Desalination has long carried a double burden. Conventional plants consume between 3 and 10 kilowatt-hours per cubic metre of freshwater they produce, and they leave behind concentrated brine that is costly to manage. A facility in Caofeidian, Tangshan, China, now claims to have solved both problems at once, cutting energy consumption by 60% against the industrial average while turning its salt residue into feedstock for the chemical industry.
- 60% energy reduction: New reverse osmosis membranes and recovered industrial waste heat combine to slash the power needed per cubic metre of water.
- Brine becomes revenue: A secondary concentration stage pushes salinity to 120 grams per litre, high enough to supply a soda ash factory instead of a waste lagoon.
- Industrial symbiosis: A 50-kilometre pipeline links the plant to chemical production, a model that depends on nearby heavy industry.
From Disposal Problem to Marketable Product
Instead of discarding the concentrated brine left over from reverse osmosis — the standard residue of the process — the system runs it through a secondary stage that lifts salt concentration to 120 grams per litre. That is the threshold needed to use the stream as raw material in the manufacture of sodium carbonate, better known as soda ash. A 50-kilometre pipeline connects the desalination site to a soda ash factory that previously depended on salt extracted through mining.
The economics are what make the model interesting. Brine shifts from an environmental liability into a sellable asset. Soda ash is a base input for glass, paper and detergent production, and its global market is worth more than $60 billion (roughly €56.4 billion) a year. This is not a marginal by-product stream: the co-processing arrangement can finance a significant share of the plant’s operating costs.
Where the 60% Energy Saving Comes From
Two factors drive the reduction. The first is technical: next-generation reverse osmosis membranes with higher salt-rejection efficiency, which cut the number of passes required to deliver potable water. The second is systemic: waste heat from the neighbouring soda ash plant’s industrial process is channelled into the brine concentration stage rather than being released into the atmosphere. In effect, adjacent industrial systems feed each other.
In its third phase, the facility aimed to treat nearly 100 million tonnes of water per year, a figure that would place it among China’s largest industrial desalination installations. Detailed capacity data for the first two phases has not been published.
Can the Model Travel Beyond China?
Caofeidian is a heavy-industry development zone on China’s northern coast, with an infrastructure density that makes precisely this type of industrial symbiosis viable. Replicating the approach along a Mediterranean coastline or in North Africa, where desalination plants typically operate far from chemical manufacturing, would require redesigning the entire value chain around new partners.
The underlying principle, however, is exportable: industrial symbiosis — where the waste of one process becomes the input of the next — is the core of the design and can be adapted to different pairs of industries. The same logic already appears elsewhere in the energy debate, such as proposals to cool AI data centres with wastewater from the oil industry, converting one sector’s problem into another’s solution.
The number that matters most is not the 60% saving, impressive as it is but partly dependent on local conditions. It is the demonstration that brine can be a value stream rather than a cost centre. If that idea generalises, the biggest non-technological obstacle to large-scale desalination — the expense of managing waste — begins to erode, and coastal regions facing water stress gain a far more viable route to supply.