Mercury removal from mining wastewater by bioaccumulation and thermal separation in Eichhornia crassipes

Environmental problems persist due to mercury from artisanal and small-scale gold mining (ASGM) as well as ecological problems associated with the macrophyte Eichhornia crassipes Martius (EC). Environmental problems persist due to mercury contamination from artisanal and small-scale gold mining (ASGM) and ecological issues related to the macrophyte Eichhornia crassipes Martius (EC). A bioaccumulation study was conducted on mercury-laden wastewater (WWm) from ASGM using a pilot treatment plant, specifically a constructed wetland system (CW) with the macrophyte species EC. The study monitored the CW for 50 days, with the initial mercury concentration in the wastewater being 62.4 µgTHg L^-1, a hydraulic retention time (HRT) of 1 h, a flow rate (Q) of 0.3 L s^-1, and 7.3 kg of EC. After bioaccumulation, the EC tissues containing mercury were treated using a recovery system (RT) through thermal separation at 400 °C for 10 min. A mathematical model (AcMod) was developed to simulate bioaccumulation under continuous flow and non-stationary conditions, with a kinetic constant (k) of 0.01148 h^-1, to compare simulated data with real data from the CW. The CW showed an 89% reduction in mercury. However, the AcMod simulation indicated low bioaccumulation yields due to the low biomass of EC used. The thermal separation system reduced the total mercury (THg) in EC tissues by an average of 87.43%. The combination of CW and RT offers a nature-based solution (NBS) and promotes the circularity of resources and waste, demonstrating how this system can be integrated into the production process of ASGM.