In this study, a dynamic model was developed to find the behavior of constituents and microorganisms in the sludge bed of UASB (upflow anaerobic sludge blanket) reactor in terms of the bed height. Also it was attempted to predict process variables including pH and volatile fatty acids produced from the influent organic COD to propose the optimum operational conditions.
Modeling made it possible to predict the behavior of constituents and microorganisms, and the changes of process variables with respect to the bed height by assuming the sludge bed zone in UASB (upflow anaerobic sludge blanket) reactor to be a series of CFSTRs (continuous flow stirred tank reactors) of which the volume is proportioned to the gas quantity passing the segmented zone.
The microorganisms presented in the bed zone could be divided into two groups of acidogenic and methanogenic bacteria, according to the microbial functions.
Mathematical simulations were attempted to identify the balance and distribution of these two microbial populations as well as the responses of reactor to the operational conditions in terms of the bed height.
Considering the constituents as complex substrates composed of hydrolyzed and non-hydrolyzed materials and VFAs (volatile fatty acids), prediction of the concentration of each constituent was allowed.
The model presented in this study was based on the ionization of VFAs, ionic equilibrium equations and incorporation of the CO2/HCO3 equilibrium so that the prediction of pH, accumulation of VFAs and alkalinity at different shock loading rates could be made.
This research indicated that the UASB reactor was relatively stable to shock loadings and that the lower part placed below the height of 20%-30% of the sludge bed probably served as a shock absorbing zone. About 70% of organic COD was removed in the lower 55% portion of the sludge bed height.
