Waste Heat from Waste Pyrolysis for Desalination, with Biochar for Water Treatment
Introduction
Desalination can provide freshwater from seawater, but it normally requires a large amount of energy. At the same time, waste pyrolysis produces useful heat while converting waste biomass or other waste materials into products such as biochar, gases and oils.
This creates an interesting circular system: waste → pyrolysis → useful heat → desalination → freshwater, while the resulting biochar can potentially be used for further water treatment.
Research already shows that waste heat can successfully drive thermal desalination, although the exact combination of waste biomass pyrolysis + desalination is still an emerging area. [1][2]
1. Using Waste Heat for Desalination
Desalination does not always need high-quality electricity. Thermal desalination systems can use heat directly to evaporate water.
A major review by Elsaid et al. found that around 20–50% of industrial energy can be lost as waste heat. Much of this is low-temperature heat, but it can still be useful for certain desalination technologies. The review found that using waste heat can reduce both the energy cost and environmental impact of desalination. [1]
Another review found that 63% of industrial waste-heat streams are low-temperature heat, showing why technologies designed around low-grade heat are particularly important. [2]
This is important for waste-processing facilities because heat that would otherwise be released into the environment could instead become a useful input for producing freshwater.
2. Pyrolysis and Desalination Can Be Combined
A 2025 study by Hu et al. investigated an integrated system combining waste-tire pyrolysis, waste-heat recovery, power generation, desalination and carbon capture.
The researchers used process simulation to design a system where heat produced by pyrolysis and energy-generation processes was recovered and used across the system, including for desalination.
The proposed system achieved:
- 51.5% energy efficiency
- 48.76% exergy efficiency
- Waste tires were converted into useful products instead of being discarded.
- Waste heat was used for desalination rather than requiring separate heating energy.
- Carbon capture was also incorporated into the system. [3]
However, this study is a simulation and process-design study, not a demonstration of a commercial plant. The authors also found that economic viability depends strongly on waste prices, product prices and financial support. [3]
This provides a strong example of the broader idea: one waste-processing facility can potentially produce several useful outputs instead of treating heat, waste and water as separate problems.
3. Biochar Can Add Another Water-Treatment Function
Biochar is the carbon-rich solid produced when organic material is heated with little or no oxygen. Because it can have a porous structure and chemically active surfaces, it can also act as an adsorbent.
Research has already investigated biochar for removing salts and other contaminants from water.
For example, Salazar Rojas et al. produced biochar from pruning waste and used it as a photothermal membrane in a solar desalination system. Their system reported a 91.08% reduction in measured salinity, along with reductions in chlorides, dissolved solids, turbidity, sulfates and phosphates. [4]
Another study used rice-straw biochar to remove barium and strontium from saline water. The biochar removed up to 97.5% of Ba/Sr ions, while also achieving a 25.7% reduction in salt concentration during the tested pre-desalination process. This could potentially help reduce mineral scaling in desalination equipment. [5]
A newer 2026 study also produced biochar using concentrated seawater, a desalination by-product, as part of the biochar-production process. The resulting material showed useful porosity and adsorption properties, demonstrating another possible connection between desalination waste and biochar production. [6]
Economic and Environmental Potential
The strongest opportunity is not simply to make freshwater. It is to connect several waste and resource streams together:
Organic waste → pyrolysis → biochar + energy/heat → desalination → freshwater
This can potentially:
- Reduce the amount of waste requiring disposal.
- Recover useful energy that would otherwise be wasted.
- Reduce the external energy required for desalination.
- Produce biochar as a saleable or useful material.
- Create additional water-treatment applications for biochar.
- Reduce greenhouse-gas emissions compared with systems relying entirely on fossil-fuel energy.
For developing regions, the combination could be particularly interesting where waste management, energy access and water scarcity occur together.
Important Limitation
The evidence should not yet be presented as proof that biochar production from waste can commercially power desalination. The research strongly supports the individual links:
waste heat → desalination [1][2][3] and waste-derived biochar → water treatment/desalination [4][5][6]
But fully integrating waste biomass pyrolysis, heat recovery, desalination and biochar-based water purification into one practical system still needs further engineering, pilot testing and economic assessment.
WF23 Relevance
This is particularly relevant to a circular waste-to-value approach. Instead of treating waste, heat, water and carbon as separate problems, they can potentially become interconnected resource streams.
The most interesting future concept is therefore:
Waste → Biochar + Energy → Desalination → Clean Water → Biochar-based Polishing/Treatment
References
[1] Elsaid, K., et al. (2020). Recent progress on the utilization of waste heat for desalination: A review. Energy Conversion and Management, 221, 113105. DOI / paper
[2] Charitar, D. & Madhlopa, A. (2022). Integration of waste heat in thermal desalination technologies: A review. Journal of Energy in Southern Africa, 33(1), 68–84. Full article
[3] Hu, Y., Zhou, J., Qian, Q. & Ren, J. (2025). Innovative valorization of waste tire by integrating pyrolysis with Steam Rankine Cycle, multi-generation, and desalination. Energy, 323, 135812. DOI / paper
[4] Salazar Rojas, J. C., et al. (2022). Photothermal Membrane of Biochar from Pruning Residues for the Reduction of Seawater Salinity. Chemical Engineering Transactions, 92, 181–186. DOI / paper
[5] Use of rice straw-based biochar for batch sorption of barium/strontium from saline water: Protection against scale formation in petroleum/desalination industries. Journal of Cleaner Production, 250, 119442 (2020). DOI / paper
[6] Yu, et al. (2026). Concentrated Seawater-Assisted Greener Production of Biochar: Waste Valorization and Its Implication in Circular Economy. CleanMat. DOI / paper