Search

This study explores the impact of granular activated carbon (GAC) and L-arginine supplementation on biogas upgrading and acetic acid production employing Clostridium thailandense. GAC and L-arginine concentrations ranged from 0 to 20 g/L and 0 to 5 g/L, respectively, with H2 acting as the electron donor at an H2 to CO2 ratio of 2:1 (v/v). Experiments were conducted at 30 °C with an agitation speed of 150 rpm. Additionally, gene annotation of the C. thailandense genome using Rapid Annotations using Subsystems Technology (RAST) identified genes involved in CO2 to acetic acid conversion. Results indicate that adding 7.5 g/L GAC boosts CH4 purity in biogas, elevating CO2 and H2 consumption efficiencies to 88.3 % and 98.7 %, respectively. This enhancement leads to a CH4 content increase to 93.3 %, accompanied by 0.90 g/L acetic acid production. Conversely, L-arginine demonstrates no significant impact on CO2 conversion. Leveraging RAST, the study identifies hydrogenase genes and NADH-dependent ferredoxin-NADP+ oxidoreductase (Nfn), as crucial for heightened H2 consumption efficiencies and cell growth facilitated by GAC, thus enhancing biogas upgrading efficiency in C. thailandense. This research provides vital insights into optimizing sustainable biogas production through strategic GAC utilization and elucidates the roles of hydrogenase genes and Nfn.

This study investigated the effects of various pretreatment methods on the anaerobic digestibility of oil palm empty fruit bunches (EFB) for methane production. Pretreatment methods included weak alkaline (2 % Ca(OH)2), weak acid (2 % acetic acid), acidified palm oil mill effluent (POME), biogas effluent, hydrothermal (180 °C, 190 °C, and 200 °C), and microwave pretreatments. All pretreatment methods enhanced methane yield compared to untreated EFB (189.45 mL-CH4/g-VS), with weak alkaline pretreatment being the most effective (277.11 mL-CH4/g-VS), followed by hydrothermal pretreatment at 180 °C (244.33 mL-CH4/g-VS) and biogas effluent pretreatment (238.32 mL-CH4/g-VS). The enhanced methane yield was attributed to increased cellulose content (45.5 % for weak alkaline pretreatment), reduced hemicellulose (18.0 % for hydrothermal pretreatment at 200 °C), and lignin contents (19.0 % for hydrothermal pretreatment at 200 °C), decreased crystallinity index (40.0 % for hydrothermal pretreatment at 200 °C), and increased surface area. Weak alkaline pretreatment also showed the highest net energy balance (8.73 kJ/g-VS) and a short break-even point (2 years). Microbial community analysis revealed that weak alkaline pretreatment favored the growth of syntrophic acetate-oxidizing bacteria and hydrogenotrophic methanogens, contributing to improved methane yield. This study demonstrates the potential of EFB pretreatment, particularly weak alkaline and biogas effluent pretreatment, for enhancing methane production and sustainable management of palm oil mill waste.

This study aimed to convert CO2 in biogas into acetic acid using immobilized Clostridium thailandense cells on various support materials, including activated carbon, expanded clay, and coir. Immobilized cells and free cells were evaluated for their CO2 conversion ability into acetic acid using H2 as an electron donor at an H2 to CO2 in biogas ratio of 2:1 (v/v), 30 °C, 150 rpm. Results showed that immobilized cells on activated carbon increased CH4 content to 96.9% (v/v), and acetic acid production to 15.65 mmol/L within 96 h. These values outperformed free cells. The activated carbon-immobilized cells could be reused two times without losing efficacy in the purification of biogas and acetic acid production. This work indicates that using the immobilized cells offers a sustainable approach to biogas upgrading, reducing the environmental footprint of biogas production by increasing its energy content and purity.

