Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Wastewater treatment in rural areas - Functionality of sand filters and suitability of filter media for reuse

Auteur : Martikainen, Kati

Université de soutenance : University of Eastern Finland

Grade : Doctoral dissertation 2023

Résumé partiel
Sand filters are a cheap and easy alternative to treat wastewaters in areas outside the centralized sewerage systems. Previous studies have shown that the use of sand alone in the filter may not be sufficient for removing the most important impurities. There are, however, only limited research results available on the functionality of soil filtration systems. Wastewater may represent also a hygiene risk, if inadequately treated effluent comes into contact with nearby wells or recreational waters. Furthermore, from a circular economy perspective, it is important to identify the potential of the decommissioned filter masses for nutrient reuse. The purpose of this thesis was to investigate real scale sand filters and their removal efficiencies of nutrients and microorganisms and compare the results against the treatment requirements set by the Government Decree (157/2017) of Finland. The sand filters tested had either no, or had some phosphorus-binding material layers and the age of the filters varied. Pilot and laboratory-scale experiments were conducted to investigate the nutrient and microbial removal efficiencies of different types of enhanced P removal materials under different wastewater and P loads. The thesis also evaluated the reuse of used filter masses, based on their nutrient content and hygienic quality. It was observed that phosphorus removal was generally adequate and both sand and biotite filters met the requirement of the regulation of the Government Decree, 157/2017 i.e. a 70% reduction. However, it was noted that the extent of removal could be reduced with the age of filter, especially for filters composed only of sand. The most effective solution for removing P and nitrogen from wastewater was found to be a filter with a biotite layer. There did not seem to be any seasonal dependence on the microbial or nutrient removal efficiencies of these filters. The results revealed that sand filtration of wastewater may pose a hygiene risk with or without phosphorus-binding materials, but this can be reduced with a separate phosphorus removal unit, resulting in a significant reduction in effluent microbial levels.

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