Abstract
Used engine oil (UEO) contains toxic substances that pose serious threats to ecosystems and human health, underscoring the need for efficient bioremediation techniques. The improved bioremediation capacity of native bacteria isolated from soil polluted with UEO is examined in this work. Ochrobacterium intermedium LMG 3301 and Bacillus paramycoides MCCC1A04098, two native isolates, were used. The main goal was to assess these strains’ combined biosorptive-bioremediation capacities utilizing a unique composite material made of calcium carbonate (AAC), attapulgite, and alginate. In 0.675% (v/v) UEO-enriched minimum salt medium (EMSM), the effectiveness of the immobilized mixed-cell (IC) system was directly compared to a free cell (FC) system. After 24 days, significant kinetic and degradation findings showed the AAC-IC system’s quantitative advantage. A remarkable 98.42% total petroleum hydrocarbon (TPH) degradation was attained by the mixed bacterial consortia immobilized in AAC, much outperforming the mixed FC system (93.03%) and proving the AAC-IC consortium to be a very effective biocatalyst. The generation time was reduced in half to 5.45 days as a result of the AAC-IC systems’ about two-fold higher specific growth rate (0.127 day−1) than that of the FC systems (0.063 day−1). Increased biocatalytic activity is indicated. Results demonstrated a dual-functionality mechanism where synergistic biological digestion drove nearly total removal of the heavier nC18–nC29 fraction, while the IC system demonstrated a dual-action mechanism and enhanced adsorption, which contributed to high removal (89%) of the lighter nC9–nC17 fraction. Furthermore, regarding mass transfer efficiency, the experimental effectiveness factor (η) for the IC systems (1.04–1.05) crucially approached that of the FC systems (η = 1.00). This finding is novel for the (∅≈0.45 cm) beads and indicates negligible mass transfer resistance within the AAC matrix, a constraint often plaguing large-scale immobilization. The findings demonstrate that the AAC-IC system provides a protective, self-regenerating matrix that maximizes synergistic microbial activity, offering a kinetically superior, cost-effective, and highly efficient approach for UEO bioremediation.