Trace Elements Affect Methanogenic Activity and Diversity in Enrichments from Subsurface Coal Bed Produced Water

Burcu Ünal,Verlin Ryan Perry,Kuk-Jeong Chin,Mili Sheth,Vicente Gomez-Alvarez,Klaus Nüsslein

doi:10.3389/fmicb.2012.00175

Abstract

Microbial methane from coal beds accounts for a significant and growing percentage of natural gas worldwide. Our knowledge of physical and geochemical factors regulating methanogenesis is still in its infancy. We hypothesized that in these closed systems, trace elements (as micronutrients) are a limiting factor for methanogenic growth and activity. Trace elements are essential components of enzymes or cofactors of metabolic pathways associated with methanogenesis. This study examined the effects of eight trace elements (iron, nickel, cobalt, molybdenum, zinc, manganese, boron, and copper) on methane production, on mcrA transcript levels, and on methanogenic community structure in enrichment cultures obtained from coal bed methane (CBM) well produced water samples from the Powder River Basin, Wyoming. Methane production was shown to be limited both by a lack of additional trace elements as well as by the addition of an overly concentrated trace element mixture. Addition of trace elements at concentrations optimized for standard media enhanced methane production by 37%. After 7 days of incubation, the levels of mcrA transcripts in enrichment cultures with trace element amendment were much higher than in cultures without amendment. Transcript levels of mcrA correlated positively with elevated rates of methane production in supplemented enrichments (R2 = 0.95). Metabolically active methanogens, identified by clone sequences of mcrA mRNA retrieved from enrichment cultures, were closely related to Methanobacterium subterraneum and Methanobacterium formicicum. Enrichment cultures were dominated by M. subterraneum and had slightly higher predicted methanogenic richness, but less diversity than enrichment cultures without amendments. These results suggest that varying concentrations of trace elements in produced water from different subsurface coal wells may cause changing levels of CBM production and alter the composition of the active methanogenic community.

Highlights

Coal bed methane (CBM) is a form of natural gas that is trapped at large quantities in deep unmineable coal bed basins and produced from boreholes (Thielemann et al, 2004)
This study examined the effects of eight trace elements on methane production, on mcrA transcript levels, and on methanogenic community structure in enrichment cultures obtained from coal bed methane (CBM) well produced water samples from the Powder River Basin, Wyoming
This study has enhanced our understanding of trace element effects on methane production, and on the activity and diversity of methanogens in enrichments of water produced from a CBM well

Summary

Introduction

Coal bed methane (CBM) is a form of natural gas that is trapped at large quantities in deep unmineable coal bed basins and produced from boreholes (Thielemann et al, 2004). CBM is held at coal internal surfaces by the combination of physical sorption and hydrostatic pressure of subsurface water. Gas extraction is accomplished by pumping water from subsurface coal bed basins to the surface through drilled access wells that end within the coal bed. As water is pumped to the surface, methane is no longer held by the hydrostatic pressure in micro pore structures of coal beds and migrates from the subsurface coal into the water stream flowing to the well. Seventy percentage of the world’s CBM production is supplied by the United States while the remainder is produced by Australia, India, Canada, China, United Kingdom, Columbia, Russia, Ukraine, and Austria primarily from shallow to deep subsurface coal beds (Flores et al, 2008)

Objectives

Methods

Results

Conclusion