Xianzheng Yuan

Effect of inoculum/substrate ratio on methane yield and orthophosphate release from anaerobic digestion of Microcystis spp.

A batch anaerobic test was conducted to evaluate the effects of inoculum/substrate ratios (ISRs) on the methane yield and orthophosphate release from the anaerobic digestion of Microcystis spp. The results demonstrated an obvious influence on methane yield and orthophosphate release by ISR. The maximum methane yield decreased from 140.48 to 94.42 mL/gVS when the ISR decreased from 2.0 to 0.5. The highest maximum methane yield calculated from Ørskov equation was 153.66 mL/gVS at ISR value of 1.0. The values of pH, ammonia and volatile fatty acids (VFAs) corroborated the appropriate stability of this anaerobic process.

Biogas production and microcystin biodegradation in anaerobic digestion of blue algae

In order to demonstrate the potentials of both bioenergy production and microcystin (MC) biodegradation in methanogenic conditions, the biogas production, process stability and the variation of MC concentration in anaerobic digestion of blue algae from Taihu Lake were studied. A methane yield of 189.89 mL g−1 VS was obtained from the digester, and the average methane concentration in the biogas was 36.72%. During the digestion, the pH value was fairly constant (6.8 to 7.6), and soluble chemical oxygen demand (SCOD) kept at a relatively stable level. The concentration of total volatile fatty acid (VFA) increased significantly in the first 8 days, and then decreased, showing no inhibition on the digestion. The results also showed that the concentration of MC could be significantly reduced from 1220.19 μg L−1 to 35.17 μg L−1 during the methanogenic process, which followed the first order kinetics well. These findings suggest that anaerobic digestion of blue algae can both generate renewable energy biogas and lead to biodegradation of MC, presenting significant potentials for bioremediation of MC and post-treatment of blue algae.

Bioconversion of wheat stalk to hydrogen by dark fermentation: Effect of different mixed microflora on hydrogen yield and cellulose solubilisation

This study determined hydrogen production, volatile fatty acids (VFAs) generation and cellulose solubilisation from anaerobic dark fermentation of wheat stalk and showed the effect of different mixed microflora. The cumulative hydrogen yields of anaerobic digested activated sludge (AS)-inoculated and anaerobic digested dairy manure (DM)-inoculated system were 23.3 and 37.0 mL/g VS at 204 h, respectively. A modified Gompertz equation was able to adequately describe the production of hydrogen from the batch fermentation by both mixed microflora. During the process, acetate and butyrate accounted for more than 76.1% of total VFAs for both fermentations. The extent of cellulose solubilisation approached 46.6% and 75.2% for AS- and DM-inoculated fermentation, respectively. The X-ray diffraction (XRD) showed that the crystallinities of both fermented stalks were partly disrupted by the mixed microflora, and DM-inoculated fermentation had more disruption than AS-inoculated one.

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.

Anaerobic biohydrogen production from wheat stalk by mixed microflora: Kinetic model and particle size influence

This study investigated the influence of particle size on anaerobic biohydrogen production from wheat stalk by mixed microflora. In addition, the kinetic model for the formation of main products was also mentioned. The results demonstrated that all the cumulative productions of hydrogen, acetate and butyrate decreased as the particle size increasing from 1 to 10mm at a constant TS value of 2%, 5% and 8%, respectively. However, this difference for aqueous products was not very obvious compared with hydrogen. A modified Gompertz equation was able to adequately describe the cumulative production of hydrogen, acetate and butyrate (R² higher than 0.989). The results also indicated that the formation of the main products were all associated with the degradation of cellulose and hemicellulose (R² higher than 0.855).

Fermentation of Chlorella sp. for anaerobic bio-hydrogen production: influences of inoculum-substrate ratio, volatile fatty acids and NADH.

This study evaluated the influences of inoculum-substrate ratio (ISR), volatile fatty acids (VFAs) and nicotinamide adenine dinucleotide, the reduced form (NADH) on hydrogen production during the anaerobic fermentation of Chlorella sp. in batch tests at 35 °C. The results indicated that the hydrogen concentration and lag time increased when ISR decreased, and the maximum hydrogen production and hydrogen content, 7.13 mL/g VS and 45.3%, respectively, were obtained when ISR was equal to 0.3. On the other hand, VFAs concentrations increased with the increase of hydrogen. The NADH increased while the daily output of hydrogen decreased as the fermentation carried on. The results suggested that ISR, VFAs, and NADH were important parameters for effective anaerobic hydrogen production using Chlorella sp. as substrate.

Acetobacteroides hydrogenigenes gen. nov., sp. nov., an anaerobic hydrogen-producing bacterium in the family Rikenellaceae isolated from a reed swamp.

