Evolution of urban black and odorous water: The characteristics of microbial community and driving-factors.

Urban black blooms that are primarily caused by organic carbon are deleterious environmental problems. However, detailed studies on the microbial characteristics that form urban black blooms are lacking. In this study, we observed the composition, diversity, and function of bacterial community in the overlying water and sediments during the occurrence and remediation of urban black blooms using high-throughput 16S rRNA gene amplicon sequencing analysis. First, we found that pivotal consortia in the overlying water increased significantly during the formation of black blooms, including the genera Acidovorax, Brevundimonas, Pusillimonas, and Burkholderiales involved in the degradation of refractory organics, as well as the genera Desulfovibrio, Dechloromonas, and Rhizobium related to the production of black and odorous substances. An RDA analysis revealed that chemical oxygen demand, dissolved oxygen, and oxidation reduction potential were related to the changes in microbial community composition. Furthermore, aeration was found to accelerate the removal of ammonia nitrogen and enhance the function of microbial community by stimulating the growth of order Planktomycetes during the remediation of black blooms, but aeration substantially damaged the microbial diversity and richness. Therefore, the health of the aquatic ecosystem should be comprehensively considered when aeration is applied to restore polluted waterbodies. Notably, we observed a large number of pathogenic bacteria in urban black blooms, which emphasizes the importance of treating domestic sewage so that it is harmless. Together, these findings provide new insights and a basis to prevent and manage urban black blooms.

Characterization and coagulation-flocculation performance of a composite flocculant in high-turbidity drinking water treatment.

Klebsiella variicola B16, a microbial bioflocculant (MBF-B16)-producing bacteria, was isolated and identified by its 16S rRNA sequence, biochemical properties, and physiological characteristics. The effects of culture conditions on MBF-B16 production, including carbon source, nitrogen source, C/N ratio, initial pH, and culture temperature, were investigated in this study. Results showed that 6.96 g of MBF-B16 could be extracted from a 1-L culture broth under optimized conditions. Chemical analysis showed that polysaccharide and protein were the main components. The neutral sugar consisted of galactose only, which was proposed in Klebsiella genus for the first time. In addition, a composite flocculant (CF) that contains polyaluminum ferric chloride (PAFC) and MBF-B16 for the removal of turbidity and SS in drinking water was optimized by response surface methodology. CF could reduce PAFC dosage by about 56.2-72%. Charge neutralization and adsorption bridging effect were the primary flocculation mechanisms.