Performance of an integrated system composed of native soil amended with ZVI/FeS nanoparticles-based technosols and a bioreactor for the treatment of acid rock drainage

We assessed combined, low-cost physical–chemical and biological treatment system for the remediation of acid rock drainage (ARD). Two columns composed of native soil amended with zero valent iron and iron sulfide (ZVI/FeS) nanoparticles-based Technosols were connected to a sulfate-reducing (SR) bioreactor; this integrated treatment system was fed with ARD obtained from mines in El Oro, Ecuador. A control sulfate-reducing bioreactor fed directly with ARD was run in parallel. The bioreactors were operated dynamically for four periods, and every 21 days, the fraction of ARD in the influent was increased stepwise from 25 to 100%. The integrated treatment system demonstrated superior removal efficiencies for Fe (99%), As (99.9%), Cd (99%), Cu (98%), Mn (91%), and Zn (99.9%), while both bioreactors achieved similar sulfate reduction (50–52%) and raised ARD pH from 2.75 to ~ 8. However, the ZVI/FeS nanoparticles-based Technosols significantly improved the removal of As (99.9% vs. 68%) and Mn (91% vs. 71%), compared to the control bioreactor. Molecular ecology analysis of the biomass in the bioreactors using 16S rRNA sequencing revealed that higher ARD concentrations enhanced sulfidogenesis, promoting beneficial interactions within communities in the sulfate-reducing niche. This study highlights the value of the ZVI/FeS nanoparticles-based Technosols in optimizing ARD bioremediation, offering a promising solution for mining effluent management in low-middle-income countries (LMIC).