Enhanced bioremediation of heavy metals and bioelectricity generation in a macrophyte-integrated cathode sediment microbial fuel cell (mSMFC)

Abstract

Sediment microbial fuel cell (SMFC) and constructed wetlands with macrophytes have been independently employed for the removal of heavy metals from polluted aquatic ecosystems. Nonetheless, the coupling of macrophytes at the cathode of SMFCs for efficient and synchronous heavy metal removal and bioelectricity generation from polluted river sediment has not been fully explored. Therefore, a novel macrophyte biocathode SMFC (mSMFC) was proposed, developed, and evaluated for heavy metals/organics removal as well as bioelectricity generation in an urban polluted river. With macrophyte-integrated cathode, higher heavy metal removals of Pb 99.58%, Cd 98.46%, Hg 95.78%, Cr 92.60%, As 89.18%, and Zn 82.28% from the sediments were exhibited after 120 days' operation. Total chemical oxygen demand, total suspended solids, and loss on ignition reached 73.27%, 44.42 ± 4.4%, and 5.87 ± 0.4%, respectively. A maximum voltage output of 0.353 V, power density of 74.16 mW/m3, columbic efficiency of 19.1%, normalized energy recovery of 0.028 kWh/m3, and net energy production of 0.015 kWh/m3 were observed in the Lemna minor L. SMFC. Heavy metal and organic removal pathways included electrochemical reduction, precipitation and recovery, bioaccumulation by macrophyte from the surface water, and bioelectrochemical reduction in the sediment. This study established that mSMFC proved as an efficient system for the remediation of heavy metals Pb, Cd, Hg, Cr, As, and Zn, and TCOD in polluted rivers along with bioelectricity generation.