Development of a fully automatic microwave assisted chemical oxygen demand (COD) measurement device

In this work, a fast and fully automatic microwave assisted chemical oxygen demand (COD) measurement device is described. In this instrument, the absorbance of Cr(III) generated during sample oxidation is measured at 590 nm. Chemical oxygen demand values can be obtained in just 12 min. This represents a significant reduction in digestion time, compared with the standard convective-conductive method; this is mainly due to the more efficient microwave heating. The device is absolutely controlled by a personal computer (PC) and a user-friendly Labview(TM) software specially written for this application, which makes the instrument flexible, since all the experimental parameters can be modified individually. The optimized experimental conditions are 8 min, 70% (v/v), and 7 g L-1 for the digestion time, acid concentration, and silver concentration, respectively. The application range extends from 0 mg to 15,000 mg O-2 L-1, and the interference of Cl- can be removed up to 8,000 mg L-1. Particular attention has been given to the device clean-up; thereby a specific clean-up program, using 3M ammonia, was developed in order to eliminate solid particles of AgCl. Finally, the reliability of the microwave (MW) assisted device is assessed against a standard conductive-convective method by using a very complex real wastewater from a textile industry source. The automatic device has been able to cope with an industrial effluent with a great variability in COD values, chloride concentrations, and difficult-to-oxidize organic matter (e.g., phenol).