Mesophilic and Thermophilic Anaerobic Digestion of Wheat Straw in a CSTR System with ‘Synthetic Manure’: Impact of Nickel and Tungsten on Methane Yields, Cell Count, and Microbiome

Abstract

Lignocellulosic residues, such as straw, are currently considered as candidates for biogas production. Therefore, straw fermentations were performed to quantitatively estimate methane yields and cell counts, as well as to qualitatively determine the microbiome. Six fully automated, continuously stirred biogas reactors were used: three mesophilic (41 °C) and three thermophilic (58 °C). They were fed every 8 h with milled wheat straw suspension in a defined, buffered salt solution, called ‘synthetic manure’. Total reflection X-ray fluorescence spectrometry analyses showed nickel and tungsten deficiency in the straw suspension. Supplementation of nickel and subsequently tungsten, or with an increasing combined dosage of both elements, resulted in a final concentration of approximately 0.1 mg/L active, dissolved tungsten ions, which caused an increase of the specific methane production, up to 63% under mesophilic and 31% under thermophilic conditions. That is the same optimal range for pure cultures of methanogens or bacteria found in literature. A simultaneous decrease of volatile fatty acids occurred. The Ni/W effect occurred with all three organic loading rates, being 4.5, 7.5, and 9.0 g volatile solids per litre and day, with a concomitant hydraulic retention time of 18, 10, or 8 days, respectively. A maximum specific methane production of 0.254 m3 CH4, under standard temperature and pressure per kg volatile solids (almost 90% degradation), was obtained. After the final supplementation of tungsten, the cell counts of methanogens increased by 300%, while the total microbial cell counts increased by only 3–62%. The mesophilic methanogenic microflora was shifted from the acetotrophic Methanosaeta to the hydrogenotrophic Methanoculleus (85%) by tungsten, whereas the H2-CO2-converter, Methanothermobacter, always dominated in the thermophilic fermenters.

Anaerobic co-digestion of human excreta, food leftovers and kitchen residue: 1 ternary mixture design, synergistic effects and RSM approach

“…Contrarily, R9 and R10 with the highest methane yields, were found to contain the highest concentrations of Zn. These results confirm the positive influence of Zn on enzymes such as coenzyme M. methyltransferase , involved in methanogenesis [ 78 ]. Similarly, optimum concentrations of Ni in R5 (0.043 mg/L), R7 (0.033 mg/L), R8 (0.027 mg/L), R9 (0.053 mg/L) and R10 (0.022 mg/L) significantly increased their methane yields ( Fig.…”

“…Arthur et al [ 78 ] reported an increase in the number of methanogens present in reactors containing nickel. The author also documented that nickel concentration of less than 0.1 mg/L improved the stability of the anaerobic digestion process because intermediary products were readily digested by methanogens [ 78 ]. Further, Schmidt et al [ 79 ] reported a rapid accumulation of VFAs when Ni was depleted.…”

Evaluating the performance of an integrated membrane-aerated biofilm reactor (MABR) system for high-strength brewery wastewater treatment

“…The large presence of Cloacimonadia in MABR2-S1 was likely due to the initial air supply into the membrane, as previous studies suggested the Cloacimonadia preferences to microaeration conditions. 30,31 In addition, Cloacimonadia is a syntrophic microorganism which can hardly survive without obligatory syntrophism with other microorganisms. 32 In this study, Synergistia, another syntrophic bacterium, 32 was likely to be the key contributor along with Cloacimonadia in MABR2-S1.…”

Improvement of the Thermo-Oxidative Stability of Biobased Poly(butylene succinate) (PBS) Using Biogenic Wine By-Products as Sustainable Functional Fillers

“…In the present research, an industrial-scale method for WP preparation was used. WP was simultaneously dried and micronized with a TurboRotor mill-dryer, which is well-established in the food industry; e.g., for milling spices [36]. This method is characterized by high throughputs enabling upscaling [37] and its suitability for processing temperature-sensitive materials, such as phenolic compounds, due to its very short residence times and reduced thermal stress compared to conventional methods [38].…”