The effect of mixing on the treatment of paint wastewater with Fe3+ and Al3+ salts

Abstract

A 169.2 g of paint was diluted in 1 L of potable water. A 200 ml of sample was poured into 500 ml glass beakers and dosed with 10, 20, and 30 ml of 0.043 M of all coagulants (Iron: Fe and Aluminum: Al salts), respectively in jar tests. Samples were mixed at 250 rpm for 30, 45, and 60 s, respectively. Additional set of experiments was conducted with combined rapid mixing at 250 rpm for 30, 45 and 60 s followed by slow mixing at 100 rpm for a further 10 min, pH and turbidity were measured on the samples. The turbidity in the samples with 30, 45, and 60 s rapid mixing showed that most of the flocs are formed within 30 s. The results also showed a correlation between the pH and turbidity. Fe3+ and Al3+ of the same concentration yield a similar pH and turbidity trend. The added slow mixing showed no appreciable benefits. This was confirmed by microscope experiments using 2 drops of the same solution from rapid mixing only (Experiment A) and placed them in microscope slides after mixing. A similar experiment was conducted with combined and slow mixing. Images were captured after 30 min of settling using a camera. The results showed that the percentage area covered by the flocs in Experiment A are not different to the corresponding percentage area covered by the flocs in Experiment B. Key words: Paint, dosed, mixing, turbidity, correlation.