ETH Zurich invention may be used in Fukushima nuclear clean-up

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ETH Zurich invention may be used in Fukushima nuclear clean-up

Researchers in Zurich have developed a filter membrane made of whey proteins and activated carbon that can clean contaminated radioactive water. They hope to deploy their invention at the site of the Fukushima nuclear disaster in Japan.
Four years ago, scientists at the federal technology institute ETH Zurich unveiled a filter membrane that could remove metals such as uranium, gold and platinum from water.

In a new study, published in the journal Environmental Science: Water Research & Technology, the team has gone a step further to demonstrate how their membrane can also remove radioactive elements from hospital effluents.

Laboratory tests show that the filter membrane can effectively remove radionuclides used in the medical field, such as technetium-99m, iodine-123 and gallium-68, from water. It is 99.8% successful after just one filtration step.

The researchers also tested their invention with a sample of effluents from a Swiss hospital, which contained radioactive iodine-131 and lutetium-177. It removed both elements almost completely from the water.

“Thanks to our membrane, it’s possible to enormously reduce the amount of waste and to store the radiating elements as compact, dry solids,” Raffaele Mezzenga, professor of food and soft materials at ETH Zurich, said in a statement on Tuesday.

Swiss pilot project and Fukushima
As a next step, the researchers are planning a pilot project with a large Swiss hospital that wants to test the filtration of radioactive effluents.

Amyloid hybrid membranes for removal of clinical and nuclear radioactive wastewater†

Nuclear medicine uses various radioactive compounds for the administration into patients to diagnose and treat diseases, which generates large amounts of radioactively contaminated water. Currently, radioactively contaminated hospital wastewater has to be stored until the contained radionuclides have sufficiently decayed because cost-effective and efficient removal technologies are not available. Similar considerations apply in the nuclear power industry, with, however, decay times of the radionuclides several orders of magnitude higher. Previously, we reported hybrid membranes composed of amyloid fibrils produced from cheap and readily available proteins and activated carbon, which efficiently removed heavy metal ions and radioactive compounds from water. Here, we show that these membranes are highly efficient in the adsorption & removal of diverse, clinically relevant radioactive compounds from hospital wastewater by single-step filtration. The radionuclides technetium (Tc-99m), iodine (I-123) and gallium (Ga-68) can be removed from water with efficiencies above 99.8% in one single step. We also demonstrate the purification of a real clinical wastewater sample from a Swiss hospital containing iodine (I-131) and lutetium (Lu-177). With the use of single-photon emission computed tomography (SPECT) and positron emission tomography (PET), we were able to visualize the accumulation of the radioactive compounds within the membrane and demonstrate its outstanding performance. By converting large volumes of radioactive wastewater into low volumes of solid radioactive waste, the present technology emerges as a possible game-changer in the treatment of nuclear wastewater.

 

Water impact

The use of radionuclides in nuclear medicine and nuclear power industry generates large amounts of radioactively contaminated liquids. Currently, radioactive wastewater has to be stored until the radionuclides have sufficiently decayed. This puts a substantial logistical and financial burden on many hospitals and nuclear power plants. This work reports hybrid membranes composed of milk protein amyloid fibrils and activated carbon which are highly efficient in the adsorption of radioactive wastewater and allow the conversion of large volumes of liquid radioactive waste into much smaller volumes of solid radioactive waste. The technology is scalable, cost-effective, completely sustainable and highly efficient.
 

1 Introduction

Nuclear medicine comprises the administration of radioactive substances1 into a patient to treat or visualize diseases, which are mostly cancer-related.2,3 These substances are either being used in their elemental form or they are incorporated into larger molecules.4,5 In a way, nuclear medicine can be considered as “endoradiology” because it utilizes radiation emitted from within the patient's body,6 opposite to radiology, where the patient is being exposed to radiation sources, coming from outside.

After the administration of nuclear medicine,7 the radionuclides leave the patient via excretion through their body fluids. Therefore, until having reached sufficiently low levels of radioactivity,8,9 all excretions of the patient have to be collected and treated as radioactive liquid waste.10,11 At the moment, there is no satisfactory solution to the problem of radioactive wastewater disposal.12–14 Depending on the nature of the radionuclides, hospitals rely on on-site storage of radioactively contaminated liquid waste until radionuclide decay, after which liquid waste has to be either conditioned (solidified) or suitably disposed depending on its hazard. Both processes are very costly. The Swiss Federal Office of Health calculates 94[thin space (1/6-em)]000 CHF m−3 only for the conditioning and interim storage of liquid radioactive waste.15,16 Similar consideration, but on a much larger scale, apply to the storage and disposal of liquid radioactive waste in the nuclear power industry. Rahman et al. clearly described in their review about the liquid radioactive waste treatment technologies available for radioactive waste management.16 It summarizes the application of different conventional treatment processes (adsorption, ion exchange resins) and emerging technologies such as continuous electrodeionization (CEDI) technology and hydrothermal oxidation method. In both nuclear power plant and clinical radionuclide wastewater cases, traditional technologies such as reverse osmosis and nanofiltration cannot be used efficiently for the purification of radionuclides, as they lead to a many-fold increase of contaminant concentration in the residual backwater solution, thus producing lower volumes of liquid wastewater, which are, however, even more contaminated, presenting a dramatic threat to public health. It is still echoing the statement of the Japanese government announcing that they will have to dump by 2022 to the Pacific Ocean more than a million tons of radioactively contaminated water in storage since the Fukushima tragedy caused by the 2011 tsunami, due to a lack of space in nuclear radioactive liquid wastewater storage and the inefficiency of other technologies in handling radioactive liquid waste.17 The must for any remediation technology in radioactive waste, is to convert large volumes of radioactive liquid wastewater into much smaller volumes of solid radioactive waste, which is significantly easier to be stored and disposed.

