## Results and Discussion
### Bioreactor Experiments
Figure 2: The time course of total petroleum hydrocarbons (TPHs) concentrations in water (mg/Lwater), using Pad Sentec(tm), Corksorb(tm) 01025 and Barrier Sentec(tm) carrier in the influent wastewater before starting the assays (initial time) and in the effluent wastewater after the first recirculation cycle and at days 1, 3 and 7 of operation time. (*) Significant differences between “initial time” and the rest of the sampling times. using Pad Sentectm and Barrier Sentectm carriers, which means a theoretical removal of 440.0 and 520.0 mg/Lwater. This suggests that a share of the remaining amount of hydrocarbon was biodegradable in water and the other one was retained by the carriers and subsequently degraded by the biomass developed in the bioreactor and obviously not detected in the effluents or in the carriers. In the same way, some studies have also reported that the sorption capacity of hydrophobic cork carriers was found to be 8-10 g of pollutant per gram of carrier [26]. In our study, the hydrocarbon concentration detected in the hydrophobic cork carrier was found to be only 0.08 g/gcarrier (64.4 mg/Lwater) after the bioreactors had been operating for 7 days. In this case, water hydrocarbon content in the inlet wastewater was 526.0 mg/Lwater and after 7 days of treatment 107.7 mg/Lwater and therefore the theorical removal was 418.3 mg/Lwater, so we can consider our conclusion confirmed. Determination of the hydrocarbon concentrations in the wastewater in the bioreactor after 7 days of treatment made it possible to verify the high removal capacity of the system (Figure 2). This demonstrates how the support materials inside the bioreactors work as highly efficient submerged filters, which was previously highlighted by some authors [27; 28; 29]. It is important to note that wastewater hydrocarbon removal was not only estimated in terms of TPH values but also in relation to the different hydrocarbon fractions studied. Further, after 7 days, hydrocarbon removal concentrations in the bioreactors were much higher than those quantified in the support material, thus suggesting that a considerable number of hydrocarbons was efficiently biodegraded by suspended or fixed biomass. The hydrocarbon sorption efficacy of these sorbent bioreactors was similar to those reported for other sorbents such as activated carbon, grafted cellulose and clay materials, studied under different experimental designs. However, the efficacy of the sorption is markedly influenced by the experimental conditions or the operational variables [30]. In the treatment system studied, the presence of the microorganisms inside these bioreactors improves the efficiency of the system, probably due to the shift of microbial population in response to the amount of hydrocarbon retained in the sorbent and to the variation of the hydrocarbon fraction composition. Previous results carried out in microcosms [20] suggested that hydrocarbon compounds adsorbed to the surface carrier would be used as a carbon and energy source by adhering indigenous microorganisms and consequently, support their growth and be a factor that facilitates the survival of a hydrocarbon-tolerant microbiota. For this reason, it is necessary that the carrier or the sorbent materials are firstly able to retain the hydrocarbon pollutants and secondly, they are able to build a stable and metabolically active microbiota tolerant to pollutants. In order to obtain a more complete water analysis, an ecotoxicity test was performed. [PERSON] et al. [24] reported that GI values ranged from 80 to 100 are indicative of non-toxicity and values from 50 to 80 are indicative of moderate toxicity. Results from the ecotoxicity test revealed that influent wastewater could be considered as water containing free-phytotoxic substances, with a GI index above 80. Certainly, GI in water samples after 7 recirculation cycles using Pad Sentectm, CorkSorbtm 01025 and Barrier Sentectm was around 75-78, very close to 80, so we can assure that they are not toxic water samples (Table 3).