Role of influent split ratio in a two-line BNR process performing denitrifying phosphorus removal

• A two-line BNR process enriching DPBs was developed.
• Role of split ratios in DPB enrichment was discussed.
• The best (AN/AO) split ratio for the process is 12:8.
• DPB enrichment in the process is only 45% but the process performance is stable.

Denitrifying phosphorus removal is very effective in retarding competition between denitrifying bacteria and phosphorus removing organisms for limited carbon in influent, and can enhance performances of biological nutrient removal processes (BNR) treating low strength wastewater. The aim of this study is to demonstrate the effects of influent split ratios on enrichment of denitrifying phosphorus removing bacteria (DPB) in a two-line BNR process. Performances of the process under different influent split ratios were investigated; profiles of intracellular compounds were characterized; mass flow were also described. The results showed that influent split ratio had no obvious effects on COD and total phosphorus distribution in bulk water when influent COD concentration was in the range of 172.0–183.3 mg/L, but affected intracellular content in activated sludge significantly. Better performances for ammonia removal were observed under influent split ratios (AN/AO, ratio of influent flow rates between the anaerobic–anoxic–anoxic line and the anaerobic–aerobic–aerobic line) of 10:10, 12:8 and 8:12 than under 15:5. An optimized balance between anoxic and aerobic phosphorus removal could be reached by adjusting the influent split ratio. Total nitrogen removal rate was improved by 16% through increasing the influent AN/AO split ratio from 8:12 to 12:8. This study also helped to understand role of split ratio in balancing pollutants removal within BNR processes.