Nitrogen requirement for the mesophilic and thermophilic upflow anaerobic filters of a simulated papermill wastewater

This study determined die minimum nitrogen concentration at which the mesophilic and thermophilic upflow anaerobic filters treating a simulated paper-mill wastewater could operate efficiently. For this purpose, the chemical oxygen demand (COD) to nitrogen ratio in both digesters was increased in five consecutive steps, from 94 : 5 to 363 : 5. The maximum COD to nitrogen ratios that provided satisfactory operation were 283 : 5 (30 mg N/L) and 363 : 5 (23 mg N/L) for the mesophilic and thermophilic reactors, respectively. The nitrogen consumption of bacteria in the thermophilic digester was lower than that in the mesophilic digester. The operational efficiency of the thermophilic digester was higher than that of the mesophilic one regardless of the COD to nitrogen ratio.