Microalgal-bacterial system responses to nitrogen forms in dairy farm wastewater: Focusing on the phycosphere and nitrogen transformation

Abstract

As an environmentally friendly medium, microalgae are often used in wastewater treatment. However, few studies have examined the effects of different nitrogen forms on microalgae and bacteria, particularly regarding material and gene transfer and nitrogen metabolic pathways in phycosphere and various extracellular polymeric substance layers. To address this research gap, Chlorella vulgaris was used to treat the dairy farm wastewater with different nitrogen additives. The results showed that the dry weight and chlorophyll a production were lowest at high ammonia nitrogen concentrations (0.460 g/L and 0.883 mg/L, respectively). The ability of microalgae to remove total phosphorus and ammonia nitrogen was significantly enhanced at appropriate nitrogen concentrations. There were clear differences in community abundance between phycosphere and different extracellular polymeric substance layers bacteria. Nitrate nitrogen promoted electron transfer in photosynthesis, while organic nitrogen facilitated the synthesis of siderophores. In high-ammonia nitrogen wastewater, ammonia nitrogen conversion primarily occurred through the action of nitrifying bacteria, whereas denitrification promoted nitrate nitrogen conversion. There is an interaction between nitrogen forms and microalgal-bacterial system. The study provided critical insights for microalgae treatment of dairy farm wastewater, contributing to environmental friendly and resource recycling wastewater management.