Overestimated role of inoculation bacteria-algae ratio in wastewater treatment

Microalgae-bacteria systems present a promising approach for CO₂ reduction in wastewater treatment. The effect of inoculation bacteria-algae ratio on performance was investigated in this study. Different inoculation ratios (bacteria: algae 1:2, 1:1, 1:0.5, 1:0.25, 1:0.125, w/w) obtained comparable nutrients removal (p > 0.05). Over time, the bacteria-algae ratios converged into two groups (3:1 and 4:1), demonstrating self-adaption between bacteria and microalgae. Furthermore, principal component analysis (PCA) distinguished the performance of reactors into two groups, one group consisting of 1:2, 1:1, and 1:0.5 ratios and the other group consisting of 1:0.25 and 1:0.125 ratios, confirming their convergence in terms of nutrient removal and photosynthetic properties. The performance differed merely in sludge volume index (SVI) and nitrite accumulation, with 1:2 and 1:0.125 being the most prone to accumulate nitrite. This study implies that photobioreactor performance was not sensitive to inoculation ratio, whose role was overestimated, since microalgae and bacteria self-assemble to form niches. PRACTITIONER POINTS: Effect of inoculation bacteria-algae ratio on performance was overestimated Photosynthesis and nutrients removal were grouped at different inoculation ratios Different ratio showed similar nutrients removal efficiency Self-adaption made ratios of 1:2, 1:1, 1:0.5 converge into 3:1.