A higher C/N ratio enhances nitrogen treatment and the biodiesel characteristics of algal-bacterial bioflocs derived from aquaculture wastewater

Abstract

One of the major issues facing intensive aquaculture is controlling pollution and converting nutrients in the effluent into usable biomass. This study investigated the generation of algal-bacterial bioflocs (ABBs) from Chlorella pyrenoidosa at different C/N ratios in aquaculture wastewater supplemented with glucose. Subsequently, we evaluated the nitrogen and phosphorus metabolism of this biomass, analyzed nutrient composition and potential as a biodiesel, conducted a thorough analysis of the microbial community. During the ABBs production, higher C/N ratio promoted the utilization of various forms of nitrogen, but resulted in more nitrogen losses. ABBs produced at high C/N ratio was more favorable for nitrogen conversion in light and dark conditions, especially at C/N 15, but unfavorable for crude protein (35.08 ± 1.89 %) and crude fat (13.01 ± 1.79 %) accumulation. Additionally, ABBs produced with glucose supplementation exhibited a higher cetane number, which is advantageous for producing eco-friendly, high-performance biodiesel. The high-throughput sequencing analysis demonstrated a significant abundance of Pesudomonas and Bacillus in high C/N ratio groups, which explained the higher removal efficiency and removal rate of nitrogen from wastewater. In conclusion, the addition of carbon sources improved both nitrogen removal and biodiesel performance of ABBs.