Andrea Iris Schaefer

• PhD
• Head of Department at Karlsruhe Institute of Technology

The growing concern over micropollutants in aquatic ecosystems motivates the development of electrochemical membrane reactors (EMRs) as a sustainable water treatment solution. Nevertheless, the intricate interplay among adsorption/desorption, electrochemical reactions, and byproduct formation within EMR complicates the understanding of their mechan...

The Gambia River is a tidal and tropical river that covers 12% of the area of The Gambia and is to date not harnessed for drinking water supply purposes. While the freshwater region of the river is mainly used for irrigation, groundwater wells are predominantly used for drinking water. Salinity intrusion and wastewater treatment requirements are ch...

Vertically-aligned carbon nanotube (VaCNT) membranes allow water to conduct rapidly at low pressures and open up the possibility for water purification and desalination, although the ultralow viscous stress in hydrophobic and low-tortuosity nanopores prevents surface interactions with contaminants. In this experimental investigation, steroid hormon...

Photocatalytic membranes (PM) are promising for the removal of micropollutants from water. Limited photo-stability of polymeric PM systems is an obstacle to widespread application where a lifetime of years is required, maintaining good filtration and photodegradation efficiencies during exposure to both ultraviolet light and reactive oxygen species...

Fluctuating and intermittent solar energy cause shut‐down and reduce resilience of photovoltaic powered membrane (PV‐membrane) systems. A charge controller based on pre‐set voltage thresholds for supercapacitors (SC) is designed and employed on varied solar days to cope with these issues. Several parameters—number of shut‐down events (#SD), shut‐do...

The lack of effective technologies to remove steroid hormones (SHs) from aquatic systems is a critical issue for both environment and public health. The performance of a flow-through photocatalytic membrane reactor (PMR) with TiO2 immobilized on a photostable poly(vinylidene fluoride) membrane (PVDF-TiO2) was evaluated in the context of SHs degrada...

Chromium (Cr) is a toxic inorganic contaminant for drinking water, in which the concentration has to be controlled for human health and safety. Cr retention was investigated with stirred cell experiments using sulphonated polyethersulfone nanofiltration (NF) membranes of different molecular weight cut-off (MWCO). Cr(III) and Cr(VI) retention follow...

Drinking water in The Gambia is mostly derived from boreholes that could potentially be contaminated. The Gambia River, a major river in West Africa that covers 12 % of the country's area, could be more exploited for drinking water supply. During the dry season, the total dissolved solids (TDS), ranging from 0.02 to 33 g/L in The Gambia River, decr...

Nanofiltration (NF) membranes can retain micropollutants (MPs) to a large extent, even though adsorption into the membrane and gradual permeation result in breakthrough and incomplete removal. The permeation of MPs is investigated by examining the energy barriers (determined using the Arrhenius concept) for adsorption, intrapore diffusion, and perm...

The structure and size characterization of organic matter (OM) using flow field-flow fractionation (FFFF) is interesting due to the numerous interactions of OM in aquatic systems and water treatment processes. The estimation of hydrodynamic and electrostatic forces involved in the fractionation of OM over different molecular weight cut-off (MWCO) m...

Artificial water channel-polyamide (AWC-PA) composite membrane addresses the need for enhanced water-salt permselectivity in desalination and water treatment. An investigation of ion transport through AWCs incorporated into the active layer of a thin film composite membrane contributes to a better understanding of the selectivity of such membranes....

The application of solar-driven photocatalytic membranes (PM) for steroid hormone elimination from surface water is encouraging. However, both the limited availability and utilization of oxidizing species (singlet oxygen) inside the PM and the limited diffusion of reactants may constrain the destruction of organic pollutants. To facilitate the cont...

Organic matter (OM) in surface and ground waters may cause membrane fouling that is laborious to clean once established. Spontaneous osmotic backwash (OB) induced by solar irradiance fluctuation has been demonstrated for early mineral scaling/organic fouling control in decentralised small-scale photovoltaic powered-nanofiltration/reverse osmosis (P...

Micropollutants in the aquatic environment pose a high risk to both environmental and human health. The photocatalytic degradation of steroid hormones in a flow-through photocatalytic membrane reactor under UV light (365 nm) at environmentally relevant concentrations (50 ng l–1 to 1 mg l–1) was examined using a polyethersulfone–titanium dioxide (PE...

