Valorization of invasive water hyacinth for nutrients removal from eutrophic waterbodies and biochar production

Among many plights caused by eutrophication, the overabundance of algae and aquatic plants is grossly a major concern for aquatic ecosystems. Specifically, water hyacinth is an invasive plant species that disrupts waterways and poses detrimental environmental and health risks. This non-native (alien or exotic) species is already impairing aquatic ecosystems in South Africa, while vast harvested quantities, currently considered a waste, further exacerbate the problem. However, when viewed under the circular economy and waste valorisation lenses, water hyacinth can be an important resource. Here, this was used for biochar production, with a temperature of 500 °C providing high carbon content. HR-SEM-EDS and HR-TEM-EDS revealed varying biochar enriched with notable phosphorus levels. This reflects the highly degraded state of freshwater bodies in South Africa since water hyacinth is a known phosphorus (P) hyperaccumulator. It further suggests that among the different uses, such as water treatment or even carbon dioxide removal (CDR), the produced biochar could be a good candidate for soil improvement and agriculture. Thermal analysis showed that the raw water hyacinth mainly (96%) comprises water, while weight losses for biochar at 167–990 °C correspond to moisture and volatile matter removal. Furthermore, biochar yield decreased from 32.5% at 300 °C to 24.7% at 700 °C, confirming progressive devolatilization and carbon enrichment at higher temperatures. Overall, it is evident that water hyacinth can be sustainably managed for the removal of nutrients from degraded freshwater bodies in the Global South and then used for nutrients recycling in agriculture.