Study On The Removal Of Humic Substances From Aqueous Solution Using Activated Carbon And Fly Ash

Humic substances (HS) is the main component of the organic matter in natural waters. Humic acids (HAs) and Tannic acids (TAs) are two kinds of polymer compounds with different molecular weight distribution in the HS. The existence of HAs and TAs in water resources is troublesome not only for causing color, odor, and taste problems but also for forming trihalomethanes and other harmful disinfection byproducts that exhibit mutagenic properties during the chlorination step in drinking water treatment. Therefore, the removal of HAs and TAs from natural water sources is a major issue faced by people currently.In this thesis, the removal performance of HAs and TAs from aqueous solution was studied under the static adsorption conditions using commercial activated carbons (ACs) and fly ashes (FAs) as testing materials.The effect of temperature, initial pH, coal ash dose on HA removal was discussed. The HA removal mechanisms by ACs and FAs were proposed in conjunction with a sets of chemical and structural characterization techniques.Firstly, the correlation between porous structure parameters and adsorption performance indicators of ACs was analyzed. It is found that the adsorption capacities of iodine and methylene blue on ACs were closely correlated with the microporous volums and specific surface areas of ACs.Secondly, the static adsorption tests were conducted to investigate dependence between porous structure parameters of ACs and removal efficiency (Re) of HAs and TAs from aqueous solutions. The results show that:(1) iodine and methylene blue adsorption capacities are unable to reflect the Re of TAs and HAs by ACs; and (2) caramel indicator can be used as a valid prediction for the removal capacity of TAs by ACs, however, it fails to predict the removal capacity of HAsfrom aqueous solution by ACs.Finally, a series of batch experiments were conducted to study the removal mechanism of HAs and TAs by FAs. The influences of ash dosage, initial pH and temperature on the removal of HAs by calcium-rich FA were also analyzed. The following conclusions can be deduced:(1) The removal process of TAs on ACs and FAs is mainly a physical adsorption process;(2) Physical adsorption is the major process in the AC-HAs system while aggregation predominately occurs in the calcium-enriched FA-HAs system due to the contribution of Ca2+cations;(3) The removal performance of HAs by calcium-enriched FA is strongly dependent on temperature, initial pH, and dosage of FA. All these factors are considered to be associated with the concentration of Ca+cations in solution.The results obtained in this study suggested that calcium-enriched FA could be useful and cost-effective in the treatment of wastewaters containing HAs-like organic macro-molecules instead of commercial ACs.