GT/ Scientists enhance recyclability of post-consumer plastic
Energy & green technology biweekly vol.40, 16th December — 5thJanuary
TL;DR
- Scientists have developed a new method for recycling high-density polyethylene (HDPE).
- Organic photovoltaics (OPVs) are a promising, economical, next-generation solar cell technology for scalable clean energy and wearable electronics. But the energy conversion loss due to the recombination of photogenerated charge carriers in OPVs has hindered further enhancement of their power conversion efficiency (PCE). Recently, researchers overcame this obstacle by inventing a novel device-engineering strategy to successfully suppress energy conversion loss, resulting in record-breaking efficiency.
- A new pathway to creating durable, efficient perovskite photovoltaics at industrial scale has been demonstrated through the first effective use of lead acetate as a precursor in making formamidinium-caesium perovskite solar cells.
- Researchers have shown how nitrogen fertilizer could be produced more sustainably. This is necessary not only to protect the climate, but also to reduce dependence on imported natural gas and to increase food security.
- Though plants can serve as a source of food, oxygen and décor, they’re not often considered to be a good source of electricity. But by collecting electrons naturally transported within plant cells, scientists can generate electricity as part of a ‘green,’ biological solar cell. Now, researchers have used a succulent plant to create a living ‘bio-solar cell’ that runs on photosynthesis.
- Consumers told that not recycling their batteries ‘risked polluting the equivalent of 140 Olympic swimming pools every year’ were more likely to participate in an electronic waste recycling scheme, a new study has found.
- Biodegradable medical gowns, designed to be greener than conventional counterparts, actually produce harmful greenhouse gases, according to new research.
- Engineers compare wastewater ‘snapshots’ to daylong composite samples and find snapshots lead to bias in testing for the presence of antibiotic-resistant genes.
- An international team of scientists has studied the propagation of electromagnetic waves in near-Earth space for three years. The team has studied the waves in the area where the solar wind collides with Earth’s magnetic field called foreshock region, and how the waves are transmitted to the other side of the shock.
- Researchers have developed accurate nation-wide mapping of the carbon content of trees based on aerial images.
- And more!
Green Technology Market
Green technology is an applicable combination of advanced tools and solutions to conserve natural resources and environment, minimize or mitigate negative impacts from human activities on the environment, and ensure sustainability development. Green technology is also referred to as clean technology or environmental technology which includes technologies, such as IoT, AI, analytics, blockchain, digital twin, security, and cloud, which collect, integrate, and analyze data from various real-time data sources, such as sensors, cameras, and Global Positioning System (GPS).
Green technology, also known as sustainable technology, protects the environment by using various forms of sustainable energy. Some of the best examples of green technologies include solar panels, LED lighting, wind energy, electric vehicles, vertical farming, and composting.
The global Green Technology and Sustainability market size to grow from USD 11.2 billion in 2020 to USD 36.6 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 26.6% during the forecast period. The growing consumer and industrial interest for the use of clean energy resources to conserve environment and increasing use of Radio Frequency Identification sensors across industries are driving the adoption of green technology and sustainability solutions and services in the market.
The blockchain segment is estimated to grow at the highest CAGR: Energy-intensive cryptocurrency mining has caused a spike in carbon emission, and hence blockchain is capable of driving innovation in the field of green technology.
Latest Research
Catalytic Chemical Recycling of Post-Consumer Polyethylene
by Alejandra Arroyave, Shilin Cui, Jaqueline C. Lopez, Andrew L. Kocen, Anne M. LaPointe, Massimiliano Delferro, Geoffrey W. Coates in Journal of the American Chemical Society
Scientists at the U.S. Department of Energy’s (DOE) Institute for Cooperative Upcycling of Plastics (iCOUP) have developed a new method for recycling high-density polyethylene (HDPE).
Using a novel catalytic approach, scientists at DOE’s Argonne National Laboratory and Cornell University converted post-consumer HDPE plastic into a fully recyclable and potentially biodegradable material with the same mechanical and thermal properties of the starting single-use plastic.
HDPE is ubiquitous in single-use applications because it is strong, flexible, long-lasting and inexpensive. But the ways we produce and dispose of HDPE pose serious threats to our own health and that of our planet.
Many HDPE products are produced from fossil fuels, and most post-consumer HDPE is either incinerated, dumped in landfills or lost in the environment. When it is recycled with current methods, the quality of the material degrades.
