*3.2. Removal of Phenolic Compounds*

The concentration of total phenolic compounds in the initial AL effluent and in AL effluent after fungal treatment was analysed. The phenolic compounds cause severe pollution of surface and ground water, soils, and vegetation. Its presence has a negative effect on microorganisms due to its high antibacterial activity [35,36].

As is shown in Figure 4, the best efficiencies of phenolic compound removal were reached with the inoculation of *P. chrysosporium* in E1, where around 30% of phenolic compounds were degraded after 10 days of treatment reaching values of 91 mg/L. This percentage of removal was slightly lower when glucose was added (E2), obtaining final removals of 25%. For the non-inoculated samples with fungus (C1 and C2), the amount of phenolic compounds removed was lower, with removal percentage of 12% in both cases. Results proved that the fungus inoculation increases the degradation of phenolic compounds with removal percentages almost three times greater than in the non-inoculated samples. However, higher efficiencies have been reported by other authors when the AL effluent was previously sterilised.

Elisashvili et al. [23], who treated a diluted and sterilised olive pomace effluent by submerged fermentation with *Cerrena unicolor*, reported a removal of phenolic content of around 80%. Additionally, this fungus showed a good capacity to release laccases, which are involved in the degradation of phenolic compounds. The low removals achieved in this study it could be because a non-sterilised AL effluent. Moreover, low laccase activity has been reported for *P. chrysosporium* [24]. García et al. [35] reported a 92% total phenol degradation using *P. chrysosporium* to treat a sterilised OMW supplied with a nitrogen source. Additionally, great phenolic removals were obtained when AL was dried, and the concentrate was treated. For example, Sampedro et al. [37] reported removals around 85% using the fungus *Phlebia* sp. immobilized in polyurethane sponge, while 43% was achieved when the effluent was treated by free mycelia.

**Figure 4.** Changes in total phenolic content for non-inoculated tests C1 (-) and C2 (-), and inoculated tests E1 (-) and E2 (-). The standard deviation (SD) of the experimental data were in all cases less than 4% of mean value.
