Newsletter #121 for October 2025

Wastewater plants produce twice as much greenhouse gas as estimated

Princeton researchers have found that municipal wastewater treatment plants in the U.S. emit nearly twice as much methane and nitrous oxide gas as previously estimated, posing a significant challenge for climate-conscious systems. Both methane and nitrous oxide are potent greenhouse gases, collectively responsible for about 22 percent of global warming since 1850. This work highlights the importance of monitoring greenhouse gas emissions from wastewater systems, which plays a key role in improving public and environmental health.

Using a mobile laboratory called the “Princeton Atmospheric Chemistry Experiment”, an electric vehicle equipped with laser-based systems, the research team took direct measurements from 96 wastewater plants that together treat 9% of U.S. wastewater. Graduate students drove the mobile lab quarterly from the East Coast to California and monitored emissions (gas plumes) from plants each season over the 14-month period. The researchers would drive by a facility about 10 times to gather a sample, and they sampled numerous facilities multiple times under different weather conditions and times of day. Individual emissions were analyzed and reported anonymously to better understand wastewater system operations and to capture trends in wastewater operations. 

The study, which was published in the journal Nature Water, highlights how the data was utilized to develop statistically robust estimates of methane (CH₄), nitrous oxide (N₂O) and ammonia (NH₃) emissions from the US wastewater treatment sector for the first time. The researchers reported that much of the emissions are produced by a small number of wastewater plants, which means relatively few plants taking steps to improve emissions can have a major impact on overall emissions. However, the challenge is that many of these systems are focusing on providing clean water. Thus, air emissions are not their top priority. Researchers are planning to work closely with plant operators to help them better understand what is happening inside their plant to help minimize emissions, and to promote economic ways to recapture methane or nitrogen gas.

Source

Addressing water insecurity and building trust in rural Arizona

Arizona State University’s Arizona Water for All (AW4A) initiative is tackling water insecurity in rural Arizona communities by combining residential water testing and community engagement. In partnership with the Rural Community Assistance Corporation (RCAP), researchers are working with water insecure households in Yuma County, many of which rely on private wells, small systems, or hauled water, to identify unsafe water sources and help implement sustainable solutions. The research team is piloting the initiative's modular, adaptive and decentralized water solutions, which are tailored interventions that combine engineering with social engagement. 

Rural Community Assistance Corporation (RCAC) staff conducted household surveys to better understand their drinking water and to offer water testing. They asked questions such as:

• Whether they used treatment systems

• Whether they trusted or distrusted certain water sources

• Wow they made decisions about bottled water versus tap

• If they relied on neighbors during water shortages

• How strong were their community ties

This helped the team design interventions that are not just technical but socially sustainable. For many of the families surveyed, the water testing provided their first clear understanding of what was in their water. In other cases, simply learning that their water was safe to drink brought relief and reduced reliance on bottled water. By learning whether their water is safe or how to improve it, households gained peace of mind, removing this daily source of anxiety. This initiative aims to expand to 80 more households and train local partners, including RCAC staff and grassroots groups, to use water testing kits and help maintain community engagement even after the project’s funding ends.

Eco-friendly technology removes toxic PFAS from water

Rice University researchers, in collaboration with international partners, have developed an innovative, eco-friendly technology to rapidly capture and destroy per- and polyfluoroalkyl substances (PFAS) from water. Traditional PFAS removal methods typically rely on adsorption, where molecules cling to materials like activated carbon or ion-exchange resins. These processes have become widely accepted, but suffers from major drawbacks such as low efficiency, slow performance, limited capacity and the creation of additional waste that requires disposal. Thus, the research team aimed to develop a more sustainable and effective alternative process.

This research, which was published in Advanced Materials, highlight the team’s innovate process, which utilizes a layered double hydroxide (LDH) material made from copper and aluminum. These materials demonstrated record-breaking efficiency, capturing PFAS over 1,000 times better and 100 times faster than commercial carbon filters. The material’s unique structure enables rapid and strong binding of PFAS molecules, and it performed effectively across various water sources, including river, tap, and wastewater. The team also developed a thermal decomposition process using calcium carbonate that eliminated over half of the captured PFAS without releasing toxic by-products. Additionally, the LDH material could be regenerated and reused for at least six cycles, making this the first known sustainable system for PFAS remediation.

What the latest research says about the fate of PFAS in wastewater

In this video interview, Patrick McNamara of Black & Veatch discusses the evolving role of thermal technologies in managing PFAS in wastewater and biosolids. While thermal processes like drying, pyrolysis, and incineration are still emerging and not yet widely adopted, they show promise for reducing PFAS concentrations in biosolids, up to 80% in some cases, making land application more feasible. However, there still is the challenge of understanding the fate of PFAS during these thermal processes, particularly whether they are destroyed or released into the air or water vapor. Air pollution control technologies such as regenerative thermal oxidizers (RTOs) and activated carbon have shown high PFAS removal efficiency, but air sampling remains expensive, complicating regulation and monitoring.

As many utilities start considering thermal processes as part of long-term planning, especially in anticipation of future PFAS regulations, it is becoming more important to design flexible biosolids management systems that allow for future pivots, such as starting with drying and later adding thermal treatment. The interview highlights that the industry is optimistic about continued research and innovation, aiming for scalable, reliable solutions that can be widely adopted in the coming years.

Upcoming Events

A listing of webinars, symposia, and conferences relevant to this work.

Recent Publications

Wastewater | Open Access

Aeration of wastewater with a ceramic membrane nanobubble generator: Experimental validation and modelling of its oxygen transfer

Messina, G., & Christensen, M.L. (2025). Aeration of wastewater with a ceramic membrane nanobubble generator: Experimental validation and modelling of its oxygen transfer. Chemical Engineering Journal. 524(169390). https://doi.org/10.1016/j.cej.2025.169390.

