Polski
Science, Issue 16/2025
Artificial wetlands as an idea for water purification
Nov
Constructed wetlands(CWs) are increasingly common natural wastewater treatment systems. They use the interaction of plants and microorganisms to neutralize pollutants in a low-cost, sustainable and environmentally friendly way. In them, microorganisms are
The study, conducted by a team of scientists from India and China led by Aradhna Kumari of the College of Agriculture in Madhya Pradesh, the results of which were published on October 13 of this year, is an analysis of the ecological functions of microorganisms living in artificial wetlands and used for water purification.
A wealth of microscopic life
The microflora of artificial wetlands is an extremely diverse community of bacteria, archaeons and fungi. Its most numerous type is Proteobacteria – they account for 25 to 48 percent of all microorganisms. They are distinguished by their metabolic versatility, making them adaptable to changing oxygen conditions. Among them, the most important are Pseudomonas, Acinetobacter or Nitrosomonas, which are involved in nitrogen metabolism and decomposition of organic compounds.
The second most abundant type is Bacteroidetes (10-28 percent), responsible for the initial decomposition of complex organic matter, including plant residues.
Around the roots of plants, so-called rhizosphere zones, or local points of biological activity, are formed, in which the density of microorganisms is up to 2 to 10 times higher than in the sediments of the extra-root zone.
Biogeochemical transformations – nature’s laboratory
Microorganisms in artificial wetlands are the driving force behind key purification processes. Denitrification, the reduction of nitrate to gaseous nitrogen, is the main mechanism for nitrogen removal. It requires an anaerobic environment and the presence of organic carbon, which bacteria take up from dead plant parts or wastewater.
Phosphorus, which does not have a gas phase of circulation, is removed much more difficult. Bacteria accumulate it inside cells in the form of polyphosphates. Species of the genus Accumulibacter or Tetrasphaera can efficiently store this element in aerobic-anaerobic cycles.
Organic carbon is decomposed in both aerobic zones (thanks to heterotrophic bacteria) and anaerobic zones, where fermentation, acetogenesis and methanogenesis take place. As a result, the reduction of such indicators as BOD (biochemical oxygen demand) and COD (chemical oxygen demand) reaches up to 85-98 percent.
Effectiveness of purification – the numbers speak for themselves
Artificial wetlands can remove suspended solids with an efficiency of 80-95 percent. Ammonia and other forms of nitrogen are reduced by 70-99 percent, while total nitrogen removal reaches 60-85 percent, depending on the design of the system. Phosphorus is more difficult to remove – its reduction ranges from 40 to 80 percent, depending on the type of substrate and operating conditions.
Thanks to microorganisms, artificial wetlands also neutralize heavy metals. Bacteria bind metal ions in biofilms, convert them into insoluble sulfides or oxides and reduce toxicity. Pseudomonas, Bacillus, Clostridium and cyanobacteria can convert dangerous forms of chromium or arsenic into less harmful forms.
New challenges – micropollutants and microplastics
An issue of increasing urgency is the removal of so-called micropollutants – residues of drugs, cosmetics and other compounds from industry – from water. In artificial wetlands, specialized microorganisms can break down antibiotics with 50-90 percent efficiency, and hormones and endocrine-disrupting compounds with 60-95 percent efficiency. Some bacteria, such as Dehalococcoides, even work under anaerobic conditions to break down chlorinated organic compounds.
Artificial wetlands also trap microplastics, whose particles accumulate in the sediment and become a substrate for biofilms. Microorganisms from the genus Pseudomonas, Rhodococcus or Aspergillus fungi produce enzymes (PETases, laccase, cutinases) that are able to degrade some plastics.
Artificial wetlands and climate – a troubling feedback loop
The functioning of artificial wetlands is fundamentally affected by temperature. In winter, bacterial diversity decreases, and the activity of processes such as nitrification and denitrification decreases markedly. In summer, an increase in temperature accelerates the decomposition of matter, but too high values can disrupt the stability of the ecosystem.
Climate change – temperature fluctuations, droughts or rapid rainfall – affects the microflora of artificial wetlands. Flooding can flush out microorganisms, and periods of drought reduce their activity. Therefore, the design of modern systems requires consideration of resistance to extreme weather events.
There is also the other side of the coin. Artificial wetlands are effective in treating wastewater, but they are a source of greenhouse gases: methane (
To reduce emissions, the researchers recommend, among other things, using plants that have root zone aeration (ROL) capabilities, adding biochar (a high-carbon soil improver) or iron-rich materials, and periodic aeration to reduce methanogenesis processes.
Towards the technology of the future
The study’s authors suggest that the direction of artificial wetlands development should combine ecology with a closed-loop economy. Modern projects plan to recover nutrients (nitrogen and phosphorus) for fertilizer production, generate energy in microbial cells, and use new materials – biochar or engineered media – to improve process efficiency.
While artificial wetlands are inexpensive and environmentally friendly, they also have limitations: they need large areas, a long start-up period, and have variable efficiency in removing phosphorus and micropollutants. They can also emit greenhouse gases and become a reservoir of antibiotic resistance genes. These are problems that will have to be confronted.
According to the authors of the study, artificial wetlands are a low-cost and effective idea for natural treatment with microorganisms, which fits perfectly with the idea of sustainable development. In the future, their effectiveness may increase, thanks to the integration of biotechnology, new materials and precise microbiological monitoring.
Source:
Kumari, A.; Raj, S.; Singh, S.K.; Verma, K.K.; Mishra, P.K. Ecological Functions of Microbes in Constructed Wetlands for Natural Water Purification. Water 2025, 17, 2947. https://doi.org/10.3390/w17202947
