Optimization of polystyrene nanoparticles (PS-NPs) degradation by coupling zerovalent iron (ZVI) and photo-Fenton processes in seawater (simulated and real) for the production of green microalgae

• Grant number: 25/08568-3
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: December 01, 2025
• End date: November 30, 2028
• Field of knowledge: Engineering - Sanitary Engineering - Water Supply and Wastewater Treatment
• Principal Investigator: Cauê Ribeiro de Oliveira
• Grantee: Pedro Henrique da Costa
• Host Institution: Instituto de Química de São Carlos (IQSC). Universidade de São Paulo (USP). São Carlos , SP, Brazil

Abstract

With the growth of the global population and the advancement of the global economy, plastics have become essential components of modern life due to their wide range of applications and low production costs. However, the sharp increase in global plastic production has led to the annual disposal of approximately 10 to 20 million tons into the oceans. Once in the environment, plastics can sink, remain suspended in the water column, or float on the surface, gradually fragmenting into microplastics (< 5 mm) and nanoplastics (< 1,000 nm). Given humanity's strong dependence on the oceans, plastic pollution has emerged as one of the most urgent environmental challenges of our time, particularly affecting microalgae. In addition to forming the foundation of the marine food web, microalgae are important for enhancing the nutritional value of food and for the production of biodiesel and edible oils. Nevertheless, the improper disposal of nanoplastics - especially polystyrene, one of the most widely used polymers - threatens these organisms by impairing photosynthesis and reducing biomass production. Accordingly, this doctoral project proposes the development and optimization of a nanoplastic degradation system specifically targeting nanoparticles of polystyrene (NP-PS) in both simulated and natural seawater, through the coupling of zero-valent iron (ZVI) and photo-Fenton processes. The goal is to mitigate the environmental impacts of plastic pollution and to promote the safe cultivation of marine microalgae (Chaetoceros calcitrans). To achieve this, the ZVI and photo-Fenton processes will be integrated, as they combine reductive and oxidative stages, providing high efficiency in the degradation of persistent organic compounds while utilizing metallic iron as a continuous source of ferrous/ferric ions required by the photo-Fenton process and reducing solid waste generation. Initially, a screening of statistically significant factors (at a 95% confidence level) affecting the degradation of NP-PS in a continuous flow system will be conducted using a Plackett-Burman experimental design. Subsequently, the degradation process will be optimized using response surface methodology. The degradation of NP-PS will be evaluated based on their mineralization (via carbon analysis) and by employing techniques such as Raman spectroscopy, mass spectrometry, scanning electron microscopy, and dynamic light scattering. At the end of the optimization phase, the cytotoxicity and ecological safety of the identified degradation products will be assessed through growth and photosynthetic pigment production assays of the microalga Chaetoceros calcitrans, as well as through ECOSAR 2.2 and Chemicalize software tools. (AU)