Food waste is categorized as organic solid waste, which has a negative impact on environmental sustainability. Food waste was simultaneously used for the feasible generation of mixed volatile fatty acids (VFAs) and bio-hydrogen by deploying dark fermentation. Original anaerobic digested sludge was prepared via the shock technique with 50 g/L glucose under thermophilic temperature (55 °C). The pretreated inoculum was found capable of converting 10 g VS/L food waste to hydrogen with a rather high yield of 135.2 ± 7 mL H2/VSadded. The effect of various concentrations of food waste, including 10.2, 16.3, 20.3, and 26.4 g VS/L, on mixed VFAs production was subsequently carried out in batch dark fermentation. The highest butyric acid concentration (5.26 ± 0.22 g/L) in soluble metabolites was obtained from batch dark fermentation with 26.4 g VS/L of food waste. The dominant Clostridium thermobutyricum, Clostridium sporogenes, and Octadecobacter sp. found in the batch of dark fermentation of food waste could confirm the effectiveness of the load shock pretreatment method for inoculum preparation. The continuous stirred tank reactor (CSTR) inoculated with mixed cultures, also prepared via the load shock pretreatment method and without the addition of external nutrients, was operated by feeding 26.4 g VS/L food waste at the kinetically designed HRT for 4 days, corresponding to an organic loading rate (OLR) of 7.6 g VS/L·d. Under steady state conditions, promising butyric acid (5.65 ± 0.51 g/L)-rich mixed VFAs were achieved along with the hydrogen yield of 104.9 ± 11.0 mL-H2/g VSadded, which is similar to the upper side of the previously reported yields (8.8 ± 0.6–103.6 ± 0.6 mL-H2/g VS).

Temperature plays a significant role in anaerobic digestion (AD) as it affects the microbial communities and ultimately controls the efficiency of the process. Few studies have looked at temperature-adjusted AD, but it is unclear how the temperature shifts affect biogas production and the dynamics of microorganisms involved in methanogenesis. This study tested two temperature shift scenarios in fed-batch mode using anaerobically digested sewage sludge and glucose-based substrate. The first scenario was acclimatized to upshifting temperatures from 42 °C to 48 °C while the second was acclimatized to downshifting temperatures from 55 °C to 45 °C. Both temperature shift scenarios resulted in a decrease in biogas production, especially at 45 °C. The upshifted scenario experienced a maximum decrease of 83%, and the downshifted scenario experienced a 16–33% decrease in methane production. Next-generation 16S rRNA sequencing revealed the domination of Methanoculleus in the upshifted scenario. However, a low correlation between the number of Methanoculleus and the other hydrogenotrophic methanogens to biogas production indicates inhibition in the hydrogenotrophic pathway. The downshifted scenario showed better biogas production due to the substantial domination of acetoclastic Methanosaeta and the low abundance of sulfate-reducing bacteria. Hence, the temperature shift affects the microbial communities, significantly affecting biogas production performance.

This study aims to create a quantitative polymerase chain reaction (q-PCR) methodology for monitoring the hydrogen-producing mixed cultures enriched from elephant dung using alpha-cellulose as a carbon source through five generations of repetitive sub-culture. The enriched thermophilic mixed cultures from the fifth cultivation cycle gave the highest hydrogen yield of 170.3 mL H2/g cellulose and were used to generate hydrogen from sawdust. Clostridium sp. and Thermoanaerobacterium sp. were the dominant bacteria in thermophilic mixed cultures with high hydrogen yield, according to polymerase chain reaction-denatured gradient gel electrophoresis (PCR-DGGE). q-PCR primers Chis150F and ClostIR, TherF and TherR, and BacdF and BacdR were developed to amplify the 16S rRNA genes of Clostridium sp., Thermoanaerobacterium sp., and Bacillus sp., respectively, for the quantification of hydrogen-producing bacteria in biohydrogen fermentation. Similar q-PCR analysis of Clostridium sp., Thermoanaerobacterium sp., and Bacillus sp. 16S rRNA gene amplification during hydrogen production from cellulose and sawdust revealed increasing gene copy number with time. The molecular approaches developed in this study can be used to monitor microbial communities in hydrogen fermentation processes efficiently.