KIT researchers have been awarded one of the inaugural Undine Awards for 2022 for their long-standing contribution to R&D in the field of solar-powered water treatment, especially targetting small-scale distributed systems for the treatment of brackish groundwater in remote areas of Africa.

Selenium (Se) is a dissolved oxyanion drinking water contaminant requiring appropriate removal technologies. The removal of selenite (SeIV) and selenite (SeVI) with nanofiltration (NF) was investigated with an emphasis on the role of Se speciation and membrane charge screening on the retention mechanisms. The pH (2 to 12) showed strong pH dependenc...

Organic fouling is a major issue of nanofiltration/reverse osmosis (NF/RO) membranes because it causes severe and usually irreversible flux decline. Consequently, NF/RO requires frequent chemical cleaning and/or replacement. In directly coupled photovoltaic (PV) powered NF/RO systems for brackish water desalination, solar energy fluctuations can in...

In the field of ultrafiltration (UF) membranes for water treatment, fouling is a severe problem that limits the potential of the technology UF membranes and results in increased energy consumption. In this study, a small-scale photovoltaic-powered membrane system was employed to investigate the energy consumption of two UF backwashing configuration...

Given the crucial role of noble metals in promoting singlet oxygen (¹O2) production, the feasibility of relying on cheaper and more abundant metals remains challenging. This work investigates the continuous-flow photocatalytic degradation of steroid hormone micropollutants, achieved with photocatalytic membranes based on noble-metal (Pd) and noble-...

This chapter describes the relevance of nanofiltration (NF) as a reliable technology to remove trace contaminants from water. A variety of organic and inorganic trace contaminants, their occurrences in various water bodies, and their health effects are summarized. An overview of the current water guidelines for the most representative types of orga...

Renewable energy-powered nanofiltration allows to (i) overcome the operational energy costs of nanofiltration and (ii) design decentralized treatment where advanced water treatment removal of dissolved contaminants is required and no reliable energy supply is available. Such decentralized treatment is a relatively a new paradigm that is required in...

In this concluding chapter, the editor summarizes the contents of the three parts that make up the book and highlights key developments in each area that have happened since the publication of the previous edition. The contribution of nanofiltration to meeting challenges in the global water supply is outlined, and market and technology trends are r...

The fouling chapter provides a comprehensive overview of fouling characteristics, common foulant types, fouling characterization methods, and membrane autopsy as well as a review of current models. A detailed description of the main fouling categories, namely organic fouling, scaling, colloidal and particulate fouling, and biofouling, is followed b...

The removal of arsenic(III) (As(III)) with nanofiltration (NF) was investigated with emphasis on the role of salinity, pH and organic matter on retention mechanisms. While no measurable impact of salinity on As(III) retention with NF membranes (NF270 and NF90) was observed, a significant increase in As(III) retention occurred from pH 9 to pH 12. Th...

A novel way of removing micropollutants – especially steroid hormones – from water has been developed in Germany at the Institute for Advanced Membrane Technology (IAMT) of the Karlsruhe Institute of Technology (KIT). As this article shows, it is based on the combination of a polymeric ultrafiltration (UF) membrane and activated carbon. The two res...

The efficient degradation of steroid-hormone micropollutants is demonstrated in a single-pass, continuous operation of the photocatalytic membrane reactor (PMR) holding a visible-light excited Pd(II)-porphyrin-coated poly(vinylidene fluoride) microfiltration membrane. The PMR operated at a water flux of 600 L m⁻² h⁻¹ exhibited a residence time of 0...

A breakthrough curve in nanofiltration (NF) is observed when micropollutants adsorption and subsequent diffusion through the membrane occur at environmentally relevant low concentrations. The role of hydrodynamics and operative conditions to characterize the curve shape is unknown. In this study, the impact of mass transport and residence time on t...

The potential for lithium-ion (Li-ion) batteries and supercapacitors (SCs) to overcome long-term (one day) and short-term (a few minutes) solar irradiance fluctuations with high-temporal-resolution (one s) on a photovoltaic-powered reverse osmosis membrane (PV-membrane) system was investigated. Experiments were conducted using synthetic brackish wa...

Mineral scaling is common in brackish water treatment and causes higher energy consumption and cleaning frequency [1, 2]. In photovoltaic-powered nanofiltration/reverse osmosis (PV-NF/RO) membrane system application energy fluctuations cause discontinuous operation and impacts on scaling are unclear. Osmotic backwash (OB) occurs naturally during fl...

