Even nanofiltration (NF) plus ultraviolet (UV) disinfection is not enough to be sure of removing some persistent pharmaceuticals from wastewater, a study in Sweden has found.
In a paper, Nanofiltration and ozonation for potable water reuse: a pilot study of pharmaceutical removal, presented at the Universitas 21 International Graduate Research Conference: Sustainable Cities for the Future in Melbourne and Brisbane, Australia (29 November – 5 December 2009), Lena Flyborg of Lund University stated, “From a sustainable outlook, persistent substances should be removed from the environment and the water cycle.”
Flyborg was studying wastewater reuse and looked at a volume reduction factor (VRF) of 60, which she said, would provide a reasonable volume of retentate and a large quantity of advanced treated wastewater for reuse purposes.
“Substances with a molecular weight of over 300 g/mol were reduced to between 30% and 90% at VRF 60 although the retention of pharmaceuticals by the NF was lower than desired,” she concluded. “However, in combination with ozone, the reduction is comparable to reverse osmosis and UV with a reduction of 99% expressed as the total sum of pharmaceuticals. Even low molecule weight substances, MW < 200 g/mol, are removed although the main removal occurred in the ozonation." Nevertheless, she warns, the metabolites and degradation byproducts of pharmaceuticals are of concern. “Their toxicity may be similar or even higher than the parent substance and may not be detected during analysis (Nikolaou, et al., 2007),” she writes. “At volume reduction factor 60, the retentate volume is reasonable to handle in a post treatment step and high in concentration of trace substances, but to achieve higher retention of low molecular substances a tighter nanofilter or reverse osmosis is required.”