Practice question

Land farming represents oldest, simplest ex situ bioremediation for oily sludges from refineries and crude pits where biodegradable fraction high. Approach involves excavation, spreading soil in thin layer 30 to 50 cm over lined area with berms preventing runoff, periodic tilling every one to two weeks improving aeration 10-fold, breaking clods and mixing nutrients like urea, diammonium phosphate correcting deficiency. Indigenous degraders Pseudomonas aeruginosa, Arthrobacter, Rhodococcus and Aspergillus carrying alkane hydroxylases and catechol cleavage proliferate 10 to 100 fold oxidizing hydrocarbons aerobically with irrigation moisture. Low energy using farm equipment, solar heating, minimal infrastructure yields costs $30 to 60 per ton versus incineration $300 to 1000 per ton or slurry reactors. Limitations include large land requirement 1 acre per 10,000 tons, volatile emissions requiring BTEX air monitoring, unsuitability for high toxic metal or highly chlorinated solvent soils inhibiting biology, and seasonal dependence on temperature and rainfall limiting year-round operation in temperate zones.