Simultaneous treatment of wastewater and direct blue 2 azo dye in a biological aerated filter under different oxygen concentrations

Abstract

Wastewater discharges containing dyes are a compromising situation in many parts of the world. Azo dyes are the most widely used and contribute more than half of the total production of dyes. The mineralization of azo dyes is difficult due to its complex and recalcitrant structure. Biological treatment has proven to be a cost-effective and efficient alternative for dye degradation. An aerated biological filter fed with synthetic wastewater and dye, was strategically reduced it, the dissolved oxygen concentration (5 to 0 L/min). In this filter packed with porous material (lava stone) grows a biofilm, and presents simultaneous aerobic and anaerobic zones. This filter is able to remove organic matter and ammonia nitrogen efficiently. In general terms, as the air flow decreases and consequently the dissolved oxygen concentration, the removal of organic matter and ammonia nitrogen decreases, however, the removal of the Direct Blue 2 dye increases. In addition to this, the removal of ammonia nitrogen and phosphorus increases when dye is added to the wastewater. The Redox potential decreased along with the oxygen concentration and reflected reducing conditions from before stopping the aeration. The cell retention time decreased, but as the air supply was cut off, it increased. In the last stage of experimentation (DO at 0 mg/L) turbidity appeared, typical of fermentations, making it impossible to determine the majority of the biochemical parameters of the reactor.