In 2016, we reported a broadly applicable and highly efficient filtering system made of amyloid–carbon hybrid membranes,18 which were made of β-lactoglobulin, the major component of whey by-product of the dairy industry, and activated carbon.19 Initial studies have shown filtering efficacies of three to five orders of magnitude for a broad spectrum of heavy metal ions as well as for numerous other compounds including fluoride,20 organic pollutants21 and bacteria. These adsorption-based depth filter membranes were also found to be able to remove model radioactive waste such as uranyl acetate and phosphorus-32.18 Based on the outstanding performance of these membranes, the absence of secondary pollutants and notably the affordable and sustainable nature of the main components, active charcoal and by-product proteins from the cheese-making process, this technology is emerging as a game-changer in the broad water purification field, although the potential in the remediation of radioactive wastewater contamination remains to be assessed.

In our earlier reports, we demonstrated the generality of the approach by studying the filtering efficiency of various hybrid amyloid fibrils based on egg lysozyme fibrils, bovine serum albumin, whey protein isolate and β-lactoglobulin fibrils.18 Amyloid fibrils produced from the very inexpensive whey protein isolate (a by-product of the dairy industry and the industrial precursor of β-lactoglobulin) showed efficiencies comparable to those of purified β-lactoglobulin, at a significantly lower cost related to the waste nature of the original protein source, since no separation/purification steps are needed using this protein compared to β-lactoglobulin (obtained by dialysis from whey). Here we show that hybrid adsorption membranes for efficient removal efficiency of radionuclides can be produced in a scalable, easy and cost-effective way by employing whey protein fibrils instead of β-lactoglobulin.

Here, we demonstrate that amyloid–carbon hybrid membranes can provide a highly sought solution to the problem of hospital radioactive wastewater purification and nuclear wastewater in general. In order to demonstrate the feasibility of the approach in real context, we use membranes made not of pure β-lactoglobulin, as in our previous works, but made using the more affordable low-grade by-product whey protein. We test the purification performance of amyloid–carbon hybrid filters for various clinically relevant radioactive substances with different half-life periods such as Tc-99m,22–24 I-123,25,26 and Ga-68.27,28 Further real wastewater obtained from Inselspital in Bern (Switzerland) containing I-13129 and Lu-17730 was also tested with an outstanding performance of the membranes. We finally, assessed the reusability of the membranes, as well as the scalability of the whey amyloid membranes for large-scale wastewater treatment, inferring that large-scale use of this technology on radioactive wastewater treatment is possible.

2 Results and discussion

Fig. 1a shows the schematic representation of the experimental unit developed to conduct clinical radioactive material removal using the amyloid hybrid membrane. The membrane is cropped into a disk of a diameter of 53 mm (Fig. 1b). The radioactively contaminated water is passed through the filtration cell by applying gentle pressure with a syringe (ESI† Fig. S1) with a flow rate of approximately 5 ml min−1. We used 10 wt% whey hybrid membrane for all testing protocols. Fig. 1c shows the scanning electron microscope (SEM) image of the amyloid hybrid membrane surface. The SEM image clearly shows the cellulose scaffold and the activated carbon components, while amyloids are revealed only at higher magnification, as in the transmission electron microscope image of Fig. 1d, the amyloid fibrils have contour lengths of the order of 1 μm or beyond and an average diameter of 4–6 nm (see ESI† Fig. S2 for AFM images). The pore distribution in the membrane and additional SEM images are provided in ESI† Fig. S3 and S4. We assume that the amyloid fibrils specifically bind and therefore adsorb the radioactive heavy metal compounds. As will be shown below, amyloids are the main radionuclide-adsorbing component of the membranes: Fig. 1e schematically illustrates the antiparallel cross-beta sheet structure of the amyloid fibrils and the putative binding sites for the radionuclide ions. The separation mechanism of heavy metal ions by the amyloid fibrils has been discussed in detail in our earlier reports.18,31 The basic concept and technology are inspired by the growth of amyloid plaques in vivo catalyzed by the presence of the metal ions. Accordingly, also in artificial amyloid membranes heavy metal ions adsorb very strongly via supramolecular metal–ligand interactions, providing an outstanding separation performance. In our earlier reports, we extensively studied the thermodynamic binding process of metal ions by amyloid fibrils by performing adsorption isotherms, isothermal titration calorimetry (ITC)31 and molecular docking simulations.
image file: d0ew00693a-f1.tif
  Fig. 1  (a) Schematic diagram of syringe-aided filtration setup. (b) Cropped filter membrane. (c) SEM image of the membrane surface. (d) Transmission electron microscope image of the amyloid fibrils. (e) Schematic representation of the putative binding of radionuclides on to the amyloid fibrils surface.

 

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