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Climate change and sea level rise pose an acute challenge for cities with combined sewer systems
Older coastal cities, like Philadelphia, New York and Boston are at risk of being inundated by untreated sewage during floods. Due in part to the design of their combined sewer systems and in part due to sea level rise, these cities could be facing a growing public health crisis as climate change also drives more extreme precipitation, according to researchers at Drexel University who study urban stormwater management. The group recently published research that modeled the potential extent of the problem in a section of the coastal city of Camden, New Jersey, and the effectiveness of one proposed intervention to help protect these communities.
Beginning in 1855 many of America’s coastal communities were designed with a combined sewer system. In these systems, stormwater and sewage are collected using the same pipes. Originally, these pipes discharged to streams and rivers; later they were directed toward wastewater treatment facilities. But the pipes can only convey a certain amount of flow. During wet weather events, to avoid inundating the wastewater treatment plants some portion of the flow still overflows into the natural water bodies through features known as combined sewer overflows — or CSOs.
While the Federal Pollution Control and Clean Water Act has pushed communities to upgrade their infrastructure and take steps to curtail CSOs, climate change brings an entirely new dimension to this regulatory compliance challenge.
When the water level in the receiving water body is high, the CSO flap gates that ordinarily keep river water from backing up into the sewer pipes can’t open as easily. Without these relief valves fully open, the combined sewage generated during wet weather can back up in the system, even spilling out onto the street or into people’s basements.
As climate change brings more heavy rain and higher river levels, the problem worsens and cannot be mitigated with conventional approaches to stormwater management.
“Climate change is making what was already a difficult problem even more challenging,” said Franco Montalto, PhD, a professor in the College of Engineering who led the research. “The combination of sea level rise and precipitation intensification is particularly difficult for urban stormwater managers because it means the combined sewer system is being loaded from both sides. In many cases, there’s no place for the water to go but up and out onto the street creating environmental and health risks.”
Montalto’s team has been working closely with the Camden County Municipal Utilities Authority (CCMUA) to study potential solutions to this problem.
Looking for a Better Answer
In their research, recently published in the Journal of Water Management Modeling, the group reported on the results of their detailed hydrologic and hydraulic models of flooding and combined sewer overflows in the Cramer Hill section of Camden. This is a flood-prone portion of the city located very close to the largest CSO point on the East side of the Delaware River.
Once they calibrated their models to historical conditions, they used them to simulate how flooding and CSOs would change in the future, as the climate changes. The same models are also being used to evaluate the potential effectiveness of different conceptual solutions.
“CCMUA has been working diligently for years to reduce environmental injustices in Camden,” Montalto said. “It has worked to reduce odors from its wastewater treatment plant and reduce the frequency and pollution associated with CSOs. It’s exciting to work with them now on the development of solutions that can also reduce flooding and make Camden’s neighborhoods more resilient to climate change. Our modeling will support CCMUA as it develops multifunctional infrastructure strategies.”
Drexel’s model is unique because it is an “all-pipes” model built by assembling many different geospatial data sets into one computer model. This allows the team to simulate stormwater flows through virtually every surface, catch basin, and pipe in the area.
To check the accuracy of the modeling program, the researchers compared the model’s prediction of annual combined sewer overflow discharge volume to CCMUA records. Simulated flood patterns were compared to photographs of actual floods taken by the research team during storms over the summer of 2021.
“It was important to perform a thorough validation process because we will be relying on this model to simulate future climate and infrastructure conditions,” Montalto said. “Not every municipality has been making recordings of all the necessary data to build a complete model, so part of this research was showing that the ad-hoc process we developed could reliably validate our model without some of the data it would normally require.”
Projecting Future Challenges
Montalto’s team used the validated model to simulate what would happen if precipitation increased by up to 30% and if the sea level rose by up to 1.8 meters. They simulated each of these climatic changes independently, and together.
The model projected that increased precipitation would result in overflow discharges 21-66% above the current annual discharge volume. And, although each of the sea-level-rise scenarios resulted in a reduction in the number of overflow events and annual overflow discharge, the duration of flooding increased with each compounding factor.
Testing a Theory
One key strategy that Camden has been considering for Cramer Hill’s water management challenges involves diverting upstream stormwater away from its sewer system. With Drexel’s modeling program, the municipality was finally able to test the idea.
Dubbed the “Pennsauken disconnection,” the suggestion is to divert stormwater generated in the town of Pennsauken, New Jersey, which is immediately northeast of Camden, away from Cramer Hill’s combined sewer system via an intermediary pumping station.
The team found that the disconnection will help under all future climate scenarios. However, even with the disconnection, the impacts of climate change and sea level rise still resulted in an increase in the number of flooding events; and a significant increase in the duration of flooding under the sea-level-rise conditions.
Setting a New Course
Overall, the results suggest that increased precipitation events due to climate change will cause more combined sewer overflows. And sea level rise will make it more difficult for these systems to discharge into nearby bodies of water. Some 40 million people currently live in areas served by combined sewer systems, so this is both a pressing issue and one that could affect a significant number of people throughout the country.
Montalto’s group plans to continue refining its Cramer Hill model, as they collect information about water flow through the sewage network and surface flooding. They will also model other infrastructure interventions to manage stormwater.
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Early dark energy could resolve cosmology’s two biggest puzzles
A new study by MIT physicists proposes that a mysterious force known as early dark energy could solve two of the biggest puzzles in cosmology and fill in some major gaps in our understanding of how the early universe evolved.
Now, the MIT team has found that both puzzles could be resolved if the early universe had one extra, fleeting ingredient: early dark energy. Dark energy is an unknown form of energy that physicists suspect is driving the expansion of the universe today. Early dark energy is a similar, hypothetical phenomenon that may have made only a brief appearance, influencing the expansion of the universe in its first moments before disappearing entirely.
Some physicists have suspected that early dark energy could be the key to solving the Hubble tension, as the mysterious force could accelerate the early expansion of the universe by an amount that would resolve the measurement mismatch.
The MIT researchers have now found that early dark energy could also explain the baffling number of bright galaxies that astronomers have observed in the early universe. In their new study, reported in the Monthly Notices of the Royal Astronomical Society, the team modeled the formation of galaxies in the universe’s first few hundred million years. When they incorporated a dark energy component only in that earliest sliver of time, they found the number of galaxies that arose from the primordial environment bloomed to fit astronomers’ observations.
“You have these two looming open-ended puzzles,” says study co-author Rohan Naidu, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research. “We find that in fact, early dark energy is a very elegant and sparse solution to two of the most pressing problems in cosmology.”
The study’s co-authors include lead author and Kavli postdoc Xuejian (Jacob) Shen, and MIT professor of physics Mark Vogelsberger, along with Michael Boylan-Kolchin at the University of Texas at Austin, and Sandro Tacchella at the University of Cambridge.
Big city lights
Based on standard cosmological and galaxy formation models, the universe should have taken its time spinning up the first galaxies. It would have taken billions of years for primordial gas to coalesce into galaxies as large and bright as the Milky Way.
But in 2023, NASA’s James Webb Space Telescope (JWST) made a startling observation. With an ability to peer farther back in time than any observatory to date, the telescope uncovered a surprising number of bright galaxies as large as the modern Milky Way within the first 500 million years, when the universe was just 3 percent of its current age.
“The bright galaxies that JWST saw would be like seeing a clustering of lights around big cities, whereas theory predicts something like the light around more rural settings like Yellowstone National Park,” Shen says. “And we don’t expect that clustering of light so early on.”
For physicists, the observations imply that there is either something fundamentally wrong with the physics underlying the models or a missing ingredient in the early universe that scientists have not accounted for. The MIT team explored the possibility of the latter, and whether the missing ingredient might be early dark energy.
Physicists have proposed that early dark energy is a sort of antigravitational force that is turned on only at very early times. This force would counteract gravity’s inward pull and accelerate the early expansion of the universe, in a way that would resolve the mismatch in measurements. Early dark energy, therefore, is considered the most likely solution to the Hubble tension.
Galaxy skeleton
The MIT team explored whether early dark energy could also be the key to explaining the unexpected population of large, bright galaxies detected by JWST. In their new study, the physicists considered how early dark energy might affect the early structure of the universe that gave rise to the first galaxies. They focused on the formation of dark matter halos — regions of space where gravity happens to be stronger, and where matter begins to accumulate.
“We believe that dark matter halos are the invisible skeleton of the universe,” Shen explains. “Dark matter structures form first, and then galaxies form within these structures. So, we expect the number of bright galaxies should be proportional to the number of big dark matter halos.”
The team developed an empirical framework for early galaxy formation, which predicts the number, luminosity, and size of galaxies that should form in the early universe, given some measures of “cosmological parameters.” Cosmological parameters are the basic ingredients, or mathematical terms, that describe the evolution of the universe.
Physicists have determined that there are at least six main cosmological parameters, one of which is the Hubble constant — a term that describes the universe’s rate of expansion. Other parameters describe density fluctuations in the primordial soup, immediately after the Big Bang, from which dark matter halos eventually form.
The MIT team reasoned that if early dark energy affects the universe’s early expansion rate, in a way that resolves the Hubble tension, then it could affect the balance of the other cosmological parameters, in a way that might increase the number of bright galaxies that appear at early times. To test their theory, they incorporated a model of early dark energy (the same one that happens to resolve the Hubble tension) into an empirical galaxy formation framework to see how the earliest dark matter structures evolve and give rise to the first galaxies.
“What we show is, the skeletal structure of the early universe is altered in a subtle way where the amplitude of fluctuations goes up, and you get bigger halos, and brighter galaxies that are in place at earlier times, more so than in our more vanilla models,” Naidu says. “It means things were more abundant, and more clustered in the early universe.”
“A priori, I would not have expected the abundance of JWST’s early bright galaxies to have anything to do with early dark energy, but their observation that EDE pushes cosmological parameters in a direction that boosts the early-galaxy abundance is interesting,” says Marc Kamionkowski, professor of theoretical physics at Johns Hopkins University, who was not involved with the study. “I think more work will need to be done to establish a link between early galaxies and EDE, but regardless of how things turn out, it’s a clever — and hopefully ultimately fruitful — thing to try.”
“We demonstrated the potential of early dark energy as a unified solution to the two major issues faced by cosmology. This might be an evidence for its existence if the observational findings of JWST get further consolidated,” Vogelsberger concludes. “In the future, we can incorporate this into large cosmological simulations to see what detailed predictions we get.”
This research was supported, in part, by NASA and the National Science Foundation.
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Plant-derived secondary organic aerosols can act as mediators of plant-plant interactions
A new study published in Science reveals that plant-derived secondary organic aerosols (SOAs) can act as mediators of plant-plant interactions. This research was conducted through the cooperation of chemical ecologists, plant ecophysiologists and atmospheric physicists at the University of Eastern Finland.
The study showed that Scots pine seedlings, when damaged by large pine weevils, release VOCs that activate defences in nearby plants of the same species. Interestingly, the biological activity persisted after VOCs were oxidized to form SOAs. The results indicated that the elemental composition and quantity of SOAs likely determines their biological functions.
“A key novelty of the study is the finding that plants adopt subtly different defence strategies when receiving signals as VOCs or as SOAs, yet they exhibit similar degrees of resistance to herbivore feeding,” said Professor James Blande, head of the Environmental Ecology Research Group. This observation opens up the possibility that plants have sophisticated sensing systems that enable them to tailor their defences to information derived from different types of chemical cue.
“Considering the formation rate of SOAs from their precursor VOCs, their longer lifetime compared to VOCs, and the atmospheric air mass transport, we expect that the ecologically effective distance for interactions mediated by SOAs is longer than that for plant interactions mediated by VOCs,” said Professor Annele Virtanen, head of the Aerosol Physics Research Group. This could be interpreted as plants being able to detect cues representing close versus distant threats from herbivores.
The study is expected to open up a whole new complex research area to environmental ecologists and their collaborators, which could lead to new insights on the chemical cues structuring interactions between plants.
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Folded or cut, this lithium-sulfur battery keeps going
Most rechargeable batteries that power portable devices, such as toys, handheld vacuums and e-bikes, use lithium-ion technology. But these batteries can have short lifetimes and may catch fire when damaged. To address stability and safety issues, researchers reporting in ACS Energy Letters have designed a lithium-sulfur (Li-S) battery that features an improved iron sulfide cathode. One prototype remains highly stable over 300 charge-discharge cycles, and another provides power even after being folded or cut.
The team coated iron sulfide cathodes in different polymers and found in initial electrochemical performance tests that polyacrylic acid (PAA) performed best, retaining the electrode’s discharge capacity after 300 charge-discharge cycles. Next, the researchers incorporated a PAA-coated iron sulfide cathode into a prototype battery design, which also included a carbonate-based electrolyte, a lithium metal foil as an ion source, and a graphite-based anode. They produced and then tested both pouch cell and coin cell battery prototypes.
After more than 100 charge-discharge cycles, Wang and colleagues observed no substantial capacity decay in the pouch cell. Additional experiments showed that the pouch cell still worked after being folded and cut in half. The coin cell retained 72% of its capacity after 300 charge-discharge cycles. They next applied the polymer coating to cathodes made from other metals, creating lithium-molybdenum and lithium-vanadium batteries. These cells also had stable capacity over 300 charge-discharge cycles. Overall, the results indicate that coated cathodes could produce not only safer Li-S batteries with long lifespans, but also efficient batteries with other metal sulfides, according to Wang’s team.
The authors acknowledge funding from the National Natural Science Foundation of China; the Natural Science Foundation of Sichuan, China; and the Beijing National Laboratory for Condensed Matter Physics.
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