In a world where demands for freshwater are ever-growing, wastewater remediation becomes a global concern. Especially, water, which is contaminated by oil, dyes, poses challenges to the management of water resources. The development of innovative processes for wastewater treatment is still a major obstacle. With regard to its fast removal rate and environmental compatibility, cellulose aerogel composites are recently considered as a potential contributor for water remediation. In this study, cellulose aerogel composites are fabricated using the sol-gel method from two-agroindustrial wastes: pineapple leaf fibers and cotton waste fibers in alkali-urea solution followed by freeze-drying. The prepared cellulose aerogel composites are extremely lightweight with a low density (0.053−0.069 g.cm−3) and high porosity of nearly 95%. It is worth noting that the mechanical strength of the cellulose aerogel composites is remarkably improved with their Young’s modulus increasing by 5-9 times compared to that of the previous aerogel composites using polyvinyl alcohol as a binder. The as-synthesized aerogel composites are directly applied to adsorb cationic methylene blue and exhibit a maximum adsorption uptake of 34.01 g.g-1. The methyltrimethoxysilane-coated cellulose aerogel composites also show their ability to deal with oil pollution with a maximum oil adsorption capacity of 15.8 g.g−1 within only 20 sec. Besides the oil removal, our developed cellulose aerogel composites have demonstrated their capability in treating dye-contaminated wastewater for the first time based on their evidenced ability to eliminate methylene blue.