This new approach could reduce carbon emission and pollution associated with HDPE by using waste plastic as untapped feedstock and transforming it into a new material that can be recycled repeatedly without loss of quality.
Current HDPE recycling approaches yield materials with inferior properties. The team’s alternative approach uses a series of catalysts to cleave the polymer chains into shorter pieces that contain reactive groups at the ends. The smaller pieces can then be put back together to form new products of equal value. The end groups have the added benefit of making the new plastic easier to decompose, both in the lab and in nature.
Suppressed recombination loss in organic photovoltaics adopting a planar–mixed heterojunction architecture
by Kui Jiang, Jie Zhang, Cheng Zhong, Francis R. Lin, Feng Qi,et al in Nature Energy
Organic photovoltaics (OPVs) are a promising, economical, next-generation solar cell technology for scalable clean energy and wearable electronics. But the energy conversion loss due to the recombination of photogenerated charge carriers in OPVs has hindered further enhancement of their power conversion efficiency (PCE). Recently, researchers from City University of Hong Kong (CityU) overcame this obstacle by inventing a novel device-engineering strategy to successfully suppress the energy conversion loss, resulting in record-breaking efficiency.
The best-performing OPVs developed by the CityU team have achieved PCE of over 19%, and the team expects to exceed 20% very soon. The discovery is promising for the commercialisation of OPVs. OPVs, a solar cell technology based on organic semiconductors, are regarded as a promising candidate for clean energy because of their low material toxicity and vast molecular tunability in photoactive materials. Currently, most high-performance organic photovoltaics adopt a “bulk-heterojunction” (BHJ) structure, consisting of electron donor and acceptor materials intermixed throughout the active layer of the device.
When converting sunlight into electricity in OPVs, energy from sunlight creates excitons (a negatively charged electron and a positively charged hole bound together), which then dissociate into free electrons and holes at the nanoscale donor-acceptor interface, generating charge carriers (photocurrent) and hence electricity. However, if these charge carriers are not collected by the electrodes and encounter each other again at the donor-acceptor interface, they may recombine to form a so-called low-energy “spin-triplet exciton” (T1), which consecutively relaxes back to ground state, causing energy loss in the form of heat and hence photocurrent loss. This irreversible process strongly limits the maximum achievable PCE of OPVs.
A research team led by Professor Alex Jen Kwan-yue, Lee Shau Kee Chair Professor of Materials Science and Director of the Hong Kong Institute for Clean Energy at CityU, overcame this obstacle by inventing a novel device-engineering strategy to suppress T1 formation and minimise the associated recombination loss, which led to the record-breaking efficiency of OPVs.
“We are the first team that managed to modulate T1 formation through device engineering without changing the properties of the photoactive materials and to reveal the fundamental mechanism,” said Professor Jen. “Using this strategy, we have expanded it to 14 other material systems to show the universal applicability of this study.”
By replacing the traditional highly intermixed bulk-heterojunction (BHJ) architecture inside the solar cell with a rather de-mixed “planar-mixed heterojunction” (PMHJ) to reduce the donor-acceptor interface inside the active layer of OPVs, the team managed to alleviate the energy conversion loss in OPVs by suppressing the recombination of the charge carriers. This discovery maximized the photocurrent of OPVs, resulting in devices with a high PCE of over 19%.
“Compared to the traditional inter-mixed bulk-heterojunction (BHJ) architecture, our rather de-mixed planar-mixed heterojunction (PMHJ) strategy is capable of suppressing the loss pathway mediated by charge-transfer states at the donor-acceptor interface,” Professor Jen explained. “We revealed that having fewer donor-acceptor contacts in planar-mixed heterojunction minimizes the chance of recombination and results in reduced T1 concentration. This fundamentally changes researchers’ previous impression of OPVs — that the more donor-acceptor contacts, the higher the OPV performance.”
“The achieved optimum photovoltage-photocurrent trade-off resulting from our strategy enables OPVs with competitive efficiency comparable to that of inorganic photovoltaics,” added Dr Francis Lin, postdoc in the Department of Chemistry, who also took part in the study. He explained that organic photovoltaic cells have several advantages over inorganic counterparts, such as being lightweight and flexible, like a thin plastic film, and allowing cost-effective fabrication, using roll-to-roll printing production.
The team believes that its latest discovery provides a comprehensive basis for future organic photovoltaics to reach their full promise and stimulate a new wave of studies on the versatile photophysical processes in organic semiconductors. They are applying for a patent for the discovery.
