Biological phosphate removal by model based fed-batch cultivation of Acinetobacter calcoaceticus

Abstract

A simpler phosphate removal process has been proposed involving only aerobic cultivation of Acinetobacter calcoaceticus in a fed-batch mode of treatment. Batch cultivation of A. calcoaceticus was conducted under statistically optimized culture conditions in order to study the kinetics of growth and phosphate uptake. Studies with respect to carbon, nitrogen and phosphate were performed to quantify their inhibitory effect on specific growth rate (if any). Using kinetics/inhibition data, a mathematical model was proposed. The batch model was extrapolated for fed-batch cultivation by incorporating the dilution terms in the model equations so as to predict, suitable nutrient feeding strategy for better phosphate removal. According to the developed feed-strategy, the bioreactor was operated in batch mode for 4 h, after which model based predetermined fresh nutrient feeding (sodium acetate 5.0 g/l) at 2.25 ml/min was started. Model predictions indicated that after 7 h of cultivation process phosphate would be totally consumed. Upon implementation of this model based fed-batch cultivation strategy a biomass accumulation of 4.02 g/l was obtained experimentally against 3.88 g/l concentration predicted by model after 7 h with a residual phosphate concentration of 0.01 g/l. An improvement to 94% phosphate removal efficiency (initial loading 0.175 g/l) in only 7 h was observed in fed-batch cultivation as opposed to 78% (initial loading 0.175 g/l) in 11 h for batch cultivation.