Removal of naturally occurring strontium (Sr) from groundwater is vital as excessive exposure may lead to bone growth problems in children. Nanofiltration/reverse osmosis (NF/RO) is commonly used in groundwater treatment due to the high effectiveness and simple maintenance of these pressure driven membrane processes. In this research, a pilot-scale...

Mineral scaling is a key limiting factor for membrane desalination and results in increased operation and maintenance costs. In directly coupled battery-less photovoltaic-powered nanofiltration/reverse osmosis (PV–NF/RO) membrane systems, solar energy fluctuations cause intermittent operation and direct osmotic backwash (OB) spontaneously. This pot...

The occurrence of steroid hormones in water and their serious impact on human and ecosystem demand high performance materials for efficient removal of such micropollutants. Here, an affinity membrane is developed for hormone removal with regenerable binding sites. By using photodynamic disulfides as a linker, UV induced detachment of β‐CD ligands f...

Climate change will affect water quality through a change in salinity, pH and organic matter (OM) content due to seawater intrusion, temperature change and subsurface biological processes. Therefore, a systematic evaluation of the impact of water quality variations is of particular importance to maintain the performance of a treatment process desig...

Directly-powered photovoltaic membrane filtration (PV-membrane) systems possess no energy storage components, hence operate under energy fluctuations that result in variations in the membrane performance. Here, the resilience of a PV-membrane system under such conditions as a function of membrane type and feedwater quality is investigated. Five Tan...

The European Union has proposed the value of 1 ng L⁻¹ as a drinking water quality standard for estradiol. With conventional technologies only partially removing estradiol, the investigation of novel alternatives is more than ever required. Tagliavini and Schäfer proposed that the use of a thin activated carbon layer combined with a membrane is wort...

Photocatalytic membrane reactors with different configurations (design, flow modes and light sources) have been widely applied for pollutant removal. A thorough understanding of the contribution of reactor design to performance is required to be able to compare photocatalytic materials. Reactors with different flow designs are implemented for proce...

Cyclodextrin loaded composite nanofibers have been widely applied in water treatment. Electrospun polyethersulfone (PES) nanofibers with β-cyclodextrin-epichlorohydrin (βCDP) deposited on PES ultrafiltration (UF) membranes were prepared. Steroid hormone micropollutants (MP) were removed from the water over a broad concentration range (0.01–100 μg/L...

The occurrence of micropollutants (MPs) including steroid hormones is a global environmental and health challenge. Carbon-based nanoparticles can be incorporated with water treatment processes to allow MP removal by adsorption. The aim was to compare the suitability of such nanoparticles (graphene, graphene oxide, carbon nanotubes and C60) to adsor...

Detection of micropollutants such as steroid hormones occurring in the aquatic environment at concentrations between ng/L and µg/L remains a major challenge, in particular when treatment efficiency is to be evaluated. Steroid hormones are typically analysed using mass-spectrometry methods, requiring pre-concentration and/or derivatisation procedure...

An effective way to remove micropollutants is desirable for water purification. In this work, a dual-functional ultrafiltration (DFUF) membrane was fabricated by loading hollow mesoporous carbon nanospheres (HMCNs) into the finger-like support layer pores of the polymeric ultrafiltration (UF) membrane. The designed DFUF membrane combines the high s...

Direct osmotic backwash (OB) during solar energy fluctuations is an important observation in directly coupled, battery-less solar energy powered nanofiltration/reverse osmosis (NF/RO) membrane systems. OB occurs spontaneously and has the potential to induce membrane self-cleaning. The impact of controlled solar irradiance fluctuation conditions, fe...

Photocatalytic membranes operating under flow-through conditions are promising for continuous single-pass water treatment, while factors influencing pollutant removal require further understanding. In this work, anodized aluminium oxide membranes with pore sizes of 20 nm and 200 nm were coated with a titanium dioxide (TiO2) photocatalyst via atomic...

Short activated carbon fibers (ACF) with high surface area were fabricated via carbonization in N2 and activation in CO2 at high temperatures, with cellulose fibers as the raw materials. The obtained ACF were subsequently deposited into the support layer of a polyethersulfone (PES) ultrafiltration membrane by a facile filtration process to obtain t...

