Effect of supplemented diet on the kinetic profile of polystyrene biodegradation by Tenebrio molitor larvae: Physical, chemical, thermal, wettability and zeta potential measurements

Abstract

Polystyrene (PS), a major contributor to plastic pollution, is non-biodegradable and widely produced. However, Tenebrio molitor larvae (mealworms) can degrade plastics, including PS, making them ideal for this study. This research is one of the few to offer a daily assessment of PS degradation rates and describes the kinetic profile (equation) of degradation. We assessed daily degradation rates and described the kinetic profiles. A Hill 1 equation best fit the supplemented diet, while the non-supplemented diet followed a two-phase exponential decay function. Larvae on the supplemented diet degraded 50.77 ± 2.62 % of PS, compared to 24.66 ± 5.79 % on pure PS. Physicochemical analyses revealed significant changes in PS after contact with larvae. Thermogravimetric analysis showed maximum degradation temperatures near 350°C for both samples, with a slight difference of 14°C. Infrared spectroscopy identified new chemical groups, and contact angles increased from 69.7º to 120.7º in exposed PS, indicating alterations. Zeta potential also rose in PS exposed to larvae. A 30-day viability study showed no significant differences in survival between groups. However, larvae fed wheat bran or supplemented diets had only 0.5 % mortality, whereas 17.5 % of those without food died. These findings highlight that a supplemented diet enhances PS biodegradation by more than two-fold (2.06). Plastic alone lacks sufficient nutrients for T. molitor larvae development, limiting their biodegradation capacity.