Journal of Environmental Sciences study reveals insights into passive water purification by constructed wetlands
Recent review article summarizes crucial information and techniques for the practical, full-scale deployment of constructed wetlands for micro-polluted water cleanup
Editorial Office of Journal of Environmental Sciences
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Constructed wetlands can effectively remove pollutants at low concentrations from water, making it safe for release into freshwater bodies. Adding biochar, metal ore waste, and regularly harvesting plants improves their pollutant removal efficacy
view moreCredit: "Experimental Wetlands" by born1945 on Flickr Image Source Link: https://www.flickr.com/photos/12567713@N00/130418769
Micro-polluted water, which is wastewater with low levels of carbon, nitrogen and phosphorus, is emerging as a significant contamination threat to freshwater bodies. Dissolved carbon, nitrogen, and phosphorous in micro-polluted water can accumulate in freshwater lakes and cause algal blooms, increased die-off of fish, and loss of biodiversity. Traditional wastewater treatment plants (WWTPs) cannot efficiently remove dissolved pollutants at low concentrations. In fact, WWTP discharge is actually a source of micro-polluted water. Other major sources include agricultural run-off and polluted rivers carrying untreated sewage.
Constructed wetlands (CWs) are a widely deployed solution to purify micro-polluted water. These systems use a combination of plants, microbes, and soil substrates to mimic the water purification processes seen in natural wetlands. However, experimental small-scale CWs may not accurately replicate how a full-scale CW functions, and studies of full-scale CWs have been limited.
Understanding the factors that affect the efficiency of full-scale CWs can help improve their efficacy for a variety of environments. To this end, a review of full-scale CWs was conducted by a team of researchers led by Professor Haiming Wu of the School of Environmental Science and Engineering, Shandong University. Their findings were first made available online on 28 March 2025 in the Journal of Environmental Sciences and will be published in Volume 159 of the journal in January 2026.
Describing the purpose of this study, Prof. Wu mentions, “We aimed to identify the characteristics of influent water and their impact on purification performance, design and operational factors influencing CW efficiency, and emerging strategies for enhancing pollutant removal.”
Prof. Wu’s team first noted that the profile of pollutants varies greatly depending on the source. Agricultural runoff has the highest dissolved carbon / chemical oxygen demand (COD), whereas polluted river water has the highest dissolved total nitrogen, phosphorus and significant levels of heavy metals and pharmaceutical compounds.
Next, they reviewed studies of 78 full-scale CWs, covering a variety of designs, utilizing many kinds of plants and microbes, and designed to treat one or more sources of micro-polluted water. They identified several factors that affect the removal of dissolved pollutants, including:
- Direction of water flow: Horizontally across the CW surface or vertically through substrates
- Rate of water flow: Slower flow allows for more effective removal, but very slow flow increases odor generation
- Rapidly growing plants to absorb pollutants in their growth phase
- Carbon-to-nitrogen ratio in the untreated water
- Electron donors such as manganese in the substrate
- Dissolved oxygen to increase both microbial growth and the removal of heavy metals
“All of these factors can be altered by public utilities to improve the pollutant removal efficacy of their CWs”, Prof. Wu explains.
Adding carbon sources (e.g., agricultural by-products, biochar and modified biochar) or inorganic substrates (e.g., natural ores and industrial or mine waste) can enhance the purification performance of CWs for micro-polluted water. Additionally, optimization of hydraulic parameters (e.g., aeration and hydraulic loading), selection of suitable plants, and regular harvesting are also recommended.
Due to their proven efficacy at removing micro-pollution, as well as their relatively low setup and maintenance costs, full-scale CWs are an attractive solution for utilities. However, challenges like the high cost of substrate enhancements and the growing presence of persistent pollutants such as PFAS (Per- and polyfluoroalkyl substances) remain. Prof. Wu believes that these are ripe areas for future research on improving the removal efficacy and cost effectiveness of CWs.
Other avenues for future research include developing predictive models to optimize factors such as system footprint, substrate selection, plant species, and hydraulic conditions. “These models will enhance our understanding of the complex pollutant removal processes and facilitate more effective CW designs and operations,” says Prof. Wu.
One hopes that future research will keep our freshwater sources safe from contamination.
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Reference
DOI: https://doi.org/10.1016/j.jes.2025.03.049
About Shandong University
First established as the Imperial Shandong University in 1901, Shandong University (SDU) is the second oldest university in China. Spread over seven campuses in Shandong province, the university serves over 41,000 undergraduate and over 24,000 postgraduate students. Over 4,500 faculty members work at SDU, including 21 members of the Chinese Academy of Sciences and Chinese Academy of Engineering. The university is involved in several high-profile national and provincial research projects, and houses over 1,200 international students.
