BIOCHEMICAL OXYGEN DEMAND OF SAMPLES UNDER DIFFERENT INCUBATION TIMES

Abstract

The biochemical oxygen demand (BOD) is an factor of great importance for monitoring and design of biological treatment systems, as well as a reference for legislation and verifi cation of environmental impacts. The standard measure for quantifying the organic material concentration is performed by reading after 5 days of incubation at 20 oC (?"DBO" ?_5^20) of the water sample, allowing comparisons between different authors and different climatic conditions. However, the long period needed for analysis hinders decision-making in wastewater treatment stations. Moreover, the lack of fl exibility regarding the day of determining the BOD values indicates operational problems. Few studies have attempted to relate the values of BOD obtained at different times with those measured after fi ve days. In literature there is only information between the values of?"BOD" ?_5 and the ultimate biochemical oxygen demand (UBOD), and between the?"BOD" ?_5 and chemical oxygen demand (COD). Thus, this study aimed to obtain the BOD values at different times of sample incubation, which were compared with the values of?"BOD" ?_5, assessing the possibility of relating them by correction factors in samples of sewage, swine and dairy wastewaters. The results showed that the correction factors vary with the type of wastewater, with the organic matter concentration that it presents, and with the relationship between biochemical and chemical oxygen demand (biodegradability of organic material), requiring that it be determined on a case by case basis for each situation, which is hardly feasible.