Options for reducing oil content of sludge from a petroleum wastewater treatment plant

Materials and energy recovery from oily sludges removed from crude oil storage tanks (tank bottoms): A review of technologies

Sludge and solids accumulating in crude oil storage tanks (referred as tank bottoms) reduces tank volume and requires periodic removal and disposal. Effective management of tank bottoms require considerations to reduce the toxicity of wastes and reduce potential environment impacts. This review compares alternative technologies for economical and environmentally beneficial management of oily sludges for recovery of hydrocarbons and energy with and without oil recovery. Management options with oil recovery include solvent extraction, centrifugation, surfactant oil recovery, and pyrolysis. Management options without oil recovery include incineration and anaerobic co-digestion. The selection of the appropriate technology depends on the characteristics of oily sludge, treatment capacity, as well as operation and maintenance costs. An efficient treatment can involve integration of different technologies for recovery of different oil fractions and to reduce energy demand. Technologies that utilize renewable energy (e.g., solar pyrolysis) can offset the high energy demand of pyrolysis process while recovering marketable products.

Application of Fenton process to remove organic matter and PCBs from waste (fuller's earth) contaminated with insulating oil

Polychlorinated biphenyls (PCBs) are carcinogenic to humans and can be found in fuller's earth used for the treatment of used transformer oil. This work describes an optimization of the Fenton process for the removal of contaminants from fuller's earth. The effects of pH (2.5 and 4.0), [H₂O₂] (1.47 and 2.07 mol L^-1), and [Fe²⁺] (1.7 and 40 mmol L^-1) were studied. The Fenton process efficiency was monitored using the decreases in the chemical oxygen demand (COD) and the concentrations of oil and grease, total carbon (TC), PCBs, and H₂O₂. The fuller's earth contaminated with insulating oil presented 35% (w/w) of TC, 34% (w/w) of oil and grease, 297.0 g L^-1 COD, and 64 mg of PCBs per kg. The material could therefore be considered a dangerous waste. After Fenton treatment, using a slurry mode, there was a removal of 55% of COD, 20% of oil and grease, and 20% of TC, achieved at pH 2.5 using 2.07 mol L^-1 of H₂O₂ and 40.0 mmol L^-1 of Fe²⁺. No PCBs were detected in the samples after the Fenton treatment, even using smaller amounts of Fenton reagents (1.47 mol L^-1 of H₂O₂, 1.7 mmol L^-1 of Fe²⁺, pH 2.5). The results indicated that the treated fuller's earth was free from PCB residues and could be disposed of in a simple landfill, in accordance with Brazilian PCB regulations.