Upgrade of aerated lagoon

Hi everyone.

What do you think  about upgrade of aerated lagoon for remove carbone،nitrogen،phosphor،

With economical process؟

I know that return of activated sludge is best way for nitrification. And anoxic for denitrification And anaerobic for remove phosphor.

But I want proper way to reduce Changes.

For example،use of anaerobic Tank befor anoxic And aerobic lagoon With SRT=40 days ؟ is it proper؟

Type of  wwtp:

3 aerated lagoons+ 2 setting lagoons

Depth of lagoons=4 m

 

Thanks for your attention