Biodegradation of High Concentrations of Benzene and Diesel in a Fixed-Film Reactor

Abstract

The degradation of benzene in groundwater at concentrations as high as 2,000 mg L −1 was studied using a four-column trickling-flow fixed-film biological reactor with recirculation. A decrease in the content of benzene was achieved, its concentration falling to 0.55 µg L −1 . On the contrary, high levels of diesel fuel were not diminished sufficiently with this mode of operation of the reactor. Thus, a submerged reactor was tested as a modification to the conventional trickling-flow configuration. This modified fixed-film reactor was effective when high loadings of diesel were present as an emulsion. The concentration of diesel was reduced from 2,000 to 0.12 mg L −1 after 8 days of treatment. In both cases, the reactors were packed with a carbonaceous material and were operated in semibatch mode with recirculation. The final concentration of benzene fell below the permissible limit established by Mexican law, and the results for both pollutants also met the concentration limits required by the German law for drinking water, 0.001 mg L −1 for benzene and 0.1 mg L −1 for total hydrocarbons.

Biofilm Fixed Film Systems

“…A submerged reactor was tested by Bravo and Spyra [58] as a modification to the conventional trickling-flow configuration. This modified fixed-film reactor was effective when high loadings of diesel were present as an emulsion.…”

Integral Approach for Improving the Degradation of Recalcitrant Petrohydrocarbons in a Fixed-Film Reactor

“…Sampling was made according to the Mexican standard NOM-EM-138-ECOL-2002 and stored at 4°C until use. An inoculum adapted to degrade diesel hydrocarbons for a previous research was also used (Bravo et al 2009). …”

“…The microbial consortium inoculated in the column for the biofilm growth experiments had a prior adaptation process which followed the methodology explained in previous experiments (Bravo et al 2009): a mixture of microorganisms extracted from soil and water samples was added in a batch medium with diesel to suitable growth conditions for the biomass. This experiment determines if the initial density of microorganisms was adequate for degradation.…”

“…This concentration was based on analysis of typical wastewater form petrochemical refineries. In previous studies, a trickling-flow fixed-film reactor with recirculation presented problems of high adsorption of diesel in the package medium, which provoke a lack of bioavailability; this problems were avoided by using a submerged fixed-film column which allows the degradation of diesel in high concentrations (up to 2000 mg L −1 Bravo et al 2009). The biodegradation of diesel were monitored in the trickle-bed fixed-film submerged column.…”

“…This is because the immobilization of biomass promotes the biological stability (Horn and Mongenroth 2006), as reflected in the decrease of the following parameters: (a) competition of the native microorganisms (Decho 2000), (b) death of microorganisms, (c) effect of extreme changes in the pH, and (d) effect of toxic compounds (Debarati et al 2005). Also, the cost of operation has to be considered; therefore, it would be desirable to use an inexpensive package material (Venus et al 2000;Bravo et al 2009). Furthermore, it is important to consider the origin of the microbial consortium inoculums that will compose the biofilm, for example previous studies showed successful results in fixed-film reactors with autochthonous microorganisms isolated from contaminated sites (Winkelmann et al 2003).…”