Efficiency assessment and pH effect in removing nitrogen and phosphorus by algae-bacteria combined system of Chlorella vulgaris and Bacillus licheniformis

• A new algae-bacteria combined system is investigated for nutrient removal.
• NH4+ and P are more efficiently removed by the combined system than by the singles.
• Bacillus licheniformis is a growth-promoting bacterium for Chlorella vulgaris.
• pH control is crucial in the removal process by the combined system.
• Algae-bacteria combined system has potential in wastewater treatment.

To achieve better removal of NH4+ and TP in wastewater, a new algae-bacteria combined system of Chlorella vulgaris and Bacillus licheniformis   was investigated in a 6-d experiment. The results showed that 78% of NH4+ could be removed in the combined system, while 29% in single algae system and only 1% in single bacteria system. Approximately 92% of TP was removed in the combined system, compared with 55% and 78% in single algae and bacteria system, respectively. B. licheniformis was proven to be a growth-promoting bacterium for C. vulgaris by comparing Chl a   concentrations in the single and combined systems. In the removal process, pH of the combined system was observed to reduce significantly from 7.0 to 3.5. Whereas with pH regulated to 7.0, higher removal efficiencies of NH4+ (86%) and TP (93%) were achieved along with the recovery of algal cells and the increase of Chl a. These results suggest that nutrients in wastewater can be removed efficiently by the algae-bacteria combined system and pH control is crucial in the process.