Molecular-Weight-Fractionation Characteristics and Coagulation Behaviors of Biorecalcitrant Dissolved Organic Matter and Colorants in Cassava Distillery Wastewater

The biorecalcitrant dissolved organic matter (DOM) and colorants in biochemically treated effluent, known for their complex and indefinite composition, are drawing increasing environmental concern in the distillery industry. The current study focuses on the evaluation of the hard DOM and colorants based on their molecular weight fractionation, which facilitates the colorant identification and the mechanism exploration in the subsequent coagulation process. It was found that the DOM was distributed most in the molecular weight (MW) range of 1–5 kDa and least in the MW range below 1 kDa; the fluorescent components in the biochemically treated distillery wastewater mainly distributed in low MW (<5 kDa, 73%). As the primary cassava-based biorecalcitrant colorants, the colorants with MWs of 1–5 kDa were probably lignin breakdown products with aromaticity. In the coagulation process, the MW of DOM was among the most significant factors influencing the floc size which decreased with the MW reduction.