Bioremediación de aguas contaminadas con hidrocarburos mediante sistemas bio-absorbentes

Resumen

Hydrocarbon polluted waters is an environmental problem which causes serious ecological damage as well as having a negative effect on different areas (health, agriculture, fishing etc.). For this reason, it attracts interest and is a cause for concern not only for the scientific community, but also on a social and political level. One of the main sources of hydrocarbon contamination are spills or dumping, both accidental and intentional. However, there exist other larger sources of pollution due to increased persistency and frequency, for example, local and industrial effluents. The aim of this research was to treat hydrocarbon polluted waters originating from hydrocarbons and oil product storage, transport and distribution facilities. For this, bioreactors were designed inside of which absorbent materials were placed. This way, the treatment of the water was based on a hydrocarbon bioremediation process by the bacteria present in the water; said bacterial degradation was the result of combining the biodegradation carried out by the microbiota present in the water, in which the contaminant was dissolved, with the degradation carried out by the microbial population adhered to the absorbent material of the hydrocarbons that were held by these. The microbiota present in the water and adhered to the surfaces via microbiological techniques was studied, as was the formation of biofilm using scanning electron microscopy, and the evolution of the content in hydrocarbons using gravimetry and gas chromatography/ mass spectrometry. The experimental design essentially consisted of a scale-up system from a laboratory scaled tests to the installation of a pilot plant. In the first tests, a series of absorbent materials made with polypropylene fibre (Pad Sentec® and Barrier Sentec®) and granulated cork (Corksorb® 01025 and Corksorb® 03025) were selected. These were then placed in microcosms with one-litre capacity. In these, the ability of these materials to promote the formation of a degrading biofilm on a surface was studied using firstly a strain whose adhesion capacity was known, Pseudoalteromonas elyakovii, and subsequently said capacity was checked with the indigenous microbiota to the polluted site. Corksorb® 03025 was ruled out on the basis of said tests. In a second test phase, two horizontal and vertical flow setting bioreactors were designed, inside of which absorbent materials that would retain part of the hydrocarbons present in the water were installed. There were two phases in the tests. The first one was called the “treatment phase”. In this one, the water was passed through an absorbent material promoting bacterial degradation of the hydrocarbons in the actual water and their retention on the absorbent surfaces. In the second, the “biodegradation phase”, the microbial degradation by the adhered microorganisms of the hydrocarbons sorbed by the surfaces was studied. Firstly, the results highlighted the need for the horizontal flow setting bioreactor to be redesigned in future studies, as the placement of the different absorbent units in different positions favoured an unequal microbial adhesion and absorption and subsequent biodegradation of the retained hydrocarbons. On the other hand, the design of the vertical flow setting bioreactor, in which the absorbent material took up the entire section through which the water passed, favoured both microbial adhesion and the retention and degradation by the attached microbiota. On the basis of this battery of tests it was ascertained that the system made up of the vertical flow setting bioreactor using the absorbent material Pad Sentec® was the most effective for the treatment of hydrocarbon polluted waters. Based on these last results, a new test was carried out with this system treating a greater volume of water with a greater load of hydrocarbons, again obtaining satisfactory results. On the other hand, from the strains identified in the microbiota attached to the absorbent surfaces, 5 bacteria were selected and hydrocarbon degradation tests were carried out using each of them individually. The tests showed that only Brevundimonas diminuta displayed degradation ability at the expense of the other four strains. Finally, in the last stage of the scale-up process, the pilot plant based on the abovementioned vertical flow setting system was installed and started functioning. The design of the plant was made up of four bioreactors, two of which had additional aeration, the other two did not, each pair working at different flow rates. In this plant, as was the case with the tests, there were two different phases: the treatment and the bioremediation phases. The plant tests displayed again the effectiveness of the system in the treatment of hydrocarbon polluted waters. It can therefore be concluded that a system which uses bio-absorbent materials for the treatment of hydrocarbon polluted waters was developed, whose effectiveness has been proven by the results obtained in this research.