Recent advances in technologies for removal and recovery of selenium from (waste)water: A systematic review

Selenium (Se) is distributed into different environmental compartments by natural and anthropogenic activities, and generally discharged in the form of selenate [SeO2xe213;4 ] and selenite [SeO2xe213;3 ], which are both toxic. Physicalchemical and biological treatment processes have been reported to exhibit good treatment efficiencies for Se from aqueous streams, only a few demonstrated to achieve effluent concentrations <5 mu g/L. Moreover, there are only a few numbers of studies that describe the progress in technological developments over the last decade. Therefore, to unify the state of knowledge, identify ongoing research trends, and determine the challenges associated with available technologies, this systematic review critically analyses the published research on Se treatment. Specific topics covered in this review include (1) Se chemistry, toxicity, sources and legislation, (2) types of Se treatment technologies, (3) development in Se treatment approaches, (4) Se recovery and circular economy and (5) future prospects. The current research has been found to majorly focused on Se removal via adsorption techniques. However, the key challenges facing Se treatment technologies are related to the presence of competing ions in the solution and the persistence of selenate compared to selenite during their reduction.