Bioremediation of petroleum hydrocarbons in soil : activated sludge treatability study

Abstract

Batch activated sludge treatability studies utilizing petroleum hydrocarbon contaminated soils (diesel oil and leaded gasoline) were conducted to determine: (1) initial indigenous biological activity in hydrocarbon-contaminated soils; (2) limiting factors of microbiological growth by investigating nutrient addition, chemical emulsifiers, and cosubstrate; (3) acclimation of an indigenous population of microorganisms to utilize hydrocarbons as sole carbon source; and (4) temperature effects. Soil samples were taken from three different contaminated sites. Four sequencing batch reactors were run from site one (southern Manitoba), three from site two (northern Manitoba), and two from site three (northern Manitoba). Substrate (diesel fuel) and nutrient were added as determined by laboratory analysis of orthophosphate, ammonia nitrogen, chemical oxygen demand (COD), and total organic carbon (TOC). Substrate was made available to the bacterial mass by experimenting with the use of four different chemical emulsifiers. All reactors were also monitored with respect to other chemical, physical, and biological parameters. Laboratory analysis followed Standard Methods. Indigenous microorganisms capable of biotransforming hydrocarbons seen to be present in all the contaminated soil samples received from all sites. Microscopic analysis of reactors revealed no visibile activity at the beginning if the study and presence of flagellated protozoa, paramecium, rotifers, and nematodes at the end of a year. Nutrient requirements (nitrogen, phosphorous) and the limiting factors in microorganisms growth have been determined for each particular site. A co-substrate was used initially to enhance bacterial mass growth. Use of an emulsifier was deemed necessary initially to make the hydrocarbons available to the microbial population. Temperature effects study (site one, temperature decreased gradually from 22 oC to 12 oC) showed a decrease in removal (TOC) and an emerging presence of filamentous bacteria. A second temperature study (site two, temperature to decrease gradually from 22 oC to 4 oC) also showed a decrease in removal. Removal efficiencies, in term of chemical oxygen demand, range from 50% to 90% in reactors from site one (16 months ongoing at room temperature, no waste sludge). Acclimation of indigenous microorganisms to hydrocarbons is possible and could reduce remediation time of contaminated soils.