A difficult coexistence: Resolving the iron-induced nitrification delay in groundwater filters.

Rapid sand filters (RSF) are an established and widely applied technology for the removal of dissolved iron (Fe2+) and ammonium (NH4+) among other contaminants in groundwater treatment. Most often, biological NH4+oxidation is spatially delayed and starts only upon complete Fe2+ depletion. However, the mechanism(s) responsible for the inhibition of NH4+oxidation by Fe2+ or its oxidation (by)products remains elusive, hindering further process control and optimization. We used batch assays, lab-scale columns, and full-scale filter characterizations to resolve the individual impact of the main Fe2+ oxidizing mechanisms and the resulting products on biological NH4+ oxidation. modeling of the obtained datasets allowed to quantitatively assess the hydraulic implications of Fe2+ oxidation. Dissolved Fe2+ and the reactive oxygen species formed as byproducts during Fe2+ oxidation had no direct effect on ammonia oxidation. The Fe3+ oxides on the sand grain coating, commonly assumed to be the main cause for inhibited ammonia oxidation, seemed instead to enhance it. modeling allowed to exclude mass transfer limitations induced by accumulation of iron flocs and consequent filter clogging as the cause for delayed ammonia oxidation. We unequivocally identify the inhibition of NH4+oxidizing organisms by the Fe3+ flocs generated during Fe2+ oxidation as the main cause for the commonly observed spatial delay in ammonia oxidation. The addition of Fe3+ flocs inhibited NH4+oxidation both in batch and column tests, and the removal of Fe3+ flocs by backwashing completely re-established the NH4+removal capacity, suggesting that the inhibition is reversible. In conclusion, our findings not only identify the iron form that causes the inhibition, albeit the biological mechanism remains to be identified, but also highlight the ecological importance of iron cycling in nitrifying environments.

Soil Sealing and Hydrological Changes during the Development of the University Campus of Elche (Spain).

The University Miguel Hernández of Elche was created in 1996 and its headquarters is located in the city of Elche. A new campus was developed where new buildings and infrastructures have been established for over 25 years in the north of the city. The university is growing, and the land cover/land use is changing, adapted to the new infrastructures. In fact, the landscape changed from a periurban agricultural area mixed with other activities into an urbanized area integrated into the city. The purpose of this work was to evaluate the progressive sealing of the soil and the consequences on the surface hydrology. The area is close to the Palmeral of Elche, a landscape of date palm groves with an ancient irrigation system, which is a World Heritage Cultural Landscape recognized by UNESCO. The evolution of the land occupation was analyzed based on the Aerial National Orthophotography Plan (PNOA). Soil sealing and the modifications of the hydrological ancient irrigation system were detected. Based on the results, proposals for improvement are made in order to implement green infrastructures and landscape recovery that can alleviate the possible negative effects of the soil sealing in the area occupied by the university.