Treatment and reuse of dyeing effluents by potassium ferrate

The use of potassium ferrate, K₂FeO₄, an environmentally-friendly chemical reagent containing iron in the + 6 oxidation state, has been investigated as a new approach for dyeing wastewater purification.The performance of this product, alone or in combination with a cationic organic polymer and/or power ultrasound, was compared to the traditional biological activated sludge process and a tertiary treatment featuring ozonation.Experimental tests showed that, thanks to its unique properties (high redox potential and simultaneous generation of ferric coagulating species), potassium ferrate can be successfully used in dyeing wastewater treatment. In fact, treatment with ferrate at the optimal dose of 70 mg/L as Fe(VI) was found to allow a high removal efficiency of relevant parameters such as turbidity, total suspended solids and chemical oxygen demand (COD).Whilst potassium ferrate alone had a minor effect on colour, the combination of ferrate with the organic polymer allowed a good decolourisation: this suggested the eventual application of this combined process for reuse of dyeing wastewater, resulting in environmental and economic benefits. The possibility of reusing the purified effluent in textile processes that do not require softened water was demonstrated through dyeing tests.