Biological Treatment of Petrochemical Wastes for Removal of Hazardous Polynuclear Aromatic Hydrocarbon Constituents

Abstract

Biodegradation of recalcitrant petrochemical sludges was carried out in sealed continuous tank stirred reactors (CSTR's). The specific sludge used in the research contained eight polynuclear aromatics (PNA's) cited by the United States Environmental Protection Agency (USEPA) as hazardous wastes. Benzo(a)pyrene {B(a)P} was selected in this research as the primary target contaminant due to its strong carcinogenic nature and low allowable release concentrations in sludges. Equilibrium conditions in the strongly stirred aerobic 1 litre reactors, were confirmed by daily monitoring of key control parameters which included: sludge oil & solids mass balances, B(a)P mass balances, pH, culture plating, carbon dioxide respiration, and biomass accumulation. B(a)P loadings varied from 285 mg/kg of dry feed solids to 3475 mg/kg and 10 out of 13 reactors produced solid wastes meeting the 1990 USEPA constituent concentration limit (CCL) for B(a)P of 12 mg/kg for allowable land disposal. Anionic surfactants - Triton N-101, Triton X-100 - were added to all petrochemical sludges augmented with B(a)P at mass concentrations of 1600 mg/kg and higher. All sampling and analytical protocols followed USEPA methodologies. Mass balance removals of B(a)P and other similar aromatic hydrocarbons were found to exceed 90 percent. It is concluded that the high removals of B (a) P demonstrated in aerobic bioremediations in high solids environments, will generate better engineered and more economical commercial waste minimization applications.