Chemical degradation of azo dyes using different reducing agents: A review

The textile industry effluents are increasingly becoming an environmental problem, and the removal of dyes from aqueous waste streams has great potential for environmental engineering. Among many commonly applied methods, chemical reduction is an emerging prospect in the field of wastewater treatment. This paper reviews a recent 15-year survey on chemical reduction of dyes in the azo family. With respect to the nature of the reducing agents, the scope of the literature was divided into several categories. The available studies aim to reduction of azo dyes using zero-valent iron, other zero-valent metals, amorphous alloys, and finally, a catalytic reduction utilizing different electron donor agents in co-action with a wide range of metal-based catalysts. This paper includes summarization of different configurations of reaction conditions used for the reductive degradation of azo dye, their efficiency, and the influences of various operating parameters of the degradation processes. Several factors affecting the degradation of azo dyes have also been critically analyzed and future perspectives are proposed in this review. From the present study, it can be concluded that a selected reducing agents used for chemical reduction are very effective and environmentally friendly methods for the removal of azo dyes from wastewater.