Substrate flux into storage and growth in relation to activated sludge modeling

The recently proposed IAWQ activated sludge model No. 3 (ASM3) was evaluated for itʹs capacity in describing heterotrophic aerobic COD conversions. Hereto model simulations were compared to observed conversions in a laboratory sequencing batch reactor (SBR) with acetate as the sole substrate in the influent; no nitrification occurred. ASM3 was simplified to take only those processes which were important in the reactor studied into account. In general it was possible to describe the overall conversions including oxygen uptake rates. However, the difference in growth rate between feast and famine phase could not be described accurately. This was due to the fact that ASM3 allows growth on storage polymers only. Therefore a new model structure was proposed in which growth on external substrate is allowed. This model structure was further compared to experimental results at different temperatures. Since the polymer formation seemed to be strongly reduced at higher temperatures it was needed to describe this process with a negative temperature coefficient.