Olli H. Tuovinen

Biogenic hydrogen and methane production from Chlorella vulgaris and Dunaliella tertiolecta biomass

BackgroundMicroalgae are a promising feedstock for biofuel and bioenergy production due to their high photosynthetic efficiencies, high growth rates and no need for external organic carbon supply. In this study, utilization of Chlorella vulgaris (a fresh water microalga) and Dunaliella tertiolecta (a marine microalga) biomass was tested as a feedstock for anaerobic H2 and CH4 production.ResultsAnaerobic serum bottle assays were conducted at 37°C with enrichment cultures derived from municipal anaerobic digester sludge. Low levels of H2 were produced by anaerobic enrichment cultures, but H2 was subsequently consumed even in the presence of 2-bromoethanesulfonic acid, an inhibitor of methanogens. Without inoculation, algal biomass still produced H2 due to the activities of satellite bacteria associated with algal cultures. CH4 was produced from both types of biomass with anaerobic enrichments. Polymerase chain reaction-denaturing gradient gel electrophoresis profiling indicated the presence of H2-producing and H2-consuming bacteria in the anaerobic enrichment cultures and the presence of H2-producing bacteria among the satellite bacteria in both sources of algal biomass.ConclusionsH2 production by the satellite bacteria was comparable from D. tertiolecta (12.6 ml H2/g volatile solids (VS)) and from C. vulgaris (10.8 ml H2/g VS), whereas CH4 production was significantly higher from C. vulgaris (286 ml/g VS) than from D. tertiolecta (24 ml/g VS). The high salinity of the D. tertiolecta slurry, prohibitive to methanogens, was the probable reason for lower CH4 production.

Significance of earthworms in stimulating soil microbial activity

Abstract The stimulatory effect of earthworms (Lumbricus terrestris L.) on soil microbial activity was studied under microcosm-controlled conditions. The hypothesis was tested that microbial stimulation observed in the presence of a soil invertebrate would be due to the utilization of additional nutritive substances (secretion and excretion products) that it provides. Changes in microbial activity were monitored by measuring simultaneously CO2 release and protozoan population density. The increase in CO2 released in the presence of earthworms was found to result from both earthworm respiration and enhanced microbial respiration. The stimulation of microbial activity was confirmed by a significant increase in protozoan population density, which was 3–19 times greater in the presence of earthworms. The respiratory rate of L. terrestris was estimated to be 53 μl O2 g–1 h–1. Earthworm respiration significantly correlated with individual earthworm weight, but there was no correlation between the increase in microbial respiration and earthworm weight. This finding does not support the hypothesis given above that enhanced microbial respiration is due to utilization of earthworm excreta. A new hypothesis that relationships between microbial activity and earthworms are not based on trophic links alone but also on catalytic mechanisms is proposed and discussed.

Biodegradation of the Acetanilide Herbicides Alachlor, Metolachlor, and Propachlor

Alachlor, metolachlor, and propachlor are detoxified in biological systems by the formation of glutathione-acetanilide conjugates. This conjugation is mediated by glutathione-S-transferase, which is present in microorganisms, plants, and mammals. Other organic sulfides and inorganic sulfide also react through a nucleophilic attack on the 2-chloro group of acetanilide herbicides, but the products are only partially characterized. Sorption in soils and sediments is an important factor controlling the migration and bioavailability of these herbicides, while microbial degradation is the most important factor in determining their overall fate in the environment. The biodegradation of alachlor and metolachlor is proposed to be only partial and primarily cometabolic, and the ring cleavage seems to be slow or insignificant. Propachlor biodegradation has been reported to proceed to substantial (> 50%) mineralization of the ring structure. Reductive dechlorination may be one of the initial breakdown mechanisms under anaerobic conditions. Aerobic and anaerobic transformation products vary in their polarity and therefore in soil binding coefficient. A catabolic pathway for chloroacetanilide herbicides has not been presented in the literature because of the lack of mineralization data under defined cultural conditions.

Effect of external resistance on bacterial diversity and metabolism in cellulose-fed microbial fuel cells.

External resistance affects the performance of microbial fuel cells (MFCs) by controlling the flow of electrons from the anode to the cathode. The purpose of this study was to determine the effect of external resistance on bacterial diversity and metabolism in MFCs. Four external resistances (20, 249, 480, and 1000 Ω) were tested by operating parallel MFCs independently at constant circuit loads for 10 weeks. A maximum power density of 66 mW m(-2) was achieved by the 20 Ω MFCs, while the MFCs with 249, 480, and 1000 Ω external resistances produced 57.5, 27, and 47 mW m(-2), respectively. Denaturing gradient gel electrophoresis analysis of partial 16S rRNA genes showed clear differences between the planktonic and anode-attached populations at various external resistances. Concentrations of short chain fatty acids were higher in MFCs with larger circuit loads, suggesting that fermentative metabolism dominated over anaerobic respiration using the anode as the final electron acceptor.

