Color indicators for industrial effluents, including the transparency (TRA), dilution ratio (DR), ADMI tristimulus filter (ADMI) and Lavibond unit (LU), are adopted in many countries. The aims of this study were to (1) investigate the effects of suspended solids (SS) and color on the TRA values, (2) study the effects of water sample pH and pore size of filter papers on the color values, and (3) evaluate the relationships among these color indicators. Results showed that the TRA measurement is markedly affected by both the hues of color and SS. For an effluent of the same TRA value, the ADMI value ratio varied by a factor of 2 to 50. This implies that TRA is not a suitable indicator in quantifying the effluent color strength. The pore size of filter papers affects the ADMI values more than the water sample pH does. Furthermore, although the TRA does not correlate to any of the other three indicators, i.e., DR, LU or ADMI, the statistical analysis from both synthetic and real colored effluents shows that there exists a high correlation among DR, LU and ADMI values. The information presented in this study enables the conversion of color value from one country (area) to another depending on the color indicator adopted.
