Phagotrophic microalgae production from waste activated sludge under non-sterile conditions

Application of phagotrophic algae in waste activated sludge conversion and stabilization

“…The O. danica specific growth rate (μ) on the VS in sonication-generated supernatant was found to be 0.1 h −1 or 2.4 d −1 in this study. This finding is consistent with previous studies, which reported that O. danica can grow on Escherichia coli (in deionized water) and VS released from thickened WAS with maximum μ of 0.1 h −1 and 0.2 h −1 , respectively (Lin & Ju, 2017;Xiao & Ju, 2018b). Having an algal yield of 0.3 (g algae/g VS), the phagotrophic alga could consume the bacteria-sized VS (as substrate) at a specific rate of 8 d −1 (or 8 g VS/g algae-d), estimated by U sub = μ/Y = 2.4/0.3, where U sub is the substrate utilization rate and Y is the algal yield from consumed substrate.…”

“…Each batch of bacteria-sized VS released by the sequential sonication was fed to the phagotrophic alga O. danica separately to evaluate its suitability for algal growth. As shown in Table 1, the raw WAS without sonication supported only a small extent of O. danica growth, increasing the cell number from 5.7 × 10 9 to 1.4 × 10 10 per L. The individual algal dry-cell weight was previously measured to be approximately 2.4 × 10 −11 g/cell (Xiao & Ju, 2018b). Accordingly, the raw WAS was estimated to support the O. danica growth with a small increase of 0.14 g/L of algal biomass.…”

“…While ultrasonication had been shown to release bacteriasized particles from WAS flocs for supporting growth of the phagotrophic alga O. danica (Xiao & Ju, 2018b), how a process that couples ultrasonication and phagotrophic algal cultivation would perform for WAS stabilization had never been examined.…”