(225i) Sonication Treatment of Sump Water Containing Diesel Fuel

Pervasive use of diesel fuel around rail yards impacts stormwater, by increasing petroleum releases to surface waters. On-site treatment of diesel sump water generally involves gravity oil-water separation. However, oil-water separators cannot meet National Pollution Discharge Elimination System (NPDES) stormwater discharge standards for oil and grease because they best remove “free” oil, not emulsified oil. Oil-water gravity separation treatment is least effective during stormwater runoff events. An on-site, cost-effective treatment technology treatment technology of diesel sump water is lacking. 

This research had as its objective to determine sonication’s potential to treat diesel laden stormwater. Sonication effectively oxidizes and pyrolyses a wide range of hydrocarbons in aqueous solution. A mass balance, using gravimetry and chromatography, determined the physical-chemical fate of diesel range organics (DRO). The rate of DRO decrease as a function of sonication time was investigated. Bench-scale sonication results from an initial diesel fuel concentration of 203 mg/L achieved the NPDES discharge level of 15 mg/L within 10 minutes treatment time. Sonication of diesel fuel produced carbon monoxide, short-chain hydrocarbon gases, short-chain hydrocarbons in aqueous solution, solid hydrocarbon precipitates, and residual diesel range organics. After 20 minutes treatment of No.2 diesel fuel (198 mg/L, 203 mg/L, and 2033 mg/L) all produced carbon monoxide and short-chain carbon compounds (< C6) in the gas phase. This indicated that lysis and oxidation of the diesel fuel hydrocarbons occurred. Evidence of diesel fuel hydrocarbon lysis was found in the sequence of changing chromatograms from each initial concentration’s subjugation to sonication over a period of 20 minutes. The chromatograms showed a decrease of hydrocarbons in the diesel fuel range and a simultaneous shift of carbon compounds appearing the shorter (< C10) region of the chromatogram and “shouldering” into the solvent peak. There was a shift of the longer carbon chains to shorter carbon chains as sonication time increased from 0 to 10 minutes.

Sonication was more energy intensive per unit mass treated than oil water separation. However, sonication’s [potential to eliminate peripheral costs required by oil-water gravity separation may prove cost effective.