Abstract
Conventional biological nutrient removal (BNR) processes require intensive energy input, involving aeration and additional carbon sources, which increase operating costs and may introduce unwanted contamination. This study investigates the nitrogen removal performance from synthetic wastewater using microalgae-photoautotrophic simultaneous nitrification and denitrification (SND) in novel inverse fluidized bed bioreactors (IFBBRs). Two lab-scale IFBBRs were operated under varying hydraulic retention times (HRT) for 465 days, achieving a total nitrogen removal efficiency of 72% for IFBBR2. The reduction of HRT from 48 hours to 21 hours led to an increase in the total nitrogen removal rate, indicating the system’s adaptability to varying operational conditions.
This study highlights the role of microalgae in microalgae-bacterial consortia, providing a biodegradable carbon source and producing oxygen through photosynthesis, which supports the growth of nitrifying bacteria during the day and denitrifying bacteria at night. Microalgal growth, simultaneous nitrification-denitrification, and autotrophic denitrification were successfully established in the IFBBRs. After 465 days of operation, IFBBR2 achieved 75% total nitrogen removal, with influent concentrations of NH4-N and NO2–N at 75 mg-N/L and 93 mg-N/L, respectively, and a nitrogen removal rate (NRR) of 0.15 kg N/m³d without the need for additional carbon sources or aeration.
This study suggests new perspectives on nitrogen removal with lower energy input, economical operating expenses, and reduced carbon emissions.