Comparative study of different heating systems used for chemical oxygen demand determination: Convective-conductive heating, microwave radiation and ultrasound energy

MÜLLER, A.; DOMINI, C.E.; CANALS, A

Granada

Congreso; Ultrasonics International, 2003.; 2003

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Chemical oxygen demand (COD) is an important parameter in water-pollution control analysis since it is closely related to the organic contamination level of a water or wastewater sample. By definition, COD is “a measure of the oxygen equivalent to the organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant”Commonly, a silver compound is added as a catalyst to promote the oxidation of certain classes or rganic compounds. In Addition, a mercuric compound may be added to reduce the interference from oxidation of chloride ions. Dichromate has benn used to oxidize organic matter for morre than 70 years. It has been preferred over other oxidants because of is superior oxidizing ability on a large variety of samples and for its case of use. After the oxidation step is completed, the amount of dichromate consumed is determined titrimetrically of colorimetrically. In all the procedures developed a preliminary heating step of reaction mixture is needed.A convective-conductive heating method is commonly used, however this heating method presents some drawbacks, amoung them the low efficiency in heat transfer(i.e. two hours of heating es needed). For this reason new heating methods have been studied and between them are the microwave radiation and more recently ultrasonic energyThe objective of this work to optimize a rapid procedure in order to determine COD heating method present some value in water and wastewater by digestiong samples by means of both open and closed micreowave systems and specially designed ultrasound instruments.Hence, this work will present the results obtained in this comparative study or three different processes used for sample heating: (i) conventional convective-conductive, (ii) microwave radiation and (iii) ultrasound energy. Microwave radiation and ultrasound energy reduce significantly the reaction time (i.e. a few minutes) and the sample and reagents consumption (more ecological):