Bioelectrochemical systems-based metal removal and recovery from wastewater and polluted soil: Key factors, development, and perspective

Bioelectrochemical systems (BES) are considered efficient and sustainable technologies for bioenergy generation and simultaneously removal/recovery metal (loid)s from soil and wastewater. However, several current challenges of BES-based metal removal and recovery, especially concentrating target metals from complex contaminated wastewater or soil and their economic feasibility of engineering applications. This review summarized the applications of BES-based metal removal and recovery systems from wastewater and contaminated soil and evaluated their performances on electricity generation and metal removal/recovery efficiency. In addition, an in depth review of several key parameters (BES configurations, electrodes, catalysts, metal concentration, pH value, substrate categories, etc.) of BES-based metal removal and recovery was carried out to facilitate a deep understanding of their development and to suggest strategies for scaling up their specific application fields. Finally, the future intervention on multifunctional BES to improve their performances of mental removal and recovery were revealed.

Understanding the interdependence of strain of electrotroph, cathode potential and initial Cu(II) concentration for simultaneous Cu(II) removal and acetate production in microbial electrosynthesis systems

Metallurgical microbial electrosynthesis systems (MES) are holding great promise for simultaneous heavy metal removal and acetate production from heavy metal-contaminated and organics-barren waters. How critical parameters of strain of electrotroph, cathode potential and initial heavy metal concentration affect MES performance, however, is not yet fully understood. Heavy metal of Cu(II) and four Cu(II)-tolerant electrotrophs (Stenotrophomonas maltophilia JY1, Citrobacter sp. JY3, Pseudomonas aeruginosa JY5 and Stenotrophomonas sp. JY6) were employed to evaluate MES performance at various cathode potentials (-900 or -600 mV vs. standard hydrogen electrode) and initial Cu(II) concentrations (60-120 mg L^-1). Each electrotrophs exhibited incremental Cu(II) removals with increased Cu(II) at -900 mV, higher than at -600 mV or in the abiotic controls. Acetate production by JY1 and JY6 decreased with the increase in initial Cu(II), compared to an initial increase and a decrease thereafter for JY3 and JY5. For each electrotrophs, the biofilms than the planktonic cells released more amounts of extracellular polymeric substances (EPS) with a compositional diversity and stronger Cu(II) complexation at -900 mV. These were higher than at -600 mV, or in the controls either under open circuit conditions or in the absence of Cu(II). This work demonstrates the interdependence of strain of electrotroph, cathode potential and initial Cu(II) on simultaneous Cu(II) removal and acetate production through the release of different amounts of EPS with diverse composites, contributing to enhancing the controlled MES for efficient recovery of value-added products from Cu(II)-contaminated and organics-barren waters.

A loop of catholyte effluent feeding to bioanodes for complete recovery of Sn, Fe, and Cu with simultaneous treatment of the co-present organics in microbial fuel cells

A loop of catholyte effluent feeding to the bioanodes of air-cathode microbial fuel cells (MFCs) achieved complete recovery of mixed Sn(II), Fe(II) and Cu(II), with simultaneous treatment of the co-present organics in synthetic wastewater of printed circuit boards (PrCBs). This in-situ utilization of caustic in the cathodes and the neutralization of acid in the anodes achieved superior metal recovery performance at an optimal hydraulic retention time (HRT) of 24 h. Cathode chambers primarily removed Sn of 91 ± 4% (bottom: 74 ± 3%; electrode: 17 ± 1%), Fe of 89 ± 8% (bottom: 64 ± 4%; electrode: 25 ± 2%), and Cu of 92 ± 7% (electrode: 63 ± 5%; bottom: 29 ± 1%), compared to Sn of 9 ± 3% (electrode: 7 ± 1%; bottom: 2 ± 1%), Fe of 9 ± 3% (electrode: 8 ± 3%; bottom: 1 ± 0%), and Cu of 7 ± 3% (electrode: 4 ± 1%; bottom: 3 ± 1%) in the bioanodes. Bacterial communities on the anodes were well evolutionarily developed after the feeding of catholyte effluent, with the increase in abundance of Rhodopseudomonas and Geobacter, and the shift from Thiobacillus and Acinetobacter to Pseudomonas, Comamonas, Aeromonas and Azospira. This loop of cathodic effluent feeding to the bioanodes of MFCs may represent a unique method for complete metal recovery with simultaneous extraction of renewable electrical energy from the co-present organics. This study also offers new insights into the development of compact microbial electro-metallurgical processes for simultaneous recovery of value-added products from PrCBs processing wastewaters and accomplishing the national wastewater discharge standard for both metals and organics.