Biodegradation of diethyl phthalate from synthetic wastewater in a batch operated internal loop airlift bioreactor

In the present study, biodegradation of diethyl phthalate (DEP) was carried out with a mixed culture of aerobic bacterial strains isolated from soil contaminated with municipal wastewater. They were identified as Bacillus sp. and Micrococcus sp. based on morphological, biochemical and molecular characteristics. For the treatment of synthetic wastewater containing DEP, an internal loop airlift bioreactor was designed and fabricated. Experiments were carried out for various initial concentrations (100-1500 mg/l) in a batch mode using a mixed culture of isolates. Mass balance and stoichiometric investigation suggested efficient degradation of DEP with a yield of 0.81 g/g if two-thirds of carbon from substrate converted to biomass. Gas chromatography-Mass spectroscopy analysis detected monoethyl phthalate (MEP) and phthalic acid (PA) sequentially to confirm hydrolysis of DEP. Enzymatic assay of the esterase production (929.5 U/l for 1000 mg/l of DEP) was responsible for hydrolysis of DEP to MEP. Growth kinetic study delivered the best fit of experimental data with the Haldane model with the correlation coefficient (r(2)) 0.95. Biokinetic constants indicated that the high concentrations of DEP inhibited the growth rate of bacteria while dissolved oxygen estimation suggested that the DEP biodegradation was oxygen limited.