Systematic Approach for Quick Quality Assessment of Ink Effluents for Treatment and Discharge

Abstract

A characterization study on synthetic wastewaters containing various commercially available ink-jet inks was conducted. Analysis of this resulted in the identification of seven high-risk noncompliance parameters, namely, chemical oxygen demand (COD), biochemical oxygen demand at 5 days (BOD\d5), total dissolved solids (TDS), phenols, copper, iron, and sulphate concentrations. Of these, COD reduction was found to be the most stringent treatment criterion based on the industry-accepted standard Fenton’s oxidation reaction for treatment. TDS and COD were also proposed as critical parameters for the initial assessment of the quality of untreated ink effluents. To provide for rapid and robust indications of the TDS and COD of the untreated ink effluents, a correlation for TDS as a function of conductivity and turbidity was obtained. Furthermore, a deterministic approach based on Beer’s law of absorbance additivity was developed for determining COD of mixtures of ink effluents using absorbance measurements at 210, 436, 525, and 620 nm. These were validated successfully against experimental data. Based on an in-depth analysis of the compositions of ink effluents, a list of simple and rapid on-site water quality parameters was proposed for monitoring the quality of the treated ink wastewater. This consisted of measurements of UV-absorbance at 210 nm, conductivity, pH, turbidity, and color. Based on the discharge limits imposed by a particular country, one can then develop a range of values for these quality parameters in order to meet the discharge regulations of that country. The Singapore context was used as a case study to illustrate this approach. In addition, it was found that the copper content in the cyan ink effluents was substantially reduced by more than 96% along with the standard Fenton’s reaction. Through the course of investigating the Fenton’s oxidation reaction, it was found that measurements of oxidation-reduction potential and/or temperature are suitable indicators of the progress of the reaction.