Role of KOH-activated biochar on promoting anaerobic digestion of biomass from Pennisetumgianteum.

Pennisetum giganteum is a promising non-food crop feedstock for biogas production due to its high productivity and bio-methane potential. However, the accumulation of volatile fatty acids (VFA) usually restricts the conversion efficiency of P. giganteum biomass (PGB) during anaerobic digestion (AD). Here, the role of KOH-activated biochar (KB) in improving the AD efficiency of PGB and the related mechanisms were investigated in detail. The results revealed that KB exhibited excellent electrical conductivity, electron transfer capacity and specific capacitance, which might be related to the decrease in the electron transfer resistance after adding KB to the AD process. In addition, the KB addition not only reinforced metabolisms of energy and VFAs but also promoted the conversion of VFAs to methane, leading to a 52% increase in the methane production rate. Bioinformatics analysis showed that Smithella and Methanosaeta were key players in the KB-mediated AD process of PGB. The stimulatory effect of methanogenesis probably resulted from the establishment of direct interspecies electron transfer (DIET) between VFA-oxidizing acetogens (e.g., Smithella) and Methanosaeta. These findings provided a key step to improve the PGB-based AD process.

Magnetite-boosted syntrophic conversion of acetate to methane during thermophilic anaerobic digestion.

Using a batch thermophilic anaerobic system established with 60 mL serum bottles, the mechanism on how microbial enrichments obtained from magnetite-amended paddy soil via repeated batch cultivation affected methane production from acetate was investigated. Magnetite-amended enrichments (MAEs) can improve the methane production rate rather than the methane yield. Compared with magnetite-unamended enrichments, the methane production rate in MAE was improved by 50%, concomitant with the pronounced electrochemical response, high electron transfer capacity, and fast acetate degradation. The promoting effects might be ascribed to direct interspecies electron transfer facilitated by magnetite, where magnetite might function as electron conduits to link the acetate oxidizers (Anaerolineaceae and Peptococcaceae) with methanogens (Methanosarcinaceae). The findings demonstrated the potential application of MAE for boosting methanogenic performance during thermophilic anaerobic digestion.

Nano magnetite-loaded biochar boosted methanogenesis through shifting microbial community composition and modulating electron transfer.

A batch anaerobic fermentation system was employed to clarify how nano magnetite-loaded biochar can improve methanogenic performance of the propionate-degrading consortia (PDC). The nano magnetite-loaded biochar was prepared in a sequential hydrothermal and pyrolysis procedure using the household waste (HW), biogas residue (BR) and Fe (NO3)3 as pristine materials. Comprehensive characterization showed that the nano magnetite-loaded biochar ameliorated the biochar properties with large specific surface area, high electrochemical response and low electron transfer resistance. PDC supplemented with the magnetite/BR-originated biochar composites displayed excellent methanogenic performance, where the methane production rate was enhanced by 1.6-fold compared with the control. The nano magnetite-loaded biochar promoted methane production probably by promoting direct interspecies electron transfer between syntrophic bacteria (e.g., Syntrophobacter and Thauera) and their partners (e.g., Methanosaeta). In this process, magnetite might be responsible for triggering rapidly extracellular electron release, whereas both external functional groups and intrinsic graphitic matrices of biochar might work as electron bridges for electron transport.

Promoting biomethane production from propionate with Fe2O3@carbon nanotubes composites.

Using a batch anaerobic system constructed with 60 mL serum bottles, potential of a composite material with Fe2O3 nanoparticles decorated on carbon nanotubes (CNTs) to enhance biomethane production was investigated. The composites (Fe2O3@CNTs) with well dispersed Fe2O3 nanoparticles (4.5 nm) were fabricated by a facile thermal decomposition method in a muffle furnace under nitrogen atmosphere. Compared with Fe2O3, Fe2O3@CNTs showed a large specific surface area and good electrical conductivity. Supplementation of Fe2O3@CNTs to the propionate-degrading enrichments enhanced the methane production rate, which was 10.4-fold higher than that in the control experiment without material addition. The addition of Fe2O3@CNTs also not only showed a clearly electrochemical response to flavin and cytochrome C, but also reduced the electron transfer resistance when compared to the control. Comparative analysis showed that Fe2O3 in Fe2O3@CNTs played a key role in initiating electrochemical response and triggering rapid methane production, while CNTs functioned as rapid electron conduits to facilitate electron transfer from iron-reducing bacteria (e.g., Acinetobacter, Syntrophomonas, and Geobacter) to methanogens (e.g. Methanosarcina).

Increasing the methane production rate of hydrogenotrophic methanogens using biochar as a biocarrier.

The existence of CO2 in biogas will affect its practicality, so the methanation of CO2 is of great significance. Carrier materials play a key role in bioconversion of CO2 to methane during biogas upgrading. Herein, different materials were used to evaluate the bioconversion process of CO2 to methane, which consisted of black ceramsite (BC) and biochars prepared from corn straw and digestate. The results showed that after adding the carrier materials, the methane production rate increased by more than 20%, and the corn straw biochar (CSB) group even increased by more than 70%. This may be attributed to the large specific surface area and more functional groups in corn straw biochar which was suitable for the immobilization of hydrogenotrophic methanogens (HMs). Therefore, corn straw biochar is a good carrier material for the accelerated bioconversion of CO2 to methane.

