MICROCALORIMETRIC ASSESSMENT OF THE BIODEGRADATION KINETICS OF DIETHYL PHTHALATE AND DIBUTYL PHTHALATE BY PURE MICROBIAL CULTURES

Phthalic acid esters (PAEs) are ubiquitous environmental contaminants with documented endocrine-disrupting properties, yet comprehensive understanding of their biodegradation kinetics remains incomplete. This study employed isothermal microcalorimetry to investigate the biodegradation of diethyl phthalate (DEP) and dibutyl phthalate (DBP) by three pure microbial cultures: Escherichia coli, Staphylococcus aureus, and Aspergillus niger.Microcalorimetric thermograms provided real-time metabolic fingerprints, enabling quantification of growth rate constants (k), heat output (Pmax), and inhibition ratios (I). Both PAEs exhibited concentration-dependent inhibition, with DBP demonstrating greater toxicity (IC50 = 89.2 mg L⁻¹) compared to DEP (IC50 = 145.6 mg L⁻¹). First-order kinetics adequately described degradation, with rate constants of 0.085 h⁻¹ (DEP) and 0.062 h⁻¹ (DBP) at optimal concentrations. Degradation efficiencies were strain-dependent, with S. aureus achieving 96.2% DEP degradation and A. niger achieving 97.3% DBP degradation within 120 hours. Metabolite analysis identified monoethyl phthalate, monobutyl phthalate, and phthalic acid as key intermediates. Strong correlations between microcalorimetric parameters and conventional degradation kinetics validated heat output as a reliable proxy for PAE biodegradation activity. These findings establish microcalorimetry as a sensitive, real-time tool for assessing PAE biodegradation and provide kinetic parameters essential for bioremediation applications.