Design of dissolved air flotation (DAF) process for treating dyes-contaminated wastewater

The effect of using natural coagulant Aloe Vera with alum Al2 (SO4)3 was examined to remove three reactive dyes: Reactive Blue (RB), Reactive Red (RR) and Reactive Yellow (RY) from simulated textile wastewater in single and blended (ternary) systems by utilizing dissolved air flotation system (DAF) combined with the coagulation + flocculation + flotation in continuous system. This combining process showed excellent removal efficiency. The process was operated under flow rate of, 100 L h-1 and duration of 30 min at 15 mg L-1 dye concentrations; pH value was fixed at 8, and the dose of alum + AV was fixed at 10 mg L-1. DAF system was operated once using alum + AV and then using Poly aluminium chloride (PAC; AlCl3.6H2O) with dose of 10 mg L-1 as flocculant in combination with coagulant. The removal efficiency reached to 95, 93 and 92% for RR, RB and RY respectively for single system without flocculant. By using flocculant with coagulant, the removal efficiency was excellent and was 97, 96 and 95% for RR, RB and RY, respectively. Thus, combined treatment processes offer many advantages for potential treatment of sewage and industrial wastewater such as flexibility, time and coagulant/flocculant savings as well as high quality treated water.