Briefly explain biological excess phosphorus removal (BEPR) mechanism. How anaerobic-aerobic cyclic conditions make the PAOS (phosphorus accumulating organisms) dominant in a mixed culture. Explain why nitrate recycle to anaerobic zone has the adverse effect on Biological Excess Phosphorus Removal (BEPR). Explain a process decreasing this negative effect to minimum by drawing the flow chart of the system, when partial N and P removal is desired