Chapter 14: Environmental Applications of Microorganisms

Environmental Applications of Microorganisms begins by outlining the fundamental processes of modern sewage and wastewater treatment, detailing the activated sludge process and the removal of biochemical oxygen demand (BOD) and pathogens. The text explains the biochemical intricacies of anaerobic digestion for sludge treatment, describing how acid-forming bacteria and methanogenic archaea cooperate to convert organic polymers into biogas (methane and carbon dioxide) through stages of acidogenesis, acetogenesis, and methanogenesis. A significant focus is placed on advanced nitrogen removal techniques, specifically the Anammox process (anaerobic ammonium oxidation), which utilizes specific planctomycetes to convert ammonium and nitrite into nitrogen gas cost-effectively. The chapter then shifts to the challenge of xenobiotics—synthetic compounds like pesticides, PCBs, and detergents—classifying them as biodegradable, persistent, or recalcitrant, and explaining the dangers of biomagnification in food chains. The discussion expands to bioremediation strategies designed to clean up contaminated environments, including in situ treatment, composting, landfarming, and the use of bioreactors. Specific attention is given to the microbial degradation of hydrocarbons, highlighting the role of Alcanivorax borkumensis in marine oil spill remediation and the metabolic versatility of soil pseudomonads. The genetic basis of biodegradation is explored through catabolic plasmids, such as the TOL plasmid (pWW0) in Pseudomonas putida, which regulates the breakdown of toluene and xylenes via upper and lower operon pathways. The chapter also covers anaerobic degradation mechanisms, such as the fumarate addition reaction catalyzed by benzylsuccinate synthase in toluene metabolism, and halorespiration by Dehalococcoides ethenogenes to dechlorinate toxic solvents like perchloroethylene. Finally, the text details the industrial applications of bioleaching and biomining, where acidophilic chemolithotrophs like Acidithiobacillus ferrooxidans oxidize ferrous iron and sulfur to solubilize metals from low-grade ores (copper and uranium). It concludes with biological methods for detoxifying industrial effluents, such as using sulfate-reducing bacteria to precipitate heavy metals and employing biofilm trains to degrade cyanide in mining wastewater.