very complicated installation case 1

It depends on the application which you have not told us about at all.

If correctly installed and fitted with a foot valve the split case pump you have should be able to work with a three meter suction lift but whether it is the correct pump for the application i cannot say based on the information provided.

For any of us to give an opinion you would need to provide the pump curve for the split case pump and the total head, anticipated flow and the application that the pump is being used for. You also need to tell us the type of liquid that is being pumped ,whether or not it has solids in the liquid the liquid temperature and the approximate altitude above sea level of the site.

Is there a reason that the consultant wanted a positive displacement pump?

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

Why NFPA, is this a firepumps installation?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

NFPA20 section 6.1.2 forbids use of centrifugal pumps where a suction lift is required.

Therefore " I need a reference from NFPA that I can use such type of pumps in my case." is not possible

This was apparently due to foot valve failures and vacuum lift failures.

A PD pump has no such limitations in NFPA 20.

If you want to use this tank at that level then you either seen a vertical turbine pump suspended into the tank or a PD pump.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

thanks a ltot for your advice