RESUMO
When a new wastewater treatment plant is being designed by computer simulation, detailed data about organic fractions of influent wastewater [measured as chemical oxygen demand] are usually not available, but knowledge of the typical ranges of these fractions is indispensable. The influent chemical oxygen demand fractions can substantially influence the results of simulation-based design such as reactor volumes, solids residence time, effluent quality, oxygen demand, sludge production, etc. This article attempts to give an overview of wastewater organic fractions as modeling parameters and presents new chemical oxygen demand fractionation results from Hungary. According to the data from literature, the ratio of chemical oxygen demand components in raw wastewater is very different and the average composition is as follows: Inert particulate = 17.1%, slowly biodegradable = 57.9%, inert soluble = 7.8% and readily biodegradable = 17.5%. The Hungarian wastewater samples were analyzed according to STOWA [Dutch foundation for applied water research] protocol and the obtained results were not much different from those of literature [inert particulate = 23.7%, slowly biodegradable = 49.8%, inert soluble = 4.6% and readily biodegradable = 21.9%], but some typical characteristics were observed