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Horizontal subsurface flow constructed wetlands as tertiary treatment: Can they be an efficient barrier for microplastics pollution?
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Horizontal subsurface-flow constructed wetlands used as tertiary wastewater treatment removed 88% of microplastics from secondary effluent, contributing to an overall 98% reduction across the full treatment plant. Macroinvertebrates living in the wetland also ingested microplastics, suggesting biological uptake plays a role in plastic retention within the wetland ecosystem.
The presence and fate of microplastics (MPs) in wastewater represent a subject of major concern, as wastewater is one of the main inputs of MPs to the environment. This study deals with the ability of horizontal subsurface-flow constructed wetlands (CWs), as tertiary treatment, to reduce the MPs concentration of secondary effluents. Different locations of a wastewater treatment plant (WWTP) including raw wastewater, CW influent and final effluent, were sampled. Macroinvertebrates were collected from the CW to evaluate their potential role in the MPs distribution along the wetland. The global WWTP efficiency for MPs removal was 98%. MPs removal efficiency by CW was on average 88%, causing a significant reduction of the MPs concentration from 6.45 to 0.77 MP/L (p < 0.05), thus preventing them from entering vulnerable aquatic systems. The areal removal rate and the first order areal rate coefficient (k) were estimated to be 3120 MPs/m/d and 1.70 m/d, respectively. The most abundant size fraction was the one comprising MPs between 75 and 425 μm (51%), while the other size ranges analysed (40-75 and 425-5600 μm) accounted for 25 and 24%, respectively. Fiber was the most abundant shape in the WWTP influent (75%), the CW influent (54%) and effluent (71%). Non-significant differences were found between sites regarding size and shape distributions (p > 0.05). Macroinvertebrates can ingest a non-negligible quantity of MPs, with an average content of 166.2 MPs/g or 0.13 MPs/individual. Therefore, they could play a certain role in the MPs distribution inside CWs. Fiber was the most abundant shape for macroinvertebrates as well (89%), so attention should be paid to reduce their contamination at source. This study provides the first results on MPs removal in CWs as tertiary treatment and assesses the potential role of macroinvertebrates in their distribution along the CW, thus filling this gap of knowledge.
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Assessment of microplastics accumulation and aging in horizontal subsurface flow constructed wetlands.
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Researchers studied microplastic buildup in two constructed wetlands that treat wastewater in Spain, finding microplastics, mostly fibers, collected at different depths and locations depending on treatment type, with removal efficiency around 97%. Plastics showed signs of physical and chemical breakdown over time, and were also found in plant roots.
Abundance, characteristics, and removal of microplastics in the Cihu Lake-wetland microcosm system
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This study evaluated how well a multi-stage constructed wetland system could remove microplastics from wastewater treatment plant effluent, finding a total removal rate of 94.7%. Horizontal subsurface flow wetlands were particularly effective, and physical filtration through the wetland substrate was identified as the dominant removal mechanism. The findings suggest that constructed wetlands are a promising nature-based solution for reducing microplastic discharge into aquatic environments.
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Researchers investigated microplastic retention in a laboratory-scale constructed wetland, finding that the wetland effectively captured microbeads and fibers while examining how accumulated microplastics affected the treatment efficiency for carbon, nitrogen, and phosphorus removal.
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This study assessed microplastic distribution, retention, and implications within constructed wetlands used for wastewater treatment, finding that wetlands trap substantial quantities of MPs but that retention efficiency varies by plant species and wetland design. The results suggest constructed wetlands both remove and potentially accumulate MPs as a secondary pollution source.
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