The removal of phenols from wastewaters at crude oil production fields is one of the most important challenges in the Arauca-Field of ECOPETROL S.A. (Saravena, Arauca). Based on the review of available technologies for wastewaters treatment with variable phenol concentrations above maximum allowable limits, both at National and International levels, a combined alternative using biological (biodegradation) and physical (aeration - photo oxidation) technologies was considered. The implementation of this combination of technologies allowed the crude oil production field to comply with phenol concentrations at the discharge, obtaining higher than 99% removal efficiency and being consistently lower than the maximum allowable limit set by environmental authorities.
Laboratory analysis of the production wastewater from the Arauca crude oil production field had reported phenol concentrations coming out of the treatment system ranging between 2,43 and 8,77 mg/L, well above the maximum value stipulated by the environmental authorities of 0,2 mg/L (Colombian Decree 1594 of year 1984, from the Health Ministry, 1984). This situation was consistently occurring before the Arauca production field was handed over to ECOPETROL in 2005 for operation; in 2004, the regional environmental authority, CORPORINOQUIA, had imposed a preventive suspension measure to the operating company at that time, requiring a revision and increasing efficiency of the treatment system in order to maintain the discharge permit of the Field, and making viable to continue production operations.
ECOPETROL urgently required to implement an improvement of the treatment system for the industrial residual wastewaters in the field in order to comply with regulatory requirements; thus, the use of physical agents (Aeration and photolysis) that chemically destroys phenol molecules, taking them to less polluting by-products, combined with biological processes for the Bioremediation of phenol in waters, utilizing specialized phenol bacteria (isolated and identified at ECOPETROL - ICP laboratories), was an interesting approach to be used at oil production fields for eliminating phenol concentrations in residual effluents. The combination of the processes allowed phenol mineralization (that is, the destruction of the polluting agent), with efficiencies higher than 99% at laboratory scale.
Once implemented at field scale at the wastewater treatment facilities existing on the field, removal efficiencies where consistent during the evaluation period, with phenol removal greater than 99.2% for the two-month evaluation after steady state was reached; phenol concentration at the discharge was as low as 0.014 mg phenol/L (almost 15 times lower than the maximum allowable limit standard of 0,2 mg/l), obtaining the goal of the Colombian regulation in a two-day retention time oxidizing basin.
Theory and Definitions.
The improvement of the Industrial wastewater treatment system is based on the use of physical and biological agents (Parra, 2001) that chemically destroy the phenol molecules, transforming those to less polluting by-products (carbon dioxide and water) - via photolysis, eliminating the polluting agent according to the process depicted in Figure 1 (Hernandez-Moreno).