Inactivation of water pathogens with solar photo-activated persulfate oxidation

Abstract

The effect of solar activated persulfate oxidation and solar mild thermal heating on water disinfection (PS/solar) was demonstrated for the inactivation of E. coli and E. faecalis in both isotonic water (IW) and synthetic urban wastewater (SUWW). The process was studied in both bench-scale and pilot-scale (60 L CPC solar compound parabolic collector) reactors. The impact of solar ultraviolet (UV) and thermal increase on bacterial inactivation were separately studied. The thermal inactivation at 40 °C and 0.5 mM-PS shows a 3-log reduction value (LRV) for E. coli without lag phase and 5-LRV for E. faecalis with a lag phase of 1 h, during 4 h solar exposure. The thermal effect at 50 °C played a dominant role, with fast bacterial decay for both bacteria, which dominates the kinetics over the thermal activation of PS. In the presence of PS and solar irradiation, the combined thermal and UVA effects, accelerated the bacterial process. 6-LRV in E. coli and E. faecalis was observed after solar exposure periods of 20 min (solar dose), using 0.5 and 0.7 mM of PS in IW, respectively. Longer solar exposure times were required to attain similar LRV in synthetic urban wastewater, in the presence of 25 mg/L of organic matter, i.e. 80 and 100 min (solar dose) for E. coli and E. faecalis, respectively. These results were confirmed at pilot scale, where 60 L of IW were treated with 0.5 mM of PS in 50 min (solar dose). The PS/solar process uses low cost chemical reagents (0.5 mM-PS) and a free source of energy (solar radiation) for the treatment of wastewater and is able to achieve the high removals (6-LRV) of the two model faecal indicators of water contamination. This process opens a clear alternative to treat polluted water with organic matter and pathogens with implications in water-energy reclamation field.