Behavior of carbon source type on the construction of aerobic granular sludge system and its removal of quinoline: A tortoise and hare race between starch and phenol

Coal chemical wastewater contains high concentrations of toxic organic pollutants such as quinoline and phenol. Microorganisms in aerobic granular sludge (AGS) are known to efficiently degrade organic matter. This study systematically compared the cultivation characteristics of quinoline-degrading aerobic granular sludge using starch (R1), a common carbon source, and phenol (R2), a toxic carbon source, as co-metabolizing substrates. The results indicated that R2 was more conducive to improving sludge settleability, biomass retention, and the growth of quinoline-degrading bacteria when a low quinoline concentration (30 mg/L) was applied. However, as the quinoline concentration increased, the granular sludge cultured with starch eventually outperformed phenol as a co-metabolizing substrate in terms of settling performance, biomass, and pollutant removal. Analysis of the pollutant degradation characteristics during a typical operation cycle revealed that the time required to degrade quinoline to approximately 5.5 mg/L was 150 min in R1 and 420 min in R2, indicating a higher reaction rate in R1. Acidovorax was identified as the dominant quinoline-degrading bacterium in both reactors. In addition, microbial differential analysis and functional genes indicated more pronounced bacterial differentiation in R1, enriched in Firmicutes and Deinococcaceae. the relative abundance of enzymes associated with quinoline degradation was higher in R1.