Ecco will build, own, operate and design the plant which will serve the gated high-rise residential beachfront development, before later transferring ownership.
The sewage treatment plant will have a capacity of 2,000 cubic metres-a-day.
The $700m Marina West development will include restaurants, shops, leisure facilities and a private beach. It will cover 75,000 square metres.
The local Al-Hamad Construction & Development Company is the contractor on the project.