Municipal wastewater treatment by microalgal-bacterial consortium without mechanical aeration – Effect of initial inoculum Chlorella vulgaris and activated sludge addition

A mixed culture, prepared by acclimatising Chlorella vulgaris (C. vulgaris) to municipal wastewater (MWW), was used in two reactors: one was inoculated with activated sludge (AS), and the other was not (NAS). Under 12:12 h light: dark, mixing, and a hydraulic retention time of 1.17 d, both systems removed ∼92 % of 270 mg-COD/L, 57 % of 70 mg-N/L, and 27 % of PO₄³⁻-P, while achieving a sludge volume index of 42 mL/g. C. vulgaris disappeared and was replaced by other algae, including cyanobacteria, indicating that inoculation is not necessary. Higher dissolved oxygen production, IC uptake, and nitrification occurred in the NAS reactor than in the AS reactor, supported by a higher abundance of the autotrophic/aerobic community in the NAS reactor. Genomic data revealed latent mechanisms (denitrification, N-fixation, nitrate/nitrite reduction, multiple phosphorus pathways) than mass balance. Pure algae seeding is not essential, but activated sludge seeding could affect performance.