P-bacteria can combine denitrification and P-uptake. This category of P-bacteria is abbreviated DPB. Use of DPB in BNR processes, instead of obligate aerobic PAOs, reduces oxygen consumption. Moreover, less COD is needed for the nitrogen removal. Non-required COD can be removed by presettling and used for methanation. This leads to a lower sludge production. As a result, CO2 emissions are reduced owing to less net energy consumption. Simulation for a planned WWTP with the BCFS process indicates that DPB can save 53-59% of required COD. The optimal ratios of COD/N and COD/P for simultaneous N and P removal are determined to be 3.9-4.5 and 32.2-35.2 at 12-20 degrees C. 80-95% of particulate COD can be removed from the influent, thereby CH4 production is increased by 154-271%, and the total volume of reactors can be reduced by about 50% compared to a minimised process design. Less net energy consumption over the whole WWTP contributes to a net reduction of the total CO2 emissions up to 16-21%. The energy production from CH4 is excessive enough to balance the energy consumption from aeration, dewatering and incineration. It is concluded that contribution of P-bacteria to saving COD has overall positive effects on the environment.