Enhancing sludge dewatering efficiency through bioleaching facilitated by increasing reactive oxygen species

Abstract

Bioleaching facilitated by iron-oxidizing bacteria is regarded as a promising sludge dewatering method due to excellent dewaterability and low cost. However, a two-days bioleaching time for sludge conditioning decreased its daily treatment capacity. In fact, Fe2+ easily reacts with O2 to produce reactive oxygen species (ROS) with high oxidizing activity. Can bioleaching performed in Fe2+-rich system generate ROS to decompose sludge extracellular polymeric substances (EPS)? Here both contribution of ROS produced in bioleaching to improve sludge dewaterability and the increase of ROS content to shorten sludge bioleaching treatment time were investigated. The introduction of H2O2 in sludge bioleaching treatment (BS+H2O2) to increase ROS could simultaneously improve sludge dewaterability and decrease bioleaching time. Specific resistance to filtration (SRF) and capillary suction time (CST) reduction ratios (90.3% and 80.9%) in BS+H2O2 process were much higher than those in other processes after only 30 min reaction. Mechanisms of improving sludge dewaterability in BS+H2O2 mainly included ROS oxidation and Fe3+ flocculation by analysis of the contribution factors. These findings not only provide an effectively method to promote sludge dewatering efficiency of bioleaching, but also give new sights into the design of cost-efficient processes for improving the sludge dewatering.