A Parametric Study of Performance Characteristics of Upflow Anaerobic Sludge Blanket Bioreactors

Attempts have been made to perform a parametric study of the performance characteristics of UASB (upflow anaerobic sludge blanket) bioreactors. Bioreactor performance is first simulated mathematically using PFDRs – in – series model that assumes the sludge bed and the sludge blanket each equivalent to a PFDR (plug flow dispersion reactor) but with different values of axial dispersion coefficient (DL). Experimental values of DL are used in the computations. Alternate models that employ PFR – CSTR approach and the one proposed by Narayanan and Narayan are also considered for comparison. Dependence of total required height of reaction zone (L) with different system / operating parameters such as fractional conversion of substrate (α) desired, feed concentration ( CS0 ) and feed flow rate have been studied separately. Computed values of design parameters are compared with experimental data collected from industrial units / pilot plants. It is observed that the sludge bed is not a tightly packed bed, but is a partially expanded bed. Axial dispersion and resistance to substrate transfer to sludge granules are significant and cannot be neglected. Among the different kinetic pathways analysed, data based on Andrews’ kinetic model that accommodates substrate inhibition to microbial growth agree more closely with experimental data