Effect of COD: SO42- Ratio, HRT and Linoleic Acid Concentration on Mesophilic Sulfate Reduction: Reactor Performance and Microbial Population Dynamics

Biological sulfate (SO42-) reduction was examined in anaerobic sequential batch reactors (ASBRs) operated under different hydraulic retention times (HRTs) ranging from 12 to 36 h and COD (Chemical Oxygen Demand)/SO42- ratios of 2.4, 1.6 and 0.8. Competition between SO42- reducing bacteria (SRBs), methane producing archaea (MPAs) and homoacetogens (HACs) was examined in controls and cultures treated with linoleic acid (LA). The ASBR performance was influenced by the COD/SO42- ratio in control cultures with a SO42- reduction of 87% at a COD/SO42- ratio of 0.8. At a 12 h HRT, in both control and LA treated cultures, greater than 75% SO42- removal was observed under all the conditions examined. In control reactors operating at a 36 h HRT, high levels of MPAs belonging to Methanobacteriales and Methanosarcinales were detected; however, in comparison, under low COD/SO42- ratio and with decreasing HRT conditions, a relative increase in SRBs belonging to Desulfovibrio and Desulfatibacillum was observed. Adding 0.5 gL(-1) LA suppressed Methanobacteriales, while increasing the LA concentration to 1 gL(-1) completely suppressed MPAs with a relative increase in SRBs. HACs belonging to Bacteroidetes were observed in the control and in cultures operated at 12 h HRT with a COD/SO42- ratio of 1.6 and fed 0.5 gL(-1) LA; however, with all other LA levels (0.5 and 1.0 gL(-1)) and HRTs (12, 24 and 36 h), HACs were not detected

16S rRNA gene based analysis of the microbial diversity and hydrogen production in three mixed anaerobic cultures

To explore of role of microbial diversity and its functionality in commercial bioreactors, three anaerobic microbial communities from Ontario, Canada were characterized using 16S rRNA gene-based, clone library sequencing and terminal restriction fragment length polymorphism (T-RFLP) and compared with the hydrogen (H-2) and methane yields. The T-RFLP method showed more operational taxonomic units than the clone library sequence analysis; however, the two methods showed similar dominant species and relative diversity while Spearman\u27s Rank correlation coefficient (r) values ranged from 0.82 to 0.91. The Chao 1 and Shannon-Wiener indices revealed that the cultures samples have highly diverse microbial communities. Comparatively, cultures from a municipal wastewater treatment plant (CA) showed more diversity than those from facilities treating effluents from a baby food processor and a brewery. Even though culture CA has the highest microbial diversity, low H-2 and methane production yield was attributed to the presence of sulphate reducers, propionate producers and a low percentage of methanogens. This study confirms that the selection of the source of mixed anaerobic cultures plays an important role in H-2 and methane production. Crown Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Continuous hydrogen production using upflow anaerobic sludge blanket reactors: Effect of organic loading rate on microbial dynamics and H2 metabolism

BACKGROUND: Enriching hydrogen (H2)-producing bacteria by suppressing methane- producing microorganisms is a critical step in continuous biologicalH2 production. Selective inhibition ofmethanogenscanbeachievedby varying the organic loading rate (OLR) in continuous reactors. In this study, continuous H2 production was examined using mixed anaerobic cultures fed glucose in upflow anaerobic sludge blanket reactors (UASBRs) operating at 37∘C and at pH 5.0 by varying the OLR at a constant hydraulic retention time. RESULTS: A stable H2 yield of 1.64±0.04 molmol−1 glucose was obtained at OLRs from 8.6 to 12.8 g COD L−1 d−1. Increasing the OLR increased the hydrogenase flux and suppressedmethanogenesis. At high OLRs, high acetate and solvent production were associated with Clostridiaceae and Ruminococcaceae while at lowOLRs, the presence of Synergistaceae and Propionibacteriaceae were related to the production of propionate and other reduced byproducts. CONCLUSION: This study successfully demonstrated continuous H2 production using bench-scale UASBRs fed glucose. Understanding the OLR effect on H2 production and microbial interaction is important in the full-scale operation of H2 production facilities using low value feedstocks such as switch grass, corn stover and shorghum. © 2016 Society of Chemical Industr

Effect of inhibitors on hydrogen consumption and microbial population dynamics in mixed anaerobic cultures

The impact of different chemical microbial stressors (2-bromoethanesulfonate (BES), furfural, fish oil, lauric acid (LUA) and linoleic acid (LA)) on the inhibition of mesophilic hydrogen (H-2) consumption was examined in this study. Hydrogen consumption half-life values were used to compare the extent of inhibition by the different microbial stressing agents. A statistical analysis of the percent H-2 consumed using Tukey\u27s analysis revealed the following trend: Control \u3e fish oil = linoleic acid (LA (C18:2)) = furfural \u3e BES \u3e lauric acid (LUA (C12:0). The terminal restriction fragment length polymorphism (T-RLFP) results indicated that aceticlastic methanogens (Methanosaeta sp., Methanosarcina sp.) and hydrogenotrophic methanogens (Methanococcus sp.) were inhibited by the different chemical stressing agents. Cultures fed LUA and LA had a high abundance of Clostridium sp., Clostridium propionicum and Propionibacterium acnes. In comparison, BES and furfural fed cultures contained large fractions of Clostridium sp., Eubacteria sp. and Bacteroides sp. while in the fish oil fed cultures, the dominant organism detected was Eubacteria sp. This study indicated that H-2 consumption was affected by the chemical stressing agent concentration. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Statistical optimization of conditions for minimum H-2 consumption in mixed anaerobic cultures: Effect on homoacetogenesis and methanogenesis

Hydrogen (H-2) production using mixed anaerobic cultures often suffers severe yield reduction due to the syntrophic association between H-2 consumers (methanogens and homoacetogens) and H-2 producers (acidogens). The objective of this study was to uncouple the syntrophic association between H-2 producers and consumers by optimizing conditions for minimum H-2 consumption using a Box-Behnken design approach. The factors investigated in this study include temperature, pH and linoleic acid (LA) concentration. A quadratic response surface model was developed to predict the H-2 consumed by mixed anaerobic cultures and the optimum conditions for minimum H-2 consumption were 38 degrees C, pH 5.5 and 2 g L-1 LA. Methanogenesis was inhibited in cultures fed 2 g L-1 LA and maintained at pH 6.0 and 53 degrees C. In comparison, both methanogenesis and homoacetogenesis were inhibited in cultures fed 1-2 g L-1 LA and maintained at a pH of 4.5 (Fig. 2B and 2E and Table 2 Expt. # 1, 2 and 11). Microbial diversity analysis revealed that LA fed cultures was dominated by spore forming Clostridium sp. in addition to Syntrophus aciditrophus. In comparison, control cultures were dominated by Eubacterium sp., Methanocalculus halotolerans and Methanococcoides alaskense. This study described an approach for regulating H-2 consumption in mixed cultures by optimizing process and environmental factors. Understanding the effects of these individual factors and their interaction is important in the full-scale operation of H-2 production facilities. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Fermentative H-2 production using a switchgrass steam exploded liquor fed to mixed anaerobic cultures: Effect of hydraulic retention time, linoleic acid and nitrogen sparging

Fermentative hydrogen (H-2) production from a steam exploded switchgrass liquor using inhibited mixed anaerobic microbial communities was studied in upflow anaerobic sludge blanket reactors (UASBRs). Increasing the H-2 yield was accomplished by treating the inoculum with linoleic acid (LA), varying the hydraulic retention time (HRT) and sparging liquid phase with nitrogen (N-2). A maximum H-2 yield of 2.56 +/- 0.10 mol mol(-1) hexose, was obtained at a 6 h HRT in LA treated cultures sparged with N-2. Sparging or LA treatment alone was able to enhance the H-2 yield by 46 +/- 5% and 38 +/- 3%, respectively, in comparison to control cultures operating at a 6 h HRT. Of the different methods employed, N-2 sparging in combination with LA treatment proved to be more effective in enriching the H-2 producing bacteria belonging to Clostridium sp. Species belonging to Propionibacterium, Bacteroides and Eubacterium, which were associated with H-2 consumption and reduced byproducts formation, were observed in addition to Clostridium sp. in unsparged control cultures. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved