Biogeochemical Behaviours Of Indigenous Microbially Mediated CO₂ Sequestration Process In Deep Saline Aquifers

The burning of fossil fuels has substantially increased the levels of CO₂ in the atmosphere from 228 ppm in the preindustrial age to 400 ppm at present,leading to significant global climate change.Thus,research on reducing CO₂ emission for the fossil fuel-dependent development patterns became more important.Carbon capture and storage in deep saline aquifers is considered as a promising potential technology for reducing carbon emissions.In deep saline aquifers,the numerous populations and various metabolic activities make microbes having the potential ability of changing biogeochemical process.Until now,the researches about the potential influence on the microbial mediated CO₂-brine-sandstone interactions is limited,and the biogeochemical behaviors of them are not clear.In this study,laboratory experiments were conducted to investigate microbially mediated CO₂-brine-sandstone interactions in steel reactors under actual geologic CO₂ sequestration conditions.The main objectives were?1?to simulate and characterize the shifts in structure and diversity of microbial community after supercritical CO₂?sc CO₂?injection,?2?to evaluate the biogeochemical effects on interactions in the microbially mediated CO₂-brine-sandstone systems by different predominant microbe and?3?to demonstrate the positive effects of microbe for the CO₂ sequestration in deep saline aquifers by using 16 S r RNA gene profiles,q PCR and stable carbon isotope.The research was carried out and the relevant results were achieved as follows:?1?After sc CO₂ injection,the bacterial populations and activities were strongly influenced by changes in the p H.Proteobacteria and Actinobacteria showed better tolerance to sc CO₂ injection than Firmicutes initially,and both of them were the dominant phyla after the full 180 days' experiments.Alpha index had decreased continuously during the whole process.According to the analysis of Beta diversity,microbe would be adapt to the environment after 120 days with the increase of p H in the solution,and the structure of microbial community remained stable basically.At the later period,Exiguobacterium,Pseudomonas,Citrobacter and Acinetobacter became the dominant genus with the better ability of tolerance to the acidity.?2?There was no difference in p H changes between microbially mediated CO₂-saline-sandstone interactions and the control experiments.And it was demonstrated that microbe would not alter the system p H.In the SEM images,the biofilms attached on the sandstone sample can be seen.Biofilms are microbe assemblages firmly attached to a surface,which formed and encased within self-produced extracellular polymeric substances?EPS?.In extreme environments,biofilms are the predominant way of life for most microbes because they offer structural support and protection from physical and chemical stresses.Furthermore,organic acids produced by some microbial species could increase mineral dissolution rates and released amounts of ions to the solution.?3?According to the XRD analysis,more secondary carbonates,especially siderite formed on the surface of sandstone when the experiments were microbially mediated.And the??¹³Csandstone in the microbially mediated CO₂-saline-sandstone interactions was larger than that in the control experiment,which also demonstrated it.?4?With the identity of the predominant OTUs?97% similarity?in each sample following the BLASTn search,Pseudomonas mendocina and Acinetobacter soli could accelerate the dissolution of the mineral with the ability of acid-producing.Furthermore,Pseudomonas mendocina could also accelerate the release of Fe³⁺ from mineral with the ability of producing Hydroxamate type siderophores.And Citrobacter freundii could induced the precipitation of siderite with biological reduction of Fe³⁺.Exiguobacterium sp.could use low-molecular-weight organic acids produced by other species as potential carbon source to ferment.?5?Through the PICRUST?Phylogenetic Investigation of Communities by Reconstruction of Unobserved States?,the function of “ion-coupled transporter”,“iron complex outermembrane recepter protein”,“iron complex transport system permease protein” implied the microbe may promote mineralization of secondary carbonates especially siderite by directly providing a core site for adsorbing metal ions(Ca²⁺,Fe²⁺).