The Ludwig Group

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Related publications (91)

Effective removal of the rotifer Brachionus calyciflorus from a Chlorella vulgaris microalgal culture by homogeneous solar photo-Fenton at neutral pH

Jiahua Chen, Jérémie Decker, Stefanos Giannakis, Christian Ludwig, Horst Pick, Adrian Pulgarin, Dominik Refardt

In this study, a citrate-modified photo-Fenton process was successfully applied to decontaminate a Chlorella vulgaris microalgae culture spiked with the rotifer Brachionus calyciflorus (5 individuals mL−1). The applied treatment (1 mg L−1 Fe2+, 20 mg L−1 H2O2, 17.5 mg L−1 citric acid) had only moderate effects on viability and regrowth of the microalgae since, after a short post-treatment delay of a few days, they reached final cell densities similar to that obtained for microalgae cultures that were not spiked. The decontamination was effective as no regrowth of rotifers was observed in the microalgae cultures after treatment. The efficacy of the citrate-modified photo-Fenton treatment was also studied with a higher starting concentration of 20 rotifers mL−1 and was compared with a solar light/H2O2 treatment. Results show that both treatments had similar efficacies on the rotifer elimination, but that the citrate-modified photo-Fenton treatment had a lower negative impact on the regrowth of microalgae than the solar light/H2O2 treatment. However, when microalgae cultures were spiked with 20 rotifers mL−1, rotifers were only partially inactivated and post-treatment regrowth occurred, which highlights the importance to apply the photo-Fenton process at an early stage of a contamination to achieve full rotifer elimination. In any case, a contamination with 5 rotifers mL−1 is already a significant threat as numbers above 1000 rotifers mL−1 were reached after 14 days and caused the microalgae culture to fail. Overall, our treatment suggests that the citrate-modified solar photo-Fenton process is an environmentally friendly solution to support the maintenance of contaminant-free microalgal cultures.

2022

Opportunities in Critical Rare Earth Metal Recycling Value Chains for Economic Growth with Sustainable Technological Innovations

Christian Ludwig, Ajay Bhagwan Patil, Rudolf Paul Wilhelm Jozef Struis

Rare earth elements (REEs) are often referred to as the industrial vitamins and the key drivers of the industry 4.0 revolution. The current global supply chain of REEs for green and high-tech applications with more than 220 metric kilotons per year involves a huge environmental impact (backpack) as well as the piling up of radioactive by-products to about 1.5 times the amount of REEs produced. E-wastes and municipal solid waste streams are attractive secondary resources. The current opinion paper discusses the recycling of rare earth metals along the value chain with the opportunities and challenges associated with it. The way to mitigate the economic constraints has been pointed out in terms of competitive quality and recovery of the REEs when compared with the mineral exploration options in the market. It is also emphasised that the technical complexity, capital expenditures and operating expenses need to fit the economic boundary conditions to make the recycling viable. In future, the appropriate REE-rich feedstocks such as fluorescent lamp e-waste powders and magnets can be potential secondary sources of the critical raw materials necessary for the green transition. The success of the viable recycling approaches and technologies will largely depend on the public–private partnerships based on hybrid financing models and local know-how generation to compete with quasi-monopoly in the REE supply chains. However, to break the monopolies, it will not be sufficient to only recycle the REEs; it will also be relevant to diversify the industries that produce REE-containing goods from recycled waste streams.

2022

Flowing Gas Experiments Reveal Mechanistic Details of Interfacial Reactions on a Molecular Level at Knudsen Flow Conditions

Riccardo Iannarelli, Christian Ludwig, Michel Rossi

Knudsen flow experiments and its interpretation in terms of adsorption/desorption kinetics as well as quantitative uptake on substrates of interest is presented together with the description of critical design parameters of the Knudsen Flow Reactor (KFR). Hitherto focused almost exclusively on the uptake phase exposing a virgin substrate to interacting gases, we now extend the experiment and its interpretation to the desorption phase at ambient temperature. We present analytical expressions for different experimental situations in terms of adsorption (ka), desorption (kd) and effusion (ke) rate constants. The measurement of kd leads to surface residence times (1/kd) obtained under the same experimental conditions as the uptake (ka) that results in the determination of the Langmuir equilibrium constant KL = ka/kd. We emphasize the interaction of semivolatile organic probe gases and small polar molecules with amorphous carbon and mineral dust materials at ambient temperatures. The latter leads to a molecular characterization scheme based on the use of up to ten different reactive probe gases. After saturation of the uptake of each probe gas this results in a reactivity map of the interface. Several examples are used to underline the broad applicability of the technique such as the silver/air (Ag) interface and the reactivity of TiO2 materials towards uptake of CO2 and CH3OH. Following characterization of several types of amorphous carbon a model incorporating several structural elements in agreement with the reactive gas titration is proposed. For instance, an interface that is at the same time weakly basic and strongly reducing is composed of pyrones and hydroquinones whose simultaneous occurrence leads to stable free radicals that may play a role in atmospheric chemistry (EPFR). The question is raised what makes an interface hydrophobic in terms of surface functional groups when interacting with small polar molecules such as H2O(D2O), HCl, NO2 and NH2OH. Multidiagnostic studies of heterogeneous reactions are enabled using stirred-flow reactors (SRF) that are a logical extension of the KFR approach thus relaxing the Knudsen flow requirements. Previous work using SRF on low-temperature substrates such as H2O ices is highlighted that may be of interest to the exoplanetary and space sciences community.

