Solar Water Desalination

• 18 Apr 2025

Why in News? 

Indian Institutes of Technology (IIT)- Bombay scientists have developed a new material to enable water desalination and address global freshwater scarcity. 

Key Points 

• About the Innovation: 
  • Researchers have developed a Dual-Sided Superhydrophobic Laser-Induced Graphene (DSLIG) evaporator. 
  • The DSLIG addresses limitations of traditional evaporators and shows promise for large-scale desalination and wastewater treatment. 
  • The Freshwater Challenge: 
    • Only 3% of Earth’s water is freshwater, and less than 0.05% is easily accessible. 
    • Desalination of seawater and brackish water is a key solution to this scarcity. 
    • However, desalination produces brine, a concentrated salt byproduct, which poses disposal challenges, especially in landlocked areas. 
    • Industries now aim for zero liquid discharge systems to avoid environmental harm. 
• Solar Desalination: 
  • Solar energy-based desalination offers a low-carbon solution. 
    • Yet, sunlight variability and poor light absorption reduce efficiency. 
  • Interfacial evaporation systems help by heating a thin surface layer of water instead of the whole volume, enhancing efficiency. 
  • Challenges in Interfacial Evaporation: 
    • Cloud cover and fluctuating solar intensity hamper consistent performance. 
    • Evaporation peaks around 2 pm, when solar radiation is highest. 
    • Salt deposition on the evaporator surface blocks water contact, reducing long-term efficiency. 
  • DSLIG Overcomes the Challenges: 
    • DSLIG allows dual heating—solar and Joule heating (electric)—ensuring performance even in low sunlight. 
    • Superhydrophobic properties (lotus effect) prevent salt from sticking to the evaporator surface. 
• Fabrication of DSLIG: 
  • Researchers coated PVDF (polyvinylidene fluoride) on one side of PES (polyether sulfone) polymer. 
    • PDVF are polymers that can generate electric charges on the surface under pressure/strain thus converting mechanical energy into electrical energy. 
    • PES is a thermoplastic polymer known for its high thermal stability, excellent chemical resistance, and biocompatibility. 
  • They used laser engraving to inscribe graphene onto the PVDF layer. 
    • PES ensures mechanical strength, while PVDF contributes to dual-sided water repellency. 
  • The result is a durable, superhydrophobic surface effective in both electric and solar modes. 
  • Applications: 
    • It is suitable for treating industrial wastewater and brine from desalination plants. 
    • Researchers observed improved performance by stacking multiple evaporators. 
    • DSLIG is low-cost, non-toxic, and sustainable, making it ideal for large-scale applications. 

 Desalination  

 

• A desalination plant turns salt water into water that is fit to drink. 
  • Desalination is the process of removing salts from water to produce water that meets the quality (salinity) requirements of different human uses. 
• The most commonly used technology for the process is reverse osmosis. 
  • An external pressure is applied to push solvents from an area of high-solute concentration to an area of low-solute concentration through a semi-permeable membrane. 
  • The microscopic pores in the membranes allow water molecules through but leave salt and most other impurities behind, releasing clean water from the other side. 
• These plants are mostly set up in areas that have access to sea water.