Paul H. Smith

Enhancement of anaerobic methanogenesis from napiergrass by addition of micronutrients

Mesophilic anaerobic digestion of Napiergrass (Pennisetum purpureum Schum.), supplemented with nitrogen and phosphorous, resulted in a low rate of methane production and high volatile fatty acid (VFA) concentrations. Daily addition of micronutrients — nickel, cobalt, molybdenum, selenium and sulfate (as a sulfur source) — increased methane production by approximately 40% and significantly decreased the VFA concentrations.

Isolation and Characterization of a Thermophilic Marine Methanogenic Bacterium, Methanogenium thermophilicum sp. nov.†

A new species of thermophilic marine methanogenic bacteria is described. Cells of this species occurred as irregular cocci, singly or in pairs, and did not possess flagella. Colonies were translucent, beige in color, and circular with entire edges. Either formate or hydrogen and carbon dioxide could serve as a substrate for growth and methane formation, whereas ethanol, methanol, acetate, propionate, and pyruvate could not. The temperature for optimum growth was 55°C, with minimal growth below 37°C and an upper temperature limit of 65°C. The pH for optimum growth was 7.0. Sodium chloride was required for growth; the concentration for optimum growth was 0.20 M. The minimum generation time was 2.5 h. The deoxyribonucleic acid base composition was 59 mol% guanine plus cytosine. The name Methanogenium thermophilicum is proposed for this organism. The type strain is CR-1 (= ATCC 33837 = DSM 2373).

Conversion of biomass into methane gas

Land, marine and agricultural residues were subjected to a bioassay for an ultimate methane yield. Bioassays were performed in 250 ml serum bottles, incubated at 35°C. Methane yields were calculated from the percent methane in the gases formed and the total volume of gas produced. Methane yields from woody plants were lower in general than from other plant resource groups. High methane yields were obtained from several aquatic plants, some crop residues, and some root and tuber plants. Because of potentially high biomass productivity and high methane yields, water hyacinth (Eichhornia crassipes (Mart.) Solms) and Napiergrass (Pennisetum purpureum L.) were selected for intensive study. Methane yield varied among different groups, various species within each group and different parts of the same plant species. Treatment of plants with various nutrients, especially N, during the growth period and the age of the plants at harvesting time affected the methane production.

Ecology and microbiology of biogasification

Abstract The biodegradation of organic matter to form methane and carbon dioxide requires the interactions of diverse populations of bacteria. The roles of each of these organisms in the process and how they interact with each other is understood only in a rudimentary way. This paper describes the investigation of the microbial ecology of the anaerobic degradation of biomass feedstocks.

Methanogenesis from Propionate in Sludge and Enrichment Systems

The biological formation of methane from organic matter is a complex microbiological process involving many physiologically dependent relationships between and among a diversity of heterotrophic fermentative and methanogenic bacteria. The methanogenic metabolism of all organic matter leads to the formation of the same types of intermediates namely H2, C02, and formate, acetic, propionic, and butyric acids. These compounds are, in turn, converted directly or indirectly to methane by methanogenic bacteria alone or acting together with non-methanogenic heterotrophs. These latter organisms may be syntrophic partners of the methanogens or simply members of a broader food-chain. Estimates on the sum:total of the fermentative contributions by these few metabolic intermediates account for 100% of the methane formed in a typical digestor. The importance of acetate as a direct methanogenic intermediate is already well established (5,6). Evidence points to a more complicated role played by the metabolism of butyrate and propionate in this fermentation. The main focus of the present paper is to examine the role of propionate in methanogenesis not only to re-assess its importance as a source of methane or methanogenic precursors in digestors but also to examine the biochemical and physiological basis for its conversion to methane.

Effects of addition of soluble oxidants on the thermophilic anaerobic digestion of biomass to methane

Bioconversion of polymeric substrates in anaerobic digesters is slow. Exploratory research was conducted on the effects of the addition of soluble oxidants to a thermophilic, anaerobic, semicontinuous stirred tank reactor (CSTR) fed a biomass feedstock. After adaptation, added nitrate was quantitatively reduced to ammonia and isotopelabeling experiments confirmed that denitrification reactions did not occur. Addition of sulfate to a continuous nitrate amended digester resulted in sulfate accumulation, whereas sulfate addition to nonnitrate-amended digesters resulted in sulfate reduction. These results support the hypothesis that nitrate is preferentially reduced in the presence of sulfate and nitrate.

Emended Description of Strain PS (= OGC 70 = ATCC 33273 = DSM 1537), the Type Strain of Methanococcus voltae

The isolation and characterization of Methanococcus voltae PST (= OGC 70T = ATCC 33273T = DSM 1537T) (T = type strain) are described.