Netnapid Tantemsapya, Wanpen Wirojanagud, and Santi Sakolchai

pp. 1 - 12

Abstract

This study focused on removal of color, COD, and lignin in wastewater of pulp and paper mill using
white wood ash and black wood ash that generated from boilers unit in the pulp and paper mill. Batch
experiments were setup for studying the equilibrium time, pH, quantity of wood ash and adsorption
isotherm. The results from the equilibrium time experiment concluded that the equilibrium time of the white
wood ash is much more rapid than the black wood ash indicated as 2 minutes and 25 minutes, respectively.
The effect of pH on the removal of such studied parameters was different for the white and black wood ash.
Variation in pH of wastewater at the levels of 2 to 10 had no influence in removal of color (89-93%), COD
(66-70%) and lignin (78-82%) when white wood ash was used, whereas the effect of pH on the removal was
evident when using black wood ash. The highest removal of color (42.2%), lignin (31.1%) and COD (29.7%)
was found when the initial pH was adjusted to 2 and such removal was gradually decreased when pH was
raised. The optimum dose of white wood ash for the highest removal efficiency was 20 g ash /L of wastewater.
This amount of wood ash can remove color 95%, lignin 80% and COD 69%. The reason for high removal
efficiency of white wood ash might occur from the precipitation of lignin by CaO which is the major
component of the ash. For the black wood ash, the optimum dose was calculated from the isotherm equation of adsorption, both by Langmuir and Freundlich isotherm. These isotherms were applicable to color and
lignin, while they were inapplicable to COD. The isotherm for adsorption of color and lignin indicate that
the removal mechanism by black wood ash was likely to be physical adsorption. The results indicated that
the white wood ash was better than the black wood ash in treating the pulp and paper wastewater.