Water, Water, Everywhere
It could be said that the story of life on Earth is, at its core, a story of water. There’s a reason why scientists look for water on other planets as a precursor for potential life — its simple yet unique polar structure makes it a “universal solvent”, in which salts and organic compounds such as amino acids and sugars readily dissolve, and an ideal medium in which chemical reactions can occur and nutrients can be easily transported.
Although 71% of the Earth’s surface is covered in water, only 2.5% of this is freshwater, and only 31% of that is available as surface water, atmospheric moisture, or groundwater. In other words, less than 0.8% of the Earth’s water is readily accessible by humans without treatment.
Given that, is it really any surprise that water is deeply entangled in our climate, energy, and national security challenges? Energy is required to produce clean water, and freshwater is required to access energy — whether it’s for oil & gas fracking or cooling steam turbines or electrolyzing hydrogen. Between 2000–2015, droughts and heat waves led to nearly 43 power plant curtailments in the US, and more recently France’s national utility had to throttle their nuclear plant output in response to a 2023 heat wave. As populations grow and urbanization expands in the midst of changing climates, the competition for water resources will intensify, fueling geopolitical conflict. For example, Egypt has threatened to bomb Ethiopia’s years-long dam project on the Nile river.
This “wicked problem” invites innovators to find creative solutions to resolve multiple problems simultaneously. Water is, in fact, everywhere—the problem is quality and distribution. Various “dirty” sources of water, including seawater, brines, and industrial wastewaters, can be treated to recover freshwater, as well as useful resources contained within those feeds. Because water is unfortunately structurally undervalued by most regulatory regimes, technologies that can profitably recover critical minerals, energy, and nutrients while treating wastewater are particularly promising.
What goes around comes around
Doing this requires turning the original problem upside down, and treating the output effluent as input feedstock. So what industries are generating wastewaters? In the US, the National Alliance for Water Innovation (NAWI) classifies them as follows:
- Power (41% of water withdrawals): mainly fossil fuel and nuclear thermoelectric power plants; much of this water is returned to the source after relatively minor pre-/post-treatment
- Agriculture (40%): drier Western states account for 46% of harvested cropland but use 84% of irrigation water
- Municipal (12%): typically the most stringent treatment requirements, but water stressed cities are relatively early adopters of new technologies — albeit with long sales cycles
- Industry (5%): driven primarily by oil refineries, pulp & paper mills, primary metals factories, chemical manufacturing, food & beverage industries, data centers, and large campuses
- Resource extraction (1%): ample quantities of water are often obtained when mining materials are dewatered or as a byproduct of enhanced oil & gas recovery
A large percentage of water withdrawals doesn’t necessarily mean all that water is consumed — environmental regulations mean that many industries must treat water prior to discharge, and companies are incentivized to reuse water where economical.
All that is gold does not glitter
As mentioned before, wastewaters often contain constituents which — if harvested — can provide energy, nutrients, and critical minerals. What can be valorized depends on the source of that wastewater.
- Power: N/A
- Agriculture: energy (organic matter), nutrients (fertilizer runoff, manure, etc.)
- Municipal: energy (organic matter), nutrients (urea, fertilizer runoff), critical minerals (seawater desalination)
- Industry: energy (O&G, pulp & paper, food & beverage), critical minerals (metals, chemicals)
- Resource extraction: energy (i.e. organics/hydrocarbons), critical minerals
In conversations with industry operators and researchers, what’s surprising is how much value is ignored in these wastewater streams today. One major copper miner generates process waters that contain remnant copper ions, and they are collaborating with researchers to recover additional copper — but they are currently ignoring the nickel that constitutes most of the metallic ions in the feed. A metal finishing shop uses electroplating to recover valuable gold and silver — but nickel and copper, along with less valuable elements, are disposed of as a hazardous sludge. And lithium miners struggle to selectively remove lithium from magnesium, but magnesium itself is an incredibly useful critical mineral.
In municipal wastewater treatment plants (WWTPs), excess nitrogen from ammonia can cause deadly algal blooms that suffocate fish, so WWTPs employ denitrification processes to convert it into nitrogen gas. However, much of that nitrogen comes from fertilizer usage, the production of which requires enormous amounts of energy and produces over 2% of global greenhouse gas (GHG) emissions. In other words, we use immense amounts of energy to create nitrogen fertilizer, only to flush it down the drain and use additional energy to turn it back into nitrogen gas.
