Enhancing Photothermal Effects for Seawater Desalination

Overview

Much of Earth is covered by oceans; however, seawater is salty, and the planet faces increasing freshwater scarcity. Over the past two decades, 80 metropolitan areas have experienced severe droughts and freshwater shortages. This project aims to design a low-cost, solar-driven seawater desalination system using widely available materials. Design: a cup of seawater was placed inside a mini greenhouse under direct sunlight. Evaporated water was collected after condensation and weighed. The test produced a negligible amount of freshwater within one day. Redesigned experiment: To accelerate desalination, five black cellulose sponges (10cmx15cmx2cm for each) soaked with seawater were added, along with mirrors at the base of the greenhouse. Evaporated water was collected in three trials (one lasting two days and two lasting approximately 8 hours each). Results of redesign tests and analysis: Using the redesigned setup, approximately 50 g of freshwater (with salt concentration less than 0.01 %) was collected from 350 g of seawater (with salt concentration around 2.7%) within 8 hours in each trial. The black sponges and base mirrors significantly improved desalination efficiency. However, in the test, approximately 50% of the steam escaped from the greenhouse. Improving the seal is expected to increase freshwater collection over the same time period. Discussion: The black sponges and base mirrors significantly improved desalination efficiency. However, approximately 50% of the steam escaped from the greenhouse. Improving the seal is expected to increase freshwater collection over the same time period. Conclusions: This study shows that black cellulose sponges enhance the efficiency of solar-driven seawater desalination. Future work will focus on improving the greenhouse seal and scaling up the system to produce sufficient freshwater for daily personal use. Purpose/Design Goal and Background: Much of Earth is covered by oceans; however, seawater is salty, and the planet faces increasing freshwater scarcity [3]. Over the past two decades, 80 metropolitan areas have experienced severe droughts and freshwater shortages [4,5]. This project aims to design a low-cost, solar-driven seawater desalination system using widely available materials. Design-Redesign Test Description: Design: a cup of seawater was placed inside a mini greenhouse under direct sunlight. Evaporated water was collected after condensation and weighed. The test produced a negligible amount of freshwater within one day. Redesigned experiment: To accelerate desalination, five black cellulose sponges (10cmx15cmx2cm for each) soaked with seawater were added, along with mirrors at the base of the greenhouse. Evaporated water was collected in three trials (one lasting two days and two lasting approximately 8 hours each). Results of redesign tests and analysis: Using the redesigned setup, approximately 50 g of freshwater (with salt concentration less than 0.01 %) was collected from 350 g of seawater (with salt concentration around 2.7%) within 8 hours in each trial. The black sponges and base mirrors significantly improved desalination efficiency. However, in the test, approximately 50% of the steam escaped from the greenhouse. Improving the seal is expected to increase freshwater collection over the same time period. Discussion: The black sponges and base mirrors significantly improved desalination efficiency. However, approximately 50% of the steam escaped from the greenhouse. Improving the seal is expected to increase freshwater collection over the same time period. Conclusions: This study shows that black cellulose sponges enhance the efficiency of solar-driven seawater desalination. Future work will focus on improving the greenhouse seal and scaling up the system to produce sufficient freshwater for daily personal use.

Competition history

• CSEF 2026 Environmental Engineering (Junior Division) · Entry J-11-21

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