Integrated biogas upgrading and medium-chain fatty acids production for more efficient resource recovery.

The conversion of carbon dioxide (CO2) from biogas into medium-chain fatty acids (MCFAs) represents an eco-friendly resource recovery approach to reduce dependence on fossil fuels and combat global climate change. This study presented the novel concept of integrated resource recovery by coupling biogas upgrading and MCFAs production for the first time. Initially, the impact of different initial ethanol concentrations on chain elongation was examined, determining that an ethanol concentration of 160 mmol/L maximized MCFAs yield at 45.7 mmol/L. Subsequently, using this optimal ethanol supply, the integrated strategy was implemented by connecting two bioreactors in series and maintaining continuous operation for 160-day. The results were noteworthy: upgraded bio-methane purity reached 97.6 %, MCFAs production rate and carbon-flow distribution reached 24.5 mmol/L d-1 and 76.1 %, respectively. In summary, these promising outcomes pioneer a resource recovery approach, enabling the high-value utilization of biogas and the conversion of CO2 into valuable bio-chemicals.

Simultaneous biogas upgrading and medium-chain fatty acids production using a dual membrane biofilm reactor.

Utilizing H2-assisted ex-situ biogas upgrading and acetate recovery holds great promise for achieving high value utilization of biogas. However, it faces a significant challenge due to acetate's high solubility and limited economic value. To address this challenge, we propose an innovative strategy for simultaneous upgrading of biogas and the production of medium-chain fatty acids (MCFAs). A series of batch tests evaluated the strategy's efficiency under varying initial gas ratios (v/v) of H2, CH4, CO2, along with varying ethanol concentrations. The results identified the optimal conditions as initial gas ratios of 3H2:3CH4:2CO2 and an ethanol concentration of 241.2 mmol L-1, leading to maximum CH4 purity (97.2 %), MCFAs yield (54.2 ± 2.1 mmol L-1), and MCFAs carbon-flow distribution (62.3 %). Additionally, an analysis of the microbial community's response to varying conditions highlighted the crucial roles played by microorganisms such as Clostridium, Proteiniphilum, Sporanaerobacter, and Bacteroides in synergistically assimilating H2 and CO2 for MCFAs production. Furthermore, a 160-day continuous operation using a dual-membrane aerated biofilm reactor (dMBfR) was conducted. Remarkable achievements were made at a hydraulic retention time of 2 days, including an upgraded CH4 content of 96.4 ± 0.3 %, ethanol utilization ratio (URethanol) of 95.7 %, MCFAs production rate of 28.8 ± 0.3 mmol L-1 d-1, and MCFAs carbon-flow distribution of 70 ± 0.8 %. This enhancement is proved to be an efficient in biogas upgrading and MCFAs production. These results lay the foundation for maximizing the value of biogas, reducing CO2 emissions, and providing valuable insights into resource recovery.

Synergistic effect of hydrogen and nanoscale zero-valent iron on ex-situ biogas upgrading and acetate recovery.

Hydrogen (H2) assisted ex-situ biogas upgrading and liquid chemicals production can augment the fossil fuel-dominated energy market, and alleviate CO2-induced global warming. Recent investigations confirmed that nanoscale zero-valent iron (nZVI) enabled the enhancement of anaerobic digestion for biogas production. However, little is known about the effect of nZVI on the downstream ex-situ biogas upgrading. Herein, different levels (0 mg L-1, 100 mg L-1, 200 mg L-1, 500 mg L-1, 1000 mg L-1, 2000 mg L-1) of nZVI were added for H2-assisted ex-situ biogas upgrading, to study whether nZVI could impact the biomethane purity and acetate yield for the first time. Results showed that all tested nZVI levels were favorable for biogas upgrading in the presence of H2, the highest biomethane content (94.1 %, v/v), the CO2 utilization ratio (95.9 %), and acetate yield (19.4 mmol L-1) were achieved at 500 mg L-1 nZVI, respectively. Further analysis indicated that increased biogas upgrading efficiency was related to an increase in extracellular polymeric substances, which ensures the microbial activity and stability of the ex-situ biogas upgrading. Microbial community characterization showed that the Petrimonas, Romboutsia, Acidaminococcus, and Clostridium predominated the microbiome during biogas upgrading at 500 mg L-1 nZVI with H2 supply. These results suggested that nZVI and H2 contributed jointly to promoting the bioconversion of CO2 in biogas to acetate. The findings could be helpful for paving a new way for efficient simultaneous ex-situ biogas upgrading and liquid chemicals recovery.

