We are seeking an Environmental Microbiologist or Geomicrobiologist for a PhD position to study the improvement of simultaneous removal of ammonium and formation of methane by applying iron mineral nanoparticles. This project will investigate cultures of anaerobic Fe(III)-reducing ammonium-oxidizing (Feammox) and methanogenic microorganisms amended with iron mineral nanoparticles for ammonium removal, phosphorous recovery and simultaneous production of methane. We will carry out laboratory batch and bioreactor experiments with geochemical and molecular analyses (qPCR, metatranscriptomics) to follow microbial growth and activity, NH4 removal and CH4 production efficiency. In addition, the nanoparticles will be analyzed (wet-chemistry, electron microscopy, XRD, Mössbauer spectroscopy). The PhD student will be given opportunities to be creative and innovative, to apply state-of-the art microbiological and geochemical analyses, molecular techniques, microbial physiological studies, microscopy, and spectroscopy. Requirements: Strong background in Environmental Microbiology, Microbial Ecology and Geochemistry. Ability to work independently and in a team. Excellent management and communication skills. Highly motivated for interdisciplinary research. Good computer and language (English) skills. Start date for successful applicant is March 2025 (or as soon as the candidate is available). Employment (TVL E13, for 3 years; 75%) will be arranged by the University of Tübingen.