New review maps solutions to ammonia toxicity that threatens biogas production

Biochar Editorial Office, Shenyang Agricultural University

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Mitigation of ammonia inhibition during anaerobic digestion: a comprehensive update

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Credit: Anina James, Yiwei Shi, Syed Shakir Hussain, Wenjuan Guo, Qiang Liu, Yajing Wang, Yadong Yang, Junyi Ma, & Junting Pan

Anaerobic digestion is widely used around the world to treat organic waste while producing biogas, a renewable energy source that can replace fossil fuels. Yet one persistent problem continues to undermine its reliability. The buildup of ammonia during digestion can poison key microbes, sharply reduce methane production, and in severe cases cause entire reactors to fail.

A new comprehensive review published in Agricultural Ecology and Environment brings together the latest scientific advances aimed at understanding and mitigating ammonia inhibition in anaerobic digestion systems. The study synthesizes more than a decade of research and highlights emerging tools that could help stabilize biogas production from nitrogen rich wastes such as animal manure, food waste, and sewage sludge.

“Ammonia inhibition is one of the most common and costly challenges in anaerobic digestion,” said corresponding author Junyi Ma of Beijing Forestry University. “Once ammonia reaches critical levels, methane producing microorganisms become stressed or inactive, which directly impacts energy recovery and system stability.”

Ammonia exists in digesters in two forms, ammonium and free ammonia nitrogen. While ammonium can support microbial growth at low concentrations, free ammonia readily penetrates microbial cell membranes and disrupts internal energy and ion balance. Methanogens, the microorganisms responsible for methane generation, are particularly vulnerable.

The review explains how operating conditions such as temperature and pH strongly influence ammonia toxicity. Higher temperatures and alkaline conditions increase the proportion of free ammonia, making thermophilic digesters especially susceptible. Even moderate changes can shift a stable system toward inhibition if not carefully managed.

“Understanding how reactor conditions affect ammonia chemistry is critical,” said co corresponding author Junting Pan of the Chinese Academy of Agricultural Sciences. “It allows operators to anticipate risks before methane yields begin to drop.”

Beyond describing the problem, the authors provide a detailed assessment of mitigation strategies currently used or under development. Traditional approaches include adjusting feedstock composition, controlling organic loading rates, regulating pH and temperature, and diluting nitrogen rich substrates. While effective in some cases, these methods can be costly, energy intensive, or difficult to implement at scale.

The review highlights growing interest in biological and material based solutions. These include bioaugmentation with ammonia tolerant microbial consortia, acclimation strategies that allow microbes to gradually adapt to higher ammonia levels, and the addition of conductive materials such as biochar, activated carbon, and magnetite. These materials can enhance microbial cooperation and improve electron transfer, helping digesters recover methane production even under stress.

One of the most forward looking sections of the review focuses on the role of digital technologies. Advances in sensors, automation, artificial intelligence, and machine learning now allow real time monitoring of ammonia levels, volatile fatty acids, and methane output.

“Early warning is key,” Ma said. “Machine learning can analyze complex data patterns and signal instability before a reactor reaches a tipping point. This opens the door to smarter, faster interventions.”

The authors also discuss the potential of synthetic biology to engineer methanogens with improved ammonia tolerance, although they note that practical deployment will require further research and careful risk assessment.

By consolidating current knowledge and identifying research gaps, the review serves as a practical reference for scientists, engineers, and biogas operators alike. As the world seeks sustainable solutions for waste management and renewable energy, improving the resilience of anaerobic digestion systems will be increasingly important.

“Our goal was to provide a roadmap,” Pan said. “With the right combination of monitoring, management, and innovation, ammonia inhibition does not have to be a barrier to efficient biogas production.”

 

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Journal Reference: James A, Shi Y, Hussain SS, Guo W, Liu Q, et al. 2025. Mitigation of ammonia inhibition during anaerobic digestion: a comprehensive update. Agricultural Ecology and Environment 1: e012  

https://www.maxapress.com/article/doi/10.48130/aee-0025-0011   

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About Agricultural Ecology and Environment: 

Agricultural Ecology and Environment (e-ISSN 3070-0639) is a multidisciplinary platform for communicating advances in fundamental and applied research on the agroecological environment, focusing on the interactions between agroecosystems and the environment. It is dedicated to advancing the understanding of the complex interactions between agricultural practices and ecological systems. The journal aims to provide a comprehensive and cutting-edge forum for researchers, practitioners, policymakers, and stakeholders from diverse fields such as agronomy, ecology, environmental science, soil science, and sustainable development. 

Follow us on Facebook, X, and Bluesky. 

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DOI

10.48130/aee-0025-0011 

Method of Research

Literature review

Article Title

Mitigation of ammonia inhibition during anaerobic digestion: a comprehensive update

 

How shifting tectonic plates drove Earth’s climate swings

Carbon released from Earth’s spreading tectonic plates, not volcanoes, may have triggered major transitions between ancient ice ages and warm climates, new research finds.

University of Melbourne

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Published today in Communications Earth and Environment, the study, led by researchers at the Universities of Melbourne and Sydney, reconstructed how carbon moved between volcanoes, oceans and deep within the Earth over the last 540 million years.

