Tratamento de água produzida de petróleo por fungos filamentosos e microalga

Abstract

The main oil industry effluent is called produced water and has in its composition high concentrations of oil and grease (TOG), chemical oxygen demand (COD) and other compounds such as surfactants, nitrogenous compounds, phosphates, etc. With this in mind, the aim of this work was to verify the biological treatment of produced water, using filamentous fungi, individually, and in consortium with microalga in the removal of TOG, nitrogen and phosphorus. The effect of the initial TOG concentration of the effluent, varying between 312-2500 mg L-1 , of the salinity varying between 5-50 g L-1 and in different concentrations of nitrogen (25, 50 and 100 mg L-1 ) and phosphorus (around 30 mg L -1 ) were evaluated in the treatment. A synthetic effluent (modified BG-11) was used, which provided all the necessary nutrients for fungal and microalgal cultivation, with crude oil as the carbon source (characterized as light - ºAPI - rich in alkanes). The microorganisms used were the microalga Tetradesmus obliquus LCE-01 and the filamentous fungi Aspergillus niger URM 7282, Penicillium oxalicum URM 7170 and Cunninghamella echinulata, URM 7150. The initial experiments were carried out in an aerated bubble column reactor at a rate of 0.5 vvm and with 500 ppm of crude oil (synthetic effluent) using 100 µmol m-2 s -1 of light intensity (in experiments with microalgae) and room temperature between 30-35ºC, cultivating all fungi and microalgae separately and in co-cultivation and it was verified that the greatest contribution in the removal of TOG was performed by filamentous fungi an the best strain was the species Cunninghamella echinulata, reaching removal rates between 90-95%, with microbial biomass production between 250-550 mg L -1 . In this sense, the study continued only with the fungal species of C. echinulata and the microalga T. obliquus, the latter with the aim of verifying an additional contribution in the removal of other contaminants such as nitrogen and phosphorus. Since salinity is an important parameter in this type of effluent, its influence on the cultivation of these two microorganisms and was verified in the same system but using an initial TOG of 2500 mg L -1 . It was noticed that T. obliquus managed to stay alive up to concentrations of 25 g L -1 , and C. echinulata, in addition to growing in all saline concentrations tested, reaching removal rates of TOG between 80-95%, producing around 1 g L-1 of microbial biomass, these rates decreased when salinity increased. In addition, it was noticed in the two assays tested that the filamentousfungus grew with a pH stability between 6.5-7.5, while the microalga significantly raised the pH up to values of 10, which would be unfeasible for a co-culture with the filamentous fungus, thus requiring daily adjustments. Then, in the experiments varying the nitrogen concentration and verifying the removal efficiency of both nitrogen and phosphorus, an initial TOG of 2500 mg L-1 was used. High TOG removal rates were confirmed as in the previous tests (>95%), and it was noticed that the co-cultivation of the fungus with the microalgae removed higher percentages of nitrogen and phosphorus, of 63.4, 44.4 and 31.7% of the nitrogen present for the initial concentrations of 25, 50 and 100 mg L -1 , respectively; and a similar average of 36.58 ± 4.82% phosphorus for all experiments; while the fungus individually, removed around 10-15% for nitrogen and 22.28 ± 4.13% for phosphorus in all experiments, showing that the microalga contributes to the removal of additional contaminants that may be present in the effluent. In this regard, it is concluded that the work delimited important nutritional and environmental parameters that can serve as a basis for the experimental planning of a biological treatment mediated by C. echinulata alone or in its co-culture with T. obliquus in real effluent.