Rendering fecal waste safe for reuse via a cost-effective solar concentrator

The goal of this work was to design a cost-effective solar-thermal waste treatment unit and evaluate its ability to render fecal waste safe for reuse. Three trials were conducted from December 2011 through February 2012 in FAVET-Universidad de Chile, Santiago, Chile. The first two trials evaluated helminth viability daily. To calculate the inactivation rate for the solar concentrator unit, the third trial evaluated helminth viability hourly. The solar concentrator met cost requirements of less than US$0.002 per user per day to manufacture. In all three trials, temperatures of treated waste fluctuated from 15°C to 95°C and surpassed temperatures that previous literature has shown to promote pathogen inactivation. There was at least a 2.96 log10 reduction of viable helminth eggs after 1 day in the solar concentrator for all three trials. In the third trial, the inactivation rate ranged from 3 to 6.5 log10/hour⁻¹ with a corresponding t₉₉ of 0.71–1.55 hours. These results suggest that a solar concentrating unit can meet the need of cost-effectively rendering human feces safe for reuse – helping to prevent diarrheal diseases, and ultimately, saving lives.