Understanding the interaction between triclocarban and denitrifiers.

The widespread use of triclocarban (TCC) has led to its substantial release into aquatic environment. As an important microbial community in wastewater treatment, denitrifying cultures likely remove TCC and also may be affected by TCC which has not been revealed. This work therefore aims to add knowledge to these questions. Experimental results showed that 71.2 %-79.4 % of TCC was removed by denitrifying sludge in stable operation when TCC concentration was 1∼20 mg/L. Mass balance analyses revealed that TCC was dominantly removed by adsorption rather than biodegradation, and non-homogeneous multilayer adsorption was responsible for this removal, with hydroxyl groups, amides and polysaccharides acting as the possible adsorption sites. Although the physicochemical properties of denitrifying cultures were unaffected after short-term exposure, long-term exposure to TCC deteriorated the settleability, dewaterability, flocculability and hydrophobicity of denitrifying biomass. It was observed that 20 mg/L TCC decreased denitrification efficiency by 70 % in long-term operation. Mechanism studies revealed that long-term exposure to TCC resulted in the increase of extracellular polymeric substances especially proteins, and the decrease of denitrifiers' activities. High-throughput sequencing revealed that TCC decreased the diversity of microbial community and the abundances of denitrifier genera such as Hyphomicrobium, Paracoccus, Saprospiraceae and unclassified-f-Rhodocyclaceae.

Effect of citric acid on extracellular polymeric substances disruption and cell lysis in the waste activated sludge by pH regulation.

This paper investigated the effects of citric acid (CA) on extracellular polymer destruction and cell lysis in sludge at different initial pH by measuring capillary suction time (CST), extracellular polymeric substances (EPS) and intracellular bound water. The results indicated that under CA concentration at 0.05 g/g suspended solids (SS) and initial pH 4, the CST value decreased from 175.5 s to 112.3 s, slime extracellular polymeric substances (S-EPS) and loosely bound EPS (LB-EPS) content respectively to increase from 4.92 to 41.43, 2.27 to 5.49 mg/g volatile suspended solids (Vss), while tightly bound EPS (TB-EPS) content to decrease from 12.35 to 5.01 mg/g (Vss), which suggested CA could disrupt outer EPS effectively. Intracellular bound water content decreased from 1.23 g/g to 0.41 g/g dry solid (DS). As a result, CA could release intracellular bound water effectively, thereby improving sludge dewatering degree.