At Singapore's International Water Week conference in July, Siemens announced the results of its low-energy electrodialysis desalination system. The project for the Singapore government targeted energy usage of just 1.5 kWh/m3, which is near the theoretical limit* for desalination technology. Siemens operated the Singapore plant for the last three years, and during that period reduced its energy consumption to 1.7 kWh/m3. However, they explained to Lux that the system's opex and capex still needed improvement to be truly competitive with seawater reverse osmosis (RO). Contractually, failing to reach the 1.5 kWh/m3 target holds no penalty. Siemens said that it had completed optimization of the plant, but added that it's still working in the lab to reduce costs. It aims to unveil the product of that work in 12 months to 24 months.
In learning more about this technology, some things stood out to us. First, the system's membrane is 10 times more expensive than the threshold for cost effectiveness. This is especially striking given that it's an off-the-shelf product with no modifications. In addition, the system achieved a relatively low freshwater recovery of 35%. Although electrodialysis systems are not expected to require as much pretreatment as reverse osmosis, this system operated behind an existing ultrafiltration membrane, signifying a best-case scenario. Further, this solely Siemens-driven effort created more than 100 invention disclosures, suggesting the project is at least as much research as development.
While Siemens has proven it is possible to approach the theoretical limits of energy use for desalination using electrodialysis, it has yet to prove it can do so in a cost effective way. Without this, it is unlikely this system will see the widespread implementation implied from the buzz surrounding its press release.
