The mechanism of Tubificidae in a sludge reduction system with Cr(Ⅵ) stress: an environmentally friendly scavenger

Abstract The treatment of heavy metals in sewage treatment systems has gained more attention with the increase in heavy metal hazards. Tubificidae in sludge reduction has been widely studied; however, little is known about the effect of Tubificidae in the treatment of Cr-containing wastewater. In this study, the mechanism of worms in the sludge reduction system with Cr stress was studied. Predation experiments by worms in a Cr-containing sludge reduction system were conducted to investigate the changes in enzyme activities in the worms under different concentrations of Cr, and the distribution of Cr in the worm sludge reduction reactor was analyzed. The kinetic model of uptake and elimination of Cr in worms was established. The results of SOD, POD and CAT activities indicated that worms had a certain detoxification effect on Cr(Ⅵ). After 28 days of worm predation experiments, the Cr concentrations in worms, sludge and worm feces increased first and then decreased with exposure time, and the proportion of total Cr and Cr(Ⅵ) in the sludge decreased from 71.98% and 42.7–29.18% and 6.82%, respectively. The detoxification mechanism of the worms could be activated with Cr stress, and 63.22% of the Cr(VI) was converted into Cr(III) by the worms. It can be seen that Tubificidae could be considered a good scavenger of environmental Cr(Ⅵ). The hyperbolic model fits the process of Cr uptake and elimination well and can be used as a predictive tool for worm accumulation.