Concurrent dyes adsorption and photo-degradation on fly ash based substrates

Most of the dyes are organic compounds, with different degree of polarization and different groups with various steric effects, making their complete biodegradation slow or even impossible. Adsorption on fly ash and fly ash based substrates represents a possible alternative for simultaneous removal of dyes and heavy metals form wastewaters resulted in the textile industry. Adsorption (under visible light) and adsorption and photodegradation (under UV irradiation) studies were done on Methylene blue solutions and on their mixtures with heavy metals (copper and cadmium), in systems using fly ash as single substrate, or mixed with a wide band gap semiconductor (TiO 2 ). The titanium oxides and hematite content in fly ash proved to be responsible for photodegradation processes even in the absence of the TiO 2 powder, confirming that modified fly ash is a viable candidate in developing up scalable processes for advanced wastewater treatment. The kinetic and thermodynamic studies allow to calculate the parameters and to describe the complex mechanisms, involving competitive adsorption.