REMOVAL OF REACTIVE AZO DYES FROM WATER BY FE0 REDUCTION FOLLOWED BY PEROXIDASE-CATALYSED POLYMERISATION

Removing reactive azo dyes from textile effluents is a significant challenge in wastewater treatment. Although various physical, chemical and biological methods are available, reduction by zero-valent Fe followed by enzymatic treatment can be an environmentally friendly and cost effective process for removing reactive azo dyes. In the first step, azo bond is cleaved by zero-valent Fe to reduce the dyes to aromatic amines. Next, these amines are oxidized and polymerised by enzymatic treatment. Finally, these polymers are removed by sedimentation and filtration. The effectiveness of zero-valent Fe and Arthromyces ramosus peroxidase (ARP) in the proposed process was studied on two representative reactive azo dyes, Reactive Red 2 (RR2) and Reactive Black 5 (RB5). 97 to 98 % of RR2 and RB5 were reduced by zero-valent Fe within 1 hour at pH 4.8. ARP was able to remove 92 to 94% of the aromatic amines in 2 h. This three-step process could remove over 97 % of colour and around 80 to 89% of pollutants. Optimum reaction condition for this enzymatic treatment was around pH 5.5 to 7.0. Enzyme to substrate ratio was 9:1 for both dyes. Hydrogen peroxide to substrate ratio was 6:1 for RR2 and 9:1 for RB5. The colored products generated in the enzymatic process were removed within 2 hours by adding a coagulant, PEI along with alum. Optimum pH for coagulation process was between 4.8 and 7.0, and the optimum PEI concentration was within 200 and 250 mg/L along with 100 mg/L alum. A comparison with other treatment processes asserted the superior advantage of the proposed process in terms of actual pollutant removal and colour removal performance.