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Impacts of Chlorella vulgaris with or without co-existing bacteria on the removal of nitrogen, phosphorus and organic matter from wastewaters were studied by comparing the wastewater treatment effects between an algae–bacteria consortium and a stand-alone algae system. In the algae–bacteria system, C. vulgaris played a dominant role in the removal of nitrogen and phosphorus, while bacteria removed most of the organic matter from the wastewater. When treating unsterilized wastewater, bacteria were found to inhibit the growth of algae at> 231 mg/L dissolved organic carbon (DOC). Using the algae–bacteria consortium resulted in the removal of 97% NH 4+, 98% phosphorus and 26% DOC at a total nitrogen (TN) level of 29–174 mg/L. The reaction rate constant (k) values in sterilized and unsterilized wastewaters were 2.17 and 1.92 mg NH 4+–N/(mg algal cell· d), respectively.