The interaction between Chlorococcum sp. GD and indigenous bacteria in the process of municipal wastewater treatment

Abstract

Municipal wastewater contains a significant amount of indigenous bacteria that probably influences microalgae-based wastewater treatment. In this study, Chlorococcum sp. GD was cultured in sterilized and unsterilized municipal wastewater to explore the interaction between the microalga and indigenous bacteria in the process of microalgae-based wastewater treatment. The removal efficiency of nutrient in unsterilized wastewater was higher than corresponding removal efficiencies in sterilized wastewater. It is worth mentioning that the growth of the microalga in unsterilized wastewater was better than that in sterilized wastewater. Carbon metabolism genes involved in glycolysis, citrate cycle, and pentose phosphate pathway, and nitrogen metabolism genes involved in nitrification and nitrogen reduction were detected for both indigenous bacteria and the microalga via metagenomic analysis. It was found that the microalga and indigenous bacteria competed with each other for nutrient, whereas different carbon/nitrogen metabolism genes of the microalga/indigenous bacteria cooperated with each other to complete nutrient removal. Nutrient in unsterilized wastewater was removed by both the microalga and indigenous bacteria. The inoculation of the microalga into unsterilized wastewater significantly reduced the number of indigenous bacteria due to insufficient nutrient, and simultaneously affected the abundance of some bacteria, such as Pseudomonas, Terrimonas, Ardenticatena, and Nitrospira, affiliating to Proteobacteria, Bacteroidetes, Chloroflexi and Nitrospirae. However, the indigenous bacteria still assisted the microalga in the removal of nutrient. These results showed that microalgae have the potential to treat unsterilized municipal wastewater.