EFFECTS OF COOLING TIME AND MERCURY CONCENTRATION ON CHEMICAL OXYGEN DEMAND (COD) ANALYSIS IN DOMESTIC WASTEWATER SAMPLES
DOI:
https://doi.org/10.11113/aej.v16.24298Keywords:
COD analysis, Cooling time, Mercury sulfate, Chloride oxidation, COD analysis, Cooling time, Mercury sulfate, Mercury precipitates, Chloride oxidationAbstract
Chloride (Cl-) interferes with Chemical Oxygen Demand (COD) measurement, necessitating the use of mercury sulfate (HgSO4) to eliminate chloride. Typically, 33.3 g of HgSO4 is required. Excess HgSO4 introduces hazardous waste, and the effect of cooling time on COD accuracy is unexplored. This study examines the effects of cooling time and HgSO4 dosage on the accuracy of COD analysis. Water samples with a constant COD concentration were analyzed using the closed reflux method under varying chloride concentrations, cooling times, and HgSO4 dosages. The findings reveal that a reduced HgSO4 dosage of 1.67 g provides accurate results when chloride concentrations are below 1000 mg Cl-/L, even at HgSO4-to-chloride ratios below 10:1. The outcome reduces the chemical costs and hazardous waste, contributing to more sustainable laboratory practices. Higher chloride concentrations yielded elevated COD values due to chloride oxidation. The HgSO4 dosage of 33.3 g effectively mitigated chloride interference up to 2000 mg Cl-/L. Furthermore, a cooling time of 16 hours influenced COD titration when excess HgSO4 precipitated and remained in the samples, creating cloudy HgSO4 particles that interfered with endpoint detection. The findings reveal the effects of prolonged cooling time on COD measurements and contribute new information for improving COD analysis practices.
References
APHA, AWWA and WEF. 2023. Standard Methods for the Examination of Water and Wastewater. 24th ed. Washington DC: American Public Health Association. DOI: 10.2105/SMWW.2882.103
Ao, X. W., Eloranta, J., Huang, C. H., Santoro, D., Sun, W. J., Lu, Z. D. and Li, C. 2021. Peracetic Acid-based Advanced Oxidation Processes for Decontamination and Disinfection of Water: A Review. Water Research. 188: 116479. DOI: https://doi.org/10.1016/j.watres.2020.116479.
Kim, J. and Huang, C. H. 2021. Reactivity of Peracetic Acid with Organic Compounds: A Critical Review. ACS ES&T Water. 1(1):15-33.
DOI : https://doi.org/10.1021/acsestwater.0c00029
Leite, L. S., Tango, M. D., Filho, J. A. Z, Hoffmann, M. T. and Daniel, L. A. 2021. Implications of COD Analysis Use in the Peracetic Acid-based Wastewater Treatment. Water Science & Technology. 84(5): 1270-1279. DOI: https://doi.org/10.2166/wst.2021.300
Shi, X., Huang, S., Yeap, T. S., Ong, S. L. and Ng, H. Y. 2020. A Method to Eliminate Bromide Interference on Standard COD Test for Bromide-rich Industrial Wastewater. Chemosphere. 240: 124804.
DOI: https://doi.org/10.1016/j.chemosphere.2019.124804
Canelli, E., Mitchell, D. G. and Pause, R. W. 1976. An Improved Determination of Chemical Oxygen Demand in Water and Wastes by a Simplified Acid Dichromate Digestion. Water Research. 10(4):351-355. DOI : https://doi.org/10.1016/0043-1354(76)90179-2.
Dobbs, R. A. and Williams, R. T. 1963. Elimination of Chloride Interference in the Chemical Oxygen Demand Test. Analytical Chemistry. 35(8): 1064:1067. DOI: https://doi.org/10.1021/ac60201a043
Freire, D. D. C. and Sant'Anna, G. L. 1998. A Proposed Method Modification for the Determination of COD in Saline Waters. Environmental Technology. 19(12):1243-1247. DOI: https://doi.org/10.1080/09593331908616784.
Kayaalp, N., Ersahin, M. E., Ozgun, H., Koyuncu, I. and Kinaci, C. 2010. A New Approach for Chemical Oxygen Demand (COD) Measurement at High Salinity and Low Organic Matter Samples. Environmental Science and Pollution Research. 7: 1547-1552. DOI: https://doi.org/10.1007/s11356-010-0341-z.
