Book Description

Activated carbon adsorption is widely used to remove organic matters (both micropollutants and dissolved natural organic matter (DOM)) in water treatment systems. However, economic use and adsorption effectiveness have been major concerns due to not ideal physicochemical characteristics of most current activated carbons. Meanwhile, due to the competitive adsorption effect from DOM, it has been a great challenge to achieve effective micropollutants removal. Therefore, the main objective of this study was to develop activated carbon with specific selectivity for the removal of DOM and another type for effective removal of micropollutants. This will eventually lead to their application in water treatment facility as a sequence of two adsorber beds in series. Chemical activation of bituminous coal by KOH was applied to develop activated carbons. A total of 24 activated carbons with different porous structure and BET surface area were created under different activation conditions. The effect of the different variables of the activation process on critical carbon parameters was analyzed. In this study, phenolic compounds were selected as model compounds to represent micropollutants. In case of phenolic compounds, the oligomerization phenomenon that occurs in the presence of molecular oxygen, must be controlled by limiting the pore size of activated carbon. Therefore, BC-21 with highest microporosity was selected for phenolic compounds removal. In order to understand the impact of BC-21 on oligomerization of phenolics, single solute, binary solute and ternary solute isotherm adsorption were conducted. Meanwhile, commercial activated carbon F400 was used for comparison. These isotherms were collected under anoxic (absence of molecular oxygen) and oxic (presence of molecular oxygen) conditions. All isotherms demonstrated BC-21 has not only better adsorption capacity but also higher regeneration efficiency. BC-41 with highest mesoporosity was used as carbon precursor for DOM removal. Two novel tailoring methods (outgassing and manganese impregnation) were employed to modify the surface chemical characteristics of BC-41. The developed tailored activated carbons (BC-41-OG -argon outgassed and BC-41-MnN - manganese dioxide impregnated) showed much better DOM adsorption rate and equilibrium capacity than F400 and virgin carbon BC-41. The enhanced DOM removal by BC-41-MnN was attributed to the presence of manganese species on the carbon surface. The higher removal of BC-41-OG was due to the higher surface basicity created during the outgassing treatment. It is very common to have micropollutants such as phenolics in the treatment environment. Therefore, the role of phenolic compounds in determining the adsorption effectiveness of DOM using BC-41-OG and BC-41-MnN was further investigated. The results of the kinetic study indicated phenolic compounds have a significant positive effect on the removal rate of DOM. However, the effect on adsorptive capacity of DOM is highly dependent on the surface chemical characteristics of activated carbon. In addition, DOM with different molecular weight distribution demonstrated different extent of influence from oligomerization. The adsorption performance of BC-41-OG and BC-41-MnN was also examined by conducting small column study. The enhanced selectivity in the removal of DOM rather than phenolics was observed for both novel tailored activated carbon as compared to F400.