**4. Conclusions**

Biotreatment with white-rot fungus *Phanerochaete chrysosporium* is useful to degrade AL waste. When the non-inoculate AL was incubated at 26 ◦C, 27% of the sCOD was removed in 4 days, whereas the inoculation of fungus allowed the achievement of a sCOD degradation of 60% over the same time. The addition of glucose as an easy carbon source did not enhance the sCOD degradation. The addition of *P. chrysosporium* also allowed a reduction of the colour index of the residue close to 60%. In all the conditions tested, including a control test without inoculation, a reduction in the sBOD5 and in the reducing sugar content was observed after the treatment. However, the biodegradability index decreased, more highly in the inoculated effluent than those in the absence of inoculation. Finally, the treatment of the diluted AL with the fungus allowed degradation of 32% of the total phenols initially present in the effluent, whereas the endogenous microflora could only degrade around 15% of phenolic content. Results obtained in this study open the possibility of using *P. chrysosporium* fungus in the bioremediation of low-biodegradable wastes from the olive oil industry.

**Author Contributions:** Conceptualization: A.I.D., M.I., A.L. and M.D.; methodology: A.I.D., M.I., A.L. and M.D.; validation: A.I.D., M.I. and A.L.; formal analysis: A.I.D., M.I. and A.L.; investigation: A.I.D. and M.I.; data curation: A.I.D. and M.I.; writing—original draft preparation: A.I.D.; writing review and editing: A.L. and M.D.; visualization: A.I.D. and M.I.; supervision: A.L. and M.D.; project administration, M.D.; funding acquisition, M.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was co-financed by Spanish MINECO (Project CTM2015-63864-R) and Foundation for the Promotion of Applied Scientific Research and Technology in Asturias (Project FC-GRUPIN-IDI/2018/000127). Ana Isabel Díaz acknowledges an FPI grant from Spanish MICINN (BES-2016-077963).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


**Manasik M. Nour 1, Maha A. Tony 2,3 and Hossam A. Nabwey 1,2,\***


**Abstract:** The ever-increasing technological advancement and industrialization are leading to a massive discharge of hazardous waste into the aquatic environment, calling on scientists and researchers to introduce environmentally benign solutions. In this regard, the current work is based on introducing Fuller's earth, which is regarded as an environmentally benign material, as an innovative Fenton oxidation technology to treat effluent loaded with Levafix Dark Blue dye. Initially, Fuller's earth was chemically and thermally activated, then subjected to characterization using a field-emission scanning electron microscope (FE-SEM) augmented with an energy-dispersive X-ray analyzer (EDX) and Fourier transform infrared (FTIR). This detailed the morphologies of the samples and the functional groups on the catalyst leading to the reaction with the dye. Fuller's earth, augmented with hydrogen peroxide, was then introduced as a photo-Fenton oxidation system under UV illumination for dye oxidation. Moreover, a response surface mythological analysis was applied to optimize the most effective operational parameters. The experimental data revealed that the optimal Fuller's earth dose corresponded to 1.02 mg/L using the optimal H2O2 of 818 mg/L at pH 3.0, and the removal efficiency reached 99%. Moreover, the thermodynamic parameters were investigated, and the data revealed the positive ΔG and negative ΔS values that reflect the non-spontaneous nature of oxidation at high temperatures. Additionally, the negative ΔH values suggest the occurrence of the endothermic oxidation reaction. Furthermore, the reaction followed the second-order kinetic model. Finally, the catalyst stability was investigated, and reasonable removal efficiency was attained (73%) after the successive use of Fuller's earth reached six cyclic uses.

**Keywords:** wastewater; clay; Fuller's earth; Levafix Dark Blue dye; oxidation; Fenton
