Adding iron shavings in activated sludge system to enhance removal of refractory organics and nitrogen for textile-dyeing wastewater

Abstract

To improve the biodegradability of textile-dyeing wastewater, reduce the biotoxicity of refractory pollutants to activated sludge, and enhance the removal of refractory organics and nitrogen for wastewater. A new coupled system of adding iron shavings in activated sludge was developed for the treatment of textile-dyeing wastewater. The results showed that the average removal efficiencies of chemical oxygen demand and total nitrogen in the coupled system reached 74.9% and 55.0%, respectively. On day 60, the mean granular size and sludge volume index after 30 min of the coupled system reached 206 µm and 24 mL/g, respectively, and aerobic granular sludge was formed. The microbial community structure and function in the system was changed, especially the increase of autotrophic denitrifiers (Hydrogenophaga, Xanthobacter, and Unclassified_f_Comamonadaceae), hydrolytic acidification bacterias (Ottowia and Limnobacter), which enhanced the performance of simultaneous nitrification and denitrification. The monitoring of different periods showed that the specific oxygen uptake rate associated with ammonia oxidation and heterotrophic bacteria in the coupled system was significantly higher than that in the control group, which indicated that iron shavings act as a detoxification function in refractory wastewater. In addition, the iron content of the sludge in the coupled system was 9.6% higher than that of the control group. These iron by-products were good flocculants, and have a significant performance of the adsorption for pollutants. Furthermore, the mechanism of synergistic treatment of wastewater by the coupled system was proposed.