1. Microbially Induced Soil Cementation via Denitrification Nasser Hamdan 1, Edward Kavazanjian, Jr. 2, Bruce E. Rittmann 3 1 Graduate Research Associate, Department of Civil, Environmental and Sustainable Engineering, Arizona State University, Tempe, AZ 85287-5306; PH: (480) 727-8566; email: nasser.hamdan@asu.edu; 2 Professor, Department of Civil, Environmental and Sustainable Engineering, Arizona State University, Tempe, AZ 85287-5306; PH: (480) 727-8566; email: Edward.Kavazanjian@asu.edu 3 Regents’ Professor and Director, Biodesign Institute at Arizona State University, P.O. Box 875701 Tempe, AZ 85287-5701; PH: (480) 727-0434; email: Rittmann@asu.edunasser.hamdan@asu.eduEdward.Kavazanjian@asu.eduRittmann@asu.edu  Microbes Can Generate the Geochemical Conditions to Precipitate Cementing Agents  Cementing Agents Include Mineral Precipitates Such as Calcium Carbonate, Silicate, Iron and Aluminum Oxides  Microbial Metabolism of an Organic Carbon Source Produces bicarbonate (HCO 3 - ): CO 2(g) + H 2 O ↔ HCO 3 - (aq) + H + (aq)  Under Sustained Basic Conditions, Speciation Can Occur to Form Carbonate (CO 3 2- ): HCO 3 - (aq) + OH - (aq) ↔ H 2 O + CO 3 2- (aq)  Precipitation of CaCO 3 Occurs in the Presence of Calcium Ions and Basic Conditions: Ca 2+ (aq) + HCO 3 - (aq) + OH - (aq) = CaCO 3 (s) + H 2 O  Mineral Precipitates Form at Inter-particle Contacts Cementing Granular Soils  Mitigate Seismic Settlement and Liquefaction  Improving Foundation Performance  Controlling Groundwater Flow  Enhancing Soil Stability Without Inducing Ground Deformations Associated With Traditional Methods  Controlling Soil Erosion and Scour  May Reduce the Use of Energy Intensive Building Materials Such As Portland Cement for Soil Improvement  Non-disruptive Methods Employing Indigenous Microorganisms  Cost-effective Process Capable of Using Various Organic Carbon Substrates An Overview of Microbially Induced Soil Improvement  Denitrifying Bacteria Are Ubiquitous in the Subsurface  Denitrification Readily Occurs in Anoxic Environments  Denitrification Does Not Produce Toxic End Products  Is Thermodynamically More Favorable Than Ureolysis  Denitrification Has a Greater Carbonate Yield Than Ureolysis  Allows Nearly 100% Utilization of Electron Donor  Does Not Require Potentially Harmful Exogenous Organic Material  Optimization of Reaction Medium Required for Denitrification  Reduction of Total Dissolved Solids in the Nutrient Medium  Investigating Methods to Limit the Loss of Free Ca 2+ From the Pore Fluid in the Form of Calcium Phosphate (Ca 3 (PO 4 ) 2 )  Development and Testing of Soil Column Experiments Using a Closed-loop Pore Fluid Circulation System Employing Specialized Equipment for Continuous Monitoring The Advantages of Denitrification for Soil Improvement Potential Applications for Soil Improvement via Denitrification Comparison of Candidate Processes for Microbially Induced Cementation Microbial Process End Products Undesirable Side-Effect Bacterial Ureolysis NH 3 (ammonia)Toxic gas NH 4 + (ammonium)Readily forms toxic salts Sulfate ReductionH 2 S (hydrogen sulfide)Toxic gas Fermentation of Fatty Acids CH 4 (methane)Explosive gas DenitrificationN 2 (nitrogen)None Work-In-Progress At Arizona State University Sustainability of Microbially Induced Ground Improvement