I want to setup a small scale water treatment plant, what are the machines required?

You would need to know the water quality being treated, and have parameters for the water quality you wish to achieve.

An RO plant, or Desalination plant are potential solutions.  Alternatively there are Sulphate Removal Plants.

For any of these you will require Lift pumps, Coarse Filters, Booster Pumps, and Membrane filters. (note the filters would need to be contained in a pressure vessel)

All of these would be connected using pipework, assuming seawater, then the CS pipework would need to be lined, or alternatively using exotic materials or GRE materials.  Depending on the complexity, and job requirements there will be varying requirements for valves, instrumenation and electrical motors.  All of which will require cable tray, cabling, and in some cases tubing.

Without knowing more about the scope, and desired end result, it is not a simple question to answer. Hopefully the above provides at least a basic insight into what the job might entail.

Cheers

It depending on your raw water quality and what efficiency do you expect upstreem

if you have only scale issue you can go direct with softener device  , it will make the water soft so there is no scaling forming . 

A RO plant is best for treating water and for manufacture mini plant machine will used only of RO plany and different section wll constructed.

A reverse osmosis plant is a manufacturing plant where the process of reverse osmosis takes place. An average modern reverse osmosis plant needs six kilowatt-hours of electricity to desalinate one cubic metre of water.Self-contained water treatment plants using reverse osmosis, called reverse osmosis water purification units, are normally used in a military context.

Its called and RO plant. Reverse osmosis plantclick the link