Ultra-fast and low-cost electroactive biochar production for electroactive-constructed wetland applications: A circular concept for plant biomass utilization

This study demonstrates two sustainable processes to produce electroactive biochars and their application in electroactive constructed wetlands (CWs) for providing a circular route for biomass utilization and technology up-gradation for wastewater treatment along with electricity generation. With the use of Canna indica biomass generated in CWs operation, the current study produced two different biochars that differ in their physico-(electro)chemical properties related to the preparation method used. This study used plasma based processing to produce ultrafast biochar (PB) within a few minutes resulting in more crystalline biochar with high electrical conductivity compared to the amorphous biochar material produced by using the drum kiln processed biochar (KB) method. These biochars were used in developing electroactive constructed wetlands coupled with microbial fuel cells (CW-MFC) and were operated in batch mode together with commercial granular graphite (GG) substrate-based CW-MFC as control. PB was developed from high-temperature plasma processing in 6.0 min, whereas KB was prepared in bulk amount from semi-controlled combustion process in kiln method and took 3–4 days before final biochar preparation. Electrical conductivity (EC) of the biochar and GG material were found to be in the order of PB > GG > KB, indicating PB as a highly conductive material that assisted in microbial electron transfer. Accordingly, the highest current and power densities of 628 mA m^-3 and 126 mW m^-3, respectively, were also achieved with PB. The COD removal of 72.42 ± 2.61 %,72.32 ± 2.98 % and 59.91 ± 3.21 % was found in CW-MFC-GG, CW-MFC-KB and CW-MFC-PB microcosms, respectively.