an iron containing bioreactor for treating explosive compounds and other organics in contaminated surface water is disclosed . the bioreactor can be located either on - ground or in - ground at a location across which contaminated surface water flows . in one configuration the reactor is made up of indigenous microbes , acetate , a low density iron - containing bed , and contains anaerobic zones in at least one portion of the flowpath . the reactor reduces the concentration of explosive compounds to below 10 ppb and also maintains this explosive compound reduction level for a period of at least one year without replenishing the microbes or iron .