Treatment of Wastewaters Generated by Surfactant-Enhanced Washing of Soils in an Aerobic Biofilter Inoculated with a Consortium of Hydrocarbon Degraders.
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Date
2013-10
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Abstract
Aims: The aims of this work were 1) To evaluate the performance of a submerged
biofiltration system for the treatment of a surfactant-enriched wastewater that had been
generated by a soil washing process. 2) To evaluate the effect of the flux and organic load
over the performance of the system. 3) To determine the microbial evolution as an effect
of the flux at different lengths of the biofilter by using a denaturing gradient gel
electrophoresis (DGGE) analysis.
Study Design: A three factorial design was used to evaluate the effect of different fluxes
and organic loads over the performance of a continuously operated submerged aerobic
biofilter. The DGGE technique was employed to determine microbial changes in the
biofilter.
Place and Duration of Study: The study was carried out at the Bioprocess Laboratory,
Bioprocesses Department UPIBI-IPN, Mexico. The experimental stage lasted
approximately eight months and the DGGE analysis four months more.
Methodology: Contaminated soil was physicochemical and microbiologically
characterized. A total of 70 kg of contaminated soil was washed using a 1:3 ratio soil/surfactant solution (0.5% Sulfopon 30-SP30). The surfactant-enriched wastewater
was then treated in a submerged biofilter. The biofiltration system consisted of a column
with a length of 50 cm and diameter of 12 cm. The biofilter was packed with tezontle with
an average diameter of 0.2-0.4 cm and 70% void space. The biofilter working volume was
4.5 L. The samples of the packing material for the DGGE analysis were obtained from the
ports located along the biofilter: at the wastewater inlet, at the middle of the column and at
the outlet. After DNA extraction with a Power Soil DNA Isolation Kit (MO BIO), PCR
(polymerase chain reaction) analysis was conducted. The 16S rRNA gene was amplified
using universal bacterial primers. The data obtained by DGGE analysis for the microbial
population developed in the biofilter were further analyzed by the Jaccard similarity
coefficient.
Results: The soil contained 14,704 mg/kg TPH. BTEX compounds were not found, and
only two different PAHs were found in the soil samples: benzo-fluoranthene and
benzopyrene, at concentrations of 0.1280 and 0.0682 mg/kg of soil, respectively. During
the surfactant-aided soil washing, the highest removal percentage of the oil removed from
the soil was 59% with 0.5% SP30. The wastewater generated after the soil washing
process contained, in average 1,329 mg COD/L and 211 mg/L of grease and oil. Higher
COD removals were obtained at a flux of 0.4 L/h for both of the COD initial
concentrations. While the highest removal was 78.27%, determined at an initial COD
concentration of 300 mg/L. When applying fluxes of 0.28 and 0.40 L/h at a higher initial
COD concentration, the COD removals were increased; this was not the case for a flux of
0.63 L/h. For a given initial COD concentration, the removal efficiencies were higher for
lower fluxes. Analysis of the similarity between the microbial populations for varying fluxes
and levels along the length of the biofilter was determined by the Jaccard (JI) index. The
results showed that the initial microbial populations (t0) have low similarities with the
developed microbial populations at the different conditions tested.
Conclusion: Both the flux and the initial COD concentration had an impact on COD
removal and the microbial concentration in the column. The COD removal percentages
were similar at fluxes of 0.28 and 0.63 L/h. The highest removal percentage of 78.27%
was obtained at a flux of 0.4L/h; this finding was in agreement with the highest microbial
count and the specialization of microbial populations (less diversity). In general, it was
shown that the flux had an effect on changes in microbial population. Greater effects were
observed on the microbial population due to the position along the reactor, e.g., the
greatest differences were found at the different levels of the biofilter.
Description
Keywords
Biofilter, DGGE, heavy oil fraction, surfactants
Citation
Zacarías-Salinas M, Garcia-Peña E I, Torres L G. Treatment of Wastewaters Generated by Surfactant-Enhanced Washing of Soils in an Aerobic Biofilter Inoculated with a Consortium of Hydrocarbon Degraders. British Biotechnology Journal. 2013 Oct; 3(4): 471-484.