Biochar and zero-valent iron sand filtration simultaneously removes contaminants of emerging concern and Escherichia coli from wastewater effluent

Abstract

Advanced treated municipal wastewater is an important alternative water source for agricultural irrigation. However, the possible persistence of chemical and microbiological contaminants in these waters raise potential safety concerns with regard to reusing treated wastewater for food crop irrigation. Two low-cost and environmentally-friendly filter media, biochar (BC) and zero-valent iron (ZVI), have attracted great interest in terms of treating reused water. Here, we evaluated the efficacy of BC-, nanosilver-amended biochar- (Ag-BC) and ZVI-sand filters, in reducing contaminants of emerging concern (CECs), Escherichia coli (E. coli) and total bacterial diversity from wastewater effluent. Six experiments were conducted with control quartz sand and sand columns containing BC, Ag-BC, ZVI, BC with ZVI, or Ag-BC with ZVI. After filtration, Ag-BC, ZVI, BC with ZVI and Ag-BC with ZVI demonstrated more than 90% (> 1 log) removal of E. coli from wastewater samples, while BC, Ag-BC, BC with ZVI and Ag-BC with ZVI also demonstrated efficient removal of tested CECs. Lower bacterial diversity was also observed after filtration; however, differences were marginally significant. In addition, significantly (p < 0.05) higher bacterial diversity was observed in wastewater samples collected during warmer versus colder months. Leaching of silver ions occurred from Ag-BC columns; however, this was prevented through the addition of ZVI. In conclusion, our data suggest that the BC with ZVI and Ag-BC with ZVI sand filters, which demonstrated more than 99% removal of both CECs and E. coli without silver ion release, may be effective, low-cost options for decentralized treatment of reused wastewater. Graphical Abstract

Enhanced removal of estrogens from simulated wastewater by biochar supported nanoscale zero-valent iron: performance and mechanism

“…However, when the iron-carbon mass ratio was further increased to 3:1, the removal rates of E1, E2, E3 decreased to 74.3%, 78.5%, 58.2%, because nZVI particles distributed on the surface of biochar led to less active sites presented to adsorb estrogen pollutants (Devi and Saroha 2014). Furthermore, a higher dose of nZVI might promote particles agglomeration (Ai et al 2022), and block reactive sites for contaminants (Zhu et al 2023) and impede electron transfer, which made a decrease in the removal rate of estrogens. Zhang investigated almost complete removal of CB with nZVI-biochar system, and the mass ratio of 2:1 was conducive to the highest removal rate, indicating that high or low mass ratio of iron to carbon was not suitable for removing CB due to iron's influence on the electron transfer efficiency (Zhang and Wu 2017).…”