Performance and recoverability of microalgal-bacterial granular sludge under weak light-dark conditions

As an emerging process, microalgal-bacterial granular sludge (MBGS) still has insufficient research under weak light-dark conditions, which is not conducive to its operation in cloudy weathers. Therefore, the performance, characteristics and microbial dynamics of MBGS process were systematically studied under weak light (20 μ mol/m 2 /s, 12 h)-dark (0 μ mol/m 2 /s, 12 h) conditions. And further research was conducted to determine whether a normal light intensity (200 μ mol/m 2 /s) could help to recover the performance and properties of MBGS. The results showed that the effluent dissolved oxygen concentration gradually dropped, with the granule size decreased, and the settling performance deteriorated since the 12nd day to 22nd day. Subsequently, it was observed that the morphology and performance of MBGS could be entirely recovered gradually after the light intensity was adjusted to normal (200 μ mol/m 2 /s) for the light phase. Furthermore, weak light-dark conditions were found to reduce the relative abundance of Proteobacteria and Chlorophyta, but to promote the growth of Rotifera and Cyanobacteria. Specifically, Tychonema was speculated to be the possible cause for the deterioration of the MBGS system. This study is expected to offer theoretical guidance for MBGS operation under light-insufficient conditions.