Drinking water is considered one of the most essential human needs. Unfortunately, one in three people on the earth is affected by the fresh water scarcity. The situation is worse in underdeveloped areas where there is no electricity to power the conventional water treatment technologies. A novel solar thermal membrane distillation system has been designed for producing potable water from untreated surface water, seawater, and municipal wastewater, using solar thermal energy. The configuration of the system does not include photovoltaic cells, pumps or heat exchanger for its operation. Thus, it requires no electricity and is suitable for underdeveloped areas. Water vapor is evaporated from the feed water, transported through a modified polyvinylidene fluoride (PVDF) membrane, and condensed into distilled water. The system has a higher production rate of distilled water per unit area of solar thermal collector than most existing solar thermal membrane distillation and solar still systems possibly due to its localized heating of only the portion of feed water that is within or close to the membrane. The system has been tested using canal water, seawater, and municipal wastewater as the feed water. The initial production rates of distilled water in all three cases were comparable with that when deionized water was used as the feed water. The turbidity and electrical conductivity of distilled water were all lower than 0.2 NTU and 0.6 mS/cm, respectively, in all three cases. The chemical oxygen demand (COD) of distilled water extracted from the municipal wastewater was determined to be 4 mg/L, significantly lower than its feed wastewater which had a COD of 450 mg/L. The long-term experiments showed that the performance of the system in terms of both the production rate and the quality of distilled water maintained the same after 10 days of seawater desalination and no fouling was visible on the feed side of membrane. However, the performance of the system became less satisfactory after 7 days of operation using the canal water as the feed water and the fouling of membrane was observed on the feed side. The result of long-term experiments using wastewater as the feed water will also be discussed. A patent application has been filed for this system.

Novel solar thermal membrane distillation system for drinking water production in underdeveloped areas

256th National Meeting (2018)

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