The flow cell system and confocal laser scanning microscopy were applied to investigate the characteristics of biofilm formed by the nitrogenous heterocyclic compound (NHC)-degrading bacteria under different environmental conditions. The results showed that increasing the initial inoculum density and prolonging the initial attachment time were beneficial to the adhesion and biofilm formation of the NHC-degrading bacteria on the surface of the substrate. When the flow rate of the medium was reduced, the biofilm became more homogeneous and formed more water channel structures. Moreover, the biofilm under different conditions presented a same phenomenon that the inner layer (near the surface) had a low ratio of living cells and the outer layer (distant from the surface) had a high ratio of living cells. Compared with the single-strain biofilm, the dual-strain biofilm had an advantage in thickness, surface coverage ratio and living cell ratio. The target NHC concentration also had a significant effect on the morphology and cell viability of the quinoline-degrading bacteria biofilm: at lower concentration of quinoline, the bacteria formed large and developed aggregates; while at higher concentration, the bacterial aggregates became much smaller and evenly dispersive. Besides, the ratio of living cells of the biofilm formed at lower concentration was remarkably higher than that at higher concentration.

Choosing pyridine as the target pollutant, the pyridine-degrading performances and biofilm-forming properties of 12 pyridine-degrading bacterial strains, isolated from a coking wastewater treatment plant, were investigated. The results show that all the 12 strains had high degradation activity of pyridine. For two efficient degrading strains, Pseudomonas sp. ZX01 and Arthrobacter sp. ZX07, the optimal temperature and pH to degrade pyridine were 35oC and 7.0, respectively. Pyridine with initial concentration ranged in 100 to 2000 mg/L could be completely degraded by either strain. Furthermore, the biofilm-forming abilities of the 12 strains were significantly different. The cellular properties of extracellular protein secretion, extracellular polysaccharide secretion, and flagella-mediated swimming motility were identified to have significant positive correlations with their biofilmforming capacities. Our study provides scientific references for constructing a degrading-biofilm system for refractory wastewater treatment.