In this study, we describe the development of microbial inoculants for the bioremediation of hydrocarbon-contaminated soils through the enrichment of hydrocarbonoclastic populations in municipal solid waste compost (MSWC). Respirometric analyses were performed along with quantification of total heterotrophic bacteria and ester-linked fatty acid methyl ester (EL-FAME) profiling of the microbial communities o f the inoculants. CO 2 -emission rate increased sharply when the compost received application of water plus gasoline or diesel. After 8 (compost diesel) and 12 days (compost gasoline), we observed a significant increase in the number of heterotrophic bacteria. In inoculants receiving gasoline, FAME markers of fungi predominated throughout the incubation period (18 days). By the end of the incubation period, an increase in FAMEmarker for gram-positive bacteria and a decrease for gram-negative bacteria and actinobacteria were observed. In biodegradation trials (data not shown), the inoculants were very efficient, removing over 99% of hydrocarbons from a heavy soil (73% clay) contaminated with either diesel or gasoline (17,000 mg·Kg ﹣1 and 15,000 mg·Kg ﹣1 , respectively). Inoculants based on MSWC enriched in hydrocarbonoclastic microorganisms may be an effective alternative to improve bioremediation in hydrocarbon-contaminated soils.
Bioremediation has been applied to accelerate the biodegradation of contaminants and rehabilitate the contaminated environment to a condition similar to that found before contamination, either in terms of biodiversity or ecosystem functions [
The use of bioaugmentation generates much contradiction between the researches. Some studies have demonstrated that biodegradation is accelerated by inoculation [
In this study, the enrichment of hydrocarbonoclastic microbial populations was conducted under uncontrolled environmental variables such as temperature and humidity, in order to favor the selection of populations with higher adaptability to environmental variables that affect the survival and biodegradation activity. Moreover, we performed enrichment of a mixed microbial population without isolation in culture media. It was considered, for the adoption of this strategy, that uncultivable microorganisms can also play a role in hydrocarbon biodegradation.
In recent studies, the use of organic waste in biostimulation and bioaugmentation of soils contaminated with hydrocarbons hasproduced satisfactory results [
The substrate used for the development of inoculants was MSWC obtained from the composting facility of the municipality of Coimbra, MG, Brazil. The compost was sieved through a 5-mm sieve and analyzed for its physical and chemical properties (
The concentration of gasoline and diesel suitable for enrichment of hydrocarbonoclastic microbial populations was determined by applying these fuels to MSWC in doses of 7500, 15,000, and 37,500 mg∙Kg−1 dry weight for gasoline and 8500, 17,000, and 42,650 mg∙Kg−1 dry weight for diesel. The material was mixed with a spatula and analyzed for CO2 evolution in a respirometer equipped with an infrared detector with intermittent air flow (Sable System, NE, USA). The MSWC received new applications of fuels every 5 days, at the same initial concentrations. The influence of moisture on the biodegradation of hydrocarbons was evaluated under two humidity conditions: no moisture adjustment and moisture fixed at 60% of the water-holding capacity (WHC). Subsequent moisture adjustments of the least treatment were made when the moisture content reached 40% WHC. The C: N: P ratio was adjusted with ammonium sulfate to 100:10:2. The microcosms were incubated at 30˚C for 14 days without stirring. Compost not receiving gasoline or diesel was used as control. The experimental design was a completely randomized 4 × 2 factorial for each source of hydrocarbon (four doses of gasoline or diesel and two moisture level), with three replicates for each treatment.