Ação de biossurfactantes como coletores naturais na melhoria da eficiência do processo de tratamento de águas oleosas por flotação

Abstract

Oil, although it is the propeller of world economic development, generates diverse types of effluents and wastes, often complex and difficult to treat. The production of oily water effluents has caused environmental problems for several industries. Physical-chemical processes such as centrifugation and ultrafiltration can be effective when used to separate oils and greases but are inefficient when oils are emulsified. The dissolved air flotation (DAF) process, on the other hand, has been successfully used in the treatment of wastewater. This physicochemical separation technique uses small amounts of collectors that facilitate the adhesion of the particles and, consequently, the separation of the pollutants, improving the efficiency of the process. On the other hand, these chemical collectors are toxic, a factor that represents the generation of other environmental pollutants. Thus, biosurfactants, biodegradable and non-toxic amphipathic molecules produced by microorganisms, present themselves as promising collectors in increasing flotation efficiency. In this sense, the present work had as objective of carrying out an experimental study to investigate the gravitational separation of oily emulsions using the DAF process with the addition of biosurfactants. Initially, a biosurfactant was produced by the bacterium Pseudomonas aeruginosa UCP 0992 grown in 0.5% corn steep liquor and 4.0% of vegetable oil residue in a bioreactor, using a Rotational Central Compound Design (RCCD) in order to optimize the cultivation conditions for maximum yield. The best results were achieved in the fermentation condition with 1.0 vvm aeration, 3.0% of the inoculum at 225 rpm for 120 hours, resulting in a surface tension of 26.5 mN/m and a yield of 26 g/L of biosurfactant. The biosurfactant was then characterized as a glycolipid with a Critical Micellar Concentration (CMC) of 600 mg/L. Tests with the biosurfactant under temperature variations, heating time, pH and addition of salt demonstrated the stability of the biomolecule. Kinetic and static tests with motor oil adsorbed on sand demonstrated removals of 90 and 80%, respectively. Experiments of oil degradation by the bacterium and by the combination of bacteria and biosurfactant were also carried out on samples of sand and sea water. In both cases, the oil degradation reached levels higher than 90% in the presence of the biosurfactant and its producing species. After its characterization, the crude biosurfactant was applied as a collector to a bench DAF prototype built in acrylic. The flotation experiments followed a DCCR, having as independent variables the oily water flow, the microbubble water flow, the aqueous biosurfactant solution flow and the biosurfactant concentration and as a variable response the oil separation efficiency. The isolated and potassium sorbate formulated biosurfactant was also tested in the prototype after optimization of the operating conditions. The results showed that the biosurfactant increased the separation efficiency of the oil by the DAF process from 65 to 95% and that there were no great differences between the biosurfactant forms used in the system. Two biosurfactants produced by the bacteria Pseudomonas cepacia CCT6659 and Bacillus cereus 1615 were applied in the treatment of oily effluent from a thermoelectric plant, obtaining, as results, percentages of removal of 94 and 80%, respectively. It was concluded that the use of biosurfactant as a collector in flotation is a promising alternative in the treatment of oily waters generated in the industrial environment.