First, if you need to treat a ...

First, if you need to treat a lot of water, you can use multiple RO systems in parallel. Look at  online catalogs from various manufacturers to find out what units are being offered, and combine several as required to achieve your required flow. It is always advisable to have divide the flow into parallel systems, so you can take one out of service for maintenance or repair and retain part of the total capacity. Also, are you certain about the 3,600 m3/hour? This is a HUGE amount of water (23 MGD in US units), about the amount that  would be consumed by 180,000 people in the USA, and much more in developing countries. Double check your numbers.