pH and Phosphate Induced Shifts in Carbon Flow and Microbial Community during Thermophilic Anaerobic Digestion

Abstract

pH is a central environmental factor influencing CH4 production from organic substrates, as every member of the complex microbial community has specific pH requirements. Here, we show how varying pH conditions (5.0–8.5, phosphate buffered) and the application of a phosphate buffer per se induce shifts in the microbial community composition and the carbon flow during nine weeks of thermophilic batch digestion. Beside monitoring the methane production as well as volatile fatty acid concentrations, amplicon sequencing of the 16S rRNA gene was conducted. The presence of 100 mM phosphate resulted in reduced CH4 production during the initial phase of the incubation, which was characterized by a shift in the dominant methanogenic genera from a mixed Methanosarcina and Methanoculleus to a pure Methanoculleus system. In buffered samples, acetate strongly accumulated in the beginning of the batch digestion and subsequently served as a substrate for methanogens. Methanogenesis was permanently inhibited at pH values ≤5.5, with the maximum CH4 production occurring at pH 7.5. Adaptations of the microbial community to the pH variations included shifts in the archaeal and bacterial composition, as less competitive organisms with a broad pH range were able to occupy metabolic niches at unfavorable pH conditions.

Methane Recovery from Cattle Manure: Role of Granular Activated Carbon Amendment into Anaerobic Digestion-Microbial Electrolysis Cells (AD-MECs) Integrated Systems

“…Similar to our work, the results demonstrated that there were significant retarding effects on CH 4 production; the reactors with 1000 and 2000 mg/L PO 4 –P produced nearly the same amount of CH 4 as the control reactor but after 46 and 71 days, respectively . Others proved that addition of P-buffer (≥20 mM) to AD reactors specifically inhibited acetoclastic methanogenesis. , A delayed initiation of methanogenesis was due to the adaptation time needed by hydrogenotrophic methanogens . The PO 4 –P concentration in 100 mM PBS medium is approximately 3000 mg/L, and this explains the lowest CH 4 production and extended delay in the AD-no-GAC reactors.…”

“…31 Others proved that addition of P-buffer (≥20 mM) to AD reactors specifically inhibited acetoclastic methanogenesis. 32,33 A delayed initiation of methanogenesis was due to the adaptation time needed by hydrogenotrophic methanogens. 33 The PO 4 −P concentration in 100 mM PBS medium is approximately 3000 mg/L, and this explains the lowest CH 4 production and extended delay in the AD-no-GAC reactors.…”

“…32,33 A delayed initiation of methanogenesis was due to the adaptation time needed by hydrogenotrophic methanogens. 33 The PO 4 −P concentration in 100 mM PBS medium is approximately 3000 mg/L, and this explains the lowest CH 4 production and extended delay in the AD-no-GAC reactors. The amendment of both fresh GAC and the bare graphite electrodes lowered the negative impacts of a high P concentration.…”

Investigating Methane, Carbon Dioxide, Ammonia, and Hydrogen Sulphide Content in Agricultural Waste during Biogas Production

“…Regular and ongoing monitoring of pH levels is crucial to promptly identify any deviations and implement necessary corrective measures. Ensuring an adequate buffering capacity in the digester can assist in reducing pH fluctuations [90]. The inclusion of buffering agents such as bicarbonates can help maintain stable pH levels.…”