Establishment and differential performance of hyperthermophilic microbial community during anaerobic self-degradation of waste activated sludge

Dairy manure acidogenic fermentation at hyperthermophilic temperature enabled superior activity of thermostable hydrolytic enzymes linked to the genus Caldicoprobacter

In this study, fermentation experiments were conducted under mesophilic, thermophilic, and hyperthermophilic conditions to investigate adaptation of microbial communities and its effect on extracellular enzyme activities toward degradation of cellulose, hemicellulose and proteins in dairy manure. Hyperthermophilic conditions transformed the microbiome structure and stimulated activity of extracellular proteolytic, cellulolytic, and hemicellulolytic enzymes. Specifically, the activities of protease, cellulose 1,4-β-cellobiosidase, and β-glucosidase secreted by hyperthermophilic microbes were higher by 22%, 47% and 49% compared to those produced by mesophilic and thermophilic communities. Enhanced hydrolytic activity of hyperthermophilic microbes enabled improved feedstock solubilization and production of 39% and 22% more soluble COD than mesophilic and thermophilic microbes, respectively. Connections between hydrolytic function and microbial community structure at various temperatures were assessed using the PICRUSt2 computational tool. Genus Caldicoprobacter was identified as the primary candidate responsible for increased production of thermostable endo-1,4-β-glucanase, β-glucosidase and endo-1,4-β-xylanase, and enhanced hydrolytic performance of hyperthermophilic microbial community.

Determination of effects of thermophilic and hyperthermophilic temperatures on anaerobic hydrolysis and acidogenesis of pig manure through a one-year study

Improving hydrolysis and acidogenesis through thermophilic and hyperthermophilic temperatures is critical for enhancing the anaerobic decomposition of organic waste like pig manure. However, whether higher temperatures can provide more enhanced performance has not been elucidated experimentally. This study, therefore, conducted a 375-day continuous operation experiment at 55 and 70 °C with a 5-day hydraulic retention time. The two temperature reactors entered a stable state after about 200 days and long-term microbial acclimation markedly changed their performances. In the thermophilic and hyperthermophilic reactor, the hydrolysis efficiencies were obtained at 29.7 % and 27.3 % respectively, whereas the acidogenesis efficiency was relatively low at 1.0 % and 3.1 %. Due to the occurrence of methanogenesis, the volatile fatty acid concentration in the thermophilic reactor was only 45 % of that in the hyperthermophilic reactor. The thermophilic reactor exhibited higher bacterial diversity; however, this difference between the two reactors apparently did not correlate with hydrolysis and acidogenesis performance.

Viability of recuperative thickening in upgrading thermophilic and mesophilic anaerobic digestion of hydrothermal high-solid sludge

Recuperative thickening (RT) process was introduced to further upgrade anaerobic digestion of hydrothermal high-solid sludge. Continuous mesophilic (MD-R) and thermophilic (TD-R) digestion with RT (MD-R) were operated synchronously, with corresponding single digestion without RT as controls, namely MD and TD. The MD-R and TD-R increased biogas production rates by 22.8% and 11.0%, and achieved 16.6% and 9.7% higher volatile solids reductions, respectively. The improved performance was partly attributed to increased hydrolysis rate, with 11.2% and 7.4% higher for the MD-R and TD-R than the controls, respectively. The RT increased the numbers of total archaea in the mesophilic and thermophilic systems by 844% and 108%, and the numbers of dominant archaea by 50.4% and 38.1%, respectively, which promoted the degradation of organic matter and the production of biogas. Thus, RT is applicable to further upgrade digesting high-solid sludge.

Towards the understanding of hyperthermophilic methanogenesis from waste activated sludge at 70 °C: Performance, stability, kinetic and microbial community analyses

Anaerobic digestion is promising for waste activated sludge (WAS) degradation. However, conventional processes were generally stuck with limited hydrolysis and poor pathogen destruction. Hyperthermophilic digestion at 70 °C has drawn attention in overcoming those issues at a relatively low energy requirement and operating difficulties. In order to illuminate its operation characteristics, a single-stage hyperthermophilic digester was controlled at 70 °C and operated continuously to degrade WAS. 88.7 mL/g VS_added of methane yield could be achieved in the hyperthermophilic system, fourfold higher than that in the mesophilic system. Kinetic analysis revealed that hyperthermophilic digestion was advantageous in converting the non-degradable fraction. Consequently, hydrolysis under the hyperthermophilic condition was able to be significantly improved. Above 10 d was necessary for the hyperthermophilic system to gain such a high methane production. In the case of stability, the organic loading of higher than 10.2 g VS/L/d resulted in increasing limitation from methanogenesis and accumulation of propionic, butyric and valeric acids. In addition to the dominant acetoclastic genus Methanothrix for methane production in the hyperthermophilic system, two hydrogenotrophic methanogens Methanospirillum and Methanothermobacter reached 18.84% and 8.31%, respectively. The genus Coprothermobacter, affiliated with the phylum Firmicutes, made more contribution to protein hydrolysis in the hyperthermophilic digester.

Optimization of hydrothermal pretreatment conditions for mesophilic and thermophilic anaerobic digestion of high-solid sludge

Hydrothermal pretreatment (HTP) conditions were optimized for continuous mesophilic (MAD) and thermophilic (TAD) anaerobic digestion of high-solid sludge (10-11% total solids). COD solubilization increased with prolonged HTP durations, and became not significant after 210 min. According to the methane production rate and energy consumption, the optimal HTP temperature was determined at 160 °C. Regarding continuous operation without HTP, TAD achieved higher methane yield and volatile solids (VS) reduction, at 0.12 L/g VS_added and 23.9%, respectively. After HTP, methane yield and VS reduction in MAD and TAD were increased by 400% and 191% (MAD), 67% and 72% (TAD), respectively. TAD was limited due to the inhibition from about 2800 mg/L of NH₄⁺-N concentration. The methanogenic activity of MAD was enhanced, whereas TAD displayed a reduced value owing to ammonia inhibition. Ultimately, MAD with HTP and TAD without HTP achieved the higher energy balance, 5.25 and 3.27 kJ/g VS, respectively.