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).

Role of biochar and organic substrates in enhancing the functional characteristics and microbial community in a saline soil.

In sustaining the soil quality, soil salinization has become a major challenge due to the increasing salinity rate of 10% annually. Despite, the serious concerns, the influence of soil amendments on microbial communities and its related attributes have limited findings. Therefore, the present study aims to investigate the potential of three various biochars, digestate (DI), and its compost (COM) in reclamation of saline soil under closed ecosystem. The decrease in the pH was displayed by lignite char, and electrical conductivity by lignite char plus COM addition among all the treatments. The subside in Na +, with a significant rise in K +, was exhibited in soils amended with DI plus DI biochar as a combined ameliorate over control. The negative priming effects on native soil organic carbon (nSOC) due to the decreased substrate bioavailability, in corn straw and DI biochars ameliorates were noted. The urease and alkaline phosphatase activity were pronounced higher in COM. However, the catalase and fluorescein diacetate activity were greater in lignite char plus DI and COM respectively. The co-addition of biochar and organic substrates shifted microbial community, is in correspondence with the relative abundance of the phylum. Overall, the abundance of Firmicutes and Actinobacteria was higher in soils under a combination of lignite char with DI and COM respectively. Likely, the abundance of Euryarchaeota was dominant in the co-application of corn straw biochar and DI. Redundancy analysis revealed the intactness between bacterial genera and their metabolisms with K +, and Mg 2+. PICRUSt disclosed the enhanced metabolic functions in soil with amalgam of DI and its biochar. The findings showed that the application of DI and its biochar mixture, as an amendment could be a better approach in the long-term reclamation of saline soil.

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.

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.

Enrichment of thermophilic and mesophilic microbial consortia for efficient degradation of corn stalk.

Six different environmental samples were applied to enrich microbial consortia for efficient degradation of corn stalk, under the thermophilic and mesophilic conditions. The consortium obtained from anaerobic digested sludge under thermophilic condition (TC-Y) had the highest lignocellulose-degrading activity. The CO2 yield was 246.73 mL/g VS in 23 days, meanwhile, the maximum CO2 production rate was 15.48 mL/(CO2·d), which was 28.75% and 52.27% higher than that under mesophilic condition, respectively. The peak value of cellulase activity reached 0.105 U/mL, which was at least 34.61% higher than the other groups. In addition, 49.5% of corn stalk was degraded in 20 days, moreover, the degradation ratio of cellulose, hemicellulose and lignin can reach 52.76%, 62.45% and 42.23%, respectively. Microbial consortium structure analysis indicated that the TC-Y contained the phylum of Gemmatimonadetes, Acidobacteria, Chloroflexi, Planctomycetes, Firmicutes, and Proteobacteria. Furthermore, the Pseudoxanthomonas belonging to GammaProteobacteria might be the key bacterial group for the lignocellulose degradation. These results indicated the capability of degrading un-pretreated corn stalk and the potential for further investigation and application of TC-Y.

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.

Combination of bioaugmentation and biostimulation for remediation of paddy soil contaminated with 2,4-dichlorophenoxyacetic acid.

The batch and fed-batch tests were performed to evaluate the efficiency of bioaugmentation in combination with biostimulation for remediation of paddy soil contaminated with 2,4-dichlorophenoxyacetic acid (2,4-D). 2,4-D degrading enrichments were used for bioaugmentation, and effluents prepared through biological hydrogen production process were used as substrate for biostimulation. The batch tests indicated that 2,4-D degradation depended on the enrichment/substrate ratio (E/S), where E/S of 0.03 showed an excellent performance. The fed-batch tests showed that biostimulation only led to an improvement in 2,4-D degradation, while the pattern of repeated augmentation of enrichments (FRA) together with biostimulation obviously improved degradation of 2,4-D, 2-chlorophenol (2-CP) and phenol. DNA-sequencing approach showed that the FRA pattern altered the bacterial community composition, and high removal of 2,4-D, 2-CP and phenol may be attributed to the acclimation and persistence of Thauera. The findings demonstrated the importance of the FRA pattern on remediation of paddy soil contaminated with 2,4-D.

Distillers' grains anaerobic digestion residue biochar used for ammonium sorption and its effect on ammonium leaching from an Ultisol.

