Practice question

Composting as bioremediation modality exploits thermophilic and mesophilic microbial consortia developing during controlled decomposition of organic matter to co-metabolize and mineralize hazardous contaminants such as explosives trinitrotoluene, polycyclic aromatic hydrocarbons, chlorinated pesticides and petroleum hydrocarbons. System typically configured as aerated static windrows or mechanically turned piles where contaminated soil blended at 10 to 30 percent by volume with organic amendments including manure supplying nitrogen, straw providing carbon and structure, wood chips increasing porosity and sewage sludge inoculating diverse populations totaling 10^9 bacteria plus 10^6 fungi per gram comprising Bacillus subtilis, Pseudomonas fluorescens, Actinomycetes Streptomyces and fungi Phanerochaete chrysosporium, Trichoderma harzianum. Process proceeds through initial mesophilic phase 20 to 45 Celsius lasting few days where bacteria hydrolyze polymers releasing heat raising temperature to thermophilic phase 55 to 65 Celsius where extracellular lignin modifying enzymes lignin peroxidase, manganese peroxidase and laccase exhibit enhanced activity toward recalcitrant PAHs via radical generation, plus bacterial dioxygenases intensify. Turning maintains oxygen above 10 percent preventing anaerobiosis. Synergistic bacteria-fungi interactions provide complementary enzyme repertoires: bacteria perform rapid mineralization while fungi attack high molecular weight contaminants extracellularly. Final humified compost contains immobilized residues with toxicity reduction 80 to 95 percent measured via Microtox.