It provides insight into the magnitude of our rapidly changing climate today.

Lead researcher University of Melbourne Dr Ben Mather from the School of Geography, Earth and Atmospheric Sciences said the findings challenge a long-held view that chains of volcanoes – formed by colliding tectonic plates – were the Earth’s main natural source of atmospheric carbon.

“Our findings show that carbon gas released from gaps and ridges deep under the ocean from moving tectonic plates was instead likely driving major shifts between icehouse and greenhouse climates for most of Earth’s history,” Dr Mather said.

“We found that carbon emitted from volcanoes, around the Pacific ring of fire for example, only became a major carbon source in the last 100 million years, which challenges current scientific understanding.”

The work provides the first clear long-term evidence that the global climate was shaped mainly by carbon released where tectonic plates pull apart, rather than where they collide.

“This new insight not only reshapes our understanding of past climates but also helps refine future climate models,” Dr Mather said.

Co-author Professor Dietmar Müller from the University of Sydney’s School of Geosciences described that by pairing global plate tectonic reconstructions with carbon-cycle modelling, the team were able to trace how carbon was stored, released and recycled as continents shifted.

“Our study’s findings help explain key historical climate shifts, including the late Paleozoic ice age, the warm Mesozoic greenhouse world, and the emergence of the modern Cenozoic icehouse, by showing how changes in carbon released from spreading plates shaped these long-term transitions to our climate,” Professor Müller said.

Dr Mather said the research provides important context for our currently changing climate.

“This research adds to a large pool of evidence that the amount of carbon in the Earth’s atmosphere is a key trigger to cause major swings in climate,” he said.

“Understanding how Earth controlled its climate in the past highlights how unusual the present rate of change is. Human activities are now releasing carbon far faster than any natural geological process that we’ve seen to have taken place before. The climate scales are being tipped at an alarming rate.”

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Journal

Communications Earth & Environment

DOI

10.1038/s43247-025-03097-0 

 

Research spotlight: Preventive HIV drugs under prescribed to young women at increased risk

Although adolescents and young adults comprise only one quarter of the sexually active population in the United States, approximately half of new sexually transmitted infections (STIs) are diagnosed in people of these ages.

Brigham and Women's Hospital

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Infectious Diseases | Sexual Health | Research

Anne Neilan, MD, MPH, of the Medical Practice Evaluation Center (MPEC) and Department of Medicine at Mass General Brigham, and Kevin Ard, MD, MPH, also of the Department of Medicine, are the lead and senior authors of a paper published in Sexually Transmitted Diseases, “Differences in Sexual Health Clinic Services by Age and Gender in Metropolitan Boston.”

Q: How would you summarize your study for a lay audience?

Although adolescents and young adults comprise only one quarter of the sexually active population in the United States, approximately half of new sexually transmitted infections (STIs) are diagnosed in people of these ages. Compared to older adults, little is known about how teens and young adults access and use services like STI screening and treatment, sexual health vaccinations and HIV pre-exposure prophylaxis (PrEP). PrEP is a preventive medicine for people who do not have HIV but are at increased risk of exposure.

Our study examined how people of different ages and genders used sexual health services in a Boston-based clinic that provides free, comprehensive services across six hospital- and community-based sites. While our study focused on a single metropolitan area, our findings reflect broader national challenges in sexual health service utilization.

Q: What question were you investigating?

We set out to learn whether adolescents and young adults who interacted with the Massachusetts General Hospital Sexual Health Clinic utilized sexual health services differently than older adults. We also aimed to identify opportunities to increase patient engagement and deliver existing services more consistently and equitably to those who need them most.

Q: What methods or approach did you use?

We analyzed data from 7,949 visits to the Sexual Health Clinic, made by 4,004 individuals, between January 2019 to June 2021. We grouped data on visits, STI diagnoses, PrEP use and health insurance by age and gender. We then used statistical analysis to examine how outcomes—such as being prescribed preventive PrEP—were associated with factors like age and gender.

Q: What did you find?

We found that among patients at increased risk for HIV exposure, PrEP prescribing differed by age and gender. For example, cisgender males who were 26 years old or under with PrEP indications were prescribed the medicine at slightly higher rates (86%) than their counterparts over age 26 (83%). However, among cisgender females at increased risk, only 20% of those at or under age 26 were prescribed PrEP compared to 72% of those over age 26.

Looking at the data from another angle, we discovered that young cisgender females (at or under age 26) were 63% less likely to be prescribed PrEP during their visits than young cisgender males. Additionally, only 17% of visits attended by even younger cisgender females (under age 22) who were candidates for PrEP received it.

Q: What are the implications?

Addressing disparities by age, gender and race/ethnicity in HIV prevention—via PrEP prescriptions—is critical. Significant gaps for young cisgender females with PrEP indications reflect opportunities for improved programming tailored to this population, with the potential to avert new HIV diagnoses.

