Super-bridging Fibrous Materials for Water Treatment: Impacts on Removal of Plastic Particles, Phosphorus and Natural Organic Matter

Aggregation combined with gravitational separation is the most commonly used method to treat water globally, but it carries a significant economic and environmental burden as the chemicals used in the process (e.g., coagulants) generate ~8 million tons of metal-based sludge waste annually. To simultaneously deal with the issues of process sustainability, cost, and efficiency, we developed materials reengineered from pristine or waste fibers to serve as super-bridging agents, adsorbents, and ballast media. This study shows that these sustainable fiber-based materials considerably increased the floc size (~6630 µm) compared to conventional physicochemical treatment using a coagulant and a flocculant (~520 µm). The fiber-based materials also reduced coagulant (up to 40%) and flocculant usage (up to 60%). Moreover, the unprecedented size of flocs produced using fiber-based materials (up to ~13 times larger compared to conventional treatment) enabled easy floc removal by screening, thereby eliminating the need for a settling tank, a large and costly process unit. Our results show that fiber-based materials can be effective solutions at removing classical (e.g., natural organic matter (NOM) and phosphorus) and emerging contaminants (e.g., microplastics and nanoplastics). Due to their large size (> 3000 µm), some Si-grafted and Fe-grafted fiber-based materials can be easily recovered from settled/screened sludge and reused multiple times for coagulation/flocculation. Our results also show that these materials could be used in synergy with coagulants and flocculants to improve settling in existing water treatment processes. Furthermore, these reusable materials combined with separation via screening could allow global water treatment facilities to reduce their capital and operating costs as well as their environmental footprint.