Energy management is required to enable autonomous photovoltaic-powered membrane (PV-membrane) desalination systems to make the optimal use of solar energy. In this paper, a novel charge controller based on pre-set voltage sensing thresholds was designed to optimise the energy from PV panels and supercapacitors (SCs). The control algorithms were es...

Photovoltaic-powered membrane filtration (PV-membrane) systems are of interest for the provision of clean drinking water in small communities, especially in remote areas. In order to deliver clean water at the lowest cost over the lifetime of the system, a reliable and robust design is paramount. This paper provides a comprehensive review of the op...

Environmental context Contamination of surface water by micropollutants is a major environmental concern because of their high persistence and toxicity. Micropollutants are only partially removed in nanofiltration water treatment systems, encouraging the investigation of more complex systems involving partitioning with membrane materials, organic m...

A novel combination of a poly(vinylidene fluoride) (PVDF) membrane with pore size 0.2 μm and a photosensitizer 5,10,15,20-tetrakis (pentafluorophenyl)-21H,23H-porphine palladium(II) (PdTFPP) makes a promising hybrid material for the generation of singlet oxygen (¹O2) and, thus, water treatment applications. The fabricated photocatalytic membrane ex...

The present study investigated ultrafiltration (UF) membranes in a combination with a polymer-based spherical activated carbon (PBSAC) thin layer on the permeate side (UF-PBSAC) to remove the steroid hormone micropollutant (MP) estradiol (E2) from water. The impact of dissolved organic matter on the process was assessed using two types of water: on...

Osmotic backwash (OB) of dense membranes has been developed as a novel cleaning method to control membrane fouling (Qin et al. 2009, Kim 2014, Liberman 2018). OB is based on permeate backflow to the feed side due to a negative driving force between the operating and osmotic pressure of feed solution across nanofiltration/reverse osmosis (NF/RO) mem...

Comparison of nanofiltration characterization data from literature is challenging due to different hydrodynamics and system designs, which affect membrane retention. In this study, stirred cell (SC), micro and macro cross flow systems (micro and macro CF) with different configuration were used to measure salt and organic tracer retention. Minimal c...

Integration of renewable energy and membrane filtration technologies such as nanofiltration (NF) and reverse osmosis (RO) can provide drinking water in places where freshwater is scarce and grid electrical connections are unavailable. This study investigated a directly-connected photovoltaic-powered membrane system under fluctuating solar condition...

Renewable energy powered membrane systems operate with fluctuating energy. Such fluctuations affect pressure and feed flow and as such the hydrodynamic conditions in a membrane system. Hydrodynamic variations alter the membrane surface concentration and boundary layer thickness which in turn determines permeate water quality. In this work this is c...

Membranes: solar-powered filtration in rural communities A solar-powered portable filtration unit is capable of treating ground and surface water to drinking standards in rural communities in Tanzania. Water treatment in remote communities is extremely challenging because establishing permanent infrastructure is often not viable. Instead, decentral...

The Maji ya Chai River in Northern Tanzania, a fluoride-rich tropical area, shows a seasonal variation of natural organic matter (NOM) and fluoride concentration. Water samples collected monthly during one year from two locations of the River were characterized. High levels of precipitation in the rainy seasons increased the total organic carbon (T...

In the context of decentralised brackish water treatment in development applications, the influence of water quality on membrane separation was investigated with real waters. High ionic strength (low net driving pressure) on fluoride (F) retention by nanofiltration (NF) and reverse osmosis (RO) was investigated over a wide pH range (2–12). Further,...

Effective micropollutant removal requires energy intensive advanced treatment processes. A novel hybrid membrane configuration – consisting of both ultrafiltration (UF) and nanofiltration (NF) – with permeate-side polymer-based activated carbon (PBSAC) was developed and investigated for the removal of natural hormones with a particular focus on est...

Remote areas face particular infrastructure challenges relating to the provision of clean drinking water and electricity. The installation of classical centralized water and electricity systems in such areas is economically unfavorable because of low population densities. This situation provides unique opportunities for the implementation of autono...

This chapter presents an overview of the manufacture, physicochemical properties, and effective application of carbon nanotube (CNT) membranes in desalination technologies. A comprehensive discussion on the current knowledge pertinent to CNT exploitation in desalination is made. It is demonstrated that considerable efforts have been made in the pas...