The aim of this work was to explore the potential application of biochar from distillers' grains anaerobic digestion residue pyrolyzed at 700 °C (ADR-DG700) to ammonium (NH4+) adsorption from aqueous solution, as well as its effect on NH4+ leaching from an Ultisol. The adsorption kinetic of NH4+ on the ADR-DG700 could be described by an Elovich model (R2 = 0.995), and the combined Langmuir-Freundlich model (R2 = 0.997) fitted the isotherm data better than the Langmuir, Freundlich, Redlich-Peterson, and Temkin models with a maximum adsorption of 11.41 mg N g-1. The NH4+ adsorption on ADR-DG700 was mainly controlled by the cation exchange, the surface complexation with oxygen-containing functional groups of carboxyl C〓O (C▬O) and carbohydrate C▬OH, as well as the electrostatic interactions with Si▬O▬Si functional group. In addition, the ADR-DG700 soil application reduced 2.48-20.67% of NH4+-N leaching loss after nitrogen fertilizer application in an Ultisol. These results suggested that the ADR-DG700 could be a sorbent for NH4+-contaminated water as well as an inhibitor for soil NH4+ leaching.

Improved methane production from corn straw by microaerobic pretreatment with a pure bacteria system.

Thermophilic microaerobic pretreatment has been proved to be efficient in improving methane production of corn straw in previous studies. In this study, the effect of mesophilic (37 °C) microaerobic pretreatment using Bacillus Subtilis on the anaerobic digestion of corn straw was explored. Microaerobic pretreatment with a pure bacteria system was beneficial for the anaerobic digestion of corn straw, which obviously improved the methane yield. The maximum methane yield of 270.8 mL/g VS was obtained at the oxygen load of 5 mL/g VS, which was 17.35% higher than that of untreated group. Groups with mesophilic microaerobic pretreatment obtained higher glucose and VFAs concentrations, as well as higher peroxidase activities after 24 h pretreatment. In addition, the X-ray diffraction (XRD) analysis displayed the crystallinity indexes of pretreated groups were also decreased. Therefore, microaerobic pretreatment with a pure bacteria system (Bacillus Subtilis) is an efficient pretreatment method to enhance the anaerobic digestion efficiency of cellulosic biomass.

Promoting degradation of 2,4-dichlorophenoxyacetic acid with fermentative effluents from hydrogen-producing reactor.

This research aims to identifying the potential effect of using a hydrogen-producing reactor's effluent as an enrichment amendment for enhancing the degradation rates of 2,4-dichlorophenoxyacetic acid (2,4-D) during the bioremediation of contaminated paddy soils. The results showed that addition of the effluents to 2,4-D- degrading enrichment culture enhanced (up to 1.3-fold) the degradation rate constant of 2,4-D. The enhancement effect most probably resulted from the co-metabolic degradation of 2,4-D facilitated by volatile fatty acids (e.g., acetate, propionate, and butyrate) in the effluents which served as the beneficial substrates. Results from DNA sequencing analysis showed that the effluent additions shifted the bacterial community composition in the enrichment culture. Dechloromonas and Clostridium were two dominant bacterial genera involved in 2,4-D degradation. The findings will make a substantial contribution to remediation of soils contaminated with 2,4-D.

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.

Accelerated ciprofloxacin biodegradation in the presence of magnetite nanoparticles.

Ciprofloxacin (CIP) biodegradation was investigated using enrichments obtained in the presence of magnetite nanoparticles, CIP and human fecal sewage. CIP addition inhibited methanogenic activity and altered the bacterial community composition. The magnetite-supplemented enrichments significantly promoted CIP biodegradation, especially in the presence of 2-bromoethanesulfonate (BES). When BES was added, CIP biodegradation in the magnetite-supplemented enrichments was 67% higher than in the magnetite-unamended enrichments. Fe (II) concentrations were also significantly increased in the BES and magnetite-supplemented enrichments. This indicated that there might be a positive relationship of CIP biodegradation with microbial reduction of Fe (III) to Fe (II). As for the magnetite-supplemented enrichments, DNA-sequencing analysis revealed that Stenotrophomonas was the dominant genus, while Desulfovibrio became the dominant genus in the presence of BES. These two genera might be related to Fe (III) reduction in the magnetite. The findings provide a strategy for improving CIP biodegradation during waste treatment.

Rapid degradation of 2,4-dichlorophenoxyacetic acid facilitated by acetate under methanogenic condition.

