Tank-based bioremediation of petroleum waste sludges

Petroleum waste sludges are treated in a continuous flow multistage slurry bioreactor system that operates at relatively short residence times with minimal loss of volatile constituents. The paper presents data for both pilot‐ and commercial‐scale versions of the process applied to the treatment of petroleum industry wastes of the classifications primary separation sludge (F037), API separator sludge (K051), dissolved gas flotation float (K048), and slop‐oil emulsion solids (K049). The process is shown to meet the EPA Universal Treatment Standards (UTS). The pilot‐scale system treated petrochemical‐based tarry wastes that contained volatile and semi‐volatile petroleum hydrocarbons in combination with a variety of chlorinated compounds, including polychlorinated biphenyls. The commercial‐scale system included centrifugation to recover recyclable oil and reduce sludge volume; slurry‐phase biotreatment to degrade hazardous organic constituents and convert these to carbon dioxide, water, and less toxic intermediates; and, finally, dewatering of the residual, biotreated sludge before off‐site disposal. These petroleum waste sludges are initially treated to recover oil and generate solid cake at approximately 50 wt % moisture. The solids are slurried with active cultures of facultative anaerobic bacteria, and treated in tank‐based slurry bioreactors before being disposed of in a hazardous waste landfill. The process is shown to meet UTS criteria for volatile organics (i.e., benzene through xylenes); polycyclic aromatic hydrocarbons (PAHs), including naphthalene through benzo(a)pyrene; and phenolics. The most challenging treatment targets were the PAHs, which were present at concentrations significantly above the regulatory criteria. The higher molecular weight PAHs, including the four‐ring compounds of pyrene, benzo(a)anthracene, and chrysene, were effectively treated at destruction efficiencies greater than 90%.