Enhancing biological treatment of dye wastewater with zero-valent iron

Pretreatment of authentic industrial dye wastewater with zero-valent iron (ZVI) was evaluated using a bench-scale integrated anaerobic-aerobic (ZVI-AO) biological treatment system. Average ADMI (American Dye Manufacturers' Institute) value of dye wastewater was reduced from 245 to 107 units with ZVI column pretreatment. Subsequent treatment of ZVI column effluent by a continuous AO process further reduced the ADMI values to 18-39, resulting in overall decolorization efficiency of 78-89%. A control AO system without ZVI pretreatment, which was operated in parallel, achieved just 44-69% of ADMI removal efficiency. In addition, the ZVI integrated system yielded effluents with much lower COD and BOD concentrations than the control system. The aerobic batch respiration tests confirmed that ZVI treatment transformed the recalcitrant dye compounds to slowly biodegradable fractions, thus enhancing the overall biodegradability of dye wastewater.