“We hope to further boost the performance of OPVs following our novel discovery of modulating the photophysical processes. This redefines the maximum potential of OPVs to facilitate their commercialisation,” said Professor Jen.
Efficient and stable formamidinium–caesium perovskite solar cells and modules from lead acetate-based precursors
by Jie Zhao, Sebastian O. Fürer, David P. McMeekin, et al in Energy & Environmental Science
A new pathway to creating durable, efficient perovskite photovoltaics at industrial scale has been demonstrated through the first effective use of lead acetate as a precursor in making formamidinium-caesium perovskite solar cells.
Members of Exciton Science, based at Monash University, were able to create perovskite solar cells with 21% efficiency, the best results ever recorded for a device made from a non-halide lead source. A mini prototype solar panel featuring these cells achieved 18.8% efficiency. The large-area perovskite layer was fabricated in ambient atmosphere and was made via a single-step blade coating, demonstrating its potential viability for industrial-scale manufacturing. The test devices also showed strong thermal stability, continuing to function with no efficiency loss after 3,300 hours running at 65°C.
First author Jie Zhao, a PhD student at Monash University, said: “We’ve been able to use lead acetate in a one-step, spin-coating process to get the perfect, high-quality formamidinium-caesium perovskite thin film. “And because we don’t need an anti-solvent agent, we can do this via large-scale techniques, such as blade coating, which means it’s viable at industrial scale.”
Corresponding author and Monash University colleague Dr Wenxin Mao said: “The vast majority of perovskite solar cell research uses lead halides, particularly lead iodide. “The lead iodide needs to be 99.99% pure and it’s very expensive to synthesise cells using lead iodide.
“We’re the first group to make highly stable formamidinium-cesium perovskite solar cells using lead acetate rather than lead iodide. “We have provided the entire research community a second way to make high-quality perovskite solar cells.”
Thin film solar cells made from perovskites have the potential to disrupt the solar energy sector, thanks to their relatively low manufacturing cost, flexibility and tunable band gap relative to silicon. However, researchers are struggling to solve reliability issues, and they also need to find a way to create devices at a viable commercial scale. Perovskites are solution processed (made in liquid) using a variety of different ingredients. Most approaches use lead halides and require the inclusion of strong polar solvents with high boiling points and antisolvent quenching agents to control the perovskite crystallisation process. This complicated mechanism can lead to defects in the thin films, which causes the resulting device to rapidly lose efficiency. It’s also hard to control. The chemical compound lead acetate has emerged as a promising alternative precursor, because it can create ultrasmooth thin films with fewer defects.
Until now, lead acetate had only been used to make methylammonium or cesium-based perovskites, which are relatively unstable and not suitable for real-world applications. A better candidate for commercial use can be found in perovskites made using formamidinium and caesium, thanks to their superior stability. Previous attempts to synthesise them using lead acetate as the precursor failed. To investigate and solve this issue, the researchers, together with their collaborators at Wuhan University of Technology in China, examined the underlying molecular mechanisms. Through X-ray diffraction and nuclear magnetic resonance spectroscopy, they identified the need to use ammonium as a volatile cation (positively charged ion) at a critical stage.
Contributing author Dr Sebastian Fürer said: “The presence of ammonium served to drive away the residual acetate during annealing, without forming unwanted side products.”
The researchers hope their work on the fundamental chemistry governing precursor behaviour can encourage a greater focus on scalable synthesis and fabrication methods of metal halide perovskite devices.
Energy and food security implications of transitioning synthetic nitrogen fertilizers to net-zero emissions
by Lorenzo Rosa, Paolo Gabrielli in Environmental Research Letters
Intensive agriculture is possible only if the soil is fertilised with nitrogen, phosphorus and potassium. While phosphorus and potassium can be mined as salts, nitrogen fertiliser has to be produced laboriously from nitrogen in the air and from hydrogen. And, the production of hydrogen is extremely energy-intensive, currently requiring large quantities of natural gas or — as in China — coal. Besides having a correspondingly large carbon footprint, nitrogen fertilizer production is vulnerable to price shocks on the fossil fuels markets.