Gaps between PrEP need and prescription may also reflect patient preferences or other barriers such as the need for quarterly visits for oral PrEP or anticipated costs. They could also reflect provider-related barriers, such as limited knowledge of the drug or failure to consider PrEP for individuals other than men who have sex with men. Policy efforts focused on alleviating these barriers may help reduce HIV incidence by improving how well PrEP reaches those who would benefit from it.

Q: What are the next steps?

Future work should explore why PrEP prescription rates among young cisgender females are much lower than their counterparts, as well as evaluate targeted interventions to improve PrEP access for indicated young women.

Authorship: In addition to Neilan and Ard, Mass General Brigham authors include Yiqi Qian, Grace Chamberlin, Scott E. Hadland, Madhava Narasimhadevara, Vandana Madhavan and Fatma M. Shebl.

Paper cited: Neilan, A., et al. “Differences in Sexual Health Clinic Services by Age and Gender in Metropolitan Boston.” Sexually Transmitted Diseases. DOI: 10.1097/OLQ.0000000000002275

Funding: This work was supported by the Morton N. Swartz Transformative Scholar Award in Infectious Diseases, the Claflin Distinguished Scholars Award and the Eunice Kennedy Shriver National Institute for Child Health and Human Development (K08 HD094638-S).  

Disclosures: None.

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Journal

Sexually Transmitted Diseases

DOI

10.1097/OLQ.0000000000002275 

Method of Research

Data/statistical analysis

Subject of Research

People

Article Title

Differences in Sexual Health Clinic Services by Age and Gender in Metropolitan Boston.

 

Critical review maps corrosion threats and mitigation options for supercritical offshore carbon dioxide pipelines

KeAi Communications Co., Ltd.

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Summary figure 

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Credit: Xinran Yu, et al.

 Offshore carbon capture, utilization and storage (CCUS) can be coupled with offshore energy resources, but it also adds a harsh marine environment to the carbon dioxide (CO2)-transport problem. In a review in the KeAi's Journal of Pipeline Science and Engineering, a team of researchers from China described the recent progress on corrosion and anti-corrosion measures for supercritical offshore CO2 pipelines, and organize the offshore CO2 pipeline corrosion problem into a practical engineering map. This map focuses on four areas: (1) external corrosion driven by the marine environment, (2) internal corrosion driven by CO2-water-impurity chemistry and operating conditions, then (3) prediction models and standards, and finally (4) mitigation options and research priorities for safer deployment.

Unlike onshore pipelines, offshore pipelines face combined stressors such as seawater exposure and erosion, hydrostatic pressure, and microbiologically influenced corrosion (MIC). The review notes that offshore pipelines are often installed on or buried in seabed mud, where low oxygen and rich microbial communities can strongly influence corrosion behavior; seawater pH and salinity, plus flow-induced scouring, further shape degradation risk. Thus, in this condition, corrosion is not just an engineering nuisance, but also a leading contributor to CO2 pipeline failure risk.

The review separates corrosion in offshore supercritical CO2 pipelines into external and internal processes, then links them to prediction needs, standards, and mitigation. Notably, external corrosion depends strongly on marine exposure conditions across atmospheric, splash, tidal, immersion, and mud zones, with microbiologically influenced corrosion highlighted as a major offshore driver and scouring by currents accelerating damage by removing protective films and enhancing mass transfer.

Meanwhile, internal corrosion is governed by operating pressure-temperature conditions, water availability, and multi-impurity chemistry in CO2 streams, with seawater cooling and phase transitions potentially promoting precipitation and free-water formation; the review also reiterates that water is the enabling condition for corrosion in supercritical CO2 systems.

For engineering control, the authors stressed that multiple impurities can change mechanisms and undermine existing models. Further, there is an absent of a unified international CO2 pipeline fluid-quality standard. Mitigation is framed as matching measures to drivers, using internal coatings and inhibitors alongside external coatings and cathodic protection, and calling for durable, non-toxic antifouling and coating solutions suitable for offshore deployment.

In the paper's own words, the review “identifies significant challenges...such as understanding corrosion mechanisms of CO2 with multiple impurities...and developing corrosion inhibitors and new non-toxic antifouling coatings.”

Looking ahead, the authors propose research priorities including international standards, improved understanding of multi-species biofilm interactions in MIC, better thermodynamic models for CO2-water-impurity systems, and more durable coatings/inhibitors suitable for high-pressure offshore conditions.

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Contact the author: Yuxing Li, Shandong Key Laboratory of Oil & Gas Storage and Transportation Safety, China University of Petroleum (East China), Qingdao, Shandong 266580, China. E-mail address: liyx@upc.edu.cn

The publisher KeAi was established by Elsevier and China Science Publishing & Media Ltd to unfold quality research globally. In 2013, our focus shifted to open access publishing. We now proudly publish more than 200 world-class, open access, English language journals, spanning all scientific disciplines. Many of these are titles we publish in partnership with prestigious societies and academic institutions, such as the National Natural Science Foundation of China (NSFC).

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Journal

Journal of Pipeline Science and Engineering

DOI

10.1016/j.jpse.2025.100401 

Method of Research

Literature review

Subject of Research

Not applicable

Article Title

A critical review on corrosion challenges and prospects in supercritical offshore CO₂ pipelines