Problem 3 A three stage RO system (Fig. 1) is designed using the following module data of the osmonics permeator Module data Membrane recovery ratio: 10% -Salt rejection: 99.8% - Maximum applied pressure: 6895 kPa - Permeate flow rate of each module: 0.99 L/min - Water permeability 2.05x10 m³/m².s.kPa -Salt permeability 2.03x105 m/m².s Design data Feed salinity: 30,000 ppm Plant capacity: 56,750 m³/d -Permeate pressure: 101 kPa 3.1 Calculate the number of modules in each stage for the following configuration, flow rates and salinity of all streams, and the specific power consumption (assume pump efficiency is 80%). 3.2 Develop energy consumption profile if the reject brine stream is recycled back and mixed with the feed at different ratios (i.e. from 10% to 100% with 10% incremental increase). Express your opinion from both process economics (i.e. based on energy requirements) and environmental aspects if recycling the reject brine can be considered as a feasible option in the design of RO systems. Feed Fig. 1. A three-stage RO system Product Brine