Long-term observation of the end-of- treatment sludge quality from a Parisian WWTP treating wastewater from 6.5 M inhabitants

International audienc

Photoelectrocatalytic conversion of urea under solar illumination using Ni decorated Ti-Fe2O3 electrodes

International audienceTo reduce the energy cost and environmental impact of biological nitrogen removal in wastewater treatment plants, it would be advantageous to treat urea contained in urine at the source. In this perspective, FTO/Ti-Fe2O3 (nanorods) photoelectrodes decorated with Ni as catalyst are developed and tested for urea photoelectrocatalytic oxidation under solar illumination. Gains up to 0.50 V in oxidation onset potential vs. metallic Ni are obtained thanks to a Ni photoelectrodeposition method. In situ transmission measurements (based on NiOOH light absorption) during electrochemical cycling allowed to evaluate the state of active Ni sites and confirmed that urea oxidation mechanism is of EC type. Photoelectrolyses give faradaic efficiencies of 10–18% and 9-35% for N2 and O2 formation, respectively. A significant and unexpected NO2− production (∼65%) is detected indicating another or incomplete reaction pathway. The photoelectrocatalytic removal of nitrogen from urea solutions is demonstrated but requires catalysts with higher selectivity towards N2

Tracking the formation potential of vivianite within the treatment train of full-scale wastewater treatment plants

Funding Information: The authors would like to thank Aino Peltola for assisting with laboratory analysis in Finland, and Jennifer Mas for assisting during sampling campaigns in France. The research was funded by Helsingin seudun ympäristöpalvelut (HSY), Maa-ja vesitekniikan tuki ry (MVTT), and by Syndicat interdépartemental pour l'assainissement de l'agglomération parisienne (SIAAP) in the framework of MOCOPEE program. Publisher Copyright: © 2023 The AuthorsPhosphorus recovery is a vital element for the circular economy. Wastewater, especially sewage sludge, shows great potential for recovering phosphate in the form of vivianite. This work focuses on studying the iron, phosphorus, and sulfur interactions at full-scale wastewater treatment plants (Viikinmäki, Finland and Seine Aval, France) with the goal of identifying unit processes with a potential for vivianite formation. Concentrations of iron(III) and iron(II), phosphorus, and sulfur were used to evaluate the reduction of iron and the formation potential of vivianite. Mössbauer spectroscopy and X-ray diffraction (XRD) analysis were used to confirm the presence of vivianite in various locations on sludge lines. The results show that the vivianite formation potential increases as the molar Fe:P ratio increases, the anaerobic sludge retention time increases, and the sulfate concentration decreases. The digester is a prominent location for vivianite recovery, but not the only one. This work gives valuable insights into the dynamic interrelations of iron, phosphorus, and sulfur in full-scale conditions. These results will support the understanding of vivianite formation and pave the way for an alternative solution for vivianite recovery for example in plants that do not have an anaerobic digester.Peer reviewe