Key Takeaways & Executive Findings
- •• • Ammonia and phosphate removal efficiencies exceeded 90% and 80%, respectively, at influent concentrations up to 0.4 mg/L and 0.2 mg/L, demonstrating robust performance for nutrient polishing in reclaimed water. • • Manganese sand enhanced organic matter decomposition, achieving a 26% reduction in maximum 3D fluorescence intensity, 48% reduction in humic substances, and 38% decrease in UV254, indicating effective removal of residual organic pollutants. • • Four target antibiotics were removed at 70.8%, highlighting the medium's capability to mitigate micropollutants of emerging concern. • • Purified reclaimed water showed no significant genotoxicity (micronucleus rate near tap water) and no acute biotoxicity in non-concentrated samples, but concentrated samples exhibited acute toxicity, implying distinct toxicants for different endpoints.
Abstract
Reclaimed water serves as an alternative water source for replenishing natural water bodies, yet residual pollutants pose ecological risks. A pilot-scale hybrid vertical flow constructed wetland filled with manganese ore sand, quartz sand, and cobblestones was operated for approximately 140 days to assess nutrient and organic matter removal, ecotoxicity, and the suitability of manganese sand as a functional medium. Influent concentrations were up to 0.4 mg/L ammonia, 0.2 mg/L phosphate, 8 mg/L nitrate, and 30 mg/L COD. After 2–3 months of operation, ammonia and phosphate removal efficiencies exceeded 90% and 80%, respectively. Average reductions for nitrate and COD were 0.67 mg/L and 4.2 mg/L. Manganese sand enhanced organic decomposition, reducing maximum 3D fluorescence intensity by 26%, humic substances by 48%, UV254 by 38%, and achieving 70.8% removal of four target antibiotics. Purified water exhibited no significant genotoxicity, with micronucleus rates approaching tap water levels, and non-concentrated samples showed no acute biotoxicity. However, concentrated samples displayed acute toxicity, suggesting different causative pollutants for genotoxicity and acute toxicity. The study supports manganese sand as an effective medium for improving reclaimed water quality and controlling ecological risks.
1. Introduction
Reclaimed water, as a non-conventional water source, is increasingly vital for replenishing natural water bodies and mitigating water scarcity. However, residual pollutants in reclaimed water, including nutrients, organic matter, and trace contaminants, pose potential ecological risks. Constructed wetlands offer a cost-effective and sustainable solution for advanced treatment, yet their performance heavily depends on substrate selection. Conventional substrates like gravel often exhibit limited removal of nitrogen and phosphorus, especially at low influent concentrations typical of reclaimed water. Manganese sand, with its high specific surface area and redox activity, has emerged as a promising functional medium to enhance pollutant removal, but its long-term efficacy and ecological safety require systematic evaluation.
This study addresses the bottleneck of insufficient nutrient and organic removal in constructed wetlands treating reclaimed water by employing manganese sand as a functional filler. A pilot-scale hybrid vertical flow constructed wetland was operated for 140 days, monitoring nitrogen, phosphorus, and organic matter removal, alongside ecotoxicological assessments. The results demonstrate that manganese sand significantly improves removal efficiencies for ammonia, phosphate, and organic matter, while also reducing antibiotic residues. Importantly, the treated water exhibited no significant genotoxicity or acute biotoxicity, underscoring the ecological safety of the effluent. These findings provide technical evidence for the application of manganese-sand-based constructed wetlands in reclaimed water quality enhancement and risk control.
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XU Bin, LIU Xiaoyu, GAO Mengjia, ZHAO Wei, LIU Hao, LIU Li, CHANG Feng, BI Xuejun, CAI Yan'an (2026). Enhanced Treatment of Reclaimed Water Using Functional Manganese-Sand Media in Constructed Wetlands. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202604013
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Frequently Asked Questions
What is the long-term stability of manganese sand as a substrate in constructed wetlands for nutrient removal?
The study operated for 140 days, and after 2–3 months, ammonia and phosphate removal efficiencies stabilized above 90% and 80%, respectively, indicating sustained performance. However, long-term stability beyond 140 days requires further investigation, particularly regarding potential saturation or fouling of manganese sand.
How does manganese sand compare to conventional substrates like gravel in terms of cost and scalability?
Manganese sand is a naturally occurring material with relatively low cost, but its availability and processing may vary. The study demonstrates enhanced removal of organic matter and antibiotics, which could offset higher material costs by reducing the need for additional treatment steps. Scalability would depend on local availability and engineering design.
What are the mechanisms behind enhanced organic matter removal by manganese sand?
Manganese sand likely promotes oxidative degradation of organic compounds due to its high redox potential and catalytic properties. The study observed reductions in fluorescence intensity and UV254, indicating breakdown of humic substances and aromatic compounds. Manganese oxides may also facilitate abiotic oxidation or enhance microbial activity.
Why did concentrated samples exhibit acute biotoxicity while non-concentrated samples did not?
Concentration of samples may increase the levels of trace toxicants to detectable thresholds. The study suggests that different pollutants may be responsible for genotoxicity and acute toxicity, as genotoxicity was not significant even in concentrated samples. Further chemical analysis is needed to identify specific toxicants.
What is the impact of influent organic matter concentration on nitrogen removal performance?
The study noted that nitrogen removal was influenced by influent organic matter levels. Higher organic loads may enhance denitrification by providing carbon sources, but excessive organic matter could compete for oxygen or adsorption sites. The average nitrate reduction was 0.67 mg/L, indicating moderate denitrification under the tested conditions.
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