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Effect of light intensity on the characteristics of algal-bacterial granular sludge and the role of N-acyl-homoserine lactone in the granulation

Zhang, Bing, Guo, Yuan, Lens, Piet N.L., Zhang, Zhiqiang, Shi, Wenxin, Cui, Fuyi, Tay, Joo Hwa
The Science of the total environment 2019 v.659 pp. 372-383
biofilm, biomass, chemical oxygen demand, lactones, light intensity, microbial communities, municipal wastewater, nitrogen content, particle size distribution, protein synthesis, proteins, quorum sensing, sludge, statistical analysis, tryptophan
The effects of light intensity on the development of algal-bacterial granular sludge (ABGS) were investigated over a period of 12 weeks. The ABGS developed at low light intensity (142 ± 10 μmol m−2·s−1) exhibited excellent settling ability (SVI30 of 30.9 mL/g), COD and TN removal efficiencies (97.6% and 60.4%, respectively). High light intensity (316 ± 12 μmol m−2·s−1) accelerated granular biomass growth (5.3 g/L) and enhanced the TP removal efficiency (83.7%). Extracellular polymeric substance (EPS) analysis revealed that low light intensity induced more large weight distribution protein production (9–12 kDa and 50–150 kDa), predominantly tryptophan and aromatic proteins. Furthermore, N-acyl-homoserine lactones (AHLs) with a side chain ≤ C10 were commonly shared in the ABGS, and the ABGS developed at low light intensity had a higher C6- and 3OC8-HSL content, which effectively promoted the biofilm formation. The add-back studies showed that the AHLs facilitated the regulation of EPS synthesis. Statistical analysis indicated that the AHLs content had a close correlation with the EPS production, the 50th percentile of the particle size distribution and microbial community assembly, suggesting that AHLs-mediated quorum sensing have an important ecological role in EPS expression and algal-bacterial granulation. Overall, this study describes the ABGS development at different light intensities and the mechanisms of ABGS formation treating synthetic domestic wastewater.