2022

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The present study evaluates the ionization efficiency (IE) of linear and branched C2–C14 dicarboxylic acids (DCAs) by electrospray ionization (ESI) under different conditions. The influence of the concentration of organic modifier (MeOH); mobile phase additive; and its concentration, pH, and DCA structure on IE values is studied using flow injection analysis. The IE values of DCAs increase with the increase of MeOH concentration but also decrease with an increase of pH. The former is due to the increase in solvent evaporation rates; the latter is caused by an ion-pairing between the diacid and the cation (ammonium), which is confirmed by the study with different amines. The investigation of DCA ionization in the presence of different acidic mobile phase additives showed that a significant improvement in the (−)ESI responses of analytes was achieved in the presence of weak hydrophobic carboxylic acids, such as butyric or propanoic acid. Conversely, the use of strong carboxylic acids, such as trichloroacetic acid, was found to cause signal suppression. The results of the IE studies were used to develop the liquid chromatography–high-resolution mass spectrometry (LC-HRMS) method that provided instrumental limits of detection in the range from 6 to 180 pg. Furthermore, upon applying the nonparametric Gaussian process, a model for the prediction of IE values was developed, which contains the number of carbons in the molecule and MeOH concentration as model parameters. As a case study, dicarboxylic acids are quantified in salt-rich effluent and blood serum samples using the developed LC-HRMS method.

2022

Insights about inductively coupled plasma optical emission spectroscopy interferences of major rare earth elements in complex e-waste feeds

Christian Ludwig, Ajay Bhagwan Patil, Rudolf Paul Wilhelm Jozef Struis, Mohamed Tarik

The advent of rare earth elements (REEs) with optoelectronic properties has shifted the technology paradigm from digital to a smart and hybrid world. Their substantial uses also resulted in a large piling up of e-waste. Therefore, e-waste is now a lucrative recycling target for the recovery of such critical raw materials. Their recycling from e-waste is often challenged by dilute metal concentration, complex composition, and difficult chemical characterisation. Generally, the characterisation of e-waste involves elemental determination techniques, such as inductively coupled plasma optical emission spectroscopy (ICP-OES) or inductively coupled plasma mass spectrometry (ICP-MS). ICP-OES is attractive for a recycling or research sector because it has a higher matrix tolerance and lower cost than ICP-MS. In this work, the intensity at 445 line positions measured by an ICP-OES instrument was compiled in a 2D diagram to map interferences by 27 prominent lines from 9 REEs. The second diagram shows the impact at 230 neighbouring line positions measured in each of, in total, 17 (i.e., 9 REEs and 8 non-REEs) single-standard solutions in terms of the concentration of the element type affected. The spectral interference correction algorithm proposed here had been developed by us for a recycling process to obtain pure Y, Eu, and Tb from fluorescent powder (FP) in spent lamps. The ICP-OES analysis and spectral interference correction approach presented here can be applied to any element and e-waste type. To underline this, the paper gives examples for elements in dissolved FP and surrogate NdFeB magnet samples.

2022

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This review explores the potential of separating and recycling rare earth elements (REEs) from different energy conversion systems, such as wind turbines, electric vehicles batteries, or lighting devices. The REEs include 17 elements (with global production of 242 kilometric tons in 2020) that can be found abundantly in nature. However, they are expensive and complicated to extract and separate with many environmental challenges. The overall demand for REEs is continuously growing (with a 10% yearly increase) and it is quite clear that recycling has to be developed as a supply strategy in addition to conventional mining. However, the success of both mining and recycling depends on appropriate separation and processing technologies. The overall REE recycling situation today is very weak (only 2% of REEs are recovered by recycling processes compared with 90% for iron and steel). The biggest recycling potentials rely on the sectors of lamp phosphors (17%), permanent magnets (7%), and NiMH batteries (10%) mainly at the end-of-life stage of the products. The profitability of rare earth recycling mostly depends on the prices of the elements to accommodate the processing costs. Therefore, end-of-life REE recycling should focus on the most valuable and critical REEs. Thus, the relevant processes, feed, and economic viability warrant the detailed review as reported here.

