The removal of organic dyes in aquatic media is, nowadays, a very pressing environmental problem. These dyes usually come from industries, such as textiles, food, and pharmaceuticals, among others, and their harm is produced by preventing the penetration of solar radiation in the aquatic medium, which leads to a great reduction in the process of photosynthesis, therefore damaging the aquatic ecosystems. The feasibility of implementing a process of nanofiltration in the purification treatment of an aqueous stream with small size dyes has been studied. Six dyes were chosen: Acid Brown-83, Allura Red, Basic Fuchsin, Crystal Violet, Methyl Orange and Sunset Yellow, with similar molecular volume (from 250 to 380 Å). The nanofiltration membrane NF99 was selected. Five of these molecules with different sizes, shapes and charges were employed in order to study the behavior of the membrane for two system characteristic parameters: permeate flux and rejection coefficient. Furthermore, a microscopy study and a behavior analysis of the membrane were carried out after using the largest molecule. Finally, the Spiegler–Kedem–Katchalsky model was applied to simulate the behavior of the membrane on the elimination of this group of dyes.

Sludge from drinking water treatment plants is usually disposed of in landfill sites as nonhazardous waste. However, a review of the legislation at European, Spanish, and regional levels identifies uncertainty regarding this type of waste. For example, it is unclear whether the drinking water sludge can be sent to inert landfill sites, which would be less expensive, or whether it could be reused for other purposes. According to Article 5 of Spanish Law 22/2011 on waste and contaminated soil, various physicochemical and biological parameters must be determined before alternative uses can be established. At present, sludge from drinking water treatment plants is wrongly associated with sludge from wastewater treatment plants. In this study, parameters of the sludge produced in drinking water treatment plants that may lead to a new waste status for the same are analyzed. The principal problems that may limit its reuse are its low organic matter and high silica contents.