Characteristics and treatability of persistent colors in biologically treated wastewater effluents

Abstract

Wastewater effluents have recently gained a great deal of attention as a new water resource due to the increasing fresh water demand in Korea. The color content was one of the troublesome parameters to reuse wastewater effluents for indirect purposes such as toilet flushing and cleaning buildings in urban areas (which are the most popular reuse methods in Korea). The color removal was investigated with UV radiation and a UV/H2O2 process. The UV/H2O2 process was effective in removing the persistent color in the wastewater effluents. The kinetic rate constants of removal of color in the wastewater effluents were obtained with different initial H2O2 concentration in the UV/H2O2 process. There was an optimum initial concentration of hydrogen peroxide, about 44.3 mg/L H2O2, above which the removal rate of the color decreased. The rate constant showed the maximum value, approximately 0.087min(-1). The rate constant of the removal of color in the wastewater was relatively high compared to the humic acid, repeated in previous work. In addition, the color content in wastewater effluents and after each process was characterized with aquatic humic substance concentrations and molecular weight distributions. The results implied that aquatic humic substances were closely related with organic matter, which exhibit color in wastewater effluents. The results also showed that most of the color material in wastewater effluents were present in the organic matter fraction with molecular weight of less than 3 kDa.