A simple kinetic modeling approach for aerobic stabilization of real waste activated sludge

•Aerobic stabilization of WAS was able to be simulated either with ASM1 or ASM3.•Proposed general approach was validated for modeling of aerobic stabilization.•Sensitivity analyses confirmed the uniqueness of estimated model parameters.•Removal of active biomass is main mechanism involved in aerobic digestion.•Organic loading should be high enough to achieve acceptable removal efficiency.

The objective of this study is to propose a procedure to simplify the modeling of aerobic stabilization process. In order to achieve this, the activated sludge models no. 1 (ASM1) and no. 3 (ASM3) were evaluated based on uncomplicated chemical oxygen demand and volatile suspended solid data gathered from batch aerobic digesters. The aerobic digestion period of real waste activated sludge was modeled and then the modeling results were validated at different volumetric organic loading rates. The uniqueness of given model parameters were confirmed by sensitivity analyses. According to experimental results, at the end of 30 days, the maximum volatile suspended solid removal rate was as 51.50%. The model simulations indicated the viability of both models, with regression coefficients of >0.978 without requiring the addition of any process or component to the original model structures contrary to those suggested by prior studies. According to sensitivity analyses used to determine the identifiability of estimated model parameters, the active biomass fraction, production rate of microbial products, endogenous decay rate and heterotrophic yield coefficient are the most sensitive and identifiable parameters in both models. As a result of modeling, the endogenous decay process was determined to be the main microbial mechanism involved in aerobic digestion, while the hydrolysis of particulate organic matter and removal of storage products were found as insignificant mechanisms during aerobic digestion process. Additionally, the modeling studies indicated the importance of the organic loading to achieve satisfactory organic removal since microbial kinetic rates were decreased under a threshold level of organic loading.