Determination of Hexavalent Chromium (Cr(VI)) Concentrations via Ion Chromatography and UV-Vis Spectrophotometry in Samples Collected from Nacogdoches Wastewater Treatment Plant, East Texas (USA)

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 530nm and 540nm, respectively. Via ion chromatography Cr(VI) concentrations were in the range of 0.00190 ± 0.0020 and 0.0010 ± 0.0006ppm at the influent and effluent, respectively. With the use of standard addition wastewater samples were spiked with a 0.5ppm 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 ± 0.0060ppm and 0.0040 ± 0.0061ppmattheinfluentandinfluentwastewater,respectively.ThedeterminedCr(VI)concentrationsthroughtheion chromatography and UV-Vis spectrophotometry are below the maximum USEPA contaminant concentration of 0.1ppm. From theanalysis,theNWWTPefficientlyremovesCr(VI)beforedischargeintotheenvironmentthroughLaNanaCreek.Theremoval efficiencyforCr(VI)wasdeterminedtobe ≥92.8%alongthewastewatertreatmentstagesfromtheinfluent(aerationstage)tothe effluentstagespriortodischargeintotheLaNanaCreek.