Stable acetate production in extreme-thermophilic (70°C) mixed culture fermentation by selective enrichment of hydrogenotrophic methanogens

Abstract

The control of metabolite production is difficult in mixed culture fermentation. This is particularly related to hydrogen inhibition. In this work, hydrogenotrophic methanogens were selectively enriched to reduce the hydrogen partial pressure and to realize efficient acetate production in extreme-thermophilic (70°C) mixed culture fermentation. The continuous stirred tank reactor (CSTR) was stable operated during 100 days, in which acetate accounted for more than 90% of metabolites in liquid solutions. The yields of acetate, methane and biomass in CSTR were 1.5 ± 0.06, 1.0 ± 0.13 and 0.4 ± 0.05 mol/mol glucose, respectively, close to the theoretical expected values. The CSTR effluent was stable and no further conversion occurred when incubated for 14 days in a batch reactor. In fed-batch experiments, acetate could be produced up to 34.4 g/L, significantly higher than observed in common hydrogen producing fermentations. Acetate also accounted for more than 90% of soluble products formed in these fed-batch fermentations. The microbial community analysis revealed hydrogenotrophic methanogens (mainly Methanothermobacter thermautotrophicus and Methanobacterium thermoaggregans) as 98% of Archaea, confirming that high temperature will select hydrogenotrophic methanogens over aceticlastic methanogens effectively. This work demonstrated a potential application to effectively produce acetate as a value chemical and methane as an energy gas together via mixed culture fermentation.

Acetate Production from Cafeteria Wastes and Corn Stover Using a Thermophilic Anaerobic Consortium: A Prelude Study for the Use of Acetate for the Production of Value-Added Products

“…For both the incubation temperatures, the presence of BES and shaking at 100 rpm had a positive influence on acetate Average acetate production at an incubation temperature of 60 • C (1739.44 mg L −1 ) was more than two-folds higher than the acetate production at 45 • C (775.68 mg L −1 ). Previous studies have also shown the prominent effect of temperature on acetate production [4,12,51]. For both the incubation temperatures, the presence of BES and shaking at 100 rpm had a positive influence on acetate production.…”

“…Average acetate production at an incubation temperature of 60 °C (1739.44 mg L −1 ) was more than two-folds higher than the acetate production at 45 °C (775.68 mg L −1 ). Previous studies have also shown the prominent effect of temperature on acetate production [4,12,51]. For both the incubation temperatures, the presence of BES and shaking at 100 rpm had a positive influence on acetate Average acetate production at an incubation temperature of 60 • C (1739.44 mg L −1 ) was more than two-folds higher than the acetate production at 45 • C (775.68 mg L −1 ).…”

“…Thermophilic conditions have additional benefits of high substrate degradation rate, pathogen removal, and efficient heat utilization of SOWs. The thermophilic microbial consortium also harbors distinct microbial species that possess metabolic functions related to biomass degradation and utilization [12,13]. Therefore, a TAD system fed with SOWs can be rewired to an acetate-producing system by inhibition of methanogenesis.…”

“…Among the different VFAs, acetic acid has the highest market size, with 3,500,000 tons/y and a price per ton of $800 [21]. The production of predominant acetate together with methane in extreme-thermophilic (70 • C) mixed culture fermentation was first studied by Zhang et al [12]. However, they used pure glucose as a substrate to achieve >90% acetate in the fermentate's metabolite pool.…”

Ammonium level induces high purity propionate production in mixed culture glucose fermentation

“…10 All these aspects signicantly increase the costs of pure culture fermentation compared to mixed culture based industrial fermentation. 11,12 So, propionic acid production in MCF becomes an attractive route. 10 Anaerobic digestion (AD) consists of multiple steps including hydrolysis, acidogenesis, acetogenesis, and methanogenesis in MCF.…”