Paolo Gabrielli, Senior Scientist at the Laboratory of Reliability and Risk Engineering at ETH Zurich, has collaborated with Lorenzo Rosa, Principal Investigator at Carnegie Institution for Science in Stanford, US, to investigate various carbon-neutral production methods for nitrogen fertiliser. In a study published in the journal Environmental Research Letters, the two researchers conclude that a transition in nitrogen production is possible and that such a transition may also increase food security. However, alternative production methods have advantages and disadvantages. Specifically, the two researchers examined three alternatives:
- Producing the necessary hydrogen using fossil fuels as in the business-as-usual, only instead of emitting the greenhouse gas CO2 into the atmosphere, it is captured in the production plants and permanently stored underground (carbon capture and storage, CSS). This requires not only an infrastructure for capturing, transporting and storing the CO2 but also correspondingly more energy. Despite this, it is a comparatively efficient production method. However, it does nothing to reduce dependence on fossil fuels.
- Electrifying fertiliser production by using water electrolysis to produce the hydrogen. This requires averagely 25 times as much energy as today’s production method using natural gas, so it would take huge amounts of electricity from carbon-neutral sources. For countries with an abundance of solar or wind energy, this might be an appealing approach. However, given plans to electrify other sectors of the economy in the name of climate action, it might lead to competition for sustainable electricity.
- Synthesising the hydrogen for fertiliser production from biomass. Since it requires a lot of arable land and water, ironically this production method competes with food production. But the study’s authors point out that it makes sense if the feedstock is waste biomass — for example, crop residues.
The scientists state that the key to success is likely to be a combination of all these approaches depending on the country and on specific local conditions and available resources. In any case, it is imperative that agriculture make a more efficient use of nitrogen fertilisers, as Rosa stresses: “Addressing problems like over-fertilisation and food waste is also a way to reduce the need for fertiliser.”
In the study, the scientists also sought to identify the countries of the world in which food security is currently particularly at risk owing to their dependence on imports of nitrogen or natural gas. The following countries are particularly vulnerable to price shocks in the natural gas and nitrogen markets: India, Brazil, China, France, Turkey and Germany.
Decarbonising fertiliser production would in many cases reduce this vulnerability and increase food security. At the very least, electrification via renewables or the use of biomass would reduce the dependence on natural gas imports. However, the researchers put this point into perspective: all carbon-neutral methods of producing nitrogen fertiliser are more energy intensive than the current method of using fossil fuels. In other words, they are still vulnerable to certain price shocks — not on natural gas markets directly, but perhaps on electricity markets.
Decarbonisation is likely to change the line-up of countries that produce nitrogen fertiliser, the scientists point out in their study. As things stand, the largest nitrogen exporting nations are Russia, China, Egypt, Qatar and Saudi Arabia. Except for China, which has to import natural gas, all these countries can draw on their own natural gas reserves. In the future, the countries that are likely to benefit from decarbonisation are those that generate a lot of solar and wind power and also have sufficient reserves of land and water, such as Canada and the United States.
“There’s no getting around the fact that we need to make agricultural demand for nitrogen more sustainable in the future, both for meeting climate targets and for food security reasons,” Gabrielli says.
War in Ukraine is affecting the global food market not only because the country normally exports a lot of grain, but also because the conflict has driven natural gas prices higher. This in turn has caused prices for nitrogen fertilisers to rise. Even so, some fertiliser producers are known to have ceased production, at least temporarily, because the exorbitant cost of gas makes production uneconomical for them.
Self-Enclosed Bio-Photoelectrochemical Cell in Succulent Plants
by Yaniv Shlosberg, Gadi Schuster, Noam Adir in ACS Applied Materials & Interfaces
Though plants can serve as a source of food, oxygen and décor, they’re not often considered to be a good source of electricity. But by collecting electrons naturally transported within plant cells, scientists can generate electricity as part of a “green,” biological solar cell. Now, researchers have, for the first time, used a succulent plant to create a living “bio-solar cell” that runs on photosynthesis.
In all living cells, from bacteria and fungi to plants and animals, electrons are shuttled around as part of natural, biochemical processes. But if electrodes are present, the cells can actually generate electricity that can be used externally. Previous researchers have created fuel cells in this way with bacteria, but the microbes had to be constantly fed. Instead, scientists, including Noam Adir’s team, have turned to photosynthesis to generate current. During this process, light drives a flow of electrons from water that ultimately results in the generation of oxygen and sugar. This means that living photosynthetic cells are constantly producing a flow of electrons that can be pulled away as a “photocurrent” and used to power an external circuit, just like a solar cell.
