Review on the occurrence, fate and removal of perfluorinated compounds during wastewater treatment

Perfluorinated compounds (PFCs) consist of a fully fluorinated hydrophobic alkyl chain attached to a hydrophilic end group. Due to their wide use in several industrial and household applications, they have been detected in numerous Sewage Treatment Plants (STPs) during the last ten years. The present review reports the occurrence of 22 PFCs (C4-C14, C16, C18 carboxylates; C4-C8 and C10 sulfonates; 3 sulfonamides) in municipal or/and industrial wastewater, originating from 24 monitoring studies. PFCs levels in sewage sludge have also been reported using data from 12 studies. Most of the above monitoring data originate from the USA, North Europe and Asia and concern perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA), while limited information is available from Mediterranean area, Canada and Australia. PFCs concentrations range up to some hundreds ng/L and some thousands ng/g dry weight in raw wastewater and sludge, respectively. They are not significantly removed during secondary biological treatment, while their concentrations in treated wastewater are often higher compared to raw sewage. Their biodegradation during wastewater treatment does not seem possible; whereas some recent studies have noted the potential transformation of precursor compounds to PFCs during biological wastewater treatment. PFCs sorption onto sludge has been studied in depth and seems to be an important mechanism governing their removal in STPs. Concerning tertiary treatment technologies, significant PFCs removal has been observed using activated carbon, nanofiltration, reverse osmosis or applying advanced oxidation and reduction processes. Most of these studies have been conducted using pure water, while in many cases the experiments have been performed under extreme laboratory conditions (high concentrations, high radiation source, temperature or pressure). Future efforts should be focused on better understanding of biotransformation processes occurred in aerobic and anaerobic bioreactors and result to PFCs formation and on the application of advanced treatment technologies under conditions commonly found in STPs.