Effects of supplement additives on anaerobic biogas production

Biogas from lignocellulosic feedstock: current status and challenges

The organic wastes and residues generated from agricultural, industrial, and domestic activities have the potential to be converted to bioenergy. One such energy is biogas, which has already been included in rural areas as an alternative cooking energy source and agricultural activities. It is produced via anaerobic digestion of a wide range of organic nutrient sources and is an essential renewable energy source. The factors influencing biogas yield, i.e., the various substrate, their characteristics, pretreatment methods involved, different microbial types, sources, and inoculum properties, are analyzed. Furthermore, the optimization of these parameters, along with fermentation media optimization, such as optimum pH, temperature, and anaerobic digestion strategies, is discussed. Novel approaches of bioaugmentation, co-digestion, phase separation, co-supplementation, nanotechnology, and biorefinery approach have also been explored for biogas production. Finally, the current challenges and prospects of the process are discussed in the review.

Effects of Operating Parameters and Feed Gas Compositions on the Dry Reforming of Methane over the Ni/Al2O3 Catalyst

The effects of operating parameters such as reaction temperature, space velocity, and feed gas composition on the performance of the methane dry-reforming reaction (DRM) over the Ni/Al2O3 catalyst are systemically investigated. The Ni/Al2O3 catalyst, which is synthesized by conventional wet impregnation, showed well-developed mesoporosity with well-dispersed Ni nanoparticles. CH4 and CO2 conversions over the Ni/Al2O3 catalyst are dramatically increased as both the reaction temperature is increased, and space velocity is decreased. The feed gas composition, especially the CO2/CH4 ratio, significantly influences the DRM performance, catalyst deactivation and the reaction behavior of side reactions. When the CO2-rich gas composition (CO2/CH4 > 1) was used, a reverse water gas shift (RWGS) reaction significantly occurred, leading to the consumption of hydrogen produced from DRM. The CH4-rich gas composition (CO2/CH4 < 1) induces severe carbon depositions followed by a reverse Boudouard reaction, resulting in catalytic activity drastically decreasing at the beginning followed by a stable conversion. The catalyst after the DRM reaction with a different feed ratio was analyzed to investigate the amount and structure of carbon deposited on the catalyst. In this study, we suggested that the optimal DRM reaction conditions can achieve stable performances in terms of conversion, hydrogen production and long-term stability.

Trace elements effect on hydrolytic stage towards biogas production of model lignocellulosic substrates

The effect and the response of several trace elements (TE) addition to the anaerobic degradation of key compounds of lignocellulosic biomass were evaluated. Lignin, cellulose and xylose were selected as principal compounds of lignocellulosic biomass. Lignin degradation was only improved by the addition of 1000 mg Fe/L, which allowed an improvement on the methane yield coefficient of 28% compared to control. SEM images from an abiotic assay showed that this effect is more likely related with a chemical effect induced by the Fe solution, instead of an enzymatic response. Pre-treatments focused on breaking the recalcitrant structure of the lignin could be more promising than TE addition for rich lignin-content substrates. Unlike to the response observed with lignin, cellulose showed a clear effect of the TE addition on methane production rate, indicating a higher preponderance of the enzymatic activity compared to the lignin biomethanization. Experiments with xylose resulted in a strong accumulation of volatile fatty acids. TE addition should be adapted to the substrate composition given the different response of each lignocellulosic compound to the different TE addition.

H2 and Syngas Production From Catalytic Cracking of Pig Manure and Compost Pyrolysis Vapor Over Ni-Based Catalysts

Catalytic cracking of volatiles derived from wet pig manure (WPM), dried pig manure and their compost was investigated over Ni/Al2O3 and Ni-loaded on lignite char (Ni/C). Non-catalytic pyrolysis of WPM resulted in a carbon conversion of 43.3% and 18.5% in heavy tar and light tar, respectively. No tar was formed when Ni/Al2O3 was introduced for WPM gasifi cation and the gas yield signifi cantly reached to a high value of 64.4 mmol/g at 650oC. When Ni/C was employed, 5.9% of carbon in the light tar was found at 650oC, revealing that the Ni/C is not active enough for cracking of tarry materials. The pyrolysis vapor was cracked completely and gave a H2-rich tar free syngas in high yield. High water amount of WPM promotes steam gasifi cation of char support, causing the deactivation of Ni/C. Such a study may be benefi cial to the development of livestock manure catalytic gasifi cation technology.