Assessing the relative merits of mineralization and coagulation by Fenton process using humic acid of different molecular weights

摘要

In treating humic acid (HA) by Fenton process, we noticed that the process actually consists of dual functions of coagulation and mineralization. Hence, an attempt was made to clarify their relative contributions using HA of different molecular weights (MWs). Three ranges of MWs, namely, less than 100kDa (sample A), less than 10kDa (sample B), and less than 1kDa (sample C), were investigated. Their initial DOC was 10mg/L. By examining the reaction constants k(M) (for mineralization) and k(C+M) (for coagulation plus mineralization), three trends were observed. Firstly, k(C+M) and k(M) increased by increasing the dose of either Fe2+ or H2O2. Secondly, k(C+M) decreased with decreased MW. Lastly, k(M) increased with decreased MW. Therefore, Fenton mineralization for HA of smaller MW and Fenton coagulation for HA of larger MW are better for DOC removal. Specifically, the ratios of DOC removal from mineralization to that from coagulation (denoted by M/C) were 0.26-0.45, 0.52-1.36, and 1.0-6.29 for samples A, B, and C, respectively. That is, M/C of sample C>sample B>sample A; namely, the lower MW HA has a higher M/C ratio.