Everything is energy and that’s all there is to it
What technologies can we leverage to make it economically feasible, and therefore a no-brainer, to recover as much valuable resources as possible from these wastewater streams? Ultimately, this comes down to separations technologies, which can be ordered by energy efficiency:
While it’s obviously advantageous to use lower-energy processes where possible, various technologies come with their pros/cons that make them better suited for specific scenarios. While none of these techniques are novel, we’ll explore some that are particularly promising when applied towards new applications:
Supercritical water requires thermal energy but is more efficient than distillation because it avoids phase changes. At supercritical conditions, the salt solubility in water decreases drastically, allowing inorganic salts to be separated. It does, however, require high temperature/high pressure reaction chambers resistant to corrosion, which can increase equipment CapEx. If the waste feed contains hydrocarbons, these can be oxidized to provide part or all of the energy required.
Solvent extraction separates compounds or metal complexes based on their relative solubilities in two different immiscible liquids, usually water (polar) and an organic solvent (non-polar). Some more novel technologies use a liquid solvent that directly extracts water molecules instead of dissolved ions, leaving behind the salts. This is a highly specific and targeted technique that has less stringent pre-treatment requirements, and is particularly well-suited to highly-concentrated brines where traditional thermal or membrane approaches would require excessive energy. However, it is only economical when the solvents can be efficiently captured and regenerated, which is an ongoing challenge. Furthermore, some of the organic solvents are highly flammable and require extra safety precautions. Examples of companies using solvent extraction include Wacomet, Trident Desalination, and pilots run by Trevi/Idaho National Lab.
Ion exchange is a process in which the targeted ion in solution is exchanged with another species of ion present in an insoluble solid (like an organic resin). This is a flexible and highly selective technique, but tends to be a batch process. Furthermore, regeneration of the resins requires acids and the efficiency of regeneration is an ongoing challenge. Examples of companies using ion exchange include Lilac Solutions, Standard Lithium, and Olokun Minerals.
Adsorption is the process by which a substance accumulates on the surface of another material, such as a solid or a liquid, forming a thin layer or film. Adsorption is a surface phenomenon and does not involve the complete absorption of the substance into the material. Absorption, on the other hand, involves the substance of interest being incorporated into the bulk of another material, resulting in a change in the material’s composition or properties, via dissolution, diffusion, or chemical reactions. These relatively simple techniques are low-cost and tolerant of wide pH bands, but require replacement of the ad/absorbent material and struggle with selectivity. Examples of companies using adsorption include Livent/ILiAD and Summit Nanotech.
Electrochemistry is a generalizable tool that can be combined with other techniques to create a highly-tunable forcing function. For example, electrowinning is commonly used to recover pure metal from solution by reducing them at a cathode. Electrocoagulation uses electrodes to produce coagulants in solution to bind with contaminants of interest. Electrodialysis utilizes an electric current to electrolyze or dissociate water, creating an electric field that is coupled with ion-exchange membranes to selectively allow targeted ions to pass through. Other techniques include capacitive deionization (or electrosorption) and using electric fields to induce crystallization. These systems are by nature modular and don’t require chemical inputs, so they benefit decentralized systems that don’t have easy access to pipelines and treatment plants. On the other hand, they don’t deal well with high-salinity brines, require significant pre-treatment to remove contaminants, and may cause problematic secondary reactions at scale. Examples of companies leveraging electrochemistry include ElectraMet and Membrion.
Waste to wealth
As mentioned earlier, the biggest surprise so far has been how many valuable elements in waste streams are currently ignored because the entities producing them are focused on only a specific product. There are valid reasons for staying focused, but we are starting to see mining companies and other entities interested in “full ore valorization” and technologies that can recover multiple types of minerals. This is likely to require a treatment train of different processes, so there appear to be ample opportunities for innovation.
If you are working on an interesting separations technology that can enable the recovery of energy, nutrients, or critical minerals, and are interested in seeing how Roadrunner Venture Studios can help, feel free to reach out!
