Abstract
The concentration of hexavalent chromium (Cr(VI)), a toxic environmental pollutant and carcinogen, was determined in samples collected from Nacogdoches Wastewater Treatment Plant (NWWTP) using ion chromatography and UV-visible spectrophotometry (IC, UV-Vis). On reaction with 1,5-diphenylcarbazide (DPC) Cr+6 forms a 1,5-diphenylcarbazide-Cr(VI) complex, which is then analyzed at 530 nm and 540 nm, respectively. Via ion chromatography Cr(VI) concentrations were in the range of 0.00190±0.0020 and 0.0010±0.0006 ppm at the influent and effluent, respectively. With the use of standard addition wastewater samples were spiked with a 0.5 ppm Cr(VI) standard of various amounts and subsequently analyzed with UV-Vis spectrophotometry. The spiked concentrations gave Cr(VI) concentrations in the range of 0.0090±0.0060 ppm and 0.0040±0.0061 ppm at the influent and influent wastewater, respectively. The determined Cr(VI) concentrations through the ion chromatography and UV-Vis spectrophotometry are below the maximum USEPA contaminant concentration of 0.1 ppm. From the analysis, the NWWTP efficiently removes Cr(VI) before discharge into the environment through La Nana Creek. The removal efficiency for Cr(VI) was determined to be ≥92.8% along the wastewater treatment stages from the influent (aeration stage) to the effluent stages prior to discharge into the La Nana Creek.
Highlights
Chromium metal (Cr) occurs naturally in the environment and has both beneficial and potential human risks
Due to the low sensitivity to low Cr(VI) concentrations and low detection limits of Cr(VI) in wastewater samples, no pink color developed on complexation with 1,5-diphenylcarbazide
In the present study ion chromatography and UV-Vis spectrophotometry were used to assess the Cr+6 concentrations from the Nacogdoches Wastewater Treatment Plant, in East Texas, USA, along the treatment stages
Summary
Chromium metal (Cr) occurs naturally in the environment and has both beneficial and potential human risks. Cr exists in many oxidation states with Cr(III) and Cr(VI) being the primary existing oxidation states in the environment. Cr(III) is an essential nutrient for maintaining lipid, insulin, and glucose metabolism and its deficiency may lead to diabetes [1]. Of the many Cr species, hexavalent chromium (Cr(VI)) is one of the most toxic, especially when compared to trivalent chromium [2]. Carcinogenic Cr(VI) and other Cr(VI) forms are used in various industries including leather tanning, electroplating, painting, and metallurgy industries. Determination of total chromium is important, the speciation of metals is much more important for environmental impact studies [3]
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