Design of sludge drying package pilot for removal of excess sludge in petrochemical industries: Heavy metals determination in sludge by polarography and atomic absorption spectrometry

In this research, according to the high amount of sludge in a petrochemical company, an iron package type of drying sludge bed was made/designed with carbon steel. Then, the drying sludge pond was filled with layers of sand with different mesh sizes. The excess sludge from the sedimentation pond was passed over this bed, and the amount of sludge removed by the bed was obtained at %96. The values of heavy metal and microbial forms were determined usingthe proposed method based on activated sludge after was tewater treatment. For the validation process, 10 mL of deionized water (DW) was mixed with 1.0 g of dried sludge with pure nitric acid (2%HNO3), and then the solid phase was filtered with the Whatman filter(WF). The concentration of heavy metals (As, Cd, Cu, Pb, Hg, Mo,Ni, Co, Se, Zn) in the remaining solution of sludge (mg kg^-1) and was tewater (μg L^-1) was extracted/ separated based on sulfur-dopedgraphene oxide adsorbent (SDGO) by solid-phase microextraction procedure (SPME) before being determined by the flame and hydride generation atomic absorption spectrometry (F-AAS; HG-AAS) which had similar range to the polarography analysis. The limit of detection(LOD), linear range (LR) and preconcentration factor (PF) for (As,Hg) and (Cd, Cu, Pb, Mo, Ni, Co, Se, Zn) were obtained (0.016μgL^-1;3.3μg L^-1), (0.05-10μg L^-1;10-1000μg L^-1), and 10.0 by HG-AAS and F-AAS, respectively.