Abstract

Leather processing produces a large amount of wastewater with complex components. In particular, wastewater denitrification is a worldwide environmental problem. In this experiment, according to the characteristics of high concentration of suspended solid and heavy pollution load in leather wastewater, Bacillus cereus was used as the microbiota producing flocculant and its metabolites were collected as bioflocculant. Ampholytic starch was a novel selection for chemical modification, and the modified bioflocculant was used to treat leather wastewater. After determination, the removal rate of total nitrogen reached 100%, and the flocculation efficiency reached 98.17%. Exploring the flocculation mechanism of the modified bioflocculant for treating leather wastewater, shows that the modified bioflocculant and the pollutants in the wastewater were bonded by ionic bonds, and the particle size of supernatant in leather wastewater system gradually decreased from 2026nm to 147nm when the added modified bioflocculant charge was 0.08g, which indicated the existence of adsorption and bridging. In addition, the change of peak on the infrared spectrogram of the flocculation sediment indicated the chemical interaction of the functional groups such as -OH, -COOH in the flocculation process. When the pHof flocculation system rose from 4.0 to 8.0, the potential rose from -36mV to 1mV, which proved that a strong charge neutralisation occurred. Through observing the appearance of particles in leather wastewater system, it was found that multi-network overlapping structure flocs were formed after the modified bioflocculant interacted with wastewater, and the flocs could capture the remaining pollutants in wastewater, which proved that sweep-floc coagulation occurred. The results showed that the modified bioflocculant combined with a variety of flocculation ways in the treatment of leather wastewater which enhanced the flocculation ability. This study clarified the flocculation mechanism of modified bioflocculant and further, provided a reference for the development of new more efficient bioflocculant which is environment friendly.