Recovery of methane and acetate during ex-situ biogas upgrading via novel dual-membrane aerated biofilm reactor.

Biological biogas upgrading has been well-proven to be a promising approach for renewable bioenergy recovery, but hydrogen (H2)-assisted ex-situ biogas upgrading is hindered by a large solubility discrepancy between H2 and carbon dioxide (CO2). This study established a new dual-membrane aerated biofilm reactor (dMBfR) to improve the upgrading efficiency. Results showed that dMBfR operated at 1.25 atm H2 partial pressure, 1.5 atm biogas partial pressure, and 1.0 d hydraulic retention time could significantly improve the efficiency. The maximum methane purity of 97.6%, acetate production rate of 34.5 mmol L-1d-1, and H2 and CO2 utilization ratios of 96.5% and 96.3% were achieved. Further analysis showed that the improved performances of biogas upgrading and acetate recovery were positively correlated with the total abundances of functional microorganisms. Taken together, these results suggest that the dMBfR, which facilitates the precise CO2 and H2 supply, is an ideal approach for efficient biological biogas upgrading.

Overview of recent progress in exogenous hydrogen supply biogas upgrading and future perspective.

With the rapid development of renewable and sustainable energy, biogas upgrading for producing high-quality biomethane as an alternative to natural gas has attracted worldwide attention. This paper comprehensively reviews the current state of biogas upgrading technologies. The advances in physicochemical, photosynthetic autotrophic, and chemical autotrophic biogas upgrading technologies are briefly described with particular attention to the key challenges. New chemical autotrophic biogas upgrading strategies, such as direct and indirect exogenous hydrogen supply, for overcoming barriers to biogas upgrading and realizing highly efficient bioconversion of carbon dioxide are summarized. For each approach to exogenous hydrogen supply for biogas upgrading, the key findings and technical limitations are summarized and critically analyzed. Finally, future developments are also discussed to provide a reference for the development of biogas upgrading technology that can address the global energy crisis and climate change issues related to the application of biogas.

Role of residue cornstalk derived biochar for the enhanced bio-hydrogen production via simultaneous saccharification and fermentation of cornstalk.

Biochar derived from residue cornstalk left after anaerobic bio-hydrogen production (RCA-biochar) was confirmed to enhance bio-hydrogen production from cornstalk hydrolysate. However, the role of RCA-biochar in simultaneous saccharification and fermentation (SSF) during bio-hydrogen production from cornstalk has not yet been revealed. This study therefore aims to fill this knowledge gap. It was observed that with the increase in RCA-biochar concentration from 0 g/L to 10.0 g/L, the maximal cumulative SSF bio-hydrogen yield varied from 24.3 ± 1.1 mL/g-substrate to 154.3 ± 3.6 mL/g substrate under varying pH values - 5.5, 6.0, 6.5, 7.0. The increasing bio-hydrogen production was observed to correlate with both RCA-biochar level and initial pH. Batch tests confirmed that the initial pH had an obvious effect an saccharification, while RCA-biochar affected anaerobic fermentation a lot. The findings revealed the role of previously unrecognized RCA-biochar in SSF bio-hydrogen production from cornstalk, which can provide an alternative approach for lignocellulosic bio-hydrogen production.