Rapid Measurement of Chemical Oxygen Demand through Microwave Digestion Compared with Thermal Reactor Digestion

In a conventional method for determination of the chemical
oxygen demand (COD), organic compounds are oxidized by potassium dichromate in acidic
condition and thermal digestion (150°C, 2 hr). Whereas microwave produces heat through
rapid rotation of polar molecules and ionic polarization, microwave digestion was
investigated for rapid measurement of COD in present study.
Methods: In this experimental study, in order to compare the thermal and microwave
digesters for COD determination, 243 standard samples of potassium hydrogen phthalate
solution and raw wastewater and effluent samples were studied according to standard methods
based on the colorimetry of reduced chromium ion. The results were analyzed by Wilcoxon
test.
Results: The mean COD obtained from microwave digestion (360 Watt, 5 min) had no
significant difference with the one determined by thermal reactor (150 °C, 2 hr.). Energy
consumption of thermal reactor and microwave for determination of COD in each sample was
determined as 736 and 30 W.hr, respectively. Therefore, the energy consumption and
digestion time of thermal reactor in COD determination were about 24 fold higher than the
microwave digestion.
Conclusion: Application of microwave is preferred to the thermal reactor in terms of the time
and energy consumption due to its catalytic ability in chemical oxidation.