Certain plants — like the succulents found in arid environments — have thick cuticles to keep water and nutrients within their leaves. Yaniv Shlosberg, Gadi Schuster and Adir wanted to test, for the first time, whether photosynthesis in succulents could create power for living solar cells using their internal water and nutrients as the electrolyte solution of an electrochemical cell.
The researchers created a living solar cell using the succulent Corpuscularia lehmannii, also called the “ice plant.” They inserted an iron anode and platinum cathode into one of the plant’s leaves and found that its voltage was 0.28V. When connected into a circuit, it produced up to 20 µA/cm2 of photocurrent density, when exposed to light and could continue producing current for over a day. Though these numbers are less than that of a traditional alkaline battery, they are representative of just a single leaf. Previous studies on similar organic devices suggest that connecting multiple leaves in series could increase the voltage. The team specifically designed the living solar cell so that protons within the internal leaf solution could be combined to form hydrogen gas at the cathode, and this hydrogen could be collected and used in other applications. The researchers say that their method could enable the development of future sustainable, multifunctional green energy technologies.
How to enhance the sustainable disposal of harmful products
by Diletta Acuti, Linda Lemarié, Giampaolo Viglia in Technological Forecasting and Social Change
Consumers told that not recycling their batteries ‘risked polluting the equivalent of 140 Olympic swimming pools every year’ were more likely to participate in an electronic waste recycling scheme, a new study has found.
The paper from the University of Portsmouth explores how to improve our sustainable disposal of electronic waste (e-waste). With Christmas around the corner and consumers buying the latest mobile phones, tablets, headphones and televisions, older electronic products become defunct and add to the alarming quantity of potentially toxic e-waste. Experts at the University of Portsmouth carried out research to test what factors encourage consumers to safely dispose of e-waste, which will be useful for managers and policy-makers implementing disposal schemes.
Lead author of the study, Dr Diletta Acuti, from the University’s Faculty of Business and Law, said: “The world’s electronic waste is an enormous problem which needs to be addressed urgently. E-waste often contains hazardous substances, such as mercury, lead or acid, which ends up in landfills without any treatment or special precautions, causing significant long-term damage to the environment and human health.
“Adequate treatment of this waste is therefore an environmental necessity.”
In 2019, 205,000 tons of portable batteries were sold in Europe, but only half were collected for recycling. Dr Acuti’s research looks specifically at the disposal of batteries. The researchers conducted a field experiment in Northern Italy, which analysed how the proximity of bins and the language used to encourage recycling affected 100 people’s efforts to dispose of their e-waste.
She said: “We’re buying more and more technology causing mountains of e-waste and the problem is only going to get worse, but proper disposal of this waste can only be achieved if consumers actively participate in recycling. “Our research looks at what factors are effective to try and encourage people to recycle their e-waste, which we hope will be useful for implementing successful disposal schemes.”
A number of bins were installed to collect old batteries and letters were sent to inform people about the new scheme. Some of the letters included metaphorical language to see if this would encourage recycling efforts and other letters included numerical information. The researchers found that metaphorical language had a more powerful influence on consumers’ actions.
“Those who were told to consider the fact that a battery contains approximately one gram of mercury, an amount that can pollute a quantity of water equivalent to seven bathtubs and that we risk polluting the equivalent of 140 Olympic swimming pools every year, were more likely to recycle their batteries,” explained Dr Acuti.
“Metaphors elicit visual representation of an object — that is too large or too distant from the individual’s lived reality, like large quantities of water — in the consumer’s mind, which makes an abstract object more concrete and easier to understand.
“By strategically placing the bins and making the information about the disposal scheme easy to understand, we can actually change the behaviour of consumers and use marketing for a better world.”
How sustainable are the biodegradable medical gowns via environmental and social life cycle assessment?
by Xiang Zhao, Jiří Jaromír Klemeš, Michael Saxon, Fengqi You in Journal of Cleaner Production
Biodegradable medical gowns, designed to be greener than conventional counterparts, actually produce harmful greenhouse gases, according to new research published.
The use of disposable plasticized medical gowns — both conventional and biodegradable — has surged since the onset of the COVID-19 pandemic. Landfills now brim with them. Because the biodegradable version decomposes faster than conventional gowns, popular wisdom held that it offers a greener option by less space use and chronic emissions in landfills. That wisdom may be wrong.
