Fenton-type advanced oxidative processes (AOP) have been employed to treat textile dyes in aqueous solution and industrial effluent. The work focused on assisting the limitations still presented by the Fenton process regarding the use of suspended iron catalysts. Soon, a nanocomposite of bacterial cellulose (BC) and magnetite (Fe3O4) was developed. It has proven to be superior to those available in the literature, exhibiting purely catalytic properties and high reusability. Its successful production was verified through analytical characterization, while its catalytic potential was investigated in the treatment of different textile matrices. In initial tests, the photo-Fenton process irradiated and catalyzed by sunlight and BC/Fe3O4 discolored 92.19% of an aqueous mixture of four textile dyes. To improve the efficiency, the design of experiments technique evaluated the influence of the variables pH, [H2O2], and the number of BC/Fe3O4 membranes. 99.82% of degradation was obtained under optimized conditions using pH 5, 150 mg L-1 of H2O2, and 11 composite membranes. Reaction kinetics followed a pseudo-first-order model, effectively reducing the organic matter (COD = 83.24% and BOD = 88.13%). The composite showed low iron leaching (1.60 ± 0.08 mg L-1) and high stability. It was recovered and reused for 15 consecutive cycles, keeping the treatment efficiency at over 90%. As for the industrial wastewater, the photo-Fenton/sunlight/BC/Fe3O4 system showed better results when combined with the physical-chemical coagulation/flocculation process previously used in the industry's WWTP. Together they reduced COD by 77.77%, also meeting the color standards (DFZ scale) for the wavelengths of 476 nm (<3 m-1), 525 nm (<5 m-1), and 620 nm (<7 m-1). Thus, the results obtained demonstrated that employing the BC/Fe3O4 composite as an iron catalyst is a suitable alternative to materials employed in suspension. This is mainly due to the high catalytic activity and power of reuse, which will reduce treatment costs.