Hi Upal. This is not a ...

Hi Upal. This is not a question that could be answered in a few lines, but will try to.

I would say you go for vertical flow systems, 2-stages, with primary treatment(sedimentation or what I prefer, anaerobic baffled reactor) or without (if you choose the french design). Concerning dimensions, I need to know where the system is to be build (climate). Also to reduse nutrients (mainly nitrates), you should apply effluent recirculation. For further minimising of nitrogen and phosphorus, you could install a downstream zeolite/bauxite filter. If there is not enough space, aerated beds are also a very goo solution. Generally, I think that area demand would be around 400-500 m2.