Effects of different henna plant parts on enhanced removal of an azo dye Orange II: Biotic and abiotic contributions

The effects of different parts of henna (Lawsonia) plant biomass on the removal of an azo dye Orange II (AO7) were investigated. The batched system of sludge control (R1), and those with the addition of henna flower (R2), stem (R3), and seed (R4) were set up. The results indicated that henna powder all benefit the AO7 removal. At the end of batch test (76 h), the AO7 removal in R1, R2, R3, and R4 were 18.3%, 82.7%, 83.7%, and 65.6%, respectively; and the molar ratios of the reductive byproduct of sulfanic acid to the removed AO7 were 22.1%, 81.7%, 30.4% and 53.9%, respectively. AO7 removal in R2 was mainly attributed to the bio‐reducing pathway, while that in R3 was due to the abiotic adsorption pathway. These two pathways were in comparable role on AO7 removal in R4. In anaerobic conditions, henna plant biomass, especially the flower, played a multiple role in simultaneously providing electron donor and redox mediator (lawsone), thus enhancing the AO7 bio‐reduction. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 404–410, 2016