“There’s no magic bullet to this problem,” said Fengqi You, professor in energy systems engineering at Cornell University. “Plasticized conventional medical gowns take many years to break down and the biodegradable gowns degrade much faster, but they produce gas emissions faster like added methane and carbon dioxide than regular ones in a landfill,” said You, who is a senior faculty fellow in the Cornell Atkinson Center for Sustainability. “Maybe the conventional gowns is not so bad.”
According to this research led by Cornell doctoral student Xiang Zhao, biodegradable gown production poses an additional 11% higher ecotoxicity rate than conventional alternatives. Adopting landfill gas capture and utilization processes in biodegradable gown sanitary landfills can reduce 9.79% of greenhouse emissions, life-cycle landfill use by nearly 49%, and save at least 10% fossil resources by employing onsite power co-generation, the researchers found.
Conventional gowns are environmentally and socially sustainable because they can pose 14% less toxicity to humans, cause 10% fewer greenhouse gas emissions, and are nearly 10% less toxic to freshwater when compared to biodegradable gowns in landfills with extra gas emissions. Improving the gas capture efficiency above 85% can make biodegradable gowns more environmentally sustainable than conventional gowns.
“It’s nice to break down the plastic into smaller things,” Zhao said. “But those small things eventually decompose into gas and if we don’t capture them, they become greenhouse gases that go into the air.”
Snapshot ARG Removal Rates across Wastewater Treatment Plants Are Not Representative Due to Diurnal Variations
by Esther G. Lou, Priyanka Ali, Karen Lu, Prashant Kalvapalle, Lauren B. Stadler in ACS ES&T Water
Testing the contents of a simple sample of wastewater can reveal a lot about what it carries, but fails to tell the whole story, according to Rice University engineers.
Their new study shows that composite samples taken over 24 hours at an urban wastewater plant give a much more accurate representation of the level of antibiotic-resistant genes (ARGs) in the water. According to the Centers for Disease Control and Prevention (CDC), antibiotic resistance is a global health threat responsible for millions of deaths worldwide. In the process, the researchers discovered that while secondary wastewater treatment significantly reduces the amount of target ARG, chlorine disinfectants often used in later stages of treatment can, in some situations, have a negative impact on water released back into the environment.
The lab of Lauren Stadler at Rice’s George R. Brown School of Engineering reported seeing levels of antibiotic-resistant RNA concentrations 10 times higher in composite samples than what they see in “grabs,” snapshots collected when flow through a wastewater plant is at a minimum. Stadler and lead authors Esther Lou and Priyanka Ali, both graduate students in her lab, reported their results. The results could lead to better protocols for treating wastewater to lower the prevalence of antibiotic-resistant genes in bacteria that propagate at plants and can transfer those genes to other organisms in the environment.
The issue is critical because antibiotic resistance is a killer, causing an estimated 2.8 million infections in the U.S. every year, leading to more than 35,000 deaths, said Stadler, an assistant professor of civil and environmental engineering and a pioneer in the ongoing analysis of wastewater for signs of the SARS-CoV-2 virus responsible for COVID-19. Those statistics have made it a long-standing focus of efforts at Rice that led to the foundation of a new center, Houston Wastewater Epidemiology, a partnership with the Houston Health Department and Houston Public Works. The center is one of two designated by the CDC announced this year to develop tools and train other state and local health departments in the sciences of monitoring wastewater-borne diseases. The takeaway for testers is that snapshots can lead to unintended biases in their results, Stadler said.
“I think it’s intuitive that grabbing a single sample of wastewater is not representative of what flows across the entire day,” said Stadler, who is also a faculty member of the Rice-based, National Science Foundation-supported Nanotechnology Enabled Water Treatment (NEWT) Center. “Wastewater flows and loads vary across the day, due to patterns of water use. While we know this to be true, no one had shown the degree to which antibiotic-resistant genes vary throughout the day.”
For the study, the Rice team took both grab and composite samples in two 24-hour campaigns, one during the summer and another during winter, at a Houston-area plant that routinely disinfects wastewater. They took samples every two hours from various stages of the wastewater treatment process and ran PCR tests in the lab to quantify several clinically relevant genes that confer resistance to fluoroquinolone, carbapenem, ESBL and colistin, as well as a class 1 integron-integrase gene known as a mobile genetic element (MGE) for its ability to move within a genome or transfer from one species to another.
The samples they collected allowed them to determine the concentration of ARGs and loads across a typical weekday, the variability in removal rates at plants based on the grab samples and the impact of secondary treatment and chlorine disinfection on the removal of ARGs, as well as the ability to compare grabs and composites. The team found that the vast majority of ARG removal occurred due to biological processes as opposed to chemical disinfection. In fact, they observed that chlorination, used as the final disinfectant before the treated wastewater is discharged into the environment, may have selected for antibiotic-resistant organisms.