Website: http://www.en.sdu.edu.cn/
About Haiming Wu from Shandong University
Haiming Wu is a Professor and PhD supervisor at the School of Environmental Sciences and Engineering at Shandong University. Prof. Wu received his doctorate in environmental engineering in 2014 and has worked at Shandong University since 2020. His areas of research are on wetland management and wastewater treatment, and he has over 120 publications. Prof. Wu received the Science and Technology Progress Award of the Ministry of Education. In addition to his academic work, Prof. Wu is a member of the Expert Committee of the Shandong Environmental Protection Industry Association as well as several national and international environmental sciences organizations.
Funding information
This work was supported by the Natural Science Foundation of China (No. 52470105) and the Young Taishan Scholars Program of Shandong Province (No. 358 202103017).
Journal
Journal of Environmental Sciences
Method of Research
Systematic review
Subject of Research
Not applicable
Article Title
Recent advances on micro-polluted water remediation by full-scale constructed wetlands: Pollutant removal performance, key influencing factors, and enhancing strategies
Harnessing solar energy for environmental cleanup: Iron mineral-bacterial biofilms degrade pollutants
Maximum Academic Press
This process significantly enhances the degradation of antibiotics like tetracycline hydrochloride (TCH) and chloramphenicol (CPL), marking a new frontier in bioremediation techniques and sustainable pollution control.
Solar radiation is a crucial driver of biological processes, traditionally recognized for its role in plant photosynthesis. Recent studies have uncovered the ability of non-phototrophic microorganisms, such as those in soils and sediments, to harvest solar energy through mineral-microbe interactions. These findings point to the broader influence of sunlight on microbial metabolism and geochemical processes, even in saturated environments like soils and sediments. By harnessing the interaction between minerals like iron and microorganisms, this emerging field of biophotoelectrochemistry provides a new mechanism for energy storage and pollutant mitigation in dark zones of soil, where light penetration is limited.
A study (DOI: 10.48130/ebp-0025-0006) published in Environmental and Biogeochemical Processes on 15 September 2025 by Bo Pan’s & Baoshan Xing’s team, Kunming University of Science and Technology & University of Massachusetts, offers a sustainable, efficient, and scalable method for addressing soil and groundwater pollution, opening new possibilities for clean-up strategies in diverse ecosystems.
In this study, the interaction between iron minerals (Fe2O3 or FeOOH) and the bacterium Bacillus megaterium (B. megaterium) was explored to investigate the accumulation and release of electrons during light-dark cycles. The co-culturing system showed a continuous charge-discharge function and a photovoltage memory effect. The electron storage capacity, measured as the total accumulated charge (∑σ), increased with higher bacterial density, indicating that denser biofilms facilitate more efficient charge capture and storage. The system demonstrated a clear disparity between charge accumulation in the light and release in the dark, with the light-exposed systems consistently achieving higher charge values. Notably, the net accumulated charge increased from 2.87 μC·cm−2 to 4.08 μC·cm−2 after several cycles. This unique "photovoltaic memory" feature of the biofilm was further evidenced by a significant increase in the degradation efficiency of pollutants, such as TCH and CPL, during the dark phase following light exposure. After 60 minutes of light exposure, degradation efficiency for TCH and CPL improved by 66.7% and 46.7%, respectively. The mechanism behind this degradation was attributed to the synergistic interaction between the iron minerals and bacteria, which facilitated efficient electron transfer and storage, enabling the system to function as a "biological capacitor." The structural and electrochemical analyses revealed that the bacteria-mineral biofilms enhanced electron transfer and facilitated charge storage, leading to significant improvements in pollutant degradation. These findings suggest that the Fe2O3 /B. megaterium biofilm system offers a promising, sustainable method for addressing environmental pollution, particularly in soil and groundwater, through light-driven charge storage and release mechanisms.
This study provides valuable insights into the potential for using solar-powered biofilms to treat environmental pollutants in soils and sediments. The biocapacitor mechanism demonstrated by the Fe2O3/B. megaterium system offers a sustainable method for pollution control that does not require continuous illumination. The ability of these biofilms to store and release energy for pollutant degradation in dark environments could revolutionize bioremediation practices, particularly for soil and groundwater treatment. This system has the potential to enhance the effectiveness of current methods, providing a cost-effective and energy-efficient solution for cleaning up antibiotic-contaminated sites.
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References
DOI
Original Source URL
https://doi.org/10.48130/ebp-0025-0006
Funding Information
This work was supported by the National Natural Science Foundation of China (42130711, 42377250, and 42267003), the National Key Research and Development Program of China (2023YFC3709100), the Yunnan Major Scientific and Technological Projects (202202AG050019), the Yunnan Fundamental Research Projects (202301AU070078, 202201BE070001-040), and Guided by the Central Government for Local Science and Technology Development Funds (202407AB11026).
About Environmental and Biogeochemical Processes
Environmental and Biogeochemical Processes is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
A bio-photovoltage soil-microbe battery for antibiotic degradation in the dark
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