An experimental comparative study of the technical and economic performance of a small reverse osmosis desalination system equipped with an hydraulic energy recovery unit

An experimental study is presented of a small-scale conventional seawater reverse osmosis (SWRO) system with potable water production of 1.7 m3/d, and the modifications made to this system by installing an hydraulic energy recovery unit and completely changing the pumps. The measured specific energy consumption of the proposed system was experimentally found to be 3.3 kWh/m3, which is a very promising value compared to the value of 20 kWh/m3 of the conventional system. Lowering the specific energy consumption results in the reduction of the total system's installed power, which achieves lower permeate production costs. The aim of the modifications was to test, investigate and construct a SWRO system equipped with an hydraulic energy recovery unit operating under variable conditions of pressure and flow to meet the variable power supply systems for future connection with renewable energy technologies such as photovoltaics and wind turbines. The only electrical load of the system is a brushless DC motor of 510 W maximum power, coupled directly to a positive displacement rotary vane pump with a flow rate of 900 L/h. The expected permeate production cost (excluding the energy production system cost) was calculated to be 3.68 €/m3, while the reported cost of transported water to some of the Greek Islands is 7 €/m3.