The energy consumption of reverse osmosis (RO) varies significantly depending on the source water being treated, primarily due to the different pressures required to push water through the membranes.
Specifically, sea-water reverse osmosis (SWRO) desalination requires approximately 3 kWh/m³, while the RO treatment of wastewater demands considerably less, ranging from 0.1 to 1 kWh/m³.
Energy Consumption Varies by Water Source
The energy usage in reverse osmosis is not a fixed value; it is largely determined by the **total dissolved solids (TDS)** in the source water. Higher TDS levels, as found in seawater, necessitate much greater pressure to overcome osmotic pressure and effectively separate salts from water. Conversely, wastewater, having a lower TDS content than seawater, requires less energy for treatment.Specific Energy Requirements
To illustrate the difference in energy consumption, refer to the table below, which outlines the energy usage for different types of reverse osmosis applications:| RO Application | Energy Consumption (kWh/m³) |
|---|---|
| Sea-Water RO (SWRO) | ~3 |
| Wastewater RO Treatment | 0.1 to 1 |
Why the Difference?
The substantial difference in energy consumption between SWRO and wastewater RO is primarily due to the initial water quality: * **Higher Salinity:** Seawater contains a very high concentration of dissolved salts (salinity), requiring immense pressure (typically 50-80 bar or 700-1200 psi) to force the water through the RO membranes, separating the salts. This high pressure directly translates to high energy demand. * **Lower Salinity:** Wastewater, after primary and secondary treatment, has a much lower concentration of dissolved solids compared to seawater. Consequently, less pressure (typically 7-20 bar or 100-300 psi) is needed to treat it via RO, resulting in significantly lower energy usage.Understanding these differences is crucial for assessing the feasibility and cost-effectiveness of various reverse osmosis applications.
