ammonia inhibition during the anaerobic degradation of protein-rich materials. This inhibition causes ammonia-tolerant syntrophic microorganisms to become the main consumers of intermediates such as propionate and acetate, breaking them down into H2 and CO2, which hydrogenotrophic methanogens use to produce biogas. These microorganisms rely on each other for propionate and acetate degradation, a biological interaction known as syntrophy.  Yet, syntrophic microorganisms are often constrained in biogas processes, requiring optimisation strategies to enhance their activity. This is crucial for resilient biogas production processes operating under high-ammonia conditions. This thesis explored optimisation strategies for syntrophic propionate and acetate degradation and hydrogenotrophic methanogenesis. It focused on adding various materials or iron and sulfur species, and examined the effects of varying levels of ammonia, zeolites, and operating temperatures. The results demonstrated the improvement of propionate and acetate degradation, and increasing methane production rates with the addition of several materials and iron and sulfur species, while also showing the cultures’ sensitivity to changes in temperature, ammonia concentrations and high levels of certain iron and sulfur species. These findings suggest that such approaches can positively impact industrial biogas processes, but achieving maximum yield requires careful consideration of ammonia content, temperature, and microbial community structure during their implementation.