The constant search for productive improvements in the paper industry and the growing awareness of society about the problems derived from the use of fossil-based materials, are pushing the research efforts towards the development of renewable alternatives. On the one hand, several studies reported on lignocellulosic biomass as a sustainable alternative due to its high renewability, abundance, biodegradability, and low cost. On the other hand, the sludge produced during water treatments in a paper industry is a common residue which is usually discarded but can still contain high amounts of lignocellulosic material. The present study explores the revalorization of an industrial by-product coming from the water-treatment operations in a paper mill. The residue is used to obtain a nanocellulosic biomaterial, using cellulase-assisted enzymatic treatments in combination with mechanical processes. The results show that enzymatic treatments improve the processing of fibrillar nanocellulose (NCF), with an increase in the hydrophobic behavior of the NFC, giving rise to transparent films with reduced whiteness, in contrast to those which were simply refined. However, the obtained films showed a reduced tensile resistance. The enzymatic action prior to refining improves the obtaining of smaller fibres and increases the percentage of fines. Thus, a more homogeneous film formation is obtained, compared to a later enzymatic action. Several films with an increasing NFC content were produced and analyzed. Results indicate that an increasing NFC content rises the film density, air barrier, transparency, and water permeability and decreases whiteness and tensile strength. The study demonstrates that it is technically possible to use a waste from a paper wastewater treatment plant to produce NFC