Calibration of the BioWin model for N-removal: Part 1, desktop study

Abstract

This project examines the effect of certain key parameters on denitrification predictions of the BioWin® model, compared to the older UCT kinetic model and steady-state theory for activated sludge systems. It shows that earlier versions of BioWin (distributed in the period ca. 1994 to 2000 and widely used in Australia) had inappropriate default settings for certain key parameters that influence the denitrification rate. As a result, the denitrification rates predicted using the older versions of BioWin were about three times higher than the so-called K2 rate measured from bench-scale research for nitrogen-removal activated sludge systems in the UCT laboratory. Designs based on the higher denitrification rates would likely have under-sized anoxic zones and/or over-sized internal recycles, leading to higher actual effluent nitrate and total N concentrations compared to model predictions. This could have very significant contractual and cost implications for the upgrade and operation of wastewater treatment plants. The most recently released BioWin version has revised default settings, which bring it closer to the older UCT family of models in respect of denitrification rate. In this paper we present the results of a desktop study, based on a hypothetical N-removal activated sludge plant as a test case. In Part 2 (to be published in the November issue of Water), we will present actual data from a very similar fullscale plant in Australia that was used to calibrate the denitrification rate applied in BioWin