Because the results from snapshots can vary significantly during any given day, they had to be collected at a steady pace over 24 hours. That required Lou and Ali to spend several long shifts at the City of West University Place wastewater treatment plant. “They camped out,” Stadler said. “They set up their cots and ordered takeout.” Such commitment will not be necessary if real-time wastewater monitoring becomes a reality. Stadler is part of a Rice collaboration developing living bacterial sensors that would detect the presence of ARGs and pathogens, including SARS-CoV-2, without pause at different locations within a wastewater system. The project underway at Rice to build bacterial sensors that emit an immediate electrical signal upon sensing a target was the subject of a study in Nature in November.
“Living sensors can enable continuous monitoring as opposed to relying on expensive equipment to collect composite samples that need to be brought back to the lab to analyze,” she said. “I think the future is these living sensors that can be placed anywhere in the wastewater system and report on what they see in real time. We’re working towards that.”
Transmission of foreshock waves through Earth’s bow shock
by L. Turc, O. W. Roberts, D. Verscharen, A. P. Dimmock, P. Kajdič, M. Palmroth, Y. Pfau-Kempf, A. Johlander, M. Dubart, E. K. J. Kilpua, J. Soucek, K. Takahashi, N. Takahashi, M. Battarbee, U. Ganse in Nature Physics
An international team of scientists led by Lucile Turc, an Academy Research Fellow at the University of Helsinki and supported by the International Space Science Institute in Bern has studied the propagation of electromagnetic waves in near-Earth space for three years. The team has studied the waves in the area where the solar wind collides with Earth’s magnetic field called foreshock region, and how the waves are transmitted to the other side of the shock.
“How the waves would survive passing through the shock has remained a mystery since the waves were first discovered in the 1970s. No evidence of those waves has ever been found on the other side of the shock,” says Turc.
The team has used a cutting-edge computer model, Vlasiator, developed at the University of Helsinki by a group led by professor Minna Palmroth, to recreate and understand the physical processes at play in the wave transmission. A careful analysis of the simulation revealed the presence of waves on the other side of the shock, with almost identical properties as in the foreshock.
“Once it was known what and where to look for, clear signatures of the waves were found in satellite data, confirming the numerical results,” says Lucile Turc.
Around our planet is a magnetic bubble, the magnetosphere, which shields us from the solar wind, a stream of charged particles coming from the Sun. Electromagnetic waves, appearing as small oscillations of the Earth’s magnetic field, are frequently recorded by scientific observatories in space and on the ground. These waves can be caused by the impact of the changing solar wind or come from the outside of the magnetosphere. The electromagnetic waves play an important role in creating adverse space weather around our planet: they can for example accelerate particles to high energies, which can then damage spacecraft electronics, and cause these particles to fall into the atmosphere.
On the side of Earth facing the Sun, scientific observatories frequently record oscillations at the same period as those waves that form ahead of the Earth’s magnetosphere, singing a clear magnetic song in a region of space called the foreshock. This has led space scientists to think that there is a connection between the two, and that the waves in the foreshock can enter the Earth’s magnetosphere and travel all the way to the Earth’s surface. However, one major obstacle lies in their way: the waves must cross the shock before reaching the magnetosphere.
“At first, we thought that the initial theory proposed in the 1970s was correct: the waves could cross the shock unchanged. But there was an inconsistency in the wave properties that this theory could not reconcile, so we investigated further,” says Turc.
“Eventually, it became clear that things were much more complicated than it seemed. The waves we saw behind the shock were not the same as those in the foreshock, but new waves created at the shock by the periodic impact of foreshock waves.”
When the solar wind flows through the shock, it is compressed and heated. The shock strength determines how much compression and heating take place. Turc and her colleagues showed that foreshock waves are able to tune the shock, making it alternatively stronger or weaker when wave troughs or crests arrive at the shock. As a result, the solar wind behind the shock changes periodically and creates new waves, in concert with the foreshock waves. The numerical model also pinpointed that these waves could only be detected in a narrow region behind the shock, and that they could easily be hidden by the turbulence in this region. This likely explains why they had not been observed before. While the waves originating from the foreshock only play a limited role in space weather at Earth, they are of great importance to understand the fundamental physics of our universe.
Nation-wide mapping of tree-level aboveground carbon stocks in Rwanda
by Maurice Mugabowindekwe, Martin Brandt, Jérôme Chave, et al Nature Climate Change
As the first country, Rwanda can now present a national inventory based on a mapping of the carbon stock of each individual tree. Researchers at University of Copenhagen have developed a method to achieve this task in collaboration with Rwandan authorities and researchers.
“Large uncertainties exist for the current forest assessments internationally. By mapping the carbon stock of all individual trees, accuracy is greatly improved. Further, the way different countries make their inventories is not consistent due to different contexts, goals, and available datasets. We hope that this method will establish itself as a standard, thereby enabling better comparisons between countries,” says PhD Researcher Maurice Mugabowindekwe, Department of Geosciences and Natural Resources Management (IGN), University of Copenhagen. He is first author on the scientific article presenting the new method. The article has been accepted for publication by Nature Climate Change, one of the most prominent journals for the field.
Maurice Mugabowindekwe being Rwandan himself is helpful during the work, but the choice of Rwanda for development of the method was scientifically based, he emphasizes:
“The country has a rich landscape variation including savannas, woodlands, sub-humid and humid forests, shrubland, agro-ecosystem mosaics, and urban tree ecosystems which are representative of most tropical countries. We wanted to prove the method for all these landscape types. Moreover, Rwanda is a signatory to several international agreements on forest preservation and climate change mitigation. For instance, Rwanda has pledged to restore about 80 % of its surface area by 2030 under the Bonn Challenge. So, it is highly relevant to have a reliable method for monitoring tree carbon.”
Preservation of natural forests and planting of new trees are recognized as vital routes to limiting climate change. However, large uncertainties regarding the carbon content of the trees have made it hard to assess the efficiency of concrete initiatives. The University of Copenhagen researchers have overcome this problem. The new method benefits from databases which give the relationship between the extent of the crown and the total carbon content of an individual tree.
“Mapping individual trees and calculating their carbon stocks has traditionally been done in forestry, albeit at a much smaller scale. Basically, what we do equals scaling up these approaches from a very local to a national level,” says Researcher Ankit Kariryaa, working 50:50 at IGN and at the Department of Computer Sciences (DIKU). Scientists from these two University of Copenhagen departments have developed the method with IGN as lead, in collaboration with other international scientists.
The new method will support Rwanda in verifying fulfilment of commitments under schemes such as the global forestry climate change mitigation scheme REDD+ or the African Forest Landscape Restoration Initiative, AFR 100.
Manually mapping the trees of an entire country would be a huge endeavor and excessively costly. Thus, the new method constitutes a breakthrough since no other method would realistically be able to provide the same information at the level of individual trees.
“It is important to take a holistic approach and also include trees which are outside forests,” says Ankit Kariryaa, noting that 72 % of the mapped trees were in farmlands and savannas, and 17 % in plantations.
At the same time, the relatively small proportion of trees which are found in natural forests — 11 % of the total tree count — comprise about 51 % of the national carbon stock of Rwanda. This is possible mainly because natural forests have a very high carbon content per tree volume, thanks to the very low human disturbance secured through national legislation.
“This suggests that conservation, regeneration, and sustainable management of natural forests is more effective at mitigating climate change than plantation,” Maurice Mugabowindekwe comments.
It is paramount that the computer can distinguish the individual trees. This is because the relationship between the extent of the crown and the total carbon content of a tree is very different depending on the size of a tree. One very large tree will have a much higher carbon content than a group of trees with the same joint crown extent. So, if the group was mistaken for one tree, the carbon content would be significantly overestimated. A deep neural network is used for detecting the individual trees.
“Especially for the rainforest, it is highly challenging to determine how many different trees are present in an image. At first glance, the forest just appears to be one huge green blanket. But by using methods from Machine Learning and Computer Vision, our system can also be applied to identify the individual trees in overstory of dense forests,” explains Christian Igel, Professor of Machine Learning at DIKU.
Training the computer on verified samples is at the core of Machine Learning. In the Rwandan study, the computer was trained on a set of some 97,500 manually delineated tree crowns representing the full range of biogeographical conditions across the country.
The study used publicly available aerial and satellite images of Rwanda at 0.25 x 0.25 m resolution. These images were collected in June-August 2008 and 2009 and were provided by the Rwanda Land Management and Use Authority and the University of Rwanda. More than 350 million trees were mapped.
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