Mechanistic understanding and prevention of mineral scaling in vacuum blackwater transport systems
Vacuum sewer systems for source-separated blackwater are a cornerstone of circular sanitation concepts, enabling nutrient and energy recovery with minimal water use. However, full-scale systems such as Jenfelder Au (Hamburg) and Waterschoon (Sneek) suffer from recurrent clogging due to mineral scaling inside transport pipes. These deposits originate from urease-driven urea hydrolysis, which increases pH and induces supersaturation of calcium phosphate, calcite, or struvite, depending on local water chemistry. Scaling leads to operational failures, high maintenance costs, and reduced societal acceptance of innovative sanitation systems.
This project addresses a critical bottleneck for large-scale implementation of vacuum-based source separation. By developing predictive understanding and prevention strategies for mineral scaling, we contribute directly to reliable circular sanitation infrastructure and sustainable nutrient recovery.
Research challenges
Although field observations have identified mineral phases and scaling hotspots, in situ data on pH evolution, saturation indices, and ion concentrations inside operating vacuum pipes are scarce. The relative contributions of ureolytic biofilms, evaporation, local turbulence, and hydraulic conditions remain unresolved.
Furthermore, scaling mineralogy differs across systems (e.g., hydroxyapatite/calcite versus struvite), indicating strong dependence on water chemistry. This variability complicates generic prevention strategies.
Innovation opportunities lie in:
– Mechanistic coupling of microbiology, aqueous chemistry, and multiphase hydraulics;
– Controlled reproduction of vacuum sewer conditions in lab and pilot rigs;
– Development of targeted mitigation strategies, including chemical stabilization, mechanical disturbance, and urease inhibition.
A predictive framework that links chemistry, biology, hydraulics, and biomineralization is currently missing, and this is the core scientific challenge.
Your assignment
You will elucidate the mechanisms governing mineral scaling in vacuum blackwater systems and develop effective prevention strategies.
You will design and operate laboratory and pilot-scale vacuum test rigs that reproduce hydraulic and chemical conditions observed in practice. Using synthetic and real blackwater, you will monitor urea hydrolysis, pH evolution, ion speciation, and saturation indices. You will characterize biofilm development and mineral phases using microscopic, mineralogical, and chemical analyses.
Based on mechanistic insight, you will experimentally evaluate mitigation concepts, such as controlled chemical stabilization, urease inhibition, or mechanical disturbance. You will integrate your findings into a predictive framework to identify scaling hotspots and guide system design and operation. Results will be validated in collaboration with industry partners operating full-scale systems.
Your profile
You hold an MSc degree in environmental engineering, chemical engineering, process engineering, environmental chemistry, or a related field.
You have affinity with aqueous chemistry, microbiology, and experimental process research.
You work analytically, are comfortable operating laboratory setups, and can translate data into mechanistic understanding.
Keywords: Vacuum sewer systems; mineral scaling; crystallization; struvite; biofilm–mineral interactions
Professor/University group/Wetsus supervisor(s):
University promotor and co-promotor: Prof. dr. ir. Cees Buisman;
Wetsus supervisor(s): Dr. ir. Chris Schott and ir. Lilian Quispe.
Project partners: Source separated sanitation – Wetsus
Only applications that are complete, in English, and submitted via the application webpage before the deadline will be considered eligible.
Guidelines for applicants: https://phdpositionswetsus.eu/guide-for-applicants/
