Sequential Fe2O3-Powdered Activated Carbon/Activated Sludge Process for the Removal of Reactive Black 5 and Chemical Oxygen Demand from Simulated Textile Wastewater

The adsorption process is known as an effective process for the removal of dyes from textile wastewater. However, this process alone is not sufficient to reduce the organic pollutants in textile wastewater to the desired levels. On the other hand, activated sludge (AS) has been proved effective for the mineralization of the biodegradable compounds in textile wastewater. Dyes in textile wastewater are resistant to aerobic biodegradation; however, they can be removed by bisorption in AS at certain levels. This biosorption, in turn, produces dye-loaded biomass which creates a problem for land disposal of sludge. Therefore, the sequential use of an adsorption process and AS can provide advantages of both processes for the treatment of textile wastewater. In this study, the sequential use of maghemite (Fe2O3) coated powdered activated carbon (MAC) and activated sludge process (AS) to remove the Reactive Black 5 (RB5) and chemical oxygen demand (COD) from simulated textile wastewater were investigated. Powdered activated carbon provides high surface area for the removal of textile dyes. However, powdered activated carbon cannot be efficiently separated from wastewater. Due to its magnetic properties, MAC can be effectively separated from the liquid phase. The effect of MAC and Mixed Liquor Suspended Solids’ (MLSS) concentration on the RB5 and COD removal were investigated. The optimum pH for the removal of RB5 by MAC was determined as 7. The zero point charge (zpc) value of the MAC was calculated as 7.25. The adsorption capacity of MAC for RB5 was determined as 143.6 mg/g. The Koble–Corrigan isotherm model successfully described the adsorption process. In the adsorption stage of MAC/AS, RB5 and COD removal efficiencies within 90 min by 5.0 g/L MAC were achieved as 99.75 and 47.07%, respectively. The COD removal efficiency increased to 75.28% within 300 min by 6.25 g/L MAC. Meanwhile, 99.75% RB5 removal and 98.55% total COD removal efficiencies were achieved with sequential use of 3.75 g/L MAC and 4000 mg/L MLSS-AS. Experimental studies have shown that the sequential MAC/AS process has a high potential for the treatment of dye-containing textile wastewater.