Sousa, A.C., Lucio, M. M. L, Neto, O. F. B., Marcone, G. P., Pereira, A. F., Dantas, E. O., Fragoso, W. D., Araujo, M. C. U. and Galvão, R. K. H. 2007. A Method for Determination of COD in a Domestic Wastewater Treatment Plant by Using Near-infrared Reflectance Spectrometry of Seston. Analytica Chimica Acta. 588(2):231-236. DOI: https://doi.org/10.1016/j.aca.2007.02.022
Dubber, D. and Gray, N.F. 2010. Replacement of Chemical Oxygen Demand (COD) with Total Organic Carbon (TOC) for Monitoring Wastewater Treatment Performance to Minimize Disposal of Toxic Analytical Waste. Journal of Environmental Science and Health Part A. 45(12): 1595-1600. DOI: https://doi.org/10.1080/10934529.2010.506116
Aguilar-Torrejón, J. A., Balderas-Hernández, P, Roa-Morales, G., Eduardo Barrera-Díaz, C., Rodríguez-Torres, I. and Torres-Blancas, T. 2023. Relationship, Importance, and Development of Analytical Techniques: COD, BOD, and, TOC in Water-An Overview Through Time. SN Applied Sciences. 5: 118. DOI: https://doi.org/10.1007/s42452-023-05318-7
Kolb, M., Bahadir, M. and Teichgräber, B. 2017. Determination of Chemical Oxygen Demand (COD) Using an Alternative Wet Chemical Method Free of Mercury and Dichromate. Water Research. 122:645-654. DOI: https://doi.org/10.1016/j.watres.2017.06.034
Latif, U. and Dickert, F. L. 2015. Chemical Oxygen Demand. In: Moretto, L., Kalcher, K., editors. Environmental Analysis by Electrochemical Sensors and Biosensors. Nanostructure Science and Technology. New York: Springer. 719-728. DOI: https://doi.org/10.1007/978-1-4939-1301-5_1.
Tchobanoglous, G., Burton, F. L. and Stensel, H. D. 2003. Wastewater Engineering: Treatment and Reuse. 4th ed. Boston:McGraw-Hill.
Kim, Y. C., Sasaki, S., Yano, K., Ikebukuro, K., Hashimoto, K. and Karube, I. 2000. Relationship Between Theoretical Oxygen Demand and Photocatalytic Chemical Oxygen Demand for Specific Classes of Organic Chemicals. Analyst. 125(11): 1915-1918. DOI: https://doi.org/10.1039/B007005J
Dedkov, Y. M., Elizarova, O. V. and Kel'ina, S. Y. 2000. Dichromate Method for the Determination of Chemical Oxygen Demand. Journal of Analytical Chemistry. 55: 777-781. DOI: https://doi.org/10.1007/BF02757915.
Almutairi, M. S. 2021. Correlation of the Chemical Oxygen Demand of Water Using Hg and Hg-free COD Vials. Journal of Water Chemistry and Technology. 43: 401-406. DOI: https://doi.org/10.3103/S1063455X21050027.
Hahne, H. C. H. and Kroontje, W. 1973. The Simultaneous Effect of pH and Chloride Concentrations Upon Mercury (II) as a Pollutant. Soil Science Society of America Journal. 37(6): 813-1000. DOI: https://doi.org/10.2136/sssaj1973.03615995003700060016x.
Vyrides, I. and Stuckey, D. C. 2009. A Modified Method for the Determination of Chemical Oxygen Demand (COD) for Samples with High Salinity and Low Organics. Bioresource Technology. 100(2):979-982. DOI: https://doi.org/10.1016/j.biortech.2008.06.038.
Zhao, Y., Tang, H., Ge, X., Li, Y. and Wang, S. 2021. The Chloride Ion to the Chemical Oxygen Demand (COD) Analysis of the Influence of Different Analysis Method. E3S Web of Conferences. 236:02034. DOI: https://doi.org/10.1051/e3sconf/202123602034.
Averill, B. A. 2012. Solubility and Complexation Equilibriums. In: Averill, B. A., editors. Principles of General Chemistry. 2103-2104. Retrieved January 20, 2025, from https://2012books.lardbucket.org/.
Fritz. J. J. 1985. Thermodynamic Properties of Chloro-complexes of Silver Chloride in Aqueous Solution. Journal of Solution Chemistry. 14: 865: 879. DOI: https://doi.org/10.1007/BF00646296.