A strictly anaerobic, mesophilic, carbohydrate-fermenting, hydrogen-producing bacterium, designated strain RL-C(T), was isolated from a reed swamp in China. Cells were Gram-stain-negative, catalase-negative, non-spore-forming, non-motile rods measuring 0.7-1.0 µm in width and 3.0-8.0 µm in length. The optimum temperature for growth of strain RL-C(T) was 37 °C (range 25-40 °C) and pH 7.0-7.5 (range pH 5.7-8.0). The strain could grow fermentatively on yeast extract, tryptone, arabinose, glucose, galactose, mannose, maltose, lactose, glycogen, pectin and starch. The main end products of glucose fermentation were acetate, H2 and CO2. Organic acids, alcohols and amino acids were not utilized for growth. Yeast extract was not required for growth; however, it stimulated growth slightly. Nitrate, sulfate, sulfite, thiosulfate, elemental sulfur and Fe(III) nitrilotriacetate were not reduced as terminal electron acceptors. Aesculin was hydrolysed but not gelatin. Indole and H2S were produced from yeast extract. The G+C content of the genomic DNA was 51.2 mol%. The major cellular fatty acids were iso-C15 : 0, anteiso-C15 : 0 and C16 : 0. The most abundant polar lipid of strain RL-C(T) was phosphatidylethanolamine. 16S rRNA gene sequence analysis revealed that the isolate belongs to the uncultured Blvii28 wastewater-sludge group (http://www.arb-silva.de/) in the family Rikenellaceae of the phylum Bacteroidetes, and shared low sequence similarities with the related species Alistipes shahii WAL 8301(T) (81.8 %), Rikenella microfusus ATCC 29728(T) (81.7 %) and Anaerocella delicata WN081(T) (80.9 %). On the basis of these data, a novel species in a new genus of the family Rikenellaceae is proposed, Acetobacteroides hydrogenigenes gen. nov., sp. nov. The type strain of the type species is RL-C(T) ( = JCM 17603(T) = DSM 24657(T) = CGMCC 1.5173(T)).

Molecular characterization of bacterial and archaeal communities in a full-scale anaerobic reactor treating corn straw

A 16S rRNA gene-based method was used to characterize the structure of bacterial and archaeal communities in a full-scale, anaerobic reactor treating corn straw. Degradability experiment indicated biogas slurry had high microbial activity, the TS removal rate was 53% and the specific methanogenic activity was 86 mL CH4 g VSS(-1) d(-1). During anaerobic degradation of corn straw, volatile acids and aromatic compounds (p-cresol, phenylpropionate, phenol and benzoate) were detected as transient intermediates. Phylogenetic analysis revealed bacterial community exhibited high diversity, 69 bacterial phylotypes in 13 phyla were identified. Firmicutes (48.3%), Chloroflexi (20.1%), Actinobacteria (9.1%), Bacteroidetes (7.7%), and Proteobacteria (7.2%) represented the most abundant bacterial phyla. Hydrolytic and fermentative bacteria were major bacterial populations. Moreover, a relatively high proportion of syntrophic propionate and aromatic compounds degrading bacteria were detected. In the archaeal clone library, 11 archaeal phylotypes affiliated with two phyla of Crenarchaeota (10%) and Euryarchaeota (90%) were identified.

Bioaugmentation with an acetate-type fermentation bacterium Acetobacteroides hydrogenigenes improves methane production from corn straw.

The effect of bioaugmentation with an acetate-type fermentation bacterium in the phylum Bacteroidetes on the anaerobic digestion of corn straw was evaluated by batch experiments. Acetobacteroides hydrogenigenes is a promising strain for bioaugmentation with relatively high growth rate, hydrogen yields and acetate tolerance, which ferments a broad spectrum of pentoses, hexoses and polyoses mainly into acetate and hydrogen. During corn straw digestion, bioaugmentation with A. hydrogenigenes led to 19-23% increase of the methane yield, with maximum of 258.1 mL/g-corn straw achieved by 10% inoculation (control, 209.3 mL/g-corn straw). Analysis of lignocellulosic composition indicated that A. hydrogenigenes could increase removal rates of cellulose and hemicelluloses in corn straw residue by 12% and 5%, respectively. Further experiment verified that the addition of A. hydrogenigenes could improve the methane yields of methyl cellulose and xylan (models for cellulose and hemicelluloses, respectively) by 16.8% and 7.0%.

Enhanced methane production from microalgal biomass by anaerobic bio-pretreatment

Anaerobic digestion (AD) of microalgal biomass is one of the most energy efficient technologies to convert microalgae to biofuels. In order to improve the biogas productivity, breaking up the tough and rigid cell wall of microalgae by pretreatment is necessary. In this work, Bacillus licheniformis, a facultative anaerobic bacterial with hydrolytic and acidogenic activities, was adopted to pretreat Chlorella sp. In the established pretreatment process, pure bacterial culture (0%, 1%, 2%, 4%, 8%, v/v) were used to pretreat Chlorella sp. under anaerobic condition at 37°C for 60 h. The soluble chemical oxygen demands (SCOD) content was increased by 16.4-43.4%, while volatile fatty acids (VFAs) were improved by 17.3-44.2%. Furthermore, enhancement of methane production (9.2-22.7%) was also observed in subsequent AD. The results indicated that the more dosages of bacteria were used to pretreat the microalgal biomass in the range of 1-8%, the more methane was produced.