Oxidation of chalcopyrite by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans in shake flasks

Chalcopyrite oxidation was evaluated with two acidophilic thiobacilli that are important in bioleaching processes. Acidithiobacillus thiooxidans in pure culture did not oxidize CuFeS2 but oxidized externally added S0 in the presence of CuFeS2. Acidithiobacillus ferrooxidans released Cu2+ and soluble Fe from chalcopyrite, and the time course lead to a gradual passivation of chalcopyrite whereby Cu2+ dissolution leveled off. Fe3+ acted as a chemical oxidant in CuFeS2 leaching and was reduced to Fe2+. Parallel bacterial re-oxidation of Fe2+ contributed to a high Fe3+/Fe2+ ratio and an increase in redox potential. Chemical oxidation of chalcopyrite was slow compared with A. ferrooxidans-initiated solubilization. X-ray analysis revealed new solid phases: (i) jarosite, found in solids from A. ferrooxidans cultures and in chemical controls that initially received Fe2+ or Fe3+, and (ii) S0, found mostly in iron-amended A. ferrooxidans culture and the corresponding chemical controls.

Anaerobic conversion of microalgal biomass to sustainable energy carriers – A review

This review discusses anaerobic production of methane, hydrogen, ethanol, butanol and electricity from microalgal biomass. The amenability of microalgal biomass to these bioenergy conversion processes is compared with other aquatic and terrestrial biomass sources. The highest energy yields (kJ g(-1) dry wt. microalgal biomass) reported in the literature have been 14.8 as ethanol, 14.4 as methane, 6.6 as butanol and 1.2 as hydrogen. The highest power density reported from microalgal biomass in microbial fuel cells has been 980 mW m(-2). Sequential production of different energy carriers increases attainable energy yields, but also increases investment and maintenance costs. Microalgal biomass is a promising feedstock for anaerobic energy conversion processes, especially for methanogenic digestion and ethanol fermentation. The reviewed studies have mainly been based on laboratory scale experiments and thus scale-up of anaerobic utilization of microalgal biomass for production of energy carriers is now timely and required for cost-effectiveness comparisons.

Bacterial leaching of complex sulfide ore samples in bench-scale column reactors

Abstract Several variables were examined in column bioleaching of a complex sulfide ore material which contained chalcopyrite, pentlandite, pyrite, pyrrhotite and sphalerite as the main sulfide minerals. Samples were used with varying proportions of pyrrhotite, pyrite, quartzite (low acid consumption) and skarn (high acid consumption). The experiments were carried out using bench-scale column leaching reactors which were inoculated with acidophilic, Fe- and S-oxidizing bacteria, initially derived from the source mine water. Leaching rates in sterile controls were negligible. In inoculated columns new solid phases (covellite, jarosite, Fe (III) oxide and elemental sulfur) were formed. Acid consumption was highest under low pH and low redox potential conditions. The solubility of ferric iron was controlled by jarosite and an Fe (III) hydroxide (initially amorphous). The leaching rates of Co (from pyrite and pentlandite), Cu (chalcopyrite), and Zn (sphalerite) showed a tendency to increase with dissolved ferric iron concentration. The leaching of Ni (from pyrrhotite and pentlandite) did not correlate with the concentration of ferric iron in solution. Microscopic counts of bacteria in solution, deemed insufficient to represent total bacterial counts, showed a tendency to be higher at the lower pH and intermediate redox potential ranges. Trickle-leaching conditions yielded higher acid production and redox-potential values compared with flood leaching. The leaching rates of Co, Cu, Ni and Zn each responded differently to redox potential and pH regimes. The accelerating effect of a decreasing particle size on the metal leaching rates was amplified by low pH values.

