Desenvolvimento de membrana reciclada para sistema descentralizado de tratamento de água com elevada concentração de ferro e manganês para abastecimento

Abstract

Recycling of Reverse Osmosis (RO) membranes by oxidative treatment is an alternative to minimize the impacts of disposal and increase access to drinking water. The objective of this research was to develop recycled membranes capable of retaining dissolved iron (Fe) and manganese (Mn) from surface water, for supply purposes. On the bench scale, end-of-life RO module, model BW30, was deconstructed to obtain membranes with approximate area of 0.64 cm². Oxidative treatment was done by sodium hypochlorite - NaClO (10-12%) immersion at exposure dose between 4,000 ppm·h and 80,000 ppm·h. Recycled membranes were tested with synthetic solution of ferric chloride (5 mg∙L-1 of Fe3+) and manganese sulfate (5 mg∙L-1 of Mn2+). The system was rated at pressures between 4 and 12 bar. Turbidity, apparent color, electrical conductivity, pH, and redox potential were also evaluated. At pilot scale, oxidative treatment was performed in the end-of-life RO module model LP-2540, whose area is 2.6 m². The performance of the recycled module was evaluated for water treatment from Paraopeba River, collected during dry and rainy periods, in continuous operation for 50 h and 1 bar pressure. Finally, the membrane recycling costs were evaluated. All recycled membranes were effective in Fe removal (> 99%), at bench scale. For Mn, it was possible to select a membrane recycling condition (33,000 ppm·h) with Mn removal satisfactory efficiency (~87%) and permeability of 7.35 L∙h-1∙m-²∙bar-1 like commercial nanofiltration membranes (7.20 L∙h-1∙m-²∙bar-1). Mn removal efficiency (> 98%) was enhanced by including pre-oxidation of the study water with NaClO (5 mg∙L-1 of Cl- and pH 8), followed by filtration through the recycled membrane (42,000 ppm·h). At pilot scale, recycled membrane (42000 ppm·h) performed like a moderately open ultrafiltration membrane with a permeability of ~39 L∙h-1∙m-²∙bar-1. Fe and Mn removals were > 99% and > 90%, respectively, with high efficiency in color and turbidity removal. Membrane recycling cost was predicted to be $11.50, considered 97% lower than available commercial membranes. Therefore, recycled membrane was shown to be efficient in removing dissolved Fe and Mn, and it is promising for decentralized water treatment for water supply.