Practice question

Biopile technique represents engineered ex situ bioremediation approach combining features of landfarming and composting but under more controlled conditions for petroleum-contaminated soils. Contaminated soil excavated from source zone, homogenized by screening to remove debris, mixed with amendments such as wood chips bulking agents enhancing permeability, fertilizers adjusting C:N:P ratio to 100:10:1, water to maintain 50 to 70 percent water holding capacity, sometimes microbial inocula, and heaped into above-ground mounds 2 to 3 meters high overlying impermeable high-density polyethylene liner with leachate collection drainage and aeration piping connected to blowers supplying oxygen via positive or negative aeration. Contaminant concentration reduced through aerobic metabolic pathways mediated by alkB and catechol dioxygenase bearing bacteria at mesophilic temperatures 20 to 35 Celsius maintained without high thermophilic phase. Performance monitored via temperature probes, oxygen sensors, and chemical analysis of total petroleum hydrocarbons. Classification as ex situ reflects requirement for excavation and relocation; unlike in situ bioventing or biosparging which treat soil in place, biopiles demand material handling, space for construction, emission controls via covering, but remain cost-effective $130 to 300 per ton compared to slurry bioreactors $200 to 600 per ton, achieving cleanup within 3 to 12 months depending on recalcitrance.