Reclaiming Electrolysis Reject Water With a Solar Still

Abstract

Electrolysis is one sustainable pathway to hydrogen production. During this process, however, it is common to reject a large portion of the water during the pretreatment process to carry away impurities. We have been examining water-conserving approaches to this problem with low energy devices. One such approach is to couple the water purification step with a solar still, thus allowing some of the wastewater to be recycled and utilized in the hydrogen production. This paper reports on a study of a weir type solar still. A weir type solar still is an inclined solar still with the absorber plate formed to make weirs, as well as a top basin and a bottom basin. Raw water flows from the top basin through the weirs and to the bottom basin that is circulated back to the top basin by a small pump. Purified water is collected from condensate on the glass cover. The weir type solar still with 0.61 m width and 1.82 m length (net aperture area 0.97 m2) was constructed and tested for the Las Vegas weather conditions. A data acquisition system with temperature and flow rate sensors was also installed to record the transient variation of temperature and flow rate. The distillate productivity of the still with double-pane and single-pane glass covers is compared. The average distillate productivities for double-pane and single-pane glass covers were approximately 1.9 l/m2/day and 5.5 l/m2/day in the months of August and September in Las Vegas respectively. A double-pane glass reduced the productivity of a solar still significantly due to the reduced temperature difference between the raw water and the glass inner surface. The productivity of the weir type still is also compared with the basin type still tested at the same location side by side and is found that the weir type still productivity was approximately 20% higher. The quality of distillate from the still was also analyzed to verify the product will meet the purity required by electrolyzers.