Utilização de tratamento físico e biológico conjugados empregando reatores de diferentes escalas na remediação de solo contaminado por biodiesel

Abstract

The search for renewable energies and sustainable processes has made the biodiesel became an important fuel in the energetic matrix. In relation to the environment, biodiesel has important advantages compared to petroleum diesel it has greater biodegradability and low environmental impact. However, the increasing production and consumption of biodiesel has created a need to develop technologies for treating contaminated areas with this fuel. Bioremediation, a process that transforms through biological activity, contaminants in inert substances, is the form of treatment most applied for the remediation of contaminated soils with fuel. However, this method has limited application by factors such as high concentration of the contaminant or unfavorable environmental conditions for microorganisms. In such cases, it is reasonable to use a combination of two or more treatments to achieve the necessary efficiency to meet the environmental standards. A procedure that can be applied as a pretreatment before the bioremediation is the removal of contaminants from soil by physical treatment of washing. The objective of this study was to evaluate the removal of the pollutant load in the soil contaminated with biodiesel, combining techniques of physical and biological treatment. The physical treatment was performed by an agitation system of turbine Rushton, using the reuse water from a manufacturing industry as the basis of extraction solution. In the washing pretreatment, for the system using the surfactant Tween 80 (0.25% w/v), 60% solids concentration and 60 minutes of stirring, were obtained biodiesel removal percentages above 70%. In the case of not using the surfactant, the best result was shown by setting a 30% solids concentration and 35 minutes stirring. The removal percentage obtained in this case was near 65%. By separation of oil-water phases, it was able to recover about 43% of removed soil biodiesel and acid analysis, moisture and calorific value indicated that the recovered biodiesel has characteristics that allow its reuse. The treatment of the effluent from the washing step was done by biological process using the mixed culture C1 previously adapted into medium containing the contaminant. After 11 days of treatment, the concentration of biodiesel in the effluent approached zero and the value of the total organic carbon became constant with a decrease of up to 75.4%. The techniques used in bioremediation were biostimulation with temperature, humidity and nutrients (N and P) controls and bioaugmentation in two types of bioreactors: a) rotating bioreactor in laboratory scale (0.3 kg), b) bioreactor type rotary drum on a pilot scale (15 kg). The mixed culture inoculated soil was the same used in treatment of the liquid effluent. After 14 days of bioremediation, was obtain a cell concentration of approximately 1010 CFU/g soil for bacteria and fungi, showing that there was an adaptation of the microorganisms to soil. The concentration of the contaminant in the soil was determined by analysis of total petroleum hydrocarbons. The results indicated the percentage biodegradation above 90% in 35 days for treatments with rotating lab scale bioreactor and the same percentage in 70 days for the rotating pilot scale bioreactor.