Acetate can be used as an electron donor to stimulate 2,4-dichlorophenoxyacetic acid (2,4-D), which has not been determined under methanogenic condition. This study applied high-throughput sequencing and methanogenic inhibition approaches to investigate the 2,4-D degradation process using the enrichments obtained from paddy soil. Acetate addition significantly promoted 2,4-D degradation, which was 5-fold higher than in the acetate-unsupplemented enrichments in terms of the 2,4-D degradation rate constant. Dechloromonas and Pseudomonas were the dominant 2,4-D degraders. Methanogenic inhibition experiments indicated that the 2,4-D degradation was independent of methanogenesis. It was proposed that the accelerated 2,4-D degradation in the acetate-supplemented enrichment involved an unusual interaction, where members of the acetate oxidizers primarily oxidized acetate and produced H2. H2 was utilized by the 2,4-D degraders to degrade 2,4-D, but also partially consumed by the hydrogenotrophic methanogens to produce methane. The findings presented here provide a new strategy for the remediation of 2,4-D-polluted soils.

Enhanced methane production via repeated batch bioaugmentation pattern of enriched microbial consortia.

Using batch and repeated batch cultivations, this study investigated the effects of bioaugmentation with enriched microbial consortia (named as EMC) on methane production from effluents of hydrogen-producing stage of potato slurry, as well as on the indigenous bacterial community. The results demonstrated that the improved methane production and shift of the indigenous bacterial community structure were dependent on the EMC/sludge ratio and bioaugmentation patterns. The methane yield and production rate in repeated batch bioaugmentation pattern of EMC were, respectively, average 15% and 10% higher than in one-time bioaugmentation pattern of EMC. DNA-sequencing approach showed that the enhanced methane production in the repeated batch bioaugmentation pattern of EMC mainly resulted from the enriched iron-reducing bacteria and the persistence of the introduced Syntrophomonas, which led to a rapid degradation of individual VFAs to methane. The findings contributed to understanding the correlation between the bioaugmentation of microbial consortia, community shift, and methane production.

Bioaugmentation of Hydrogenispora ethanolica LX-B affects hydrogen production through altering indigenous bacterial community structure.

Bioaugmentation can facilitate hydrogen production from complex organic substrates, but it still is unknown how indigenous microbial communities respond to the added bacteria. Here, using a Hydrogenispora ethanolica LX-B (named as LX-B) bioaugmentation experiments, the distribution of metabolites and the responses of indigenous bacterial communities were investigated via batch cultivation (BC) and repeated batch cultivation (RBC). In BC the LX-B/sludge ratio of 0.12 achieved substantial high hydrogen yield, which was over twice that of control. In RBC one-time bioaugmentation and repeated batch bioaugmentation of LX-B resulted in the hydrogen yield that was average 1.2-fold and 0.8-fold higher than that in control, respectively. This improved hydrogen production performance mainly benefited from a shift in composition of the indigenous bacterial community caused by LX-B bioaugmentation. The findings represented an important step in understanding the relationship between bioaugmentation, a shift in bacterial communities, and altered bioreactor performance.

Magnetite nanoparticles facilitate methane production from ethanol via acting as electron acceptors.

Potential for interspecies hydrogen transfer within paddy soil enrichments obtained via addition of magnetite nanoparticles and ethanol (named as PEM) was investigated. To do this, PEM derived from rice field of Hangzhou (named as PEM-HZ) was employed, because it offered the best methane production performance. Methane production and Fe (III) reduction proceeded in parallel in the presence of magnetite. Inhibition experiments with 2-bromoethane sulfonate (BES) or phosphate showed that interspecies hydrogen transfer and Fe (III) reduction also occurred in methane production from ethanol. 16S rRNA-based Illumina sequencing results showed that Dechloromonas, Thauera, Desulfovibrio and Clostridium were the dominant putative Fe (III) -reducers, and that hydrogenotrophic Methanobacterium accounted for about 88% of the total archaeal community. These results indicated that magnetite nanoparticles that acted as electron acceptor could facilitate rapid oxidation of ethanol by members of the Fe (III) -reducers in PEM-HZ and establishment of the syntrophic relationship of Fe (III) -reducers with Methanobacterium via interspecies hydrogen transfer. Our results could offer a model to understand the microbial interaction with magnetite from a novel angle during methanogenesis.