Cyclodextrin-polymer-composite electrospun nanofibers were developed for micropollutant removal from water. Fibers were fabricated by electrospinning of mixed polyethersulfone and β-cyclodextrin (CD) solutions at optimal conditions. The composite-fibers were compared to bare polyethersulfone nanofibers prepared by the same method. Scanning electron...

Magnetic ion exchange resins (MIEX) were combined with nanofiltration (NF) in one single process to mitigate fouling by humic acids (HA). MIEX effectiveness in controlling NF fouling was investigated under different feed chemical conditions and employing two types of NF membranes (NF270, NF90). Fouling layer thickness was determined using novel hel...

Real water pH and ionic strength vary greatly, which influences the performance of membrane processes such as nanofiltration (NF) and reverse osmosis (RO). Systematic variation of pH (3 − 12) and ionic strength (2–10 g/L as total dissolved solids (TDS)) was undertaken with a real Tanzanian water to investigate how water quality affects retention me...

Water and energy are inextricably linked in today's society. This paper broadly introduces the water-energy nexus before focusing on sub-Saharan Africa, where residents have the poorest access to both clean drinking water and electricity worldwide. Given that many of the affected people live in remote areas, new solutions are required to improve th...

The removal of inorganic trace contaminants from a real brackish groundwater from a remote Australian community using electrodialysis was investigated. Systematic investigation of applied voltage and solution pH was aimed to elucidate removal and deposition mechanisms in a complex water. A higher applied voltage enhanced removal of arsenic (V), bor...

Removal and interaction mechanisms of four different steroid micropollutants, estrone (E1), estradiol (E2), progesterone (P) and testosterone (T) were determined for different types of polymer-based spherical activated carbon (PBSAC). Higher than 90% removal and significantly faster kinetics compared to conventional granular activated carbon (GAC)...

This chapter discusses both products representing recent incremental innovations with conventional nanomaterials that are already produced on the scale of megatons per year as well as disruptive innovations based on novel nanomaterials. It presents the case studies for composite systems, nanoporous systems, and particle-based systems. The overview...

The impact of pH and humic acid (HA) on the retention of fluoride (F) and inorganic carbon (IC) by nanofiltration (NF) and reverse osmosis (RO) membranes was determined. Synthetic waters were prepared using realistic ranges of F, IC and HA for carbonaceous waters found for example in the fluoride rich waters in Tanzania. These waters were filtered...

Background: Estrogens and their synthetic analogues are widely used as pharmaceuticals. Upon oral administration these drugs are eventually excreted via urine. The persistence of these pharmaceuticals and inefficient removal by water treatment lead to accumulation in surface water and effluents with negative effects for aquatic life and human heal...

Aqueous micropollutants such as estradiol can have a large environmental impact-even at low concentrations. Part of understanding this impact involves determining the extent to which the micropollutants interact with macromolecules in water. In environmental samples, relevant macromolecules to which micropollutants bind are referred to as dissolved...

A brackish borehole located at a rural school in northern Tanzania contains excessive salinity (TDS=3632 mg/L) and fluoride concentration (F–=47.6 mg/L). This field study evaluated the feasibility of a solar-powered nanofiltration/reverse osmosis (NF/RO) system in treating this brackish water to make it potable. Key performance parameters such as p...

Many waters in Tanzania exhibit high concentrations of organic matter and dissolved contaminants such as fluoride. Due to bacteria and virus removal, ultrafiltration (UF) is an attractive option for drinking water treatment, and when coupled with adsorbents, may compete with other established processes like nanofiltration (NF) for lower contaminant...

Fluctuations in solar irradiance were varied in frequency and magnitude to investigate the performance of a directly-connected solar energy powered reverse osmosis (RO) membrane system. Typically, the system produced acceptable quality water with constant solar irradiances ranged from 400 – 1200 W.m-2. Low average motor powers were encountered duri...

This study examined the feasibility of nanofiltration (NF) and reverse osmosis (RO) in treating challenging natural tropical waters containing high fluoride and natural organic matter (NOM). A total of 166 water samples were collected from 120 sources within northern Tanzania over a period of 16months. Chemical analysis showed that 81% of the sampl...

One of the most fascinating properties of nanotubes (NTs) and nanosheets is their smooth sur-faces that offer essentially resistance-free transport of small molecules in the form of gases, vapors, and liquids. For example, it has been shown on multiple occasions that the transport through an NT is faster than if there were no material there at all....