New ultrasound assisted chemical oxygen demand determination

A new method for the chemical oxygen demand (COD) determination assisted by ultrasonic radiation has been evaluated for the first time. The suggested method uses an instrumentation simpler and cheaper than the previous ones used for the same purpose. With this preliminary version of the method the optimized experimental conditions are: high ultrasonic power (143 W, 95% of maximum nominal power; 126.5 W/cm2 of power density); high sulphuric acid concentration (> 60%); and a sonication time of 2 min. Under these conditions this first prototype shows the same limitations as the official COD method as regards the type of organic compounds. It works successfully with easily oxidative organic matter (sodium oxalate, glucose and salicylic acid) but the COD values obtained with more difficult organic matter are poor. When the ultrasonic assisted method is applied to real waste waters the precision is statistically not different to that of the conventional semi-micro method but the COD values obtained lie between 50 and 60% of the values obtained with the conventional semi-micro method. Hence, the use of the ultrasonic radiation for COD determination seems to be an interesting and promising alternative to the conventional ones but still much more research efforts must be done in order to improve the instrumental set-up. The suggested direction of these developments must be a more efficient interaction between the ultrasonic radiation and the sample.