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Speciation and removal of selenium (IV, VI) from water and wastewaters based on dried activated sludge before determination by flame atomic absorption spectrometry

A B S T R A C T In recent decades, large amount of pollutants enters to the environment due to development of technology. Therefore, it is necessary to use ecofriendly sorbent to eliminate pollutants. In this research, 0.5 g of a dried activated sludge (DAS) was used for speciation selenium and removal of selenite [Se(IV)] from water and wastewater samples. The effect of operating parameters such as solution pH, the amount of bio-sorbent, contact time, temperature and initial concentration of selenium were studied by flame atomic absorption spectrometry (F-AAS). Kinetic data was adjusted to the Langmuir and Freundlich kinetic equations. The resulted showed that the Langmuir equation with a correlation coefficient of 0.9825 has the best match to tetravalent selenium biosorption on DAS. The FT-IR results showed that the biosorption mechanism of Se(IV) on DAS is due to functional groups on the DAS surface (Se(IV).... DAS). For reduction of soluble selenate [Se(VI), SeO4 2−] to selenite [Se(IV), SeO3 2−], the concentrated HCl was used at 70oC (30 min). So, the Se(VI) reduced to Se(IV) and total selenium (TSe) was determined and the Se (VI) was simply calculated by difference of TSe from Se(IV) content. The method was validated based on spiking samples in water and wastewater samples by F-AAS and using HG-AAS.