Influence of adsorption mechanisms on the fate of contaminants of emerging concern : investigation in advanced wastewater treatment and natural environments

Abstract

Aquatic environments are increasingly impacted by contaminants of emerging concern (CECs), including organic micropollutants (OMP) like pharmaceuticals, industrial chemicals and others. This thesis investigates adsorption and desorption processes in engineered and natural systems to improve wastewater treatment and support evidence-based water management. This work contributes to three objectives that were addressed in three peer-reviewed scientific publications. Objective 1: Extending filter runtimes by improved assessment of granular activated carbon (GAC) loading and a better understanding of desorption processes was addressed in the first publication “Desorption of Organic Micropollutants from Loaded Granular Activated Carbon” by performing lab tests and evaluating data from pilot scale tests. The study addressed three research questions: (1) Which factors influence extraction results from loaded GAC? (2) Is it possible to assess the current GAC loading by extraction? and (3) What drives desorption of OMP during long-term operation? The results demonstrate that extraction efficiency is strongly influenced by solvent choice, extraction time, and solid–liquid ratios, while the alteration of particle size leads to distorted results. A clear relationship between extracted OMP amounts and bed volumes (BV) confirmed that extraction can serve as an alternative to dense influent–effluent sampling for assessing filter loading. Desorption during operation was primarily driven by reversals in concentration gradients, such as during backwashing or fluctuating influent concentrations, as well as competitive displacement by better adsorbable compounds. Objective 2: Evolving powdered activated carbon (PAC) treatment for OMP removal at small to medium-sized wastewater treatment plants (WWTPs) was addressed in the second publication: “Adsorption/precipitation prototype agent for simultaneous removal of phosphorus and organic micropollutants from wastewater”, which focused on advancing PAC treatment for small to medium-sized wastewater treatment plants by evaluating a novel combined adsorption–precipitation suspension. The guiding research question was (4) Is a combined adsorption/ precipitation suspension effective in the removal of OMP? Lab and full-scale trials demonstrate that the developed product achieves substantial removal of both OMP and phosphorus. Its performance strongly depends on PAC content and matrix characteristics. The product offers practical benefits, such as reduced investment costs and simplified process complexity, making it an appealing option for small to medium-sized WWTPs to remove OMP. Objective 3: Optimizing the water management between high and less-polluted areas of natural water bodies, presented in the third publication “Pollutant source or sink? Adsorption and mobilization of PFOS and PFOA from sediments in a large shallow lake with extended reed belt”, examined adsorption and desorption processes in natural lake systems exposed to persistent OMP such as perfluoro octane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) by using data from a monitoring campaign and accompanying lab tests. These are there search questions investigated: (5) What are the drivers for the adsorption and desorption of OMP in sediments of natural water bodies? and (6) Should water transport between more and less OMP polluted areas be enhanced or restricted due to potential desorption processes? Results identified concentration-gradient reversal as the primary driver of per- and polyfluoroalkyl substances (PFAS) remobilization, particularly under dilution scenarios. Sediment characteristics, especially ferric or aluminum groups and organic carbon fractions, influenced the desorption behavior. While enhanced exchange between open water and reed belt areas can support pollutant immobilization, hydrological interventions and maintenance activities must consider remobilization risks. Overall, this thesis provides an integrated understanding of adsorption-driven mechanisms across wastewater treatment and natural aquatic systems. Its scientific contributions can be grouped into three areas: methodological development, demonstrated by improved approaches for assessing GAC filter loading; treatment and technology innovation, illustrated by the testing of an adsorption–precipitation prototype for simultaneous removal of OMP and phosphorus; and environmental system understanding, shown through insights into the adsorption and remobilization of persistent contaminants in natural water bodies. Together, these contributions support optimized carbon-based treatment strategies, better assessment of desorption risks, and sustainable water management in both engineered and environmental contexts.