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.