Chapter 43: Environmental Microbiology & Bioremediation

Applied Environmental Microbiology explores the vital functions of microbes in natural systems, focusing on decontamination, energy production, and remediation. Water purification is critical for controlling disease transmission and involves sequential steps: sedimentation, coagulation or flocculation (using chemicals like alum and lime to precipitate particles and microorganisms), filtration (e.g., rapid sand filters), and final disinfection (chlorination or ozonation). Water quality is routinely monitored for indicator organisms like coliforms using methods such as the Colilert defined substrate test or advanced molecular techniques like quantitative PCR and 16S rRNA amplification. Wastewater treatment is a controlled sequence designed to mimic and intensify natural self-purification. It progresses through primary treatment (physical removal of solids) and secondary treatment (biological degradation of dissolved organic matter, often measured by Biochemical Oxygen Demand, or BOD) . Tertiary treatment, employed to prevent ecological disruption, removes inorganic nutrients, often utilizing processes such as denitrification and the anammox reaction to yield nitrogen gas (N2). Home systems typically use septic tanks for anaerobic liquefaction, followed by aerobic biological oxidation in a leach field. In the emerging field of Microbial Fuel Cells (MFCs), bacteria generate electricity by coupling the anaerobic oxidation of biomass to the direct transfer of electrons to an anode. These MFCs offer potential applications in both water purification and power generation. Bioremediation harnesses the degradative activities of microorganisms to clean contaminated environments. This often involves stimulating indigenous microbes, for example, by adding limiting nutrients such as nitrogen and phosphorus, a technique used successfully during the Exxon Valdez oil spill cleanup. Biodegradation can result in minor molecular change, fragmentation, or complete mineralization. A significant initial step for degrading recalcitrant pollutants like organochlorides is reductive dehalogenation (replacing or removing halogens). Furthermore, microbes are utilized in bioleaching, employing acid production to solubilize metals for recovery from low-grade ores.