2022

An elution-based method for estimating efficiencies of aerosol collection devices not affected by their pressure drops

Tianyu Cen, Christian Ludwig, Jiukai Tang, Jian Wang

2022

Enhancing Algae Biomass Production by Using Dye-Sensitized Solar Cells as Filters

Christian Ludwig, Mohammad Khaja Nazeeruddin, Peng Qin, Shivom Sharma

One of the most promising options for decreasing the costs of microalgae production is enhancing the production and reducing the energy demand of the culturing systems and the high surface area requirements. Because microalgae growth requires only specific wavelengths of the solar spectrum, the remaining part of the solar spectrum may be simultaneously used by a translucent photovoltaic (PV) layer to produce electricity, which leads to a reduction of space and energy requirements. This work presents the results of a new concept of a positive energy culturing system for microalgae, where the light source is selectively shared between the needs of the algal biomass through photosynthesis and the production of PV energy through dye-sensitized solar cells (DSCs). To ascertain the DSC (DSC-Red, DSC-Green) light-filtering effects on microalgal biomass, (1) the variation of growth kinetics, (2) microalgae pigments [chlorophylls-(a + b) and carotenoids], and (3) macromolecule content (carbohydrates, proteins, and lipids) were investigated and compared to control cultures under two different solar-simulated light intensities (200 and 600 W/m2). The results showed a net improvement of the growth rate and dry weight at the higher irradiance using both colored DSC filters compared to control cultures. The highest growth rates (μ) and doubling time (td) of Chlorella vulgaris cells were obtained using the DSC-Red (DSC-R) and DSC-Green (DSC-G) solar cells as filters with μ = 0.86 ± 0.01 day–1; td = 0.80 day and μ = 0.85 ± 0.03 day–1; td = 0.81 day, respectively, compared to normal glass control μ = 0.51 ± 0.03 day–1; td = 1.35 day. A significant increase in the chlorophyll-a content was obtained under low light intensity for both DSC-colored compared to control culture, and there was no significant variation in the macromolecule content measured under the tested light intensities. Finally, a life cycle assessment based on a functional unit of 1 kg of the produced algal biomass using the DSC–photobioreactor (DSC–PBR) was performed and compared to a normal glass PBR. The results were expressed in terms of CO2 emission equivalents produced and electricity generated. A fraction of electricity generated by DSC–PBR is used for bubbling, and the extra electricity is injected into the electricity grid. This resulted in net negative GHG emissions.

2021

Integrated Aerodynamic/Electrochemical Microsystem for Collection and Detection of Nanogram-level Airborne Bioaccessible Metals

Tianyu Cen, Christian Ludwig, Jiukai Tang, Jian Wang

The soluble fraction of aerosol particulate matter containing trace metals has the potential to engender toxicity and exacerbate the adverse health effects of particulate matter. In this study, an inertial-impaction-based fluidic chip integrated with electrochemical detection was developed to achieve high collection efficiency and measurements of the bioaccessible metal fraction at the nanogram level. The average collection efficiency for ultrafine and fine particles larger than 50 nm, obtained at a flow rate of 2.5 L/min, was above 70%. The detection ranges of aerosol soluble copper depended on the collection duration and airflow rate. At a working flow rate of 3.1 L/min and collection efficiency of 70%, the microsystem was capable of detecting Cu concentrations above 53 ng/m3, 32 ng/m3 and 8 ng/m3 with 3 h, 5 h and 20 h collection periods, respectively, which were in the range of reported atmospheric concentrations. The detection ratio of real-world samples (i.e. PM10-like aerosol) was 100 ± 14%, indicating excellent aerodynamic collection and reliable electrochemical detection. The collection and sensing performance of the microsystem demonstrates a new step towards an online, mobile, low-cost, and miniaturized routine monitoring system for bioaccessible metals and possibly other soluble components in the aerosols.

2022

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Skin problems are often overlooked due to a lack of robust and patient-friendly monitoring tools. Herein, we report a rapid, noninvasive, and high-throughput analytical chemical methodology, aiming at real-time monitoring of skin conditions and early detection of skin disorders. Within this methodology, adhesive sampling and laser desorption ionization mass spectrometry are coordinated to record skin surface molecular mass in minutes. Automated result interpretation is achieved by data learning, using similarity scoring and machine learning algorithms. Feasibility of the methodology has been demonstrated after testing a total of 117 healthy, benign-disordered, or malignant-disordered skins. Remarkably, skin malignancy, using melanoma as a proof of concept, was detected with 100% accuracy already at early stages when the lesions were submillimeter-sized, far beyond the detection limit of most existing noninvasive diagnosis tools. Moreover, the malignancy development over time has also been monitored successfully, showing the potential to predict skin disorder progression. Capable of detecting skin alterations at the molecular level in a nonsurgical and time-saving manner, this analytical chemistry platform is promising to build personalized skin care.

2021