Microbial community structure and dynamics in a mixotrophic nitrogen removal process using recycled spent caustic under different loading conditions

► Heterotrophic denitrification which uses organics increases operating cost of WWTP. ► We applied MSC to nitrogen removal process instead of organic carbon. ► MSC application proved to be efficient for nitrogen removal of sewage with a low C/N. ► The NLR of 0.15 kg N/m3 d is recommended to satisfy water quality regulations. ► MSC caused the increase of genus Thiobacillus known as an autotrophic denitrifier.