Optimization of microplastics polystyrene biodegradation by Bacillus subtilis isolated from compost sample

Microplastics (MP) are polymer particles smaller than 5 mm and are divided into primary and secondary [1]. Primary microplastics are formed during industrial production. When it enters the environment, it breaks down through physical, chemical, and biological processes into smaller particles that form secondary microplastics. The most commonly produced and used polymer types are polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET) and polystyrene (PS). Microplastics pose a problem because they persist in the environment for long periods of time, are insoluble in water, are difficult to decompose, have a complex polymer composition, can transfer hydrophobic pollutants adsorbed to microplastics, have effects on aquatic organisms that can bioaccumulate, enter the food chain, and affect human health [2]. In this context, the biodegradation of secondary MP PS by the bacterium Bacillus subtilis which was isolated from compost was studied. The experiment was conducted according to the Full Factorial design. Three factors (size of PS particles, optical density of bacterial suspension, and speed of rotary shaker) were studied at three levels (minimum, average, and maximum). During the 30-day experiment, the number of live bacterial cells and the concentration of total carbon were monitored. At the end of the experiment, the PS particles were analyzed by FTIR spectroscopy. Optimal conditions were observed at average value of PS size (300-500 µm) and optical density (0.3), as well as maximum value of speed of rotary shaker (200 rpm). According to the obtained results, Bacillus subtilis is the suitable choice for biodegradation of PS.