Microbial degradation of hydrocarbons in the environment.

Microbial degradation of petroleum hydrocarbons: an environmental perspective.

Bioremediation of soil contaminated with polynuclear aromatic hydrocarbons (PAHs): A review

Bioremediation, involving bioaugmentation and/or biostimulation, being an economical and eco-friendly approach, has emerged as the most advantageous soil and water clean-up technique for contaminated sites containing heavy metals and/or organic pollutants. Addition of pre-grown microbial cultures to enhance the degradation of unwanted compounds (bioaugmentation) and/or injection of nutrients and other supplementary components to the native microbial population to induce propagation at a hastened rate (biostimulation), are the most common approaches for in situ bioremediation of accidental spills and chronically contaminated sites worldwide. However, many factors like strain selection, microbial ecology, type of contaminant, environmental constraints, as well as procedures of culture introduction, may lead to their failure. These drawbacks, along with fragmented literature, have opened a gap between laboratory trials and on-field application. The present review discusses the effectiveness as well as the limitations of bioaugmentation and biostimulation processes. A summary of experimental studies both in confined systems under controlled conditions and of real case studies in the field is presented. A comparative account between the two techniques and also the current scenario worldwide for in situ biotreatment using bioaugmentation and biostimulation, are addressed.

Bioaugmentation and biostimulation strategies to improve the effectiveness of bioremediation processes.

Much of the early work on the microbial utilization of petroleum hydrocarbons, conducted in the 1950s and 1960s, was done with the goal of using hydrocarbons as substrates for producing microbial biomass (Shennan, 1984; Champagnat, 1964; Champagnat and Llewelyn, 1962; Cooney et al., 1980; Ballerini, 1978). Petroleum was viewed as an inexpensive carbon source and single cell protein (microbial biomass) was considered as a possible solution to the perceived impending world food shortage for the predicted global population explosion. Applied studies focused on optimizing microbial growth on low- to middle-molecular-weight hydrocarbons. These studies developed fermentor designs for large-scale single cell protein production with agitation and aeration systems that permitted high rates of microbial growth on soluble and highly emulsified hydrocarbon substrates. High-speed impellers (>800 rpm) were used to mix the hydrocarbon substrates and high rates of forced aeration with baffles within the fermentors were used to supply the molecular oxygen necessary for the microbial utilization of hydrocarbons (Hatch, 1975; Prokop and Sobotka, 1975). Optimized microbial growth in these fermentors consumes as much as 100,000 g hydrocarbon/m3 per day (Kanazawa, 1975).

Hydrocarbon Biodegradation and Oil Spill Bioremediation

A laboratory study was conducted with the aim of evaluating and optimizing the environmental parameters of "landfarming", i.e., the disposal by biodegradation in soil of oily sludges generated in the refining of crude oil and related operations. Oil sludge biodegradation was monitored by CO2 evolution and by periodic analysis of residual hydrocarbons. The parameters studied were soil moisture, pH, mineral nutrients, micronutrients, organic supplements, treatment rate, teratment frequency, and incubation temperature. Oil sludge biodegradation was optimal at a soil water-holding capacity of 30 to 90%, a pH of 7.5 to 7.8, C:N and C:P ratios of 60:1 and 800:1, respectively, and a temperature of 20 degrees C or above. Addition of micronutrients and organic supplements was not beneficial; sewage sludge interfered with hydrocarbon biodegradation. Breakdown of the saturated hydrocarbon (alkane and cycloalkane) fraction was the highest at low application rates, but higher application rates favored the biodegradation of the aromatic and asphaltic fractions. An application rate of 5% (wt/wt) oil sludge hydrocarbon to the soil (100,000 liters/hectare) achieved a good compromise between high biodegradation rates and efficient land use and resulted in the best overall biodegradation rate of all hydrocarbon classes. Frequent small applications resulted in higher biodegradation than single large applications. Two 100,000-liter/hectare (255 barrels per acre) or four 50,000-liter/hectare oil sludge hydrocarbon applications per growing season seem appropriate for most temperate zone disposal sites.

R Bartha

Papers

Effect of environmental parameters on the biodegradation of oil sludge.