Biological phosphate removal by model based continuous cultivation of Acinetobacter calcoaceticus

Abstract

Batch cultivation of Acinetobacter calcoaceticus was carried out under statistically optimized culture conditions in order to study the kinetics of growth and phosphate uptake. It featured a biomass accumulation of 4.08 g L −1 with a consumption of 0.14 g L −1 phosphate (from initial phosphate concentration of 0.18 g L −1) in 11 h. Inhibition studies with respect to carbon, nitrogen and phosphate were also performed to quantify their limiting and/or inhibitory effect on specific growth rate. Using above kinetics/inhibition data, mathematical model equations were proposed and then model parameters were identified for batch cultivation of A. calcoaceticus. The batch model was extrapolated for continuous cultivation so as to predict, steady state concentrations of process variables and identify suitable nutrient feeding strategies for even better/quicker phosphate removal. In order to make a comprehensive study of the effect of dilution rate on culture growth and phosphate uptake, different dilution rates of 0.04, 0.09, 0.13, 0.19, 0.3, 0.4 h −1 were utilized in the model to predict transient and steady state data, which were experimentally verified to establish the validity of the model. It was observed that as the dilution rate increased, the steady state biomass concentration gradually decreased and residual substrate concentration increased, indicating the applicability of well-known Monod type growth pattern. Best biomass accumulation (3.5 g L −1) and phosphate uptake (∼76%) was obtained at D = 0.09 h −1 experimentally. Studies in a continuous stirred tank reactor (CSTR) demonstrated the feasibility to achieve faster phosphate removal without inherently slow anaerobic phase involvement.