Methane Elimination Using Biofiltration Packed With Fly Ash Ceramsite as Support Material.

Methane is a greenhouse gas and significantly contributes to global warming. Methane biofiltration with immobilized methane-oxidizing bacteria (MOB) is an efficient and eco-friendly approach for methane elimination. To achieve high methane elimination capacity (EC), it is necessary to use an exceptional support material to immobilize MOB. The MOB consortium was inoculated in biofilters to continuusly eliminate 1% (v/v) of methane. Results showed that the immobilized MOB cells outperformed than the suspended MOB cells. The biofilter packed with fly ash ceramsite (FAC) held the highest average methane EC of 4.628 g h-1 m-3, which was 33.4% higher than that of the biofilter with the suspended MOB cells. The qPCR revealed that FAC surface presented the highest pmoA gene abundance, which inferred that FAC surface immobilized the most MOB biomass. The XPS and contact angle measurement indicated that the desirable surface elemental composition and stronger surface hydrophilicity of FAC might favor MOB immobilization and accordingly improve methane elimination.

Improved methane elimination by methane-oxidizing bacteria immobilized on modified oil shale semicoke.

Methane is a greenhouse gas with significant global warming potential. The methane-oxidizing bacteria (MOB) immobilized on biocarrier could perform effectively and environmentally in methane elimination. To further improve the efficiencies of MOB immobilization and methane elimination, the surface biocompatibility of biocarrier needs to be improved. In this work, the oil shale semicoke (SC) was chemically modified by sodium p-styrenesulfonate hydrate (SS) and 2-(methacryloyloxy)ethyltrimethylammonium chloride (DMC) to promote surface hydrophilicity and positive charge, respectively. Results revealed that, under methane concentrations of ~10% (v/v) and ~0.5% (v/v), the MOB immobilized on semicoke modified with 1.0 mol L-1 of SS permitted improved methane elimination capacities (ECs), which were 15.02% and 11.11% higher than that on SC, respectively. Additionally, under methane concentrations of ~10% (v/v) and ~0.5% (v/v), the MOB immobilized on semicoke modified with 0.4 mol L-1 of DMC held superior ECs, which were 17.88% and 11.29% higher than that on SC, respectively. The qPCR analysis indicated that the MOB abundance on modified semicoke were higher than that on SC. In consequence, the surface biocompatibility of semicoke could be promoted by SS and DMC modifications, which potentially provided methods for other biocarriers to improve surface biocompatibility.

Improved methane removal in exhaust gas from biogas upgrading process using immobilized methane-oxidizing bacteria.

Methane in exhaust gas from biogas upgrading process, which is a greenhouse gas, could cause global warming. The biofilter with immobilized methane-oxidizing bacteria (MOB) is a promising approach for methane removal, and the selections of inoculated MOB culture and support material are vital for the biofilter. In this work, five MOB consortia were enriched at different methane concentrations. The MOB-20 consortium enriched at the methane concentration of 20.0% (v/v) was then immobilized on sponge and two particle sizes of volcanic rock in biofilters to remove methane in exhaust gas from biogas upgrading process. Results showed that the immobilized MOB performed more admirable methane removal capacity than suspended cells. The immobilized MOB on sponge reached the highest methane removal efficiency (RE) of 35%. The rough surface, preferable hydroscopicity, appropriate pore size and particle size of support material might favor the MOB immobilization and accordingly methane removal.

The thermophilic (55°C) microaerobic pretreatment of corn straw for anaerobic digestion.

Microaerobic process has been proven to be an alternative pretreatment for the anaerobic digestion (AD) process in several studies. In this study, the effect of thermophilic microaerobic pretreatment (TMP) on the AD of corn straw was investigated. Results indicated that TMP process obviously improved the methane yield. The maximum methane yield was obtained at the oxygen loads of 5ml/g VSsubstrate, which was 16.24% higher than that of untreated group. The modified first order equation analysis showed the TMP process not only accelerated the hydrolysis rates but also reduced the lag-phase time of AD process. The structural characterization analysis showed cellulosic structures of corn straw were partly disrupted during TMP process. The crystallinity indexes were also decreased. In addition, large or destroyed pores and substantial structural disruption were observed after pretreatment. The results showed that TMP is an efficient pretreatment method for the AD of corn straw.

[Simultaneous production of hydrogen and volatile fatty acid from Macrocystis pyrifera].

Batch experiments were conducted to analyze the effects of pretreatment conditions, inoculum-substrate ratio (ISR) and initial pH on the hydrogen and volatile fatty acid (VFA) production from anaerobic digestion of Macrocystis pyrifera biomass. The results indicated that M. pyrifera could produce hydrogen and VFA simultaneously. In addition, thermo-alkaline pretreatment was proved as the best method for hydrogen and VFA production. The optimal pretreatment conditions, ISR, initial pH value were determined as thermal-alkaline pretreatment at 100 degrees C with 4 g x L(-1) NaOH, 0.3 and 6, respectively. Under these conditions, the maximum hydrogen production was 36.21 mL x g(-1) per unit volatile solids, which resulted in 77.82% improvement compared with the yield from untreated M. pyrifera. Furthermore, the TVFA yield under the optimal conditions was found to be 0.15 g x g(-1) per unit volatile solids and the VFAs mainly consisted of acetate and butvrate