Practice question

Bioreactors in bioremediation function as engineered controlled systems where dissolved oxygen via sparging, agitation 100 to 500 rpm, pH 6 to 8 via dosing, temperature 20 to 35 Celsius via jackets, retention time 0.5 to 10 days, redox potential via ORP probes, and nutrient supply precisely manipulated via controllers maximizing degradation kinetics modeled by Monod equations. Configurations include stirred-tank slurry reactors 10 to 30 percent solids, packed-bed biofilters with immobilized biofilm for air and water, fluidized beds using sand carriers enhancing retention above 10 g per L, and membrane bioreactors retaining slow dechlorinators. Unlike uncontrolled natural attenuation relying on passive diffusion, open wetlands or root zones fluctuating diurnally, bioreactors provide containment preventing spread, capture off-gases via activated carbon, achieve endpoints within days to weeks. Real-time monitoring via respirometry, chromatography and qPCR of catabolic genes catA informs adaptive control optimizing aeration and feeding, though capital investment and complexity higher than in situ approaches, justifiable for industrial effluents with high contaminant loads.