Biodegradation of atrazine in surface soils and subsurface sediments collected from an agricultural research farm

The purpose of the present study was to assess atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) mineralization by indigenous microbial communities and to investigate constraints associated with atrazine biodegradation in environmental samples collected from surface soil and subsurface zones at an agricultural site in Ohio. Atrazine mineralization in soil and sediment samples was monitored as 14CO2 evolution in biometers which were amended with 14C-labeled atrazine. Variables of interest were the position of the label ([U-14C-ring]-atrazine and [2-14C-ethyl]-atrazine), incubation temperature (25°C and 10°C), inoculation with a previously characterized atrazine-mineralizing bacterial isolate (M91-3), and the effect of sterilization prior to inoculation. In uninoculated biometers, mineralization rate constants declined with increasing sample depth. First-order mineralization rate constants were somewhat lower for [2-14C-ethyl]-atrazine when compared to those of [U-14C-ring]-atrazine. Moreover, the total amount of 14CO2 released was less with [2-14C-ethyl]-atrazine. Mineralization at 10°C was slow and linear. In inoculated biometers, less 14CO2 was released in [2-14C-ethyl]-atrazine experiments as compared with [U-14C-ring]-atrazine probably as a result of assimilatory incorporation of 14C into biomass. The mineralization rate constants (k) and overall extents of mineralization (Pmax) were higher in biometers that were not sterilized prior to inoculation, suggesting that the native microbial populations in the sediments were contributing to the overall release of 14CO2 from [U-14C-ring]-atrazine and [2-14C-ethyl]-atrazine. A positive correlation between k and aqueous phase atrazine concentrations (Ceq) in the biometers was observed at 25°C, suggesting that sorption of atrazine influenced mineralization rates. The sorption effect on atrazine mineralization was greatly diminished at 10°C. It was concluded that sorption can limit biodegradation rates of weakly-sorbing solutes at high solid-to-solution ratios and at ambient surface temperatures if an active degrading population is present. Under vadose zone and subsurface aquifer conditions, however, low temperatures and the lack of degrading organisms are likely to be primary factors limiting the biodegradation of atrazine.

Fluorescence microscopy for visualization of soil microorganisms—a review

Direct microscopic observation of microorganisms is an important tool in many microbial studies. Such observations have been reported for Protozoa, fungi, inoculated bacteria, and rhizosphere microorganisms but few studies have focused on indigenous bacteria and their spatial relationship within various microhabitats. Principles and applications of epifluorescence microscopy and confocal laser scanning microscopy for visualization of soil microorganisms in situ are reviewed. Both cationic and anionic dyes (also commonly referred to as fluorochromes if they are fluorescent) have been used based on their ability to bind to specific cellular components of microbial cells. Common fluorochromes used for imaging of microbial cells include acridine orange, ethidium bromide, fluorescein isothiocyanate, 5-(4,6-dichlorotriazinyl) aminofluorescein, 4′,6-diamidino-2-phenylindole, europium chelate, magnesium salt of 8-anilino-1-naphthalene sulfonic acid, and calcofluor white M2R. Combining fluorescence staining techniques with soil thin section technology allows one to obtain images of microorganisms in situ. Soil texture and the procedures used for resin embedding are important factors affecting the quality of stained soil thin sections. Indeed, general limitations of applying fluorescence microscopy to soil ecological studies are the non-specific binding of dyes to the soil matrix and the autofluorescence of some soil components. The development of fluorescent in situ hybridization and confocal laser scanning microscopy techniques provides new potential for microbial distribution studies.

Catalytic effects of silver in the microbiological leaching of finely ground chalcopyrite-containing ore materials in shake flasks

Abstract The microbiological leaching of copper ores was evaluated with samples that contained chalcopyrite (CuFeS 2 ), pyrite (FeS 2 ), pyrrhotite (Fe 1− x S), and sphalerite (ZnS) in varying proportions as the main sulfide minerals. The solubilization of copper from chalcopyrite was slow in contrast to the rapid solubilization of zinc. The addition of up to 30 mg/l silver, either as a sulfate or nitrate salt, enhanced the bacterial leaching of copper from chalcopyrite. The positive catalytic effect was related to the concentration of the silver added. The enhancement of the copper leaching due to the silver addition was negligible in the absence of bacteria. Only trace concentrations of silver were detected in leach solution samples. The leaching of iron and zinc was inhibited by silver addition and a transient period of depressed Eh was typically associated with this phase. The addition of silver also enhanced the bacterial leaching of a purified chalcopyrite sample. Increased solubilization of copper and iron was obtained concurrently with the formation of sulfate. Mass balance studies and stoichiometric calculations indicated elemental sulfur formation and the precipitation of iron and sulfate during the leaching. Potassium jarosite [KFe 3 (SO 4 ) 2 (OH) 6 ] was identified by X-ray diffraction in Fe(III)-containing precipitates.