Why it's interesting: Aeration is a critical and energy-intensive process during wastewater treatment, often accounting for up to 80% of total energy use. This study explores the use of a ceramic membrane nanobubble generator as a novel aeration method to improve oxygen transfer efficiency and serve as an alternative method to full or supplementary aeration. Researchers investigated whether nanobubbles could act as oxygen reservoirs or if oxygen transfer occurs immediately upon bubble formation. Nanobubbles might store oxygen inside them and release it slowly over time, especially when the surrounding water becomes undersaturated (low in oxygen). If true, nanobubbles could act like tiny oxygen tanks that help maintain dissolved oxygen levels.

Through a series of experiments, including temperature variation, dilution, and chemical titration, researchers found that nanobubbles do not retain significant oxygen and instead release it rapidly during formation. The enhanced oxygen transfer was attributed to turbulent flow and microbubble formation near the membrane surface. Although the system showed promising oxygen transfer rates (increased DO levels in water), its energy efficiency was low, suggesting limited viability for full-scale aeration. However, the technology may be valuable as a supplementary aeration method during peak load periods due to its rapid oxygen delivery and flexible deployment.

Drinking Water | Open Access

Exploring use of ozone nanobubbles for removal of cyanobacteria and co-occurring antimicrobial resistance genes in water supply and reuse systems

Saththiyananthan, U., Walsh, C. J., Newham, S., Lin, K., Su, M., Chen, L., Putman, M., Flanagan, D., Rouse, K., Nelli, F., Karamati Niaragh, E., Judd, L., Mercoulia, K., Seemann, T., Yang, M., Blackall, L., Howden, B. P., Wert, E., Zamyadi, A. (2025). Exploring use of ozone nanobubbles for removal of cyanobacteria and co-occurring antimicrobial resistance genes in water supply and reuse systems. bioRxiv. https://doi.org/10.1101/2025.10.15.682302.

Why it's interesting: This study investigates the use of ozone nanobubble technology as an advanced treatment method for removing harmful cyanobacterial blooms and associated antimicrobial resistance genes (ARGs) from drinking water reservoirs and treated wastewater (water reuse) systems. Compared to conventional ozonation, ozone nanobubbles demonstrated superior performance in reducing cyanobacterial biomass and cell viability, achieving up to 90% removal in low-organic drinking water and 60–75% in wastewater, while operating at lower ozone doses. Genomic analysis revealed that although microbial loads were reduced, some ARGs remained post-treatment, highlighting the need for integrated approaches to fully eliminate genetic contaminants. The research emphasizes ozone nanobubbles as a promising, energy-efficient polishing step for contaminant control, especially in decentralized or reuse applications, but also identifies key challenges such as bubble stability, species-specific resistance, and by-product formation that require further investigation before full-scale implementation.

Wastewater | Open Access

Addressing wastewater reuse challenges in rural decentralized areas: Implementation of a solar chlor-photo-Fenton demonstration plant

Belachqer-El Attar, S., Soriano-Molina, P., Casas López, J. L., Jambrina-Hernández, E., Agüera, A., Sánchez Pérez, J. A. (2025). Addressing wastewater reuse challenges in rural decentralized areas: Implementation of a solar chlor-photo-Fenton demonstration plant. Journal of Water Process Engineering. 77(108616). https://doi.org/10.1016/j.jwpe.2025.108616.

Why it's interesting: This study provides a summary of the implementation of a solar chlor-photo-Fenton (SCPF) demonstration plant for treating wastewater at rural, decentralized areas. Using a raceway pond reactor (RPR) operated under mild oxidation conditions and solar irradiation, the system achieved up to 60% removal of organic microcontaminants and met European Class B water reuse standards with minimal disinfection by-products. The automated plant demonstrated robust performance across seasonal variations, effectively inactivating pathogens and adapting to fluctuating effluent characteristics typical of rural wastewater. The findings highlight the SCPF process as a scalable, energy-efficient, and sustainable solution for rural water reuse, particularly for agricultural irrigation.

Industry News

Making septic systems cleaner for the environment

University of Miami researchers have developed an electrohydromodulation (EHM) system that treats septic tank effluent by recovering nutrients and neutralizing contaminants using electrical processes, helping prevent septic system issues caused by high water tables due to flooding events.

Floating photocatalyst turns sunlight into radicals that disinfect water in minutes 

Researchers at Sun Yat-sen University, China have developed an ultra-light floating photocatalyst film that uses sunlight to generate long-lasting bactericidal radicals capable of disinfecting contaminated water within minutes, offering a low-cost solution for safe drinking water in underserved regions.

We tested if a specialized magnetic powder could remove microplastics from drinking water: The answer is yes

Researchers have developed a specialized magnetic nanocomposite powder that can effectively remove up to 96% of microplastics from drinking water and municipal wastewater by binding to plastic particles and extracting them with a magnet.

UA part of $38M research project to find solutions to AZ water future

University of Arizona researchers, as part of a $38 million Water Reuse Consortium, are developing advanced technologies to treat and reuse wastewater to help secure Arizona’s water future amid worsening drought conditions.

Raleigh Becomes First in North Carolina to Power Buses with Renewable Natural Gas from Wastewater

Raleigh has become the first city in North Carolina to power its bus fleet with renewable natural gas produced from its own wastewater, marking a major step toward sustainability and reducing greenhouse gas emissions.

Innovations for Small Systems is a continuation of the newsletter previously provided by the two National Centers for Innovation in Small Drinking Water Systems: DeRISK at the University of Colorado - Boulder and WINSSS at University of Massachusetts - Amherst under a U.S